Table of contents

We discuss an analytic approach for modeling structure formation in sheets, filaments, and knots. This is accomplished by combining models of triaxial collapse with the excursion set approach: sheets are defined as objects that have collapsed along only one axis, filaments have collapsed along two axes, and halos are objects in which triaxial collapse is complete. In the simplest version of this approach, which we develop here, large-scale structure shows a clear hierarchy of morphologies: the mass in large-scale sheets is partitioned up among lower mass filaments, which themselves are made up of still lower mass halos. Our approach provides analytic estimates of the mass fraction in sheets, filaments, and halos and its evolution, for any background cosmological model and any initial fluctuation spectrum. In the currently popular ΛCDM model, our analysis suggests that more than 99% of the cosmic mass is in sheets, and 72% in filaments, with mass larger than 10¹⁰ M_☉ at the present time. For halos, this number is only 46%. Our approach also provides analytic estimates of how halo abundances at any given time correlate with the morphology of the surrounding large-scale structure and how halo evolution correlates with the morphology of large-scale structure.

We develop an Lyα radiative transfer (RT) Monte Carlo code for cosmological simulations. High resolution, along with appropriately treated cooling, can result in simulated environments with very high optical depths. Thus, solving the Lyα RT problem in cosmological simulations can take an unrealistically long time. For this reason, we develop methods to speed up the Lyα RT. With these accelerating methods, along with the parallelization of the code, we make the problem of Lyα RT in the complex environments of cosmological simulations tractable. We test the RT code against simple Lyα emitter models, and then we apply it to the brightest Lyα emitter of a gasdynamics+N-body adaptive refinement tree (ART) simulation at z ≃ 8. We find that recombination rather than cooling radiation Lyα photons is the dominant contribution to the intrinsic Lyα luminosity of the emitter, which is ≃4.8 × 10⁴³ ergs s^-1. The size of the emitter is pretty small, making it unresolved for currently available instruments. Its spectrum before adding the Lyα Gunn-Peterson absorption (GPA) resembles that of static media, despite some net inward radial peculiar motion. This is because for such high optical depths as those in ART simulations, velocities of order some hundreds of kilometers per second are not important. We add the GPA in two ways: (1) we assume no damping wing, corresponding to the situation where the emitter lies within the H II region of a very bright quasar, and (2) we allow for the damping wing. Including the damping wing leads to a maximum line brightness suppression by roughly a factor of ~62. The line fluxes, even though quite faint for current ground-based telescopes, should be within reach for JWST.

Equilibrium configurations for a self-gravitating scalar field with self-interaction are constructed. The corresponding Schrödinger-Poisson (SP) system is solved using finite differences, assuming spherical symmetry. It is shown that equilibrium configurations of the SP system are late-time attractor solutions for initially quite arbitrary density profiles, which relax and virialize through the emission of scalar field bursts—a process dubbed gravitational cooling. Among other potential applications, these results indicate that scalar field dark matter models (in their different flavors) tolerate the introduction of a self-interaction term in the SP equations. This study can be useful in exploring models in which dark matter in galaxies is not pointlike.

We compute the covariance expected between the spherical harmonic coefficients a_ℓm of the cosmic microwave temperature anisotropy if the universe had a compact topology. For a fundamental cell size smaller than the distance to the decoupling surface, off-diagonal components carry more information than the diagonal components (the power spectrum). We use a maximum likelihood analysis to compare the Wilkinson Microwave Anisotropy Probe (WMAP) first-year data to models with a cubic topology. The data are compatible with finite flat topologies with fundamental domain L > 1.2 times the distance to the decoupling surface at a 95% confidence level. The WMAP data show reduced power at the quadrupole and octopole, but they do not show the correlations expected for a compact topology and are indistinguishable from infinite models.

We have observed the Corona Borealis supercluster with the Millimeter and Infrared Testa Grigia Observatory (MITO), located in the Italian Alps, at 143, 214, 272, and 353 GHz. We present a description of the measurements, data analysis, and results of the observations together with a comparison with observations performed at 33 GHz with the Very Small Array (VSA) interferometer situated at the Teide Observatory (Tenerife, Spain). Observations have been made in the direction of the supercluster toward a cosmic microwave background (CMB) cold spot previously detected in a VSA temperature map. Observational strategy and data analysis are described in detail, explaining the procedures used to disentangle primary and secondary anisotropies in the resulting maps. From a first level of data analysis, we find evidence in MITO data of primary anisotropy but still with room for the presence of secondary anisotropy, especially when VSA results are included. With a second level of data analysis using map making and the maximum entropy method, we claim a weak detection of a faint signal compatible with a SZ effect, characterized at most by a Comptonization parameter y = (7.8) × 10^-6 68% CL. The low level of confidence in the presence of a SZ signal invites us to study this sky region with higher sensitivity and angular resolution experiments such as the already-planned upgraded versions of VSA and MITO.

The magnification induced by gravitational microlensing is sensitive to the size of a source relative to the Einstein radius, the natural microlensing scale length. This paper investigates the effect of source size in the case in which the microlensing masses are distributed with a bimodal mass function, with solar-mass stars representing the normal stellar masses and smaller masses (down to 8.5 × 10^-5M_☉) representing a dark matter component. It is found that there exists a critical regime in which the dark matter is initially seen as individual compact masses, but with increasing source size the compact dark matter acts as a smooth mass component. This study reveals that interpretation of microlensing light curves, especially claims of small-mass dark matter lenses embedded in an overall stellar population, must consider the important influence of the size of the source.

