Table of contents

We present Spitzer-IRS spectra obtained along the molecular jet from the Class 0 source L1448-C (or L1448-mm). Atomic lines from the fundamental transitions of [Fe ii], [Si ii], and [S i] have been detected showing, for the first time, the presence of an embedded atomic jet at low excitation. Pure rotational H₂ lines are also detected, and a decrease of the atomic/molecular emission ratio is observed within 1' from the driving source. Additional ground-based spectra (UK Infrared Telescope/UIST) were obtained to further constrain the H₂ excitation along the jet axis and, combined with the 0–0 lines, have been compared with bow shock models. From the different line ratios, we find that the atomic gas is characterized by an electron density n_e∼ 200–1000 cm⁻³, a temperature T_e< 2500 K, and an ionization fraction ≲ 10⁻²; the excitation conditions of the atomic jet are thus very different from those found in more evolved Class I and Class II jets. We also infer that only a fraction (0.05–0.2) of Fe and Si is in gaseous form, indicating that dust still plays a major role in the depletion of refractory elements. A comparison with the SiO abundance recently derived in the jet from an analysis of several SiO submillimeter transitions shows that the Si/SiO abundance ratio is ∼ 100, and thus, that most of the silicon released from grains by sputtering and grain–grain collisions remains in atomic form. Finally, estimates of the atomic and molecular mass flux rates have been derived: values of the order of ∼ 10⁻⁶ and ∼ 10⁻⁷M_☉ yr⁻¹ are inferred from the [S i] 25 μm and H₂ line luminosities, respectively. A comparison with the momentum flux of the CO molecular outflow suggests that the detected atomic jet has the power to drive the large-scale outflow.

Clump clusters and chain galaxies in the Hubble Ultra Deep Field (UDF) are examined for bulges in Near-Infrared Camera Multi-Object Spectrometer images. Approximately 50% of the clump clusters and 30% of the chains have relatively red and massive clumps that could be young bulges. Magnitudes and colors are determined for these bulgelike objects and for the bulges in spiral galaxies, and for all of the prominent star formation clumps in these three galaxy types. The colors are fitted to population evolution models to determine the bulge and clump masses, ages, star formation rate decay times, and extinctions. The results indicate that bulgelike objects in clump clusters and chain galaxies have similar ages and two to five times larger masses compared to the star formation clumps, while the bulges in spirals have roughly six times larger ages and 20 to 30 times larger masses than the clumps. All systems appear to have an underlying red disk population. The masses of star-forming clumps are typically in a range from 10⁷ to 10⁸ M_☉; their ages have a wide range around ∼10² Myr. Ages and extinctions both decrease with redshift. Star formation is probably the result of gravitational instabilities in the disk gas, in which case the large clump mass in the UDF is the result of a high gas velocity dispersion, 30 km s⁻¹ or more, combined with a high gas mass column density, ∼100 M_☉ pc⁻². Because clump clusters and chains dominate disk galaxies beyond z ∼ 1, the observations suggest that these types represent an early phase in the formation of modern spiral galaxies, when the bulge and inner disk formed.

We extend a method for modeling synchrotron and synchrotron self-Compton radiations in blazar jets to include external Compton (EC) processes. The basic model assumption is that the blazar radio through soft X-ray flux is nonthermal synchrotron radiation emitted by isotropically distributed electrons in the randomly directed magnetic field of outflowing relativistic blazar jet plasma. Thus, the electron distribution is given by the synchrotron spectrum, depending only on the Doppler factor δ_D and the mean magnetic field B, given that the comoving emission region size scale R'_b ≲ cδ_Dt_v/(1 + z), where t_v is the variability time and z is the source redshift. Generalizing the approach of Georganopoulos, Kirk, & Mastichiadis to arbitrary anisotropic target radiation fields, we use the electron spectrum implied by the synchrotron component to derive accurate Compton-scattered γ-ray spectra throughout the Thomson and Klein–Nishina regimes for EC scattering processes. We derive and calculate accurate γ-ray spectra produced by relativistic electrons that Compton-scatter (1) a point source of radiation located radially behind the jet, (2) photons from a thermal Shakura–Sunyaev accretion disk, and (3) target photons from the central source scattered by a spherically symmetric shell of broad-line region gas. The calculations of broadband spectral energy distributions from the radio through γ-ray regimes are presented, which include self-consistent γγ absorption on the same radiation fields that provide target photons for Compton scattering. The application of this baseline flat spectrum radio/γ-ray quasar model is considered in view of data from γ-ray telescopes and contemporaneous multiwavelength campaigns.

We present molecular line mapping of the Giant Molecular Cloud G1.6−0.025, which is located at the high-longitude end of the Central Molecular Zone (CMZ) of our Galaxy. We assess the degree of star formation activity in that region using several tracers, and find very little. We made a large-scale, medium (2') resolution map in the J = 2 − 1 transition of SiO for which we find clumpy emission over a ∼08 × 03 sized region stretching along the Galactic plane. Toward selected positions we also took spectra in the easy-to-excite J_k = 2_k − 1_k quartet of CH₃OH and the carbon monosulfide (CS) 2 − 1 line. Throughout the cloud these CH₃OH lines are, remarkably, several times stronger than both the CS and the SiO lines. The large widths of all the observed lines, similar to values generally found in the Galactic center, indicate a high degree of turbulence. Several high LSR velocity clumps that have 50–80 km s⁻¹ higher velocities than the bulk of the molecular cloud appear at the same projected position as "normal" velocity material; this may indicate cloud–cloud collisions. Statistical equilibrium modeling of the CH₃OH lines observed by us and others yields relatively high densities and moderate temperatures for a representative dual velocity position. We find 8 × 10⁴ cm⁻³/30 K for material in the G1.6−0.025 cloud and a higher temperature (190 K), but a 50% lower density in a high-velocity clump projected on the same location. Several scenarios are discussed in which shock chemistry might enhance the CH₃OH and SiO abundances in G1.6−0.025 and elsewhere in the CMZ.

The Tibet-III air shower array, consisting of 533 scintillation detectors, has been operating successfully at Yangbajing in Tibet, China since 1999. Using the data set collected by this array from 1999 November through 2005 November, we obtained the energy spectrum of γ-rays from the Crab Nebula, expressed by a power law as (dJ/dE) = (2.09 ± 0.32) × 10⁻¹²(E/3 TeV)^{−2.96±0.14} cm⁻² s⁻¹ TeV⁻¹ in the energy range of 1.7–40 TeV. This result is consistent with other independent γ-ray observations by imaging air Cherenkov telescopes. In this paper, we carefully checked and tuned the performance of the Tibet-III array using data on the Moon's shadow in comparison with a detailed Monte Carlo (MC) simulation. The shadow is shifted to the west of the Moon's apparent position as an effect of the geomagnetic field, although the extent of this displacement depends on the primary energy of positively charged cosmic rays. This finding enables us to estimate the systematic error in determining the primary energy from its shower size. This error is estimated to be less than ±12% in our experiment. This energy scale estimation is the first attempt among cosmic ray experiments at ground level. The systematic pointing error is also estimated to be smaller than 0011. The deficit rate and the position of the Moon's shadow are shown to be very stable within a statistical error of ±6% year by year. This guarantees the long-term stability of pointlike source observation with the Tibet-III array. These systematic errors are adequately taken into account in our study of the Crab Nebula.

We report the discovery of a near-infrared (NIR) counterpart to the persistent neutron-star low-mass X-ray binary 4U 1705 − 440, at a location consistent with its recently determined Chandra X-ray position. The NIR source is highly variable, with K_s-band magnitudes varying between 15.2 and 17.3 and additional J- and H-band observations revealing color variations. A comparison with contemporaneous X-ray monitoring observations shows that the NIR brightness correlates well with X-ray flux and X-ray spectral state. We also find possible indications of a change in the slope of the NIR/X-ray flux relation among different X-ray states. We discuss and test various proposed mechanisms for the NIR emission from neutron-star low-mass X-ray binaries and conclude that the NIR emission in 4U 1705 − 440 is most likely dominated by X-ray heating of the outer accretion disk and the secondary star.

It has been claimed that period-luminosity (P–L) relations derived from infrared observations of Large Magellanic Cloud (LMC) Cepheids are less dependent on the metallicity of the Cepheids. In this work, infrared observations of LMC Cepheids from the SAGE survey are combined with OGLE II optical observations to model and predict mass-loss rates. The mass-loss rates are fit to the data and are predicted to range from about 10⁻¹² to 10⁻⁷ M_☉/yr; however, the rates depend on the assumed value of the dust-to-gas ratio. By comparing the relations derived from observations to the relations derived from predicted infrared stellar luminosities from the mass-loss model, it is shown that mass loss affects the structure and scatter of the infrared P–L relation. Mass loss produces shallower slopes of the infrared relations and a lower zero point. There is also evidence for nonlinearity in the predicted P–L relations, and it is argued that mass loss produces larger infrared excess at lower periods, which affects the slope and zero point, making the P–L relations more linear in the wavelength range of 3.6 to 5.8 μm. Because the dust-to-gas ratio is metallicity dependent and mass loss may have a metallicity dependence, infrared P–L relations have additional uncertainty due to metallicity.

We use the COMPLETE Survey's observations of the Perseus star-forming region to assess and intercompare the three methods used for measuring column density in molecular clouds: near-infrared (NIR) extinction mapping; thermal emission mapping in the far-IR; and mapping the intensity of CO isotopologues. Overall, the structures shown by all three tracers are morphologically similar, but important differences exist among the tracers. We find that the dust-based measures (NIR extinction and thermal emission) give similar, log-normal, distributions for the full (∼20 pc scale) Perseus region, once careful calibration corrections are made. We also compare dust- and gas-based column density distributions for physically meaningful subregions of Perseus, and we find significant variations in the distributions for those (smaller, ∼few pc scale) regions. Even though we have used ¹²CO data to estimate excitation temperatures, and we have corrected for opacity, the ¹³CO maps seem unable to give column distributions that consistently resemble those from dust measures. We have edited out the effects of the shell around the B-star HD 278942 from the column density distribution comparisons. In that shell's interior and in the parts where it overlaps the molecular cloud, there appears to be a dearth of ¹³CO, which is likely due either to ¹³CO not yet having had time to form in this young structure and/or destruction of ¹³CO in the molecular cloud by the HD 278942's wind and/or radiation. We conclude that the use of either dust or gas measures of column density without extreme attention to calibration (e.g., of thermal emission zero-levels) and artifacts (e.g., the shell) is more perilous than even experts might normally admit. And, the use of ¹³CO data to trace total column density in detail, even after proper calibration, is unavoidably limited in utility due to threshold, depletion, and opacity effects. If one's main aim is to map column density (rather than temperature or kinematics), then dust extinction seems the best probe, up to a limiting extinction caused by a dearth of sufficient background sources. Linear fits among all three tracers' estimates of column density are given, allowing us to quantify the inherent uncertainties in using one tracer, in comparison with the others.

Filaments that form either between or around active regions (ARs) are called intermediate filaments. Even though there have been many theoretical studies, the origin of the chirality of filaments is still unknown. We investigated how intermediate filaments are related to their associated ARs, especially from the point of view of magnetic helicity and the orientation of polarity inversion lines (PILs). The chirality of filaments has been determined based on the orientations of barbs observed in full-disk Hα images taken at Big Bear Solar Observatory during the rising phase of solar cycle 23. The sign of magnetic helicity of ARs has been determined using $\textsf{S}$/inverse–$\textsf{S}$ shaped sigmoids from Yohkoh SXT images. As a result, we have found good correlation between the chirality of filaments and the magnetic helicity sign of ARs. Among 45 filaments, 42 filaments have shown the same sign as helicity sign of nearby ARs. It has been also confirmed that the role of both the orientation and the relative direction of PILs to ARs in determining the chirality of filaments is not significant, against a theoretical prediction. These results suggest that the chirality of intermediate filaments may originate from magnetic helicity of their associated ARs.

This paper presents a model calculation of solar energetic particle propagation in a three-dimensional interplanetary magnetic field. The model includes essentially all the particle transport mechanisms: streaming along magnetic field lines, convection with the solar wind, pitch-angle diffusion, focusing by the inhomogeneous interplanetary magnetic field, perpendicular diffusion, and pitch-angle dependent adiabatic cooling by the expanding solar wind. We solve the Fokker–Planck transport equation with simulation of backward stochastic processes in a fixed reference frame in which any spacecraft is roughly stationary. As an example we model the propagation of those high-energy (E ≳ 10 MeV) solar energetic particles in gradual events that are accelerated by large coronal mass ejection shocks in the corona and released near the Sun into interplanetary space of a Parker spiral magnetic field. Modeled with different scenarios, the source of solar energetic particles can have a full or various limited coverages of latitude and longitude on the solar surface. We compute the long-term time profiles of particle flux and anisotropy at various locations in the heliosphere up to 3 AU, from the ecliptic to high latitudes. Features from particle perpendicular diffusion are revealed. Our simulation reproduces the observed reservoir phenomenon of solar energetic particles with constraints on either solar particle source or the magnitude of perpendicular diffusion.

We study afterglow flares of gamma-ray bursts (GRBs) in the framework of the late internal shock (LIS) model based on a careful description for the dynamics of a pair of shocks generated by a collision between two homogeneous shells. First, by confronting the model with some fundamental observational features of X-ray flares, we find some constraints on the properties of the pre-collision shells that are directly determined by the central engine of GRBs. Second, high-energy emission associated with X-ray flares, which arises from synchrotron self-Compton emission of LISs, is investigated in a wide parameter space. The predicted flux of high-energy flares may reach as high as ∼10⁻⁸ erg cm⁻² s⁻¹, which is likely to be detectable with the Large Area Telescope aboard the Fermi Space Telescope (formerly GLAST).

We propose a simple analytic model for the innermost (within the light cylinder (LC) of canonical radius ∼c/Ω) structure of open-magnetic-field lines of a rotating neutron star (NS) with relativistic outflow of charged particles (electrons/positrons) and an arbitrary angle between the NS spin and magnetic axes. We present the self-consistent solution of Maxwell's equations for the magnetic field and electric current in the pair-starved regime where the density of electron–positron plasma generated above the pulsar polar cap is not sufficient to completely screen the accelerating electric field and thus establish the E · B = 0 condition above the pair-formation front up to the very high altitudes within the LC. The proposed model may provide a theoretical framework for developing the refined model of the global pair-starved pulsar magnetosphere.

We have recently identified the widest very low mass binary (2M0126AB), consisting of an M6.5V and an M8V dwarf with a separation of ∼5100 AU, which is twice as large as that of the second widest known system and an order of magnitude larger than those of all other previously known wide very low mass binaries. If this binary belongs to the field population, its constituents would have masses of ∼0.09 M_☉, at the lower end of the stellar regime. However, in the discovery paper, we pointed out that its proper motion and position in the sky are both consistent with being a member of the young (30 Myr) Tucana/Horologium association, raising the possibility that the binary is a pair of ∼0.02 M_☉ brown dwarfs. We obtained optical spectroscopy at the Gemini South Observatory in order to constrain the age of the pair and clarify its nature. The absence of lithium absorption at 671 nm, modest Hα emission, and the strength of the gravity-sensitive Na doublet at 818 nm all point toward an age of at least 200 Myr, ruling out the possibility that the binary is a member of Tucana/Horologium. We further estimate that the binary is younger than 2 Gyr based on its expected lifetime in the galactic disk.

Observations of the SiO v = 0, J = 1 → 0 spectra from VY CMa from 2003 through 2006 indicate an unusually long-lived, highly linearly polarized maser emission at a V_lsr of approximately 18.5 km s⁻¹. A time series cross-correlation analysis has been developed for calculating the characteristic lifetime of linearly polarized spectra. Applying the cross-correlation to these spectra indicates a characteristic lifetime of 5600 ± 400 days. These emission characteristics may be generated in a region of relatively stable outflow geometry and magnetic field rather than in the more ephemeral circumstellar environment.

The soft gamma-ray repeater SGR 1900+14 lies a few arcminutes outside the edge of the shell supernova remnant (SNR) G42.8+0.6. A physical association between the two systems has been proposed—for this and other SGR–SNR pairs—based on the expectation of high space velocities for SGRs in the framework of the magnetar model. The large angular separation between the SGR and the SNR center, coupled with the young age of the system, suggests a test of the association with a proper motion measurement. We used a set of three Chandra/Advanced CCD Imaging Spectrometer observations of the field spanning approximately five years to perform accurate relative astrometry in order to measure the possible angular displacement of the SGR as a function of time. Our investigation sets a 3σ upper limit of 70 mas yr⁻¹ to the overall proper motion of the SGR. Such a value argues against an association of SGR 1900+14 with G42.8+0.6 and adds further support to the mounting evidence of an origin of the SGR within a nearby compact cluster of massive stars.

We present sensitive 7 mm observations of the H53α recombination line and adjacent continuum, made toward the Orion BN/KL region. In the continuum we detect the BN object, the radio source I (GMR I) and the radio counterpart of the infrared (IR) source n (Orion-n). Comparing with observations made at similar angular resolutions but lower frequency, we discuss the spectral indices and angular sizes of these sources. In the H53α line, we only detect the BN object. This is the first time that radio recombination lines have been detected from this source. The LSR radial velocity of BN from the H53α line, v_LSR = 20.1 ± 2.1 km s⁻¹, is consistent with that found from previous studies in near-IR lines. While the continuum emission is expected to have considerable optical depth at 7 mm, the observed H53α line emission is consistent with an optically thin nature and we discuss possible explanations for this apparent discrepancy. There is evidence of a velocity gradient, with the NE part of BN being redshifted by ∼10 km s⁻¹ with respect to the SW part. This is consistent with the suggestion of Jiang et al. that BN may be driving an ionized outflow along that direction.

A large drift in the rotation rate of Titan observed by Cassini provided the first evidence of a subsurface ocean isolating the massive core from the icy crust. Seasonal exchange of angular momentum between the surface and atmosphere accounts for the magnitude of the effect, but observations lag the expected signal by a few years. We argue that this time lag is due to the presence of an active methane weather cycle in the atmosphere. An analytic model of the seasonal cycle of atmospheric angular momentum is developed and compared with time-dependent simulations of Titan's atmosphere with and without methane thermodynamics. The disappearance of clouds at the summer pole suggests the drift rate has already switched direction, signaling the change in season from solstice to equinox.

In the dark matter (DM) halos embedding galaxies and galaxy systems the "entropy" K ≡ σ²/ρ^2/3 (a quantity that combines the radial velocity dispersion σ with the density ρ) is found from intensive N-body simulations to follow a power-law run K ∝ r^α throughout the halos' bulk, with α around 1.25. Taking up from phenomenology just that α≈ const. applies, we cut through the rich analytic contents of the Jeans equation describing the self-gravitating equilibria of the DM; we specifically focus on computing and discussing a set of novel physical solutions that we name α-profiles, marked by the entropy slope α itself, and by the maximal gravitational pull κ_crit(α) required for a viable equilibrium to hold. We then use an advanced semianalytic description for the cosmological buildup of halos to constrain the values of α to within the narrow range 1.25–1.29 from galaxies to galaxy systems; these correspond to halos' current masses in the range 10¹¹–10¹⁵ M_☉. Our range of α applies since the transition time that—both in our semianalytic description and in state-of-the-art numerical simulations—separates two development stages: an early violent collapse that comprises a few major mergers and enforces dynamical mixing, followed by smoother mass addition through slow accretion. In our range of α we provide a close fit for the relation κ_crit(α), and discuss a related physical interpretation in terms of incomplete randomization of the infall kinetic energy through dynamical mixing. We also give an accurate analytic representation of the α-profiles with parameters derived from the Jeans equation; this provides straightforward precision fits to recent detailed data from gravitational lensing in and around massive galaxy clusters, and thus replaces the empirical Navarro–Frenk–White formula relieving the related problems of high concentration and old age. We finally stress how our findings and predictions as to α and κ_crit contribute to understanding hitherto unsolved issues concerning the fundamental structure of DM halos.

Galactic winds are a prime suspect for the metal enrichment of the intergalactic medium (IGM) and may have a strong influence on the chemical evolution of galaxies and the nature of QSO absorption-line systems. We use a sample of 1406 galaxy spectra at z ∼ 1.4 from the DEEP2 redshift survey to show that blueshifted Mg iyi λλ 2796, 2803 absorption is ubiquitous in star-forming galaxies at this epoch. This is the first detection of frequent outflowing galactic winds at z ∼ 1. The presence and depth of absorption are independent of active galactic nuclei spectral signatures or galaxy morphology; major mergers are not a prerequisite for driving a galactic wind from massive galaxies. Outflows are found in co-added spectra of galaxies spanning a range of 30 times in stellar mass and 10 times in star formation rate (SFR), calibrated from K-band and from the Multiband Imaging Photometer for Spitzer IR fluxes. The outflows have column densities of order N_H ∼ 10²⁰ cm^-2 and characteristic velocities of ∼ 300–500 km s⁻¹, with absorption seen out to 1000 km s⁻¹ in the most massive, highest SFR galaxies. The velocities suggest that the outflowing gas can escape into the IGM and that massive galaxies can produce cosmologically and chemically significant outflows. Both the Mg ii equivalent width and the outflow velocity are larger for galaxies of higher stellar mass and SFR, with V_wind ∼ SFR^0.3, similar to the scaling in low redshift IR-luminous galaxies. The high frequency of outflows in the star-forming galaxy population at z ∼ 1 indicates that galactic winds occur in the progenitors of massive spirals as well as those of ellipticals. The increase of outflow velocity with mass and SFR constrains theoretical models of galaxy evolution that include feedback from galactic winds, and may favor momentum-driven models for the wind physics.

If sterile neutrinos exist and form halos in galactic centers, they can give rise to observational consequences. In particular, the sterile neutrinos decay radiatively and heat up the gas in the protogalaxy to achieve hydrostatic equilibrium, and they provide the mass to form supermassive black holes (BHs). A natural correlation between the BH mass and velocity dispersion thus arises: log(M_BH,f/M_☉) = αlog(σ/200 km s^-1) + β with α ≈ 4 and β ≈ 8.

The dark matter halo mass function is a key repository of cosmological information over a wide range of mass scales, from individual galaxies to galaxy clusters. N-body simulations have established that the friends-of-friends (FOF) mass function has a universal form to a surprising level of accuracy (≲10%). The high-mass tail of the mass function is exponentially sensitive to the amplitude of the initial density perturbations, the mean matter density parameter, Ω_m, and to the dark energy controlled late-time evolution of the density field. Observed group and cluster masses, however, are usually stated in terms of a spherical overdensity (SO) mass which does not map simply to the FOF mass. Additionally, the widely used halo models of structure formation—and halo occupancy distribution descriptions of galaxies within halos—are often constructed exploiting the universal form of the FOF mass function. This again raises the question of whether FOF halos can be simply related to the notion of a spherical overdensity mass. By employing results from Monte Carlo realizations of ideal Navarro–Frenk–White (NFW) halos and N-body simulations, we study the relationship between the two definitions of halo mass. We find that the vast majority of halos (80%–85%) in the mass-range 10^12.5–10^15.5 h⁻¹ M_☉ indeed allow for an accurate mapping between the two definitions (∼5%), but only if the halo concentrations are known. Nonisolated halos fall into two broad classes: those with complex substructure that are poor fits to NFW profiles and those "bridged" by the (isodensity-based) FOF algorithm. A closer investigation of the bridged halos reveals that the fraction of these halos and their satellite mass distribution is cosmology dependent. We provide a preliminary discussion of the theoretical and observational ramifications of these results.

We present Spitzer 8 μm transit observations of the extrasolar planet HD 149026b. At this wavelength, transit light curves are weakly affected by stellar limb darkening, allowing for a simpler and more accurate determination of planetary parameters. We measure a planet–star radius ratio of R_p/R_⋆ = 0.05158 ± 0.00077, and in combination with ground-based data and independent constraints on the stellar mass and radius, we derive an orbital inclination of $i = 85 \mbox{$.\!\!^\circ $}4 ^{+0 \mbox{$.\!\!^\circ $}9}_{-0 \mbox{$.\!\!^\circ $}8}$ and a planet radius of R_p = 0.755 ± 0.040 R_J. These measurements further support models in which the planet is greatly enriched in heavy elements.

Magnetic fields in the early universe can significantly alter the thermal evolution and the ionization history during the dark ages. This is reflected in the 21 cm line of atomic hydrogen, which is coupled to the gas temperature through collisions at high redshifts, and through the Wouthuysen–Field effect at low redshifts. We present a semianalytic model for star formation and the build-up of a Lyman-α background in the presence of magnetic fields, and calculate the evolution of the mean 21 cm brightness temperature and its frequency gradient as a function of redshift. We further discuss the evolution of linear fluctuations in temperature and ionization in the presence of magnetic fields and calculate the effect on the 21 cm power spectrum. At high redshifts, the signal is increased compared to the nonmagnetic case due to the additional heat input into the intergalactic medium from ambipolar diffusion and the decay of MHD turbulence. At lower redshifts, the formation of luminous objects and the build-up of a Lyman-α background can be delayed by a redshift interval of 10 due to the strong increase of the filtering mass scale in the presence of magnetic fields. This tends to decrease the 21 cm signal compared to the zero-field case. In summary, we find that 21 cm observations may become a promising tool to constrain primordial magnetic fields.

We explore the nature of systematic errors that can arise in measurement of black hole masses from single-epoch (SE) spectra of active galactic nuclei (AGNs) by utilizing the many epochs available for NGC 5548 and PG1229+204 from reverberation mapping (RM) databases. In particular, we examine systematics due to AGN variability, contamination due to constant spectral components (i.e., narrow lines and host galaxy flux), data quality (i.e., signal-to-noise ratio (S/N)), and blending of spectral features. We investigate the effect that each of these systematics has on the precision and accuracy of SE masses calculated from two commonly used line width measures by comparing these results to recent RM studies. We calculate masses by characterizing the broad Hβ emission line by both the full width at half maximum and the line dispersion, and demonstrate the importance of removing narrow emission-line components and host starlight. We find that the reliability of line width measurements rapidly decreases for S/N lower than ∼ 10–20 (per pixel), and that fitting the line profiles instead of direct measurement of the data does not mitigate this problem but can, in fact, introduce systematic errors. We also conclude that a full spectral decomposition to deblend the AGN and galaxy spectral features is unnecessary, except to judge the contribution of the host galaxy to the luminosity and to deblend any emission lines that may inhibit accurate line width measurements. Finally, we present an error budget which summarizes the minimum observable uncertainties as well as the amount of additional scatter and/or systematic offset that can be expected from the individual sources of error investigated. In particular, we find that the minimum observable uncertainty in SE mass estimates due to variability is ≲0.1 dex for high S/N (≳20 pixel⁻¹) spectra.