We present the first high-redshift Hubble diagram for Type II-P supernovae (SNe II-P) based on five events at redshift up to z ~ 0.3. This diagram was constructed using photometry from the Canada-France-Hawaii Telescope Supernova Legacy Survey and absorption-line spectroscopy from the Keck Observatory. The method used to measure distances to these supernovae is based on recent work by Hamuy & Pinto and exploits a correlation between the absolute brightness of SNe II-P and the expansion velocities derived from the minimum of the Fe II λ5169 P Cygni feature observed during the plateau phases. We present three refinements to this method that significantly improve the practicality of measuring the distances of SNe II-P at cosmologically interesting redshifts. These are an extinction correction measurement based on the V-I colors at day 50, a cross-correlation measurement for the expansion velocity, and the ability to extrapolate such velocities accurately over almost the entire plateau phase. We apply this revised method to our data set of high-redshift SNe II-P and find that the resulting Hubble diagram has a scatter of only 0.26 mag, thus demonstrating the feasibility of measuring the expansion history, with present facilities, using a method independent of that based on supernovae of Type Ia.

We report near-simultaneous multicolor (RIYJHK) observations made with the MAGNUM 2 m telescope of the gamma-ray burst GRB 050904 detected by the Swift satellite. The spectral energy distribution shows a very large break between the I and J bands. Using intergalactic transmissions measured from high-redshift quasars, we show that the observations place a 95% confidence lower limit of z = 6.18 on the object, consistent with a later measured spectroscopic redshift of 6.29 obtained by Kawai et al. with the Subaru telescope. We show that the break strength in the R and I bands is consistent with that measured in the quasars. Finally, we consider the implications for the star formation history at high redshift.

Whether radio-intermediate quasars possess relativistic jets as radio-loud quasars do is an important issue in the understanding of the origin of radio emission in quasars. In this paper, using the two-epoch radio data obtained during the Faint Images of the Radio Sky at Twenty cm (FIRST) and NRAO VLA Sky Survey (NVSS), we identified 89 radio-variable sources in the Sloan Digital Sky Survey (SDSS). Among them, more than half are radio-intermediate quasars (RL = f_{20 cm}/f_{2500 Å} < 250). For all objects with available multiple-band radio observations, the radio spectra are either flat or inverted. The brightness temperature inferred from the variability is larger than the synchrotron self-Compton limit for a stationary source in 87 objects, indicating relativistic beaming. Considering the sample selection and the viewing angle effect, we conclude that relativistic jets probably exist in a substantial fraction of radio-intermediate quasars.

Using cosmological hydrodynamic simulations of the ΛCDM model, we present a comparison between the simulation sample and real data sample of H I and He II Lyα transmitted flux in the absorption spectra of the QSO HE 2347-4342. The ΛCDM model is successful in simultaneously explaining the statistical features of both H I and He II Lyα transmitted flux. It includes the following features: (1) The power spectra of the transmitted flux of H I and He II can be well fitted on all scales ≥0.28 h^-1 Mpc for H and ≥1.1 h^-1 Mpc for He. (2) The Doppler parameters of absorption features of He II and H I are found to be turbulent broadening. (3) The ratio of He II to H I optical depths are substantially scattered, due to the significant effect of noise. A large part of the η scatter is due to the noise in the He II flux. However, the real data contain more low-η events than the simulation sample. This discrepancy may indicate that the mechanism leading extra fluctuations on the simulation data, such as a fluctuating UV radiation background, is needed. Yet models of these extra fluctuations should satisfy the following constraints: (1) If the fluctuations are Gaussian, they should be limited by the power spectra of observed H I and He II flux. (2) If the fluctuations are non-Gaussian, they should be limited by the observed non-Gaussian features of the H I and He II flux.

We present FUSE and HST STIS observations of the absorption-line system near the emission redshift of the radio-quiet, X-ray-bright quasar HE 0226-4110 (z = 0.495, V = 15.2). The spectra cover the rest-frame wavelength range 610-1150 Å, and we detect a wide range of ionization species, including four adjacent stages of oxygen: O III-VI, which reveal a striking change in gas kinematics with ionization. Examinaton of the O VI λλ1031, 1037 doublet profiles reveals no evidence for partial coverage or unresolved saturated structure. O III is only detected in a narrow feature that is also traced by the H I and C III lines, suggesting that they arise in the same gas. Absorption at the same velocity is also present in other species (N IV, O IV-VI, S IV, and possibly Ne VIII ), but the kinematics differ from the O III, implying production in separate gaseous phases. The combination of H I, O III , and C III information yields an estimate of both the photoionization parameter and the metallicity of the O III-bearing gas: [O/H] = +0.12, log U = -2.29. We discuss two possible locations for the gas in this associated absorption-line system: the narrow emission line region of the quasar, and the halo of the quasar host galaxy. An additional narrow (and thus photoionized) component that is only detected in O VI appears 58 km s^-1 redward of the O III-bearing gas with -0.35 ≲ log U ≲ 0.02. Additional structure is detected in the associated absorber in the form of two broad components that only appear in moderate- to high-ionization species.