We measure the two-point spatial correlation function for clusters selected from the photometric MaxBCG galaxy cluster catalog for the Sloan Digital Sky Survey (SDSS). We evaluate the correlation function for several cluster samples using different cuts in cluster richness. Fitting the results to power laws, ξ_cc(r) = (r/R₀)^−γ, the estimated correlation length R₀ as a function of richness is broadly consistent with previous cluster observations and with expectations from N-body simulations. We study how the linear bias parameter scales with richness and compare our results to theoretical predictions. Since these measurements extend to very large scales, we also compare them to models that include the baryon acoustic oscillation feature and that account for the smoothing effects induced by errors in the cluster photometric redshift estimates. For the largest cluster sample, corresponding to a richness threshold of N₂₀₀ ⩾ 10, we find only weak evidence, of about 1.4σ–1.7σ significance, for the baryonic acoustic oscillation signature in the cluster correlation function.

We investigate the physical and chemical conditions necessary for low-mass star formation in extragalactic environments by calculating various characteristic timescales associated with star formation for a range of initial conditions. The balance of these timescales indicates whether low-mass star formation is enhanced or inhibited under certain physical conditions. In this study, we consider timescales for free-fall, cooling, freeze-out, desorption, chemistry and ambipolar diffusion, and their variations with changes in the gas density, metallicity, cosmic ray ionization rate, and far-ultraviolet (FUV) radiation field strength. We find that extragalactic systems with high FUV radiation field strengths and high cosmic ray fluxes considered at a range of metallicities are likely to have enhanced low-mass star formation unless the magnetic pressure is sufficient to halt collapse. Our results indicate that this is only likely to be the case for high-redshift galaxies approaching solar metallicities. Unless this is true for all high-redshift sources, this study finds little evidence for a high-mass-biased initial mass function at high redshifts.

Brown dwarfs and low-mass stellar companions are interesting objects to study since they occupy the mass region between deuterium and hydrogen burning. We report here the serendipitous discovery of a low-mass companion in an eccentric orbit around a solar-type main-sequence star. The stellar primary, TYC 2534-698-1, is a G2V star that was monitored both spectroscopically and photometrically over the course of several months. Radial velocity observations indicate a minimum mass of 0.037 M_☉ and an orbital period of ∼103 days for the companion. Photometry outside of the transit window shows the star to be stable to within ∼6 millimags. The semimajor axis of the orbit places the companion in the "brown dwarf desert" and we discuss potential follow-up observations that could constrain the mass of the companion.

The low-redshift universe (z ≲ 0.5) is not a dull place. Processes leading to the suppression of star formation and morphological transformation are prevalent: this is particularly evident in the dramatic upturn in the fraction of S0-type galaxies in clusters. However, until now, the process and environment of formation remained unidentified. We present a morphological analysis of galaxies in the optically-selected (spectroscopic friends-of-friends) group and field environments at z ∼ 0.4. Groups contain a much higher fraction of S0s at fixed luminosity than the lower density field, with >99.999% confidence. Indeed, the S0 fraction in groups is at least as high as in z ∼ 0.4 clusters and X-ray-selected groups, which have more luminous intragroup medium (IGM). An excess of S0s at ⩾0.3h⁻¹₇₅ Mpc from the group center with respect to the inner regions, existing with 97% confidence at fixed luminosity, tells us that formation is not restricted to, and possibly even avoids, the group cores. Interactions with a bright X-ray-emitting IGM cannot be important for the formation of the majority of S0s in the universe. In contrast to S0s, the fraction of elliptical galaxies in groups at fixed luminosity is similar to the field, while the brightest ellipticals are strongly enhanced toward the group centers (greater than 99.999% confidence within 0.3h⁻¹₇₅ Mpc). Interestingly, while spirals are altogether less common in groups than in the field, there is also an excess of faint, Sc+ type spirals within 0.3h⁻¹₇₅ Mpc of the group centers (99.953% confidence). We conclude that the group and subgroup environments must be dominant for the formation of S0 galaxies, and that minor mergers, galaxy harassment, and tidal interactions are the most likely responsible mechanisms. This has implications not only for the inferred preprocessing of cluster galaxies, but also for the global morphological and star formation budget of galaxies: as hierarchical clustering progresses, more galaxies will be subject to these transformations as they enter the group environment.

We present spatially resolved near-IR spectroscopic observations of 15 young stars. Using a grism spectrometer behind the Keck interferometer, we obtained an angular resolution of a few milliarcseconds and a spectral resolution of 230, enabling probes of both gas and dust in the inner disks surrounding the target stars. We find that the angular size of the near-IR emission typically increases with wavelength, indicating hot, presumably gaseous material within the dust sublimation radius. Our data also clearly indicate Brγ emission arising from hot hydrogen gas, and suggest the presence of water vapor and carbon monoxide gas in the inner disks of several objects. This gaseous emission is more compact than the dust continuum emission in all cases. We construct simple physical models of the inner disk and fit them to our data to constrain the spatial distribution and temperature of dust and gas emission components.

The accretion of hydrogen-rich matter onto C/O and O/Ne white dwarfs (WDs) in binary systems may lead to unstable thermonuclear ignition of the accreted envelope, triggering a convective thermonuclear runaway and a subsequent classical, recurrent, or symbiotic nova. Prompted by uncertainties in the composition at the base of the accreted envelope at the onset of convection, as well as the range of abundances detected in nova ejecta, we examine the effects of varying the composition of the accreted material. For carbon mass fractions <2 × 10⁻³ and the high accretion rates ⩾10⁻⁹ M_☉ yr⁻¹ that we consider, we find that carbon, which is usually assumed to trigger the runaway via proton captures, is instead depleted and converted to ¹⁴N. Additionally, we quantify the importance of ³He, finding that convection is triggered by ³He+³He reactions for ³He mass fractions >2 × 10⁻³. These different triggering mechanisms, which occur for critical abundances relevant to many nova systems, alter the amount of mass that is accreted prior to a nova, causing the nova rate to depend on the composition of the material accreted from the companion. Upcoming deep optical surveys such as Pan-STARRS-1, Pan-STARRS-4, and the Large Synoptic Survey Telescope may allow us to detect the dependence of nova rates on accreted composition. Furthermore, the burning and depletion of ³He with a mass fraction of 10⁻³, which is lower than necessary for triggering convection, still has an observable effect, resulting in a pre-outburst brightening in disk quiescence to >L_☉ and an increase in effective temperature to 6.5 × 10⁴ K for a 1.0 M_☉ WD accreting at 10⁻⁸ M_☉ yr⁻¹.

We have observed a star behind the Cygnus Loop supernova remnant using the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite to study the line-of-sight interstellar medium structures toward and through this prototypical remnant. An sdOB star, KPD 2055+3111, was identified from Ultraviolet Imaging Telescope UV images and lies in projection within the bright northeast Cygnus Loop filaments (NGC 6992). This is the first known UV background source for the Cygnus Loop. We have observed this star as well as the directly adjacent emission-line filaments. Although the intrinsic spectrum of the star is complex, a broad O vi λ1032 absorption line due the Cygnus Loop is present in the stellar spectrum, confirming that the star lies beyond the Cygnus Loop. Optical spectroscopy of the star and model fits permits a distance estimate to the star of 576 ± 61 pc, thus providing an independent upper limit on the distance to the Cygnus Loop. Numerous absorption transitions of molecular hydrogen are present in the FUSE spectrum of KPD 2055+3111. Assessment of the properties of the H₂ indicates a column density of (3.3 ± 0.6) × 10¹⁶ cm⁻² and a two-temperature J-level population T(J = 0–1) = 106 ± 40 K and T(J = 2–5) = 850 ± 230 K. There is no direct evidence from line widths, component structure, or velocity displacements that the detected H₂ is associated with the Cygnus Loop as opposed to the interstellar gas along the sight line, so either source remains viable. The O vi emission line profiles directly adjacent to line of sight to the star show dramatic variability on small (20'') spatial scales, highlighting how differently the UV-emitting gas can be distributed compared with optical and other wave bands. This impacts the ability to directly compare the emission and absorption components along the sight line.

Axisymmetric magnetohydrodynamic simulations have been applied to investigate (1) the interrelation between a central stellar magnetosphere and stellar wind with a surrounding magnetized disk outflow, and (2) how the overall formation of a large scale jet is affected by that. The initial magnetic field distribution applied is a superposition of two components—the stellar dipole and the surrounding disk magnetic field—in either parallel or antiparallel alignment. Correspondingly, the mass outflow is launched as stellar wind plus disk wind. Our simulations evolve from an initial state in hydrostatic equilibrium with an initially force-free magnetic field configuration. Due to differential rotation between star and disk, a strong toroidal magnetic field component is induced. The stellar dipole inflates and opens up on large scale. Stellar wind and disk wind may evolve in a pair of collimated outflows. However, the existence of a reasonably strong disk wind component is essential for collimation. The classical disk jet, as known from previous numerical studies, becomes less collimated due to the pressure of the central stellar wind. In some simulations we observe the generation of strong flares triggering a sudden change in the outflow mass loss rate (or velocity) by a factor of two, accompanied by a redistribution in the radial profile of momentum flux and jet velocity across the jet. We discuss the hypothesis that these flares may trigger internal shocks in the asymptotic jets which are observed as knots.

In a systematic study, we compare the density statistics in high-resolution numerical experiments of supersonic isothermal turbulence, driven by the usually adopted solenoidal (divergence-free) forcing and by compressive (curl-free) forcing. We find that for the same rms Mach number, compressive forcing produces much stronger density enhancements and larger voids compared to solenoidal forcing. Consequently, the Fourier spectra of density fluctuations are significantly steeper. This result is confirmed using the Δ-variance analysis, which yields power-law exponents β ∼ 3.4 for compressive forcing and β ∼ 2.8 for solenoidal forcing. We obtain fractal dimension estimates from the density spectra and Δ-variance scaling, and by using the box counting, mass size, and perimeter area methods applied to the volumetric data, projections, and slices of our turbulent density fields. Our results suggest that compressive forcing yields fractal dimensions significantly smaller compared to solenoidal forcing. However, the actual values depend sensitively on the adopted method, with the most reliable estimates based on the Δ-variance, or equivalently, on Fourier spectra. Using these methods, we obtain D ∼ 2.3 for compressive and D ∼ 2.6 for solenoidal forcing, which is within the range of fractal dimension estimates inferred from observations (D ∼ 2.0–2.7). The velocity dispersion to size relations for both solenoidal and compressive forcings obtained from velocity spectra follow a power law with exponents in the range 0.4–0.5, in good agreement with previous studies.

We study the emission and dissipation of acoustic waves from cool dense clouds in pressure equilibrium with a hot, volume-filling dilute gas component. In our model, the clouds are exposed to a source of ionizing radiation whose flux level varies with time, forcing the clouds to pulsate. We estimate the rate at which acoustic energy is radiated away by an ensemble of clouds and the rate at which it is absorbed by, and dissipated in, the hot dilute phase. We show that acoustic energy can be a substantial heating source of the hot gas phase when the mass in the cool component is a substantial fraction of the total gas mass. We investigate the applicability of our results to the multiphase media of several astrophysical systems, including quasar outflows and cooling flows. We find that acoustic heating could have a substantial effect on the thermal properties of the hot phase in those systems.

A new radiative driven implosion (RDI) model based on smoothed particle hydrodynamics technique is developed and applied to investigate the morphological evolutions of molecular clouds under the effect of ionizing radiation. This model self-consistently includes the self-gravity of the cloud in the hydrodynamical evolution, the UV radiation component in the radiation transferring equations, the relevant heating and cooling mechanisms in the energy evolution, and a comprehensive chemical network. The simulation results reveal that under the effect of ionizing radiation, a molecular cloud may evolve through different evolutionary sequences. Depending on its initial gravitational state, the evolution of a molecular cloud does not necessarily follow a complete morphological evolution sequence from type A→B→C, as described by previous RDI models. When confronted with observations, the simulation results provide satisfactory physical explanations for a series of puzzles derived from bright-rimmed clouds observations. The consistency of the modeling results with observations shows that the self-gravity of a molecular cloud should not be neglected in any investigation on the dynamical evolution of molecular clouds when they are exposed to ionizing radiation.

We report the results of a Submillimeter Array (SMA) interferometric observation of 21 μm source IRAS 07134+1005 in the CO J = 3–2 line. In order to determine the morphokinematic properties of the molecular envelope of the object, we construct a model using the Shape software to model the observed CO map. We find that the molecular gas component of the envelopes can be interpreted as a geometrically thick expanding torus with an expanding velocity of 8 km s⁻¹. The inner and outer radii of the torus determined by fitting Shape models are 12 and 30, respectively. The inner radius is consistent with the previous values determined by radiative transfer modeling of the spectral energy distribution and mid-infrared imaging of the dust component. The radii and expansion velocity of the torus suggest that the central star left the asymptotic giant branch about 1140–1710 years ago, and that the duration of the equatorial enhanced mass loss is about 2560–3130 years. From the absence of an observed jet, we suggest that the formation of a bipolar outflow may lag behind in time from the creation of the equatorial torus.

Numerical simulation of magnetohydrodynamic (MHD) turbulence makes it possible to study accretion dynamics in detail. However, special effort is required to connect inflow dynamics (dependent largely on angular momentum transport) to radiation (dependent largely on thermodynamics and photon diffusion). To this end, we extend the flux-conservative, general relativistic MHD (GRMHD) code HARM from axisymmetry to full three dimensions. The use of an energy conserving algorithm allows the energy dissipated in the course of relativistic accretion to be captured as heat. The inclusion of a simple optically thin cooling function permits explicit control of the simulated disk's geometric thickness as well as a direct calculation of both the amplitude and location of the radiative cooling associated with the accretion stresses. Fully relativistic ray-tracing is used to compute the luminosity received by distant observers. For a disk with aspect ratio H/r ≃ 0.1 accreting onto a black hole with spin parameter a/M = 0.9, we find that there is significant dissipation beyond that predicted by the classical Novikov–Thorne model. However, much of it occurs deep in the potential, where photon capture and gravitational redshifting can strongly limit the net photon energy escaping to infinity. In addition, with these parameters and this radiation model, significant thermal and magnetic energy remains with the gas and is accreted by the black hole. In our model, the net luminosity reaching infinity is 6% greater than the Novikov–Thorne prediction. If the accreted thermal energy were wholly radiated, the total luminosity of the accretion flow would be ≃20% greater than the Novikov–Thorne value.

We report on–off pointed MAMBO observations at 1.2 mm of 61 Spitzer-selected star-forming galaxies from the Spitzer Wide Area Infrared Extragalactic Legacy survey (SWIRE). The sources are selected on the basis of bright 24 μm fluxes (f_24 μm > 0.4 mJy) and of stellar dominated near-infrared spectral energy distributions in order to favor z ∼ 2 starburst galaxies. The average 1.2 mm flux for the whole sample is 1.5 ± 0.2 mJy. Our analysis focuses on 29 sources in the Lockman Hole field where the average 1.2 mm flux (1.9 ± 0.3 mJy) is higher than in other fields (1.1 ± 0.2 mJy). The analysis of the multiwavelength spectral energy distributions indicates that these sources are starburst galaxies with far-infrared luminosities from 10¹² to 10^13.3L_☉, and stellar masses of ∼0.2–6 × 10¹¹M_☉. Compared to submillimeter selected galaxies (SMGs), the SWIRE-MAMBO sources are among those with the largest 24 μm/1.2 mm flux ratios. The origin of such large ratios is investigated by comparing the average mid-infrared spectra and the stacked far-infrared spectral energy distributions of the SWIRE-MAMBO sources and of SMGs. The mid-infrared spectra, available for a handful of sources, exhibit strong polycyclic aromatic hydrocarbon (PAH) features, and a warm dust continuum. The warm dust continuum contributes ∼34% of the mid-infrared emission, and is likely associated with an AGN component. This contribution is consistent with what is found in SMGs. The large 24 μm/1.2 mm flux ratios are thus not due to AGN emission, but rather to enhanced PAH emission compared to SMGs. The analysis of the stacked far-infrared fluxes yields warmer dust temperatures than typically observed in SMGs. Our selection favors warm ultraluminous infrared sources at high-z, a class of objects that is rarely found in SMG samples. Indeed SMGs are not common among bright 24 μm sources (e.g., only about 20% of SMGs have f_24 μm > 0.4 mJy). Our sample is the largest Spitzer-selected sample detected at millimeter wavelengths currently available.

We present 26 point-sources discovered with Chandra within 200'' (≈20 kpc) of the center of the barred supergiant galaxy NGC 1365. The majority of these sources are high-mass X-ray binaries, containing a neutron star or a black hole accreting from a luminous companion at a sub-Eddington rate. Using repeat Chandra and XMM-Newton, as well as optical observations, we discuss in detail the natures of two highly variable ultraluminous X-ray sources (ULXs): NGC 1365 X1, one of the most luminous ULXs known since the ROSAT era, which is X-ray variable by a factor of 30, and NGC 1365 X2, a newly discovered transient ULX, variable by a factor of >90. Their maximum X-ray luminosities ((3–5) × 10⁴⁰ erg s⁻¹, measured with Chandra) and multiwavelength properties suggest the presence of more exotic objects and accretion modes: accretion onto intermediate mass black holes (IMBHs) and beamed/super-Eddington accretion onto solar-mass compact remnants. We argue that these two sources have black hole masses higher than those of the typical primaries found in X-ray binaries in our Galaxy (which have masses of <20 M_☉), with a likely black-hole mass of 40–60 M_☉ in the case of NGC 1365 X1 with a beamed/super-Eddington accretion mode, and a possible IMBH in the case of NGC 1365 X2 with M = 80–500 M_☉.

A variety of intriguing polarization patterns are created when polarization observations of single pulses from radio pulsars are displayed in a two-dimensional projection of the Poincaré sphere. In many pulsars, the projections produce two clusters of data points that reside at antipodal points on the sphere. The clusters are formed by fluctuations in polarization amplitude that are parallel to the unit vectors representing the polarization states of the wave propagation modes in the pulsar magnetosphere. In other pulsars, however, the patterns are more complex, resembling annuli and bow ties or bars. The formation of these complex patterns is not understood and largely unexplored. An empirical model of pulsar polarization is used to show that these patterns arise from polarization fluctuations that are perpendicular to the mode vectors. The model also shows that the modulation index of the polarization amplitude is an indicator of polarization pattern complexity. A stochastic version of generalized Faraday rotation can cause the orientation of the polarization vectors to fluctuate and is a possible candidate for the perpendicular fluctuations incorporated in the model. Alternative models indicate that one mode experiences perpendicular fluctuations and the other does not, suggesting that the fluctuations could also be due to a mode-selective random process, such as scattering in the magnetosphere. A polarization stability analysis of the patterns implies that processes intrinsic to the emission are more effective in depolarizing the emission than fluctuations in the orientation of its polarization vector.

We present deep H i 21 cm and optical observations of the face-on spiral galaxy M 83 obtained as part of a project to search for high-velocity clouds (HVCs) in nearby galaxies. Anomalous-velocity neutral gas is detected toward M 83, with 5.6 × 10⁷M_☉ of H i contained in a disk rotating 40–50 km s⁻¹ more slowly in projection than the bulk of the gas. We interpret this as a vertically extended thick disk of neutral material, containing 5.5% of the total H i within the central 8 kpc. Using an automated source detection algorithm to search for small-scale H i emission features, we find eight distinct, anomalous-velocity H i clouds with masses ranging from 7 × 10⁵ to 1.5 × 10⁷M_☉ and velocities differing by up to 200 km s⁻¹ compared to the H i disk. Large on-disk structures are coincident with the optical spiral arms, while unresolved off-disk clouds contain no diffuse optical emission down to a limit of 27 r' mag per square arcsec. The diversity of the thick H i disk and larger clouds suggests the influence of multiple formation mechanisms, with a galactic fountain responsible for the slowly rotating disk and on-disk discrete clouds, and tidal effects responsible for off-disk cloud production. The mass and kinetic energy of the H i clouds are consistent with the mass exchange rate predicted by the galactic fountain model. If the HVC population in M 83 is similar to that in our own Galaxy, then the Galactic HVCs must be distributed within a radius of less than 25 kpc.

We observed a solar microflare over a wide temperature range with three instruments aboard the SOHO spacecraft (Coronal Diagnostic Spectrometer (CDS), Extreme-ultraviolet Imaging Telescope (EIT), and Michelson Doppler Imager (MDI)), TRACE (1600 Å), GOES, and RHESSI. The microflare's properties and behavior are those of a miniature flare undergoing gentle chromospheric evaporation, likely driven by nonthermal electrons. Extreme-ultraviolet spectra were obtained at a rapid cadence (9.8 s) with CDS in stare mode that included emission lines originating from the chromosphere (temperature of formation T_m ≈ 1 × 10⁴ K) and transition region (TR), to coronal and flare (T_m ≈ 8 × 10⁶ K) temperatures. Light curves derived from the CDS spectra and TRACE images (obtained with a variable cadence ≈34 s) reveal two precursor brightenings before the microflare. After the precursors, chromospheric and TR emission are the first to increase, consistent with energy deposition by nonthermal electrons. The initial slow rise is followed by a brief (20 s) impulsive EUV burst in the chromospheric and TR lines, during which the coronal and hot flare emission gradually begin to increase. Relative Doppler velocities measured with CDS are directed upward with maximum values ≈20 km s⁻¹ during the second precursor and shortly before the impulsive peak, indicating gentle chromospheric evaporation. Electron densities derived from an O iv line intensity ratio (T_m ≈ 1.6 × 10⁵ K) increased from 2.6 × 10¹⁰ cm⁻³ during quiescent times to 5.2 × 10¹¹ cm⁻³ at the impulsive peak. The X-ray emission observed by RHESSI peaked after the impulsive peak at chromospheric and TR temperatures and revealed no evidence of emission from nonthermal electrons. Spectral fits to the RHESSI data indicate a maximum temperature of ≈13 MK, consistent with a slightly lower temperature deduced from the GOES data. Magnetograms from MDI show that the microflare occurred in and around a growing island of negative magnetic polarity embedded in a large area of positive magnetic field. The microflare was compact, covering an area of 4 × 10⁷ km² in the EIT image at 195 Å, and appearing as a point source located 7'' west of the EIT source in the RHESSI image. TRACE images suggest that the microflare filled small loops.

We use the X-ray dust halo of the low-mass X-ray binary 4U 1724−307, located in the globular cluster Terzan 2, to probe the interstellar medium along this line of sight (LOS). The X-ray dust halo arises from X-rays scattering off of interstellar dust grains. Using a low optical depth sight line to determine the Chandra ACIS point-spread function, we extracted the radial profile as a function of energy and used it to determine the H column density (N_H) and cloud location along the LOS for several dust grain models, including the commonly-used models of MRN and WD. The resulting N_H values were used to determine the reddening E(B − V), which was then compared with the average E(B − V) for this sight line found by other workers. We found that for this LOS, only the ZDA BARE-AC-S, BARE-GR-FG, and BARE-GR-S models yield reddenings within 1σ of the literature average.

Supermassive black hole (SMBH) coalescence in galaxy mergers is believed to be one of the primary sources of very low frequency gravitational waves (GWs). Significant contribution of the GWs comes from mergers of massive galaxies with redshifts z < 2. Very few previous studies gave the merger rate of massive galaxies. We selected a large sample (1209) of close pairs of galaxies with projected separations 7 < r_p < 50 kpc from 87,889 luminous early-type galaxies (M_r < −21.5) from the Sloan Digital Sky Survey Data Release 6. These pairs constitute a complete volume-limited sample in the local universe (z < 0.12). Using our newly developed technique, 249 mergers have been identified by searching for interaction features. From them, we found that the merger fraction of luminous early-type galaxies is 0.8%, and the merger rate in the local universe is R_g ∼ (1.0 ± 0.4) × 10⁻⁵ Mpc⁻³ Gyr⁻¹ with an uncertainty mainly depending on the merging timescale. We estimated the masses of SMBHs in the centers of merging galaxies based on their luminosities. We found that the chirp mass distribution of the SMBH binaries follows a power law with an index of −3.0 ± 0.5 in the range 5 × 10⁸–5 × 10⁹M_☉. Using the SMBH population in the mergers and assuming that the SMBHs can be efficiently driven into the GW regime, we investigated the stochastic GW background in the frequency range 10⁻⁹–10⁻⁷ Hz. We obtained the spectrum of the GW background of h_c(f) ∼ 10⁻¹⁵(f/yr⁻¹)^−2/3, which is one magnitude higher than that obtained by Jaffe & Backer in 2003, but consistent with those calculated from galaxy-formation models.

The results of a study of the asymptotic giant branch (AGB) phase of stellar evolution are presented. Abundances have been determined for Fe, C, O, the light s-process elements, Y and Zr, the heavy s-process elements, La and Nd, and the r-process element, Eu. The expected relationship between enhanced C, increasing C/O ratio, and enhanced s-process elements has been quantified. Results are presented to provide observational data with which to compare theoretical predictions. The results in this paper confirm previously suggested relationships between C, C/O, and s-process element enhancements. It is seen that AGB stars show C/O ratios from C/O ∼ 0.4 to 1.0, while C enhancements lie between [C/Fe] = 0.1–0.9 dex. Enhancements of s-process elements are as much as [s/Fe] ∼ 1.0 dex for the stars in which C is also greatly enhanced.

This paper presents an analysis of observational data on the p-mode spectrum of the star α Cen B, and a comparison with theoretical computations of the stochastic excitation and damping of the modes. We find that at frequencies ≳4500 μHz, the model damping rates appear to be too weak to explain the observed shape of the power spectral density of α Cen B. The conclusion rests on the assumption that most of the disagreement is due to problems modeling the damping rates, not the excitation rates, of the modes. This assumption is supported by a parallel analysis of BiSON Sun-as-a-star data, for which it is possible to use analysis of very long timeseries to place tight constraints on the assumption. The BiSON analysis shows that there is a similar high-frequency disagreement between theory and observation in the Sun. We demonstrate that by using suitable comparisons of theory and observation it is possible to make inference on the dependence of the p-mode linewidths on frequency, without directly measuring those linewidths, even though the α Cen B dataset is only a few nights long. Use of independent measures from a previous study of the α Cen B linewidths in two parts of its spectrum also allows us to calibrate our linewidth estimates for the star. The resulting calibrated linewidth curve looks similar to a frequency-scaled version of its solar cousin, with the scaling factor equal to the ratio of the respective acoustic cut-off frequencies of the two stars. The ratio of the frequencies at which the onset of high-frequency problems is seen in both stars is also given approximately by the same scaling factor.