We derived the black hole fundamental plane relationship between the 1.4 GHz radio luminosity (L_r), 0.1-2.4 keV X-ray luminosity (L_X), and black hole mass (M) from a uniform broad-line SDSS AGN sample including both radio-loud and radio-quiet X-ray-emitting sources. We found in our sample that the fundamental plane relation has a very weak dependence on the black hole mass, and a tight correlation also exists between the Eddington-luminosity-scaled X-ray and radio luminosities for the radio-quiet subsample. In addition, we noticed that the radio-quiet and radio-loud AGNs have different power-law slopes in the radio-X-ray nonlinear relationship. The radio-loud sample displays a slope of 1.39, which seems consistent with the jet-dominated X-ray model. However, it may also be partly due to the relativistic beaming effect. For the radio-quiet sample the slope of the radio-X-ray relationship is about 0.85, which is possibly consistent with the theoretical prediction from the accretion-flow-dominated X-ray model. We briefly discuss the reason why our derived relationship is different from some previous works and expect the future spectral studies in radio and X-ray bands on individual sources in our sample to confirm our result.

We test the evolution of the correlation between black hole mass and bulge velocity dispersion (M_BH-σ), using a carefully selected sample of 14 Seyfert 1 galaxies at z = 0.36 ± 0.01. We measure velocity dispersion from stellar absorption lines around Mg b (5175 Å) and Fe (5270 Å) using high-S/N Keck spectra and estimate black hole mass from the Hβ line width and the optical luminosity at 5100 Å, based on the empirically calibrated photoionization method. We find a significant offset from the local relation, in the sense that velocity dispersions were smaller for given black hole masses at z = 0.36 than locally. We investigate various sources of systematic uncertainties and find that those cannot account for the observed offset. The measured offset is Δ log M_BH = 0.62 ± 0.10 ± 0.25; i.e., Δ log σ = 0.15 ± 0.03 ± 0.06, where the error bars include a random component and an upper limit to the systematics. At face value, this result implies a substantial growth of bulges in the last 4 Gyr, assuming that the local M_BH-σ relation is the universal evolutionary endpoint. Along with two samples of active galaxies with consistently determined black hole mass and stellar velocity dispersion taken from the literature, we quantify the observed evolution with the best-fit linear relation: Δ log M_BH = (1.66 ± 0.43)z + (0.04 ± 0.09) with respect to the local relationship of Tremaine and coworkers, and Δ log M_BH = (1.55 ± 0.46)z + (0.01 ± 0.12) with respect to that of Ferrarese. This result is consistent with the growth of black holes predating the final growth of bulges at these mass scales (⟨σ⟩ = 170 km s^-1).

We present a ray-tracing technique for radiative transfer modeling of complex three-dimensional (3D) structures that include dense regions of high optical depth, such as that in dense molecular clouds, circumstellar disks, envelopes of evolved stars, and dust tori around active galactic nuclei. The corresponding continuum radiative transfer problem is described, and the numerical requirements for inverse 3D density and temperature modeling are defined. We introduce a relative intensity and transform the radiative transfer equation along the rays to solve machine precision problems and to relax strong gradients in the source term. For the optically thick regions where common ray tracers are forced to perform small trace steps, we give two criteria for making use of a simple approximative solver crossing the optically thick region quickly. Using an example of a density structure with optical depth changes of 6 orders of magnitude and sharp temperature variations, we demonstrate the accuracy of the proposed scheme using a common fifth-order Runge-Kutta ray tracer with adaptive step-size control. In our test case, the gain in computational speed is about a factor of 870. The method is applied in order to calculate the temperature distribution within a massive molecular cloud core for different boundary conditions for the radiation field.

We present the results of timing analysis of XMM-Newton observations of Seyfert 2 galaxies in order to search for differences in the mean properties of Seyfert 1 galaxies and Seyfert 2 galaxies. We selected 13 Seyfert 2 galaxies from the XMM-Newton archive that have hard X-ray components in their spectra and calculated the excess variance (σ) in the 2-10 keV band. We found that six Seyfert 2 galaxies (3C 98, IRAS 05189-2524, MCG -5-23-16, NGC 6300, UGC 4203, and PKS 1814-637) have buried luminous nuclei and that the nuclei have timing properties similar to those of Seyfert 1 nuclei. This indicates that these galaxies are candidates for having buried Seyfert 1 nuclei as expected by the unified Seyfert model. The first five galaxies show significant time variability. The amplitude of the time variability of IRAS 05189-2524 is similar to that of narrow-line Seyfert 1 galaxies. In contrast, the amplitude of variability of the seven other galaxies is quite small, much smaller than that of Seyfert 1 galaxies with similar X-ray luminosity. The lack of short time variability in these objects is explained by the dominance of the reflection component in three galaxies (Mrk 3, Mrk 463, and NGC 7582), and by the presence of very massive black holes and an inferred low accretion rate in the other three galaxies (NGC 1052, NGC 4507, and NGC 7172). For Mrk 348, the significant time variability that is expected based on the estimate of the central black hole mass was not detected.