We present magnetic flux measurements in seven rapidly rotating M dwarfs. Our sample stars have X-ray and Hα emission indicative of saturated emission, i.e., emission at a high level, independent of rotation rate. Our measurements are made using near-infrared FeH molecular spectra observed with the High Resolution Echelle Spectrometer at Keck. Because of their large convective overturn times, the rotation velocity of M stars with small Rossby numbers is relatively slow and does not hamper the measurement of Zeeman splitting. The Rossby numbers of our sample stars are as small as 0.01. All our sample stars exhibit magnetic flux of kG strength. We find that the magnetic flux saturates in the same regime as saturation of coronal and chromospheric emission, at a critical Rossby number of around 0.1. The filling factors of both field and emission are near unity by then. We conclude that the strength of surface magnetic fields remains independent of rotation rate below that; making the Rossby number yet smaller by a factor of 10 has little effect. These saturated M-star dynamos generate an integrated magnetic flux of roughly 3 kG, with a scatter of about 1 kG. The relation between emission and flux also has substantial scatter.

We present our latest results on near- to mid-infrared (MIR) observation of supernova (SN) 2006jc at 200 days after the discovery using the Infrared Camera (IRC) on board AKARI. The near-infrared (2–5 μm) spectrum of SN 2006jc is obtained for the first time and is found to be well interpreted in terms of the thermal emission from amorphous carbon of 800 ± 10 K with the mass of 6.9 ± 0.5 × 10⁻⁵ M_☉ that was formed in the SN ejecta. This dust mass newly formed in the ejecta of SN 2006jc is in a range similar to those obtained for other several dust-forming core-collapse supernovae based on recent observations (i.e., 10⁻³–10⁻⁵ M_☉). MIR photometric data with AKARI/IRC MIR-S/S7, S9W, and S11 bands have shown excess emission over the thermal emission by hot amorphous carbon of 800 K. This MIR excess emission is likely to be accounted for by the emission from warm amorphous carbon dust of 320 ± 10 K with the mass of 2.7^+0.7_−0.5 × 10⁻³ M_☉ rather than by the band emission of astronomical silicate and/or silica grains. This warm amorphous carbon dust is expected to have been formed in the mass-loss wind associated with the Wolf–Rayet stellar activity before the SN explosion. Our result suggests that a significant amount of dust is condensed in the mass-loss wind prior to the SN explosion.

We show that measures of star formation rates (SFRs) for infrared galaxies using either single-band 24 μm or extinction-corrected Paα luminosities are consistent in the total infrared luminosity = L(TIR) ∼ 10¹⁰L_☉ range. MIPS 24 μm photometry can yield SFRs accurately from this luminosity upward: SFR(M_☉ yr⁻¹) = 7.8 × 10⁻¹⁰L(24 μm, L_☉) from L(TIR) = 5× 10⁹ L_☉ to 10¹¹ L_☉ and SFR = 7.8 × 10⁻¹⁰L(24 μm, L_☉)(7.76 × 10⁻¹¹L(24))^0.048 for higher L(TIR). For galaxies with L(TIR) ⩾ 10¹⁰L_☉, these new expressions should provide SFRs to within 0.2 dex. For L(TIR) ⩾ 10¹¹L_☉, we find that the SFR of infrared galaxies is significantly underestimated using extinction-corrected Paα (and presumably using any other optical or near-infrared recombination lines). As a part of this work, we constructed spectral energy distribution templates for eleven luminous and ultraluminous purely star forming infrared galaxies and over the spectral range 0.4 μm to 30 cm. We use these templates and the SINGS data to construct average templates from 5 μm to 30 cm for infrared galaxies with L(TIR) = 5× 10⁹ to 10¹³L_☉. All of these templates are made available online.

We investigate the effects of weakly interacting massive particle (WIMP) dark matter annihilation on the formation of Population III.1 (Pop III.1) stars. We consider the relative importance of cooling due to baryonic radiative processes and heating due to WIMP annihilation. We analyze the dark matter and gas profiles of several halos formed in cosmological-scale numerical simulations. The heating rate depends sensitively on the dark matter density profile, which we approximate with a power law $\rho _{\chi }\propto r^{-\alpha _\chi }$, in the numerically unresolved inner regions of the halo. If we assume a self-similar structure so that α_χ ≃ 1.5 as measured on the resolved scales ∼1 pc, then for a fiducial WIMP mass of 100 GeV, the heating rate is typically much smaller (<10⁻³) than the cooling rate for densities up to n_H = 10¹⁷ cm⁻³. In one case, where α_χ = 1.65, the heating rate becomes similar to the cooling rate by a density of n_H = 10¹⁵ cm⁻³. The dark matter density profile is expected to steepen in the central baryon-dominated region ≲1 pc due to adiabatic contraction, and we observe this effect, though with low resolution, in our numerical models. From these we estimate α_χ ≃ 2.0. Heating now dominates cooling above n_H ≃ 10¹⁴ cm⁻³, in agreement with the study of Spolyar, Freese, & Gondolo. We expect that this leads to the formation of an equilibrium structure with baryonic and dark matter density distributions exhibiting a flattened central core. Examining such equilibria, we find that the total luminosities due to WIMP annihilation are relatively constant and ∼10³ L_☉, set by the radiative luminosity of the baryonic core. We discuss the implications for Pop III.1 star formation, particularly the subsequent growth of the protostar. Even if the initial protostar fails to accumulate any additional dark matter, its contraction to the main sequence could be significantly delayed by WIMP annihilation heating, potentially raising the mass scale of Pop III.1 stars to masses ≫100 M_☉.

We have identified an X-ray transient (hereafter M15 X-3) in the globular cluster M15 from an archival Chandra grating observation. M15 X-3 appears at an X-ray luminosity of 6 × 10³³ erg s⁻¹ with a spectrum consistent with an absorbed power law of photon index 1.51 ± 0.14. The object is identifiable in archival Chandra HRC-I observations with an X-ray luminosity of (2–6)×10³¹ erg s⁻¹ and apparently soft colors, suggesting a neutron star low-mass X-ray binary in quiescence. We also observe it in outburst in a 2007 Chandra HRC-I observation, and in archival 1994–1995 ROSAT HRI observations. We identify a likely optical/ultraviolet (UV) counterpart with a (possibly transient) UV excess from archival Hubble Space Telescope data, which suggests a main-sequence companion. We argue that M15 X-3's behavior is similar to that of the very faint X-ray transients which have been observed in the Galactic center. We discuss several explanations for its very low X-ray luminosity, with the assumption that we have detected its companion. M15 X-3's uniquely low extinction and well determined distance make it an excellent target for future studies.

To evaluate the effect of turbulent heating in the thermal balance of interstellar clouds, we develop an extension of the log-Poisson intermittency model to supersonic turbulence. The model depends on a parameter, d, interpreted as the dimension of the most dissipative structures. By comparing the model with the probability distribution of the turbulent dissipation rate in a simulation of supersonic and super-Alfvénic turbulence, we find a best-fit value of d = 1.64. We apply this intermittency model to the computation of the mass-weighted probability distribution of the gas temperature of molecular clouds, high-mass star-forming cores, and cold diffuse H i clouds. Our main results are: (1) the mean gas temperature in molecular clouds can be explained as the effect of turbulent heating alone, while cosmic-ray heating may dominate only in regions where the turbulent heating is low; (2) the mean gas temperature in high-mass star-forming cores with typical full width at half-maximum of ∼ 6 km s⁻¹ (corresponding to a one-dimensional rms velocity of 2.5 km s⁻¹) may be completely controlled by turbulent heating, which predicts a mean value of approximately 36 K, two to three times larger than the mean gas temperature in the absence of turbulent heating; and (3) the intermittency of the turbulent heating can generate enough hot regions in cold diffuse H i clouds to explain the observed CH⁺ abundance, if the rms velocity on a scale of 1 pc is at least 3 km s⁻¹, in agreement with previous results based on incompressible turbulence. Because of its importance in the thermal balance of molecular clouds and high-mass star-forming cores, the process of turbulent heating may be central in setting the characteristic stellar mass and in regulating molecular chemical reactions.

Monte Carlo simulation is one of the best tools to study the complex spectra of Compton-thick active galactic nuclei (AGNs) and to figure out the relation between their nuclear structures and X-ray spectra. We have simulated X-ray spectra of Compton-thick AGNs obscured by an accretion torus whose structure is characterized by a half-opening angle, an inclination angle of the torus relative to the observer, and a column density along the equatorial plane. We divided the simulated spectra into three components: one direct component, an absorbed reflection component, and an unabsorbed reflection component. We then deduced the dependences of these components on the parameters describing the structure of the torus. Our simulation results were applied to fit the wide-band spectrum of the Seyfert 2 galaxy Mrk 3 obtained by Suzaku. The spectral analysis indicates that we observe the nucleus along a line of sight intercepting the torus near its edge, and the column density along the equatorial plane was estimated to be ∼10²⁴ cm⁻². Using this model, we can estimate the luminosities of both the direct emission and the emission irradiating the surrounding matter. This is useful to find the time variability and time lag between the direct and reflected light.

In order to better determine the physical properties of hot, massive stars as a function of metallicity, we obtained very high signal-to-noise ratio optical spectra of 26 O and early B stars in the Magellanic Clouds. These allow accurate modeling even in cases where the He i λ4471 line has an equivalent width of only a few tens of m Å. The spectra were modeled with FASTWIND, with good fits obtained for 18 stars; the remainder show signatures of being binaries. We include stars in common to recent studies to investigate possible systematic differences. The "automatic" FASTWIND modeling method of Mokiem and collaborators produced temperatures 1100 K hotter on average, presumably due to the different emphasis given to various temperature-sensitive lines. More significant, however, is that the automatic method always produced a "best" result for each star, even ones we identify as composite (binaries). The temperatures found by the TLUSTY/CMFGEN modeling of Bouret, Heap, and collaborators yielded temperatures 1000 K cooler than ours, on average. Significant outliers were due either to real differences in the data (some of the Bouret/Heap data were contaminated by moonlight continua) or the fact that we could detect the He i line needed to better constrain the temperature. Our new data agree well with the effective temperature scale we previously presented. We confirm that the "Of" emission characteristics do not track luminosity classes in exactly the same manner as in Milky Way stars. We revisit the issue of the "mass discrepancy," finding that some of the stars in our sample do have spectroscopic masses that are significantly smaller than those derived from stellar evolutionary models. We do not find that the size of the mass discrepancy is simply related to either effective temperature or surface gravity.

We detected a major X-ray outburst from M82 with a duration of 79 days, an average flux of 5 × 10⁻¹¹ erg cm^-2 s⁻¹ in the 2–10 keV band, and strong variability. The X-ray spectrum remained hard throughout the outburst. We obtained a Chandra observation during the outburst that shows that the emission arises from the ultraluminous X-ray source X41.4+60. This source has an unabsorbed flux of (5.4 ± 0.2) × 10⁻¹¹ erg cm^-2 s⁻¹ in the 0.3–8 keV band, equivalent to an isotropic luminosity of 8.5 × 10⁴⁰ erg s⁻¹. The spectrum is adequately fitted with an absorbed power law with a photon index of 1.55 ± 0.05. This photon index is very similar to the value of 1.61 ± 0.06 measured previously while the flux was (2.64 ± 0.14) × 10⁻¹¹ erg cm^-2 s⁻¹. Thus, the source appears to remain in the hard state even at the highest flux levels observed. The X-ray spectral and timing data available for X41.4+60 are consistent with the source being in a luminous hard state and a black hole mass in the range of one to a few thousand solar masses.

This paper continues our previous exploration of the effects of turbulence on mean motion resonances in extrasolar planetary systems. Turbulence is expected to be present in the circumstellar disks that give rise to planets, and these fluctuations act to compromise resonant configurations. This paper extends previous work by considering how interactions between the planets and possible damping effects imposed by the disk affect the outcomes. These physical processes are studied using three related approaches: direct numerical integrations of the three-body problem with additional forcing due to turbulence, model equations that reduce the problem to stochastically driven oscillators, and Fokker–Planck equations that describe the time evolution of an ensemble of such systems. With this combined approach, we elucidate the basic physics of how turbulence can remove extrasolar planetary systems from mean motion resonance. As expected, systems with sufficiently large damping (dissipation) can maintain resonance, in spite of turbulent forcing. In the absence of strong damping, ensembles of these systems exhibit two regimes of behavior, where the fraction of the bound states decreases as a power law or as an exponential. Both types of behavior can be understood through the model developed herein. For systems that have weak interactions between the planets, the model reduces to that of a stochastic pendulum, and the fraction of bound states decreases as a power law P_b ∝ t^−1/2. For highly interactive systems, however, the dynamics are more complicated and the fraction of bound states decreases exponentially with time. We show how planetary interactions lead to drift terms in the Fokker–Planck equation and account for this exponential behavior. In addition to clarifying the physical processes involved, this paper strengthens our original finding that turbulence implies that mean motion resonances should be rare.

We analyzed Chandra observations of three gravitational lenses, SBS 0909+523, FBQS 0951+2635, and B 1152+199, to measure the differential X-ray absorption and the dust-to-gas ratio of the lens galaxies. We successfully detected the differential X-ray absorption in SBS 0909+523 and B 1152+199, and failed to detect it in FBQS 0951+2635 due to the dramatic drop in its flux from the ROSAT epoch. These measurements significantly increase the sample of dust-to-gas ratio measurements in cosmologically distant, normal galaxies. Using the larger sample, we obtain an average dust-to-gas ratio of E(B − V)/N_H = (1.5 ± 0.5) × 10⁻²² mag cm² atoms⁻¹ with an estimated intrinsic dispersion in the ratio of ≃40%. This average dust-to-gas ratio is consistent with our previous measurement and the average Galactic value of 1.7 × 10⁻²² mag cm² atoms⁻¹, and the estimated intrinsic dispersion is also consistent with the 30% observed in the Galaxy. A larger sample size is still needed to improve the measurements and to begin studying the evolution in the ratio with cosmic time. We also detected X-ray microlensing in SBS 0909+523 and significant X-ray variability in FBQS 0951+2635.

We examine Advanced Composition Explorer and Helios 1 data in search of evidence for an anisotropic spectrum of interplanetary magnetic and velocity field fluctuations. Specifically, we focus on the power-law indices of the fluctuation spectra and associated second-order structure functions and ask whether the index varies systematically with the angle between the mean magnetic field and the wind velocity. We extend previous results to show convincingly that it does not. Several popular theories for magnetohydrodynamic turbulence predict a significant variation as part of the turbulent cascade dynamic. We offer some observations on why the predicted anisotropy is not present.

We report the serendipitous discovery of an Einstein Ring in the optical band from the Sloan Digital Sky Survey (SDSS) data and four associated images of a background source. The lens galaxy appears to be a nearby dwarf spheroid at a redshift of 0.0375 ± 0.002. The lensed quasar is at a redshift of 0.6842 ± 0.0014, and its multiple images are distributed almost 360° around the lens nearly along a ring of radius ∼60. Single-component lens models require a mass of the galaxy of almost 10¹²M_☉ within 60 from the lens center. With the available data, we are unable to determine the exact positions, orientations, and fluxes of the quasar and the galaxy, though there appears to be evidence for a double- or multiple-merging image of the quasar. We have also detected strong radio and X-ray emissions from this system. It is indicative that this ring system may be embedded in a group or cluster of galaxies. This unique ring, by virtue of the closeness of the lens galaxy, offers a possible probe of some key issues such as the mass-to-light ratio of intrinsically faint galaxies and the existence of large-scale magnetic fields in elliptical galaxies.

We present a combined X-ray and optical analysis of the cold front cluster Abell 1201 using archival Chandra  data and multi-object spectroscopy taken with the 3.9 m Anglo-Australian and 6.5 m Multiple Mirror Telescopes. This paper represents the first in a series presenting a study of a sample of cold front clusters selected from the Chandra  archives with the aim of relating cold fronts to merger activity, understanding the dynamics of mergers and their effect on the cluster constituents. The Chandra  X-ray imagery of Abell 1201 reveals two conspicuous surface brightness discontinuities that are shown to be cold fronts, and a remnant core structure. Temperature maps reveal a complex multiphase temperature structure with regions of hot gas interspersed with fingers of cold gas. Our optical analysis is based on a sample of 321 confirmed members, whose mean redshift is z = 0.1673 ± 0.0002 and velocity dispersion is 778 ± 36 km s⁻¹. We search for dynamical substructure and find clear evidence for multiple localized velocity substructures coincident with overdensities in the galaxy surface density. Most notably, we find the structure coincident with the remnant X-ray core. Despite the clear evidence for dynamical activity, we find the peculiar velocity distribution does not deviate significantly from Gaussian. We apply two-body dynamical analyses in order to assess which of the substructures are bound, and thus dynamically important in terms of the cluster merger history. We propose that the cold fronts in Abell 1201 are a consequence of its merger with a smaller subunit, which has induced gas motions that gave rise to "sloshing" cold fronts. Abell 1201 illustrates the value of combining multiwavelength data and multiple substructure detection techniques when attempting to ascertain the dynamical state of a cluster.

The discovery of the eccentric binary and millisecond pulsar J1903+03273 has raised interesting questions about the formation mechanisms of this peculiar system. Here we present a born-fast scenario for PSR J1903+03273. We assume that during the supernova (SN) explosion that produced the pulsar, a fallback disk was formed around and accreted onto the newborn neutron star. Mass accretion could accelerate the neutron star's spin to milliseconds, and decrease its magnetic field to ∼10⁸–10⁹ G, provided that there was sufficient mass (∼0.1 M_☉) in the fallback disk. The neutron star became a millisecond pulsar after mass accretion terminated. In the meanwhile the binary orbit has kept to be eccentric (due to the SN explosion) for ∼10⁹ yr. We have performed population synthesis calculations of the evolutions of neutron stars with a fallback disk, and found that there might be tens to hundreds of PSR J1903+03273 like systems in the Galaxy. This scenario also suggests that some fraction of isolated millisecond pulsars in the Galactic disk could be formed through the same channel.

We present Keck adaptive optics imaging of the L4+L4 binary HD 130948BC along with archival Hubble Space Telescope and Gemini North observations, which together span ≈ 70% of the binary's orbital period. From the relative orbit, we determine a total dynamical mass of 0.109 ± 0.003 M_☉ (114 ± 3 M_Jup). The flux ratio of HD 130948BC is near unity, so both components are unambiguously substellar for any plausible mass ratio. An independent constraint on the age of the system is available from the primary HD 130948A (G2V, [M/H] = 0.0). The ensemble of available indicators suggests an age comparable to Hyades, with the most precise age being 0.79^+0.22_−0.15 Gyr based on gyrochronology. Therefore, HD 130948BC is now a unique benchmark among field L and T dwarfs, with a well-determined mass, luminosity, and age. We find that substellar theoretical models disagree with our observations. (1) Both components of HD 130948BC appear to be overluminous by a factor of ≈ 2–3 times compared to evolutionary models. The age of the system would have to be notably younger than the gyro age to ameliorate the luminosity disagreement. (2) Effective temperatures derived from evolutionary models for HD 130948B and C are inconsistent with temperatures determined from spectral synthesis for objects of similar spectral type. Overall, regardless of the adopted age, evolutionary and atmospheric models give inconsistent results, which indicate systematic errors in at least one class of models, possibly both. The masses of HD 130948BC happen to be very near the theoretical mass limit for lithium burning, and thus measuring the differential lithium depletion between B and C will provide a uniquely discriminating test of theoretical models. The potential underestimate of luminosities by evolutionary models would have wide-ranging implications; therefore, a more refined estimate age for HD 130948A is critically needed.

We report on an XMM-Newton observation of the z = 1.055 quasar and Gigahertz Peaked Spectrum (GPS) source 3C 287. Our 62.3 ks observation provides an exceptional X-ray view of a prominent member of this important subclass of active galactic nuclei (AGNs). The X-ray spectra of 3C 287 are consistent with a simple absorbed power law with a spectral index of Γ = 1.72 ±  0.02. Our fits imply a bolometric luminosity of L = 5.8 ±  0.2 × 10⁴⁵ erg s⁻¹ over the 0.3–10.0 keV band; this gives a mass lower limit of M_BH min ⩾ 4.6 × 10⁷ M_☉ assuming X-rays contribute 10% of the bolometric luminosity and radiation at the Eddington limit. Iron emission lines are common in the X-ray spectra of many AGNs, but the observed spectra appear to rule out strong emission lines in 3C 287. The simple power-law spectrum and the absence of strong emission lines may support a picture where our line of sight intersects a relativistic jet. Milliarcsecond radio imaging of 3C 287 appears to support this interpretation. We discuss our results in the context of different AGNs subclasses and the possibility that GPS sources harbor newly formed black hole jets.

We present a catalog of 5039 broad absorption line (BAL) quasars (QSOs) in the Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) QSO catalog that have absorption troughs covering a continuous velocity range ⩾2000 km s⁻¹. We have fitted ultraviolet (UV) continua and line emission in each case, enabling us to report common diagnostics of BAL strengths and velocities in the range −25, 000 to 0 km s⁻¹ for Si iv λ1400, C iv λ1549, Al iii λ1857, and Mg ii λ2799. We calculate these diagnostics using the spectrum listed in the DR5 QSO catalog, and also for spectra from additional SDSS observing epochs when available. In cases where BAL QSOs have been observed with Chandra or XMM-Newton, we report the X-ray monochromatic luminosities of these sources. We confirm and extend previous findings that BAL QSOs are more strongly reddened in the rest-frame UV than non-BAL QSOs, and that BAL QSOs are relatively X-ray weak compared to non-BAL QSOs. The observed BAL fraction is dependent on the spectral signal-to-noise ratio (S/N); for higher S/N sources, we find an observed BAL fraction of ≈ 15%. BAL QSOs show a similar Baldwin effect as for non-BAL QSOs, in that their C iv emission equivalent widths decrease with increasing continuum luminosity. However, BAL QSOs have weaker C iv emission in general than do non-BAL QSOs. Sources with higher UV luminosities are more likely to have higher-velocity outflows, and the BAL outflow velocity and UV absorption strength are correlated with relative X-ray weakness. These results are in qualitative agreement with models that depend on strong X-ray absorption to shield the outflow from overionization and enable radiative acceleration. In a scenario in which BAL trough shapes are primarily determined by outflow geometry, observed differences in Si iv and C iv trough shapes would suggest that some outflows have ion-dependent structure.

We use the deep ground-based optical photometry of the Lyman Break Galaxy (LBG) Survey to derive robust measurements of the faint-end slope (α) of the UV luminosity function (LF) at redshifts 1.9 ⩽ z ⩽ 3.4. Our sample includes >2000 spectroscopic redshifts and ≈31000 LBGs in 31 spatially independent fields over a total area of 3261 arcmin². These data allow us to select galaxies to 0.07L* and 0.10L* at z ∼ 2 and z ∼ 3, respectively. A maximum-likelihood analysis indicates steep values of α(z = 2) = −1.73 ± 0.07 and α(z = 3) = −1.73 ± 0.13. This result is robust to luminosity-dependent systematics in the Lyα equivalent width and reddening distributions, and is similar to the steep values advocated at z ≳ 4, and implies that ≈93% of the unobscured UV luminosity density at z ∼ 2–3 arises from sub-L* galaxies. With a realistic luminosity-dependent reddening distribution, faint to moderately luminous galaxies account for ≳70% and ≳25% of the bolometric luminosity density and present-day stellar mass density, respectively, when integrated over 1.9 ⩽ z < 3.4. We find a factor of 8–9 increase in the star-formation rate density between z ∼ 6 and z ∼ 2, due to both a brightening of L* and an increasing dust correction proceeding to lower redshifts. Combining the UV LF with stellar mass estimates suggests a relatively steep low-mass slope of the stellar mass function at high redshift. The previously observed discrepancy between the integral of the star-formation history and stellar mass density measurements at z ∼ 2 may be reconciled by invoking a luminosity-dependent reddening correction to the star-formation history combined with an accounting for the stellar mass contributed by UV-faint galaxies. The steep and relatively constant faint-end slope of the UV LF at z ≳ 2 contrasts with the shallower slope inferred locally, suggesting that the evolution in the faint-end slope may be dictated simply by the availability of low-mass halos capable of supporting star formation at z ≲ 2.

We consider accretion onto newborn black holes following the collapse of rotating massive stellar cores, at the threshold where a centrifugally supported disk gives way to nearly radial inflow for low angular momentum. For realistic initial conditions taken from pre-supernova (pre-SN) evolution calculations, the densities and temperatures involved require the use of a detailed equation of state and neutrino cooling processes, as well as a qualitative consideration of the effects of general relativity. Through two-dimensional dynamical calculations we show how the energy release is affected by the rotation rate and the strength of angular momentum transport, giving rise to qualitatively different solutions in limits of high and low angular momentum, each being capable of powering a gamma-ray burst (GRB). We explore the likelihood of producing Fe-group elements in the two regimes and suggest that while large and massive centrifugally supported disks are capable of driving strong outflows with a possible SN-like signature, quasi-radial flows lack such a feature and may produce a GRB without such an accompanying feature, as seen in GRB060505.

The link between turbulence in star-forming environments and protostellar jets remains controversial. To explore issues of turbulence and fossil cavities driven by young stellar outflows, we present a series of numerical simulations tracking the evolution of transient protostellar jets driven into a turbulent medium. Our simulations show both the effect of turbulence on outflow structures and, conversely, the effect of outflows on the ambient turbulence. We demonstrate how turbulence will lead to strong modifications in jet morphology. More importantly, we demonstrate that individual transient outflows have the capacity to re-energize decaying turbulence. Our simulations support a scenario in which the directed energy/momentum associated with cavities is randomized as the cavities are disrupted by dynamical instabilities seeded by the ambient turbulence. Consideration of the energy power spectra of the simulations reveals that the disruption of the cavities powers an energy cascade consistent with Burgers'-type turbulence and produces a driving scale length associated with the cavity propagation length. We conclude that fossil cavities interacting either with a turbulent medium or with other cavities have the capacity to sustain or create turbulent flows in star-forming environments. In the last section, we contrast our work and its conclusions with previous studies which claim that jets cannot be the source of turbulence.