We calculate the irreducible triplet contribution to galaxy clustering in the cosmological many-body problem. These triplets generally represent short-lived configurations in which three close objects interact with pairwise gravitational forces. From the resulting grand canonical partition function, we obtain higher order analytical expressions for thermodynamic quantities such as specific heats, isothermal compressibility, and thermal expansion in the system. Compared with previous analyses, which included reducible but not irreducible triplets, the additional terms are usually small, especially in the limit of large N. This confirms the thermodynamic results. We also derive the modified spatial distribution functions and show that they agree with recent observational results. The inclusion of triplet and higher order irreducible clusters does not significantly modify the results of the reducible terms in the partition function or of its thermodynamic consequences such as the distribution function.

Protons gain energy in short-range collisions with heavier dark matter particles (DMPs) of comparable velocity dispersion. We examine the conditions under which the heating of baryons by scattering off DMPs can offset radiative cooling in the cores of galaxy clusters. Collisions with a constant momentum transfer cross section, σ_xp, independent of the relative velocity of the colliding particles, cannot produce stable thermal balance. In this case, avoiding an unrealistic increase of the central temperatures yields the upper bound σ_xp < 10^-25 cm²(m_x/m_p), where m_x and m_p are the DMP and proton mass, respectively. However, in clusters with T > 2 keV, a stable balance can be achieved for a power-law dependence on the relative velocity, V, of the form σ_xp ∝ V^a, with a ≲ -3. An advantage of this heating mechanism is that it preserves the metal gradients observed in clusters.

We present a survey of serendipitous extended X-ray sources and optical cluster candidates from the Chandra Multiwavelength Project (ChaMP). Our main goal is to make an unbiased comparison of X-ray and optical cluster detection methods. In 130 archival Chandra pointings covering 13 deg², we use a wavelet decomposition technique to detect 55 extended sources, of which 6 are nearby single galaxies. Our X-ray cluster catalog reaches a typical flux limit of about ~10^-14 ergs cm^-2 s^-1, with a median cluster core radius of 21''. For 56 of the 130 X-ray fields, we use the ChaMP's deep NOAO 4 m MOSAIC g', r', and i' imaging to independently detect cluster candidates using a Voronoi tessellation and percolation (VTP) method. Red-sequence filtering decreases the galaxy fore- and background contamination and provides photometric redshifts to z ~ 0.7. From the overlapping 6.1 deg² X-ray/optical imaging, we find 115 optical clusters (of which 11% are in the X-ray catalog) and 28 X-ray clusters (of which 46% are in the optical VTP catalog). The median redshift of the 13 X-ray/optical clusters is 0.41, and their median X-ray luminosity (0.5-2 keV) is L_X = × 10⁴³ ergs s^-1. The clusters in our sample that are only detected in our optical data are poorer on average (~4 σ) than the X-ray/optically matched clusters, which may partially explain the difference in the detection fractions.

We investigate the relationship between the colors, luminosities, and environments of galaxies in the Sloan Digital Sky Survey spectroscopic sample, using environmental measurements on scales ranging from 0.2 to 6 h^-1 Mpc. We find that (1) the relationship between color and environment persists even to the lowest luminosities we probe (M_r - 5h ~ -14); (2) at luminosities and colors for which the galaxy correlation function has a large amplitude, it also has a steep slope; and (3) in regions of a given overdensity on small scales (1 h^-1 Mpc), the overdensity on large scales (6 h^-1 Mpc) does not appear to relate to the recent star formation history of the galaxies. Of these results, the last has the most immediate application to galaxy formation theory. In particular, it lends support to the notion that a galaxy's properties are related only to the mass of its host dark matter halo, and not to the larger scale environment.

The hierarchical nature of the ΛCDM cosmology poses serious difficulties for the formation of disk galaxies. To help resolve these issues, we describe a new, merger-driven scenario for the cosmological formation of disk galaxies at high redshifts that supplements the standard dissipational collapse model. In this picture, large gaseous disks may be produced from high angular momentum mergers of systems that are gas dominated, i.e., M_gas/(M_gas + M_⋆) ≳ 0.5 at the height of the merger. Pressurization from the multiphase ISM prevents the complete conversion of gas into stars during the merger, and if enough gas remains to form a disk, the remnant eventually resembles a disk galaxy. We perform numerical simulations of galaxy mergers to study how supernovae feedback strength, black hole feedback, progenitor gas fraction, merger mass ratio, and orbital geometry impact the formation of remnant disks. We find that disks can build angular momentum through mergers and the degree of rotational support of the baryons in the remnant is primarily related to feedback processes associated with star formation. Disk-dominated remnants are restricted to form in mergers that are gas dominated at the time of final coalescence. We also show that the formation of rotationally supported stellar systems in mergers is not restricted to idealized orbits, and both gas-rich major and minor mergers can produce disk-dominated stellar remnants. We suggest that the hierarchical nature of the ΛCDM cosmology and the physics of the ISM may act together to form spiral galaxies by building the angular momentum of disks through gas-dominated mergers at high redshifts.