Models that reproduce the observed high-velocity clouds (HVCs) also predict clouds at lower radial velocities that may easily be confused with Galactic disk (|z|< 1 kpc) gas. We describe the first search for these low-velocity halo clouds (LVHCs) using Infrared Astronomical Satellite (IRAS) data and the initial data from the Galactic Arecibo L-band Feed Array survey in H i. The technique is based upon the expectation that such clouds should, like HVCs, have very limited infrared (IR) thermal dust emission as compared to their H i column density. We describe our "displacement-map" technique for robustly determining the dust-to-gas ratio (DGR) of clouds and the associated errors that take into account the significant scatter in the IR flux from the Galactic disk gas. We find that there exist lower-velocity clouds that have extremely low DGRs, consistent with being in the Galactic halo—candidate LVHCs. We also confirm the lack of dust in many HVCs with the notable exception of complex M, which we consider to be the first detection of dust in HVCs. We do not confirm the previously reported detection of dust in complex C. In addition, we find that most intermediate- and low-velocity clouds that are part of the Galactic disk have a higher 60 μm/100 μm flux ratio than is typically seen in Galactic H i, which is consistent with a previously proposed picture in which fast-moving Galactic clouds have smaller, hotter dust grains.

Optical spectra of the bright Type II-L supernova SN 1979C obtained in April 2008 with the 6.5 m Multiple Mirror Telescope are compared with archival late-time spectra to follow the evolution of its optical emission over the age range of 11–29 years. We estimate an Hα flux decrease of around 35% from 1993 to 2008 but noticeable increases in the strength of blueshifted emission of forbidden oxygen lines. While the maximum expansion of the broad ∼6700 km s⁻¹ Hα emission appears largely unchanged from 1993, we find a significant narrowing of the double-peaked emission profiles in the [O i] λλ6300, 6364 and [O ii] λλ7319, 7330 lines. A comparison of late-time optical spectra of a few other Type II SNe which, like SN 1979C, exhibit bright late-time X-ray, optical, and radio emissions, suggests that blueshifted double-peaked oxygen emission profiles may be a common phenomenon. Finally, detection of a faint, broad emission bump centered around 5800 Å suggests the presence of WC-type Wolf–Rayet stars in the SN's host star cluster.

Zeeman observations of molecular clouds yield the line-of-sight component B_LOS of the magnetic vector B, which makes it possible to test the two major extreme-case theories of what drives star formation—ambipolar diffusion or turbulence. However, only one of the three components of B is measurable, so tests have been statistical rather than direct, and they have not been definitive. We report here observations of the Zeeman effect in the 18 cm lines of OH in the envelope regions surrounding four molecular cloud cores toward which detections of B_LOS have been achieved in the same lines, and evaluate the ratio of mass-to-magnetic flux, M/Φ, between the cloud core and envelope. This relative M/Φ measurement reduces uncertainties in previous studies, such as the angle between B and the line of sight and the value of [OH/H]. Our result is that for all four clouds, the ratios ${\cal R}$ of the core to the envelope values of M/Φ are less than 1. Stated another way, the ratios ${\cal R^\prime }$ of the core to the total cloud M/Φ are less than 1. The extreme case or idealized (no turbulence) ambipolar diffusion theory of core formation requires the ratio of the central to total M/Φ to be approximately equal to the inverse of the original subcritical M/Φ, or ${\cal R^\prime } > 1$. The probability that all four of our clouds have ${\cal R^\prime } > 1$ is 3 × 10⁻⁷; our results are therefore significantly in contradiction with the hypothesis that these four cores were formed by ambipolar diffusion. Highly super-Alfvénic turbulent simulations yield a wide range of relative M/Φ, but favor a ratio ${\cal R} < 1$, as we observe. Our experiment is limited to four clouds, and we can only directly test the predictions of the extreme-case "idealized" models of ambipolar-diffusion driven star formation, which have a regular magnetic field morphology. Nonetheless, our experimental results are not consistent with the "idealized" strong field, ambipolar diffusion theory of star formation. Comparisons of our results with more realistic models and simulations that include both ambipolar diffusion and turbulence may help to refine our understanding of the relative importance of magnetic fields and turbulence in the star formation process.

Based on the modeling of the central emission-line width measured over subarcsecond apertures with the Hubble Space Telescope, we present stringent upper bounds on the mass of the central supermassive black hole, M_•, for a sample of 105 nearby galaxies (D < 100 Mpc) spanning a wide range of Hubble types (E−Sc) and values of the central stellar velocity dispersion, σ_c (58–419 km s⁻¹). For the vast majority of the objects, the derived M_• upper limits run parallel and above the well-known M_•–σ_c relation independently of the galaxy distance, suggesting that our nebular line-width measurements trace rather well the nuclear gravitational potential. For values of σ_c between 90 and 220 km s⁻¹, 68% of our upper limits falls immediately above the M_•–σ_c relation without exceeding the expected M_• values by more than a factor 4.1. No systematic trends or offsets are observed in this σ_c range as a function of the galaxy Hubble type or with respect to the presence of a bar. For 6 of our 12 M_• upper limits with σ_c <90 km s⁻¹, our line-width measurements are more sensitive to the stellar contribution to the gravitational potential, either due to the presence of a nuclear stellar cluster or because of a greater distance compared to the other galaxies at the low-σ_c end of the M_•–σ_c relation. Conversely, our M_• upper bounds appear to lie closer to the expected M_• in the most massive elliptical galaxies with values of σ_c above 220 km s⁻¹. Such a flattening of the M_•–σ_c relation at its high-σ_c end would appear consistent with a coevolution of supermassive black holes and galaxies driven by dry mergers, although better and more consistent measurements for σ_c and K-band luminosity are needed for these kinds of objects before systematic effects can be ruled out.

We present a detailed temporal analysis of a set of hydrodynamic and magnetohydrodynamic (MHD) simulations of geometrically thin (h/r ∼ 0.05) black hole accretion disks. The black hole potential is approximated by the Paczynski–Wiita pseudo-Newtonian potential. In particular, we use our simulations to critically assess two widely discussed models for high-frequency quasi-periodic oscillations (QPOs), global oscillation modes (diskoseismology), and parametric resonance instabilities. We find that initially disturbed hydrodynamic disks clearly display the trapped global g-mode oscillation predicted by linear perturbation theory. In contrast, the sustained turbulence produced in the simulated MHD disks by the magnetorotational instability does not excite these trapped g-modes. We cannot say at present whether the MHD turbulence actively damps the hydrodynamic g-mode. Our simulated MHD disks also fail to display any indications of a parametric resonance instability between the vertical and radial epicyclic frequencies. However, we do see characteristic frequencies at any given radius in the disk corresponding to local acoustic waves. We also conduct a blind search for any QPO in a proxy light curve based on the instantaneous mass accretion rate of the black hole, and place an upper limit of 2% on the total power in any such feature. We highlight the importance of correcting for secular changes in the simulated accretion disk when performing temporal analyses.

The detection of a dipole anisotropy in the sky distribution of sources in large-scale radio surveys can be used to constrain the magnitude and direction of our local motion with respect to an isotropically distributed extragalactic radio source population. Such a population is predicted to be present at cosmological redshifts in an isotropically expanding universe. The extragalactic radio source population is observed to have a median redshift of z ∼ 1, a much later epoch than the cosmic microwave background (z ∼ 1100). I consider the detectability of a velocity dipole anisotropy in radio surveys having a finite number of source counts. The statistical significance of a velocity dipole detection from radio source counts is also discussed in detail. I find that existing large-scale radio survey catalogs do not have a sufficient number of sources to detect the expected velocity dipole with statistical significance, even if survey masking and flux calibration complications can be completely eliminated (i.e., if both the surveys and observing instruments are perfect). However, a dipole anisotropy should be easily detectable in future radio surveys planned with next-generation radio facilities, such as the Low Frequency Array and the Square Kilometer Array; tight constraints on the dipole magnitude and direction should be possible if flux calibration problems can be sufficiently minimized or corrected and contamination from local sources can be eliminated.

We performed a Cr-K emission line survey in young supernova remnants (SNRs) with the Chandra archival data. Our sample includes W49B, Cas A, Tycho, and Kepler. We confirmed the existence of the Cr line in W49B and discovered this emission line in the other three SNRs. The line center energies, equivalent widths (EWs), and fluxes of the Cr lines are given. The Cr in Cas A is in a high ionization state, while that in Tycho and Kepler is in a much lower one. We find a good positive correlation between Cr and Fe line center energies, suggesting a common origin of Cr and Fe in the nucleosynthesis, which is consistent with the theoretical predictions. We propose that the EW ratio between Cr and Fe can be used as a supplementary constraint on the progenitors' properties and the explosion mechanism.

Sagittarius A*, the supermassive compact object at the center of the Galaxy, exhibits outbursts in the near infrared (NIR) and X-ray domains. These flares are likely due to energetic events very close to the central object, on a scale of a few Schwarzschild radii. Optical interferometry will soon be able to provide astrometry with an accuracy of this order (≃10 μas). In this article, we use recent photometric NIR data observed with the adaptive optics system NACO at the Very Large Telescope combined with simulations in order to deploy a method to test the nature of the flares and to predict the possible outcome of observations with the Very Large Telescope Interferometer. To accomplish this we implement a hot-spot model and investigate its appearance for a remote observer in terms of light curves and centroid tracks, based on general relativistic ray-tracing methods. First, we use a simplified model of a small steady source in order to investigate the relativistic effects qualitatively. A more realistic scenario is then being developed by fitting our model to existing flare data. While indications for the spin of the black hole and multiple images due to lensing effects are marginal in the light curves, astrometric measurements offer the possibility to reveal these high-order general relativistic effects. This study makes predictions on these astrometric measurements and leads us to the conclusion that future infrared interferometers will be able to detect proper motion of hot spots in the vicinity of Sagittarius A*.

Mergers between stellar-mass black holes (BHs) will be key sources of gravitational radiation for ground-based detectors. However, the rates of these events are highly uncertain, given that such systems are invisible. One formation scenario involves mergers in field binaries, where our lack of complete understanding of common envelopes and the distribution of supernova kicks has led to rate estimates that range over a factor of several hundreds. A different, and highly promising, channel involves multiple encounters of binaries in globular clusters or young star clusters. However, we currently lack solid evidence of BHs in almost all such clusters, and their low escape speeds raise the possibility that most are ejected because of supernova recoil. Here, we propose that a robust environment for mergers could be the nuclear star clusters found in the centers of small galaxies. These clusters have millions of stars, BH relaxation times well under a Hubble time, and escape speeds that are several times those of globulars; hence, they retain most of their BHs. We present simulations of the three-body dynamics of BHs in this environment and estimate that, if most nuclear star clusters do not have supermassive BHs that interfere with the mergers, tens of events per year will be detectable with the advanced Laser Interferometer Gravitational-Wave Observatory.

We describe the results from a new instrument which combines Lucky Imaging and adaptive optics (AO) to give the first routine direct diffraction-limited imaging in the visible on a 5 m telescope. With fast image selection and alignment behind the Palomar AO system we obtained Strehl ratios of 5%–20% at 700 nm in a typical range of seeing conditions, with a median Strehl of approximately 12% when 10% of the input frames are selected. At wavelengths around 700 nm the system gave diffraction-limited 35 mas full width at half-maxima (FWHMs). At 950 nm the output Strehl ratio was as high as 36% and at 500 nm the FWHM resolution was as small as 42 mas, with a low Strehl ratio but with resolution improved by a factor of ∼20 compared to the prevailing seeing. To obtain wider fields we also used multiple Lucky Imaging guide stars in a configuration similar to a ground layer AO system. With eight guide stars but very undersampled data we obtained 300 mas resolution across a 30'' × 30'' field of view in the i' band.

We use a suite of cosmological N-body simulations to study the properties of substructure halos (subhalos) in galaxy-sized cold dark matter halos. We extend prior work on the subject by considering the whole population of subhalos physically associated with the main system. These are defined as subhalos that have at some time in the past been within the virial radius of the halo's main progenitor and that have survived as self-bound entities to z = 0. We find that this population extends beyond three times the virial radius, and contains objects on extreme orbits, including a few with velocities approaching the nominal escape speed from the system. We trace the origin of these unorthodox orbits to the tidal dissociation of bound groups of subhalos, which results in the ejection of some subhalos along tidal streams. Ejected subhalos are primarily low-mass systems, leading to mass-dependent biases in their spatial distribution and kinematics: the lower the subhalo mass at accretion time, the less centrally concentrated and kinematically hotter their descendant population. The bias is strongest among the most massive subhalos, but disappears at the low-mass end: below a certain mass, subhalos behave just like test particles in the potential of the main halo. Overall, our findings imply that subhalos identified within the virial radius represent a rather incomplete census of the substructure physically related to a halo: only about one half of all associated subhalos are found today within the virial radius of a halo, and many relatively isolated halos may have actually been ejected in the past from more massive systems. These results may explain the age dependence of the clustering of low-mass halos reported recently by Gao et al., and has further implications for (1) the interpretation of the structural parameters and assembly histories of halos neighboring massive systems; (2) the existence of low-mass dynamical outliers, such as Leo I and And XII in the Local Group; and (3) the presence of evidence for evolutionary effects, such as tidal truncation or ram-pressure stripping, well outside the traditional virial boundary of a galaxy system.