We study the density profiles of collapsed galaxy-size dark matter halos with masses 10¹¹ to 5 × 10¹²M_☉ focusing mostly on the halo outer regions from the formal virial radius R_vir up to 5R_vir-7R_vir. We find that isolated halos in this mass range extend well beyond R_vir exhibiting all properties of virialized objects up to 2R_vir-3R_vir: relatively smooth density profiles and no systematic infall velocities. The dark matter halos in this mass range do not grow as one naively may expect through a steady accretion of satellites; i.e., on average there is no mass infall. This is strikingly different from more massive halos, which have large infall velocities outside the virial radius. We provide an accurate fit for the density profile of these isolated galaxy-size halos. For a wide range 0.01R_vir-2R_vir of radii the halo density profiles are fitted with the approximation ρ = ρ_s exp + ⟨ρ_m⟩, where x ≡ r/r_s, ⟨ρ_m⟩ is the mean matter density of the universe, and the index n is in the range n = 6-7.5. These profiles do not show a sudden change of behavior beyond the virial radius. For larger radii we combine the statistics of the initial fluctuations with the spherical collapse model to obtain predictions for the mean and most probable density profiles for halos of several masses. The model gives excellent results beyond 2-3 formal virial radii for the most probable profile and qualitatively correct predictions for the mean profile.

We investigate the use of spiral arm pitch angles as a probe of disk galaxy mass profiles. We confirm our previous result that spiral arm pitch angles (P) are well correlated with the rate of shear (S) in disk galaxy rotation curves by using a much larger sample (51 galaxies) than used previously (17 galaxies). We use this correlation to argue that imaging data alone can provide a powerful probe of galactic mass distributions out to large look-back times. In contrast to previous work, we show that observed spiral arm pitch angles are similar when measured in the optical (at 0.4 μm) and the near-infrared (at 2.1 μm) with a mean difference of 23 ± 27. This is then used to strengthen the known correlation between P and S using B-band images. We then use two example galaxies to demonstrate how an inferred shear rate coupled with a bulge-disk decomposition model and a Tully-Fisher-derived velocity normalization can be used to place constraints on a galaxy's baryon fraction and dark matter halo profile. We show that ESO 582-G12, a galaxy with a high shear rate (slightly declining rotation curve) at ~10 kpc, favors an adiabatically contracted halo, with high initial NFW concentration (c_vir > 16) and a high fraction of halo baryons in the form of stars (~15%-40%). In contrast, IC 2522 has a low shear rate (rising rotation curve) at ~10 kpc and favors nonadiabatically contracted models with low NFW concentrations (c_vir ≃ 2-8) and a low stellar baryon fraction <10%.

We present models of the coupled evolution of the gaseous and stellar content of galaxies incorporating the formation of H₂ out of H gas. We do so by formulating a subgrid model for gas clouds that uses observed cloud scaling relations and tracks the formation of H₂ on dust grains and its destruction by UV irradiation in the CNM phase, including the effects of shielding by dust and H₂ self-shielding, as well as its collisional destruction in the WNM phase. We then apply our model to the evolution of a typical quiescent dwarf galaxy. Apart from their importance in galaxy evolution, their small size allows our simulations to track the thermal and dynamic evolution of gas as dense as n ~ 100 cm^-3 and as cold as T_k ~ 40 K, where most of the H → H₂ transition (and star formation) takes place. Our findings include (1) a strong dependence of the resulting H₂ gas mass on the ambient metallicity and the adopted H₂ formation rate, (2) constraints on the star formation parameters from the effects of stellar feedback on H₂ formation, and (3) the possibility of a diffuse H₂ gas phase outside star-forming regions. We expect these results to be valid in other types of galaxies for which the H → H₂ phase transition is more difficult to resolve by high-resolution numerical studies (e.g., large spirals). Finally, we briefly examine using an H₂ fraction threshold as a new, more realistic, star formation criterion for use in galaxy simulations.

We aim to settle the debate regarding the fraction of the Local Group's peculiar velocity that is induced by structures beyond the Great Attractor by calculating the dipole anisotropy of the largest, all-sky, truly X-ray-selected cluster sample compiled to date. The sample is the combination of the REFLEX catalog in the southern hemisphere, the eBCS sample in the north, and the CIZA survey in the Galactic plane. The composite REFLEX+eBCS+CIZA sample overcomes many of the problems inherent to previous galaxy and cluster catalogs that limited their effectiveness in determining the origin of the Local Group's motion. From the dipole anisotropy present in the cluster distribution, we determine that 44% of the Local Group's peculiar velocity is due to infall into the Great Attractor region, while 56% is in the form of a large-scale flow induced by more distant overdensities between 130 and 180 h^-1 Mpc away. In agreement with previous analyses, we find that the Shapley supercluster is the single overdensity most responsible for the increase in the dipole amplitude beyond 130 h^-1 Mpc, generating 30.4% of the large-scale contribution. We find that a significant portion of the remainder is due to numerous groupings and loose associations of clusters at roughly the same distance as the Shapley region. We also note the presence of a significant underdensity of clusters in the northern hemisphere roughly 150 h^-1 Mpc away and suggest that the large-scale anisotropy observed in the cluster distribution near this distance may have as much to do with the presence of large overdensities in the south as it does with the lack of superclusters in the north.