Using state-of-the-art adaptive mesh refinement cosmological hydrodynamic simulations with a spatial resolution of proper 0.21h⁻¹₇₃ kpc in refined subregions embedded within a comoving cosmological volume (27.4h⁻¹₇₃ Mpc)³, we investigate the sizes of galaxies at z = 3 in the standard cold dark matter model. Our simulated galaxies are found to be significantly smaller than the observed ones: while more than one half of the galaxies observed by Hubble Space Telescope and Very Large Telescope ranging from rest-frame UV to optical bands with stellar masses larger than 2 ×  10¹⁰ M_☉ have half-light radii larger than ∼2h⁻¹₇₃ kpc, none of the simulated massive galaxies in the same mass range have half-light radii larger than ∼2h⁻¹₇₃ kpc, after taking into account dust extinction. Corroborative evidence is provided by the rotation curves of the simulated galaxies with total masses of 10¹¹–10¹² M_☉, which display values (300–1000 km s⁻¹) at small radii (∼0.5h⁻¹₇₃ kpc) due to high stellar concentration in the central regions that are larger than those of any well observed galaxies. Possible physical mechanisms to resolve this serious problem include: (1) an early reionization at z_ri ≫ 6 to suppress gas condensation and hence star formation, (2) a strong, internal energetic feedback from stars or central black holes to reduce the overall star formation efficiency, or (3) a substantial small-scale cutoff in the matter power spectrum.

In the coming years, several cosmological surveys will rely on imaging data to estimate the redshift of galaxies, using traditional filter systems with 4–5 optical broad bands; narrower filters improve the spectral resolution, but strongly reduce the total system throughput. We explore how photometric redshift performance depends on the number of filters n_f, characterizing the survey depth by the fraction of galaxies with unambiguous redshift estimates. For a combination of total exposure time and telescope imaging area of 270 hr m², 4–5 filter systems perform significantly worse, both in completeness depth and precision, than systems with n_f ≳ 8 filters. Our results suggest that for low n_f the color–redshift degeneracies overwhelm the improvements in photometric depth, and that even at higher n_f the effective photometric redshift depth decreases much more slowly with filter width than naively expected from the reduction in the signal-to-noise ratio. Adding near-IR observations improves the performance of low-n_f systems, but still the system which maximizes the photometric redshift completeness is formed by nine filters with logarithmically increasing bandwidth (constant resolution) and half-band overlap, reaching ∼0.7 mag deeper, with 10% better redshift precision, than 4–5 filter systems. A system with 20 constant-width, nonoverlapping filters reaches only ∼0.1 mag shallower than 4–5 filter systems, but has a precision almost three times better, δz = 0.014(1 + z) versus δz = 0.042(1 + z). We briefly discuss a practical implementation of such a photometric system: the ALHAMBRA Survey.

We revisit the tidal stability of extrasolar systems harboring a transiting planet and demonstrate that, independently of any tidal model, none, but one (HAT-P-2b) of these planets has a tidal equilibrium state, which implies ultimately a collision of these objects with their host star. Consequently, conventional circularization and synchronization timescales cannot be defined because the corresponding states do not represent the endpoint of the tidal evolution. Using numerical simulations of the coupled tidal equations for the spin and orbital parameters of each transiting planetary system, we confirm these predictions and show that the orbital eccentricity and the stellar obliquity do not follow the usually assumed exponential relaxation but instead decrease significantly, eventually reaching a zero value only during the final runaway merging of the planet with the star. The only characteristic evolution timescale of all rotational and orbital parameters is the lifetime of the system, which crucially depends on the magnitude of tidal dissipation within the star. These results imply that the nearly circular orbits of transiting planets and the alignment between the stellar spin axis and the planetary orbit are unlikely to be due to tidal dissipation. Other dissipative mechanisms, for instance interactions with the protoplanetary disk, must be invoked to explain these properties.

The recent detection of Sagittarius A* at λ = 1.3 mm on a baseline from Hawaii to Arizona demonstrates that millimeter wavelength very long baseline interferometry (VLBI) can now spatially resolve emission from the innermost accretion flow of the Galactic center region. Here, we investigate the ability of future millimeter VLBI arrays to constrain the spin and inclination of the putative black hole and the orientation of the accretion disk major axis within the context of radiatively inefficient accretion flow (RIAF) models. We examine the range of baseline visibility and closure amplitudes predicted by RIAF models to identify critical telescopes for determining the spin, inclination, and disk orientation of the Sgr A* black hole and accretion disk system. We find that baseline lengths near 3 Gλ have the greatest power to distinguish amongst RIAF model parameters, and that it will be important to include new telescopes that will form north–south baselines with a range of lengths. If an RIAF model describes the emission from Sgr A*, it is likely that the orientation of the accretion disk can be determined with the addition of a Chilean telescope to the array. Some likely disk orientations predict detectable fluxes on baselines between the continental United States and even a single 10–12 m dish in Chile. The extra information provided from closure amplitudes by a four-antenna array enhances the ability of VLBI to discriminate amongst model parameters.

The growth of supermassive black holes and their host galaxies are thought to be linked, but the precise nature of this symbiotic relationship is still poorly understood. Both observations and simulations of galaxy formation suggest that the energy input from active galactic nuclei (AGNs), as the central supermassive black hole accretes material and grows, heats the interstellar material and suppresses star formation. In this Letter, we show that most host galaxies of moderate-luminosity supermassive black holes in the local universe have intermediate optical colors that imply the host galaxies are transitioning from star formation to quiescence, the first time this has been shown to be true for all AGNs independent of obscuration. The intermediate colors suggest that star formation in the host galaxies ceased roughly 100 Myr ago. This result indicates that either the AGNs are very long lived, accreting for more than 1 Gyr beyond the end of star formation, or there is a ∼100 Myr time delay between the shutdown of star formation and detectable black hole growth. The first explanation is unlikely given current estimates for AGN lifetimes, so low-luminosity AGNs must shut down star formation before substantial black hole accretion activity is detected. The scarcity of AGN host galaxies in the blue cloud reported here challenges scenarios where significant star formation and black hole growth are coeval. Lastly, these observations also strongly support the "Unified Model" of AGNs as the host galaxy colors are independent of obscuration toward the central engine.

We demonstrate for the first time that gaseous halos of disk galaxies can play a vital role in recycling metal-rich gas ejected from the bulges and thus in promoting the chemical evolution of the disks. Our numerical simulations show that metal-rich stellar winds from bulges in disk galaxies can be accreted onto the thin disks owing to hydrodynamical interaction between the gaseous ejecta and the gaseous halos, if the mean densities of the halos (ρ_hg) are as high as 10⁻⁵ cm⁻³. The total amount of gas that is ejected from a bulge through a stellar wind and then accreted onto the disk depends mainly on ρ_hg and the initial velocity of the stellar wind. About ∼1% of gaseous ejecta from bulges in disk galaxies of scale length a_d can be accreted onto disks around R ∼ 2.5a_d for a reasonable set of model parameters. We discuss these results in the context of the origin of the surprisingly high metallicities of the solar neighborhood disk stars in the Galaxy. We also discuss some implications of the present results in terms of chemical evolution of disk galaxies with possibly different ρ_hg in different galaxy environments.

The MAGIC telescope observed the region around the distant blazar 3C 66A for 54.2 hr in 2007 August–December. The observations resulted in the discovery of a γ-ray source centered at celestial coordinates R.A. = 2^h23^m12^s and decl. = 43°07 (MAGIC J0223+430), coinciding with the nearby radio galaxy 3C 66B. A possible association of the excess with the blazar 3C 66A is discussed. The energy spectrum of MAGIC J0223+430 follows a power law with a normalization of (1.7 ± 0.3_stat ± 0.6_syst) × 10⁻¹¹ TeV⁻¹ cm⁻² s⁻¹ at 300 GeV and a photon index Γ = −3.10 ± 0.31_stat ± 0.2_syst.

The origin of S0 galaxies is discussed in the framework of early mergers in a cold dark matter cosmology, and in a scenario where S0s are assumed to be former spirals stripped of gas. From an analysis of 127 early-type disk galaxies (S0–Sa), we find a clear correlation between the scale parameters of the bulge (r_eff) and the disk (h_R), a correlation which is difficult to explain if these galaxies were formed in mergers of disk galaxies. However, the stripping hypothesis, including quiescent star formation, is not sufficient to explain the origin of S0s either, because it is not compatible with our finding that S0s have a significantly smaller fraction of bars (46% ± 6%) than their assumed progenitors, S0/a galaxies (93% ± 5%) or spirals (64%–69%). Our conclusion is that even if a large majority of S0s were descendants of spiral galaxies, bars and ovals must play an important role in their evolution. The smaller fraction particularly of strong bars in S0 galaxies is compensated by a larger fraction of ovals/lenses (97% ± 2% compared to 82%–83% in spirals), many of which might be weakened bars. We also found massive disklike bulges in nine of the S0 galaxies, which might have formed at an early gas-rich stage of galaxy evolution.

Magnetic field strengths inferred for relativistic outflows including gamma-ray bursts (GRBs) and active galactic nuclei are larger than naively expected by orders of magnitude. We present three-dimensional relativistic magnetohydrodynamic simulations demonstrating amplification and saturation of a magnetic field by a macroscopic turbulent dynamo triggered by the Kelvin–Helmholtz shear instability. We find rapid growth of electromagnetic energy due to the stretching and folding of field lines in the turbulent velocity field resulting from nonlinear development of the instability. Using conditions relevant for GRB internal shocks and late phases of GRB afterglow, we obtain amplification of the electromagnetic energy fraction to _B ∼ 5 × 10⁻³. This value decays slowly after the shear is dissipated and appears to be largely independent of the initial field strength. The conditions required for operation of the dynamo are the presence of velocity shear and some seed magnetization both of which are expected to be commonplace. We also find that the turbulent kinetic energy spectrum for the case studied obeys Kolmogorov's 5/3 law and that the electromagnetic energy spectrum is essentially flat with the bulk of the electromagnetic energy at small scales.

We propose a nonlinear self-consistent model of the turbulent nonresonant particle acceleration in solar flares. We simulate temporal evolution of the spectra of charged particles accelerated by strong long-wavelength MHD turbulence taking into account the back-reaction of the accelerated particles on the turbulence. The main finding is that the nonlinear coupling of accelerated particles with MHD turbulence results in prominent evolution of the spectra of accelerated particles, which can be either soft–hard–soft or soft–hard–harder depending on the particle injection efficiency. Such evolution patterns are widely observed in hard X-ray and gamma-ray emission from solar flares.

If binary intermediate-mass black holes (IMBHs; with masses between 100 and 10⁴ M_☉) form in dense stellar clusters, their inspiral will be detectable with the planned Laser Interferometer Space Antenna (LISA) out to several Gpc. Here, we present a study of the dynamical evolution of such binaries using a combination of direct N-body techniques (when the binaries are well separated) and three-body relativistic scattering experiments (when the binaries are tight enough that interactions with stars occur one at a time). We find that for reasonable IMBH masses there is only a mild effect on the structure of the surrounding cluster even though the binary binding energy can exceed the binding energy of the cluster. We demonstrate that, contrary to standard assumptions, the eccentricity in the LISA band can be in some cases as large as ∼0.2–0.3 and that it induces a measurable phase difference from circular binaries in the last year before merger. We also show that, even though energy input from the binary decreases the density of the core and slows down interactions, the total time to coalescence is short enough (typically less than a 100 million years) that such mergers will be unique snapshots of clustered star formation.

We calculate the γ-ray albedo due to cosmic-ray interactions with debris (small rocks, dust, and grains) in the Oort Cloud. We show that under reasonable assumptions a significant proportion of what is called the "extragalactic γ-ray background" could be produced at the outer frontier of the solar system, and may be detectable by the Large Area Telescope, the primary instrument on the Fermi Gamma-ray Space Telescope. If detected, it could provide unique direct information about the total column density of material in the Oort Cloud that is difficult to access by any other method. The same γ-ray production process takes place in other populations of small solar system bodies, such as Main Belt asteroids, Jovian and Neptunian Trojans, and Kuiper Belt objects. Their detection can be used to constrain the total mass of debris in these systems.

For very slow white dwarf accretors in cataclysmic variables, Townsley & Bildsten found a relation between the accretion rate $\dot{M}$ and the central temperature T_c of the white dwarf. According to this relation, for $\dot{M}$ less than 10⁻¹⁰M_☉ yr⁻¹, T_c is much lower than 10⁷ K. Motivated by this study, we follow the thermonuclear runaway on massive white dwarfs (M_WD = 1.25–1.40 M_☉) with T_c lower than 10⁷ K, accreting matter of solar composition. We demonstrate that in this range of the relevant parameter space (T_c, M_WD, and $\dot{M}$), the slope of the relation between the peak temperatures achieved during the runaway and T_c becomes much steeper than its value for T_c above 10⁷ K. The peak temperatures we derive can lead to nuclear breakout from the conventional "hot carbon–nitrogen–oxygen" cycle. When breakout conditions are achieved the heavy-element abundances can show a much wider variety than what is possible with the common enrichment mechanisms.

Magnetic field estimates for nearby isolated neutron stars (INS) help to constrain both the characteristics of the population and the nature of their peculiar X-ray spectra. From a series of XMM-Newton observations of RX J2143.0+0654, we measure a spin-down rate of $\dot{\nu }= {(-4.6\pm 2.0) \times 10^{-16}}\;{{\rm Hz}\;{\rm s}^{-1}}$. While this does not allow a definitive measurement of the dipole magnetic field strength, fields of ≳10¹⁴ G such as those inferred from the presence of a spectral absorption feature at 0.75 keV are excluded. Instead, the field is most likely around 2 × 10¹³ G, very similar to those of other INS. We not only suggest that this similarity most likely reflects the influence of magnetic field decay on this population, but also discuss a more speculative possibility that it results from peculiar conditions on the neutron-star surface. We find no evidence for spectral variability above the ∼2% level. We confirm the presence of the 0.75 keV feature found earlier, and find tentative evidence for an additional absorption feature at 0.4 keV.