We use a combination of high-resolution gas dynamics simulations of high-redshift dwarf galaxies and dissipationless simulations of a Milky Way-sized halo to estimate the expected abundance and spatial distribution of the dwarf satellite galaxies that formed most of their stars around z ~ 8, evolving only little since then. Such galaxies can be considered "fossils" of the reionization era, and studying their properties could provide a direct window into the early, pre-reionization stages of galaxy formation. We show that ~5%-15% of the objects existing at z ~ 8 do indeed survive until the present in a Milky Way-like environment without significant evolution. This implies that it is plausible that the fossil dwarf galaxies do exist in the Local Group. Because such galaxies form their stellar systems early during the period of active merging and accretion, they should have a spheroidal morphology regardless of their current distance from the host galaxy. Their observed counterparts should therefore be identified among the dwarf spheroidal galaxies. We show that both the expected luminosity function and the spatial distribution of dark matter halos that are likely to host fossil galaxies agree reasonably well with the observed distributions of the luminous (L_V ≳ 10⁶L_☉) Local Group fossil candidates near the host galaxy (d ≲ 200 kpc). However, the predicted abundance is substantially larger (by a factor of 2-3) for fainter galaxies (L_V < 10⁶L_☉) at larger distances (d ≳ 300 kpc). We discuss several possible explanations for this discrepancy.

We present ~05 resolution near-infrared integral field spectroscopy of the Hα line emission of 14 z ~ 2 UV-selected BM/BX galaxies, obtained with SINFONI at the ESO Very Large Telescope. The average Hα half-light radius is r_1/2 ≈ 4 h kpc, and line emission is detected over ≳20 h kpc in several sources. In nine galaxies, we detect spatially resolved velocity gradients, from 40 to 410 km s^-1 over ~10 h kpc. The kinematics of the larger systems are generally consistent with orbital motions. Four galaxies are well described by rotating clumpy disks, and we extracted rotation curves out to radii ≳10 h kpc. One or two galaxies exhibit signatures more consistent with mergers. Analyzing all 14 galaxies in the framework of rotating disks, we infer mean inclination- and beam-corrected maximum circular velocities of v_c ~ 180 ± 90 km s^-1 and dynamical masses from ~0.5 to 25 × 10¹⁰hM_☉ within r_1/2. The specific angular momenta of our BM/BX galaxies are similar to those of local late-type galaxies. Moreover, the specific angular momenta of their baryons are comparable to those of their dark matter halos. Extrapolating from the average v_c at 10 h kpc, the virial mass of the typical halo of a galaxy in our sample is 10^11.7±0.5hM_☉. Kinematic modeling of the three best cases implies a ratio of v_c to local velocity dispersion v_c/σ ~ 2-4 and, accordingly, a large geometric thickness. We argue that this suggests a mass accretion (alternatively, gas exhaustion) timescale of ~500 Myr. We also argue that if our BM/BX galaxies were initially gas-rich, their clumpy disks would subsequently lose their angular momentum and form compact bulges on a timescale of ~1 Gyr.

We show that in order to minimize the uncertainties in the N and O abundances of low-mass, low-metallicity (O/H ≤ 1/5 solar) emission-line galaxies, it is necessary to employ separate parameterizations for inferring T_e(N⁺) and T_e(O⁺) from T_e(O⁺²). In addition, we show that for the above systems, the ionization correction factor (ICF) for obtaining N/O from N⁺/O⁺, where the latter is derived from optical emission-line flux ratios, is = 1.08 ± 0.09. These findings are based on state-of-the-art single-star H II region simulations, employing our own modeled stellar spectra as input. Our models offer the advantage of having matching stellar and nebular abundances. In addition, they have O/H as low as 1/50 solar (lower than any past work), as well as log(N/O) and log(C/O) fixed at characteristic values of -1.46 and -0.7, respectively. The above results were used to rederive N and O abundances for a sample of 68 systems with 12 + log(O/H) ≤ 8.1, whose dereddened emission-line strengths were collected from the literature. The analysis of the log(N/O) versus 12 + log(O/H) diagram of the above systems shows that (1) the largest group of objects forms the well-known N/O plateau with a value for the mean (and its statistical error) of -1.43, (2) the objects are distributed within a range in log(N/O) of -1.54 to -1.27 in Gaussian fashion around the mean with a standard deviation of σ = , and (3) a χ² analysis suggests that only a small amount of the observed scatter in log(N/O) is intrinsic.

Spitzer mid-infrared images of the dusty warped disk in the galaxy Centaurus A show a parallelogram-shaped structure. We successfully model the observed mid-infrared morphology by integrating the light from an emitting, thin, and warped disk, similar to that inferred from previous kinematic studies. The models with the best match to the morphology lack dust emission within the inner 0.1-0.8 kpc, suggesting that energetic processes near the nucleus have disturbed the inner molecular disk, creating a gap in the molecular gas distribution.

We present moderate-resolution spectrophotometry of 36 red supergiants (RSGs) in the LMC and 37 RSGs in the SMC. Using the MARCS atmosphere models to fit this spectrophotometry, we determine the stars' physical properties and compare the results to evolutionary models. The (V - R)₀ broadband colors agree with those from fitting the optical spectrophotometry, but (V - K)₀ results show metallicity-dependent systematic differences in the physical properties. We conclude that this is likely due to the limitations of static 1D models, and accept that there is still some uncertainty in the effective temperature scale. We find that the temperature scales for Milky Way, LMC, and SMC K-type supergiants agree with each other, while for M-type supergiants the LMC and SMC scales are cooler than the Galactic scale by 50 and 150 K, respectively. Since spectral classification of RSGs is based on TiO line strengths, it follows that stars with lower abundances of these elements must be cooler in order to have the line strengths associated with a given spectral type. However, this effect is not sufficient to explain the shift in average spectral type between the three galaxies. Instead, metallicity's effect on the coolest extent of stellar evolution is primarily responsible. Our results bring RSGs into much better agreement with stellar evolutionary theory, although the SMC RSGs show a considerably larger spread in effective temperatures at a given luminosity than the LMC stars. This is expected due to the larger effects of rotational mixing in lower metallicity stars. We also find that the reddening distribution of RSGs in the Clouds is skewed significantly toward higher values, consistent with our recent finding that Galactic RSGs show extra extinction due to circumstellar dust.

We have observed a sample of 36 objects in the Small Magellanic Cloud (SMC) with the Infrared Spectrometer on the Spitzer Space Telescope. Nineteen of these sources are carbon stars. An examination of the near- and mid-infrared photometry shows that the carbon-rich and oxygen-rich dust sources follow two easily separated sequences. A comparison of the spectra of the 19 carbon stars in the SMC to spectra from the Infrared Space Observatory (ISO) of carbon stars in the Galaxy reveals significant differences. The absorption bands at 7.5 and 13.7 μm due to C₂H₂ are stronger in the SMC sample, and the SiC dust emission feature at 11.3 μm is weaker. Our measurements of the MgS dust emission feature at 26-30 μm are less conclusive, but this feature appears to be weaker in the SMC sample as well. All of these results are consistent with the lower metallicity in the SMC. The lower abundance of SiC grains in the SMC may result in less efficient carbon-rich dust production, which could explain the excess C₂H₂ gas seen in the spectra. The sources in the SMC with the strongest SiC dust emission tend to have redder infrared colors than the other sources in the sample, which implies more amorphous carbon, and they also tend to show stronger MgS dust emission. The weakest SiC emission features tend to be shifted to the blue; these spectra may arise from low-density shells with large SiC grains.

Self-enrichment processes occurring in the early stages of a globular cluster lifetime are generally invoked to explain the observed CNONaMgAl abundance anticorrelations within individual Galactic globular clusters. We have tested, with fully consistent stellar evolution calculations, whether theoretical isochrones for stars born with the observed abundance anticorrelations satisfy the observational evidence that objects with different degrees of these anomalies lie on essentially identical sequences in the color-magnitude diagram (CMD). To this purpose, we have computed for the first time low-mass stellar models and isochrones with an initial metal mixture that includes the extreme values of the observed abundance anticorrelations and varying initial He mass fractions. Comparisons with "normal" α-enhanced isochrones and suitable Monte Carlo simulations that include photometric errors show that a significant broadening of the CMD sequences occurs only if the helium enhancement is extremely large (in this study, when Y = 0.35) in the stars showing anomalous abundances. Stellar luminosity functions up to the red giant branch tip are also very weakly affected, apart from—depending on the He content of the polluting material—the red giant branch bump region. We also study the distribution of stars along the zero-age horizontal branch and derive general constraints on the relative location of objects with and without abundance anomalies along the observed horizontal branches of globular clusters.

Both diffuse high-energy gamma rays and an extended electron-positron annihilation line emission have been observed in the Galactic Center (GC) region. Although X-ray observations indicate that the Galactic black hole Sgr A* is inactive now, we suggest that Sgr A* can become active when a captured star is tidally disrupted and matter is accreted into the black hole. As a consequence the Galactic black hole could be a powerful source of relativistic protons. We are able to explain the current observed diffuse gamma rays and the very detailed 511 keV annihilation line of secondary positrons by p-p collisions of such protons, with appropriate injection times and energy. Relativistic protons could have been injected into the ambient material if the black hole captured a 50 M_☉ star at several tens times 10⁶ yr ago. An alternative possibility is that the black hole continues to capture stars with ~1 M_☉ every 10⁵ yr. Secondary positrons produced by p-p collisions at energies ≳30 MeV are cooled down to thermal energies by Coulomb collisions and are annihilated in the warm neutral and ionized phases of the interstellar medium with temperatures about several eV, because the annihilation cross section reaches its maximum at these temperatures. It takes about 10 million years for the positrons to cool down to thermal temperatures so that they can diffuse into a very large extended region around the GC. A much more recent star capture may also be able to account for recent TeV observations within 10 pc of the GC, as well as for the unidentified GeV gamma-ray sources found by EGRET at GC. The spectral difference between the GeV and TeV flux could be explained naturally in this model as well.

Resonant relaxation (RR) of orbital angular momenta occurs near massive black holes (MBHs) where the potential is spherical and stellar orbits are nearly Keplerian and so do not precess significantly. The resulting coherent torques efficiently change the magnitude of the angular momenta and rotate the orbital inclination in all directions. As a result, many of the tightly bound stars very near the MBH are rapidly destroyed by falling into the MBH on low angular momentum orbits, while the orbits of the remaining stars are efficiently randomized. We solve numerically the Fokker-Planck equation in energy for the steady state distribution of a single-mass population with an RR sink term. We find that the steady state current of stars, which sustains the accelerated drainage close to the MBH, can be ≲10 larger than that due to noncoherent two-body relaxation alone. RR mostly affects tightly bound stars, and so it increases only moderately the total tidal disruption rate, which is dominated by stars originating from less bound orbits farther away. We show that the event rate of gravitational wave (GW) emission from inspiraling stars, originating much closer to the MBH, is dominated by RR dynamics. The GW event rate depends on the uncertain efficiency of RR. The efficiency indicated by the few available simulations implies rates ≲10 times higher than those predicted by two-body relaxation, which would improve the prospects of detecting such events by future GW detectors, such as LISA. However, a higher, but still plausible, RR efficiency can lead to the drainage of all tightly bound stars and strong suppression of GW events from inspiraling stars. We apply our results to the Galactic MBH and show that the observed dynamical properties of stars there are consistent with RR.

Potential condensed clouds of gas in the Galactic halo are examined in the context of the recent models of cooling, fragmenting clouds building up the baryonic mass of the Galaxy. Five hundred and eighty-two high-velocity clouds are defined as the potential condensed clouds, and the sample's spatial and velocity distributions are presented. With the majority of the hydrogen in the clouds ionized (~85%), the clouds at a distribution of distances within 150 kpc, and their individual total masses below 10⁷M_☉, the total mass in potentially condensed clouds is (1.1-1.4) × 10⁹M_☉. If the tighter distance constraint of <60 kpc is adopted, this mass range drops to (4.5-6.1) × 10⁸M_☉. The implications for the condensing cloud models, as well as feedback and additional accretion methods, are discussed.

Charged energetic particles propagating in solar wind magnetic fields span field irregularities down to very short turbulent scales, not described by the original quasi-linear theory for weak magnetic turbulence. This theory only predicts a field line diffusion on the largest scales, well above the correlation length, inverse of the spectral flattening wavenumber. The quasi-linear prediction for the transport and behavior of magnetic field lines is generalized here to all scales and arbitrary three-dimensional turbulence spectra. New analytical expressions are derived for the field line mean square cross-field displacement ⟨Δx²⟩, and analytical proof is presented for the anomalous transport of the field lines. We find ⟨Δx²⟩ ∝ (Δz)^β, where Δz is the elapsed distance along the average field and β, the transport exponent, can take any value between 0 and 2. A decreasing turbulence spectrum results in a field line supradiffusion (β > 1), while an inverted spectrum implies a subdiffusion (β < 1). Simple expressions are derived for the transport exponent and coefficient. A powerful new method is presented to compute magnetic field lines in the quasi-linear regime of turbulence that allows rapid computation of field lines generated from any three-dimensional turbulence spectrum, including some 10¹⁵ modes and more. Individual field lines computed with this method show how a spectral steepening results in a smoothing of the field lines and how harder spectra give increasingly more short-scale fluctuations. The field line self-similarity, characteristic of power-law spectra, is demonstrated visually, and the anomalous transport of the field lines is confirmed numerically.

New 1.4 GHz VLA observations of the pulsar-powered supernova remnant 3C 58 have resulted in the highest quality radio images of this object to date. The images show filamentary structure over the body of the nebula. The present observations were combined with earlier ones from 1984 and 1991 to investigate the variability of the radio emission on a variety of timescales. No significant changes are seen over a 110 day interval. In particular, the upper limit on the apparent projected velocity of the wisp is 0.05c. The expansion rate of the radio nebula was determined between 1984 and 2004 and is 0.014% ± 0.003% yr^-1, corresponding to a velocity of 630 ± 70 km s^-1 along the major axis. If 3C 58 is the remnant of SN 1181, it must have been strongly decelerated, which is unlikely given the absence of emission from the supernova shell. Alternatively, the low expansion speed and a number of other arguments suggest that 3C 58 may be several thousand years old and not the remnant of SN 1181.

Photoelectric emission from dust plays an important role in grain charging and gas heating. To date, detailed models of these processes have focused primarily on grains exposed to soft radiation fields. We provide new estimates of the photoelectric yield for neutral and charged carbonaceous and silicate grains, for photon energies exceeding 20 eV. We include the ejection of electrons from both the band structure of the material and the inner shells of the constituent atoms, as well as Auger and secondary electron emission. We apply the model to estimate gas-heating rates in planetary nebulae and grain charges in quasar environments. For these applications, secondary emission can be neglected; the combined effect of inner shell and Auger emission is small, although not always negligible. Finally, we investigate the survivability of dust in quasar host galaxies. For unobscured lines of sight, dust can be destroyed out to distances ~1 kpc.

Prestellar cores are unique laboratories for studying the chemical and physical conditions preceding star formation. We observed the prestellar core L1544 in the fundamental transition of ortho-H₂D⁺ (1_1,0-1_1,1) at different positions over 100'' and found a strong correlation between its abundance and the CO depletion factor. We also present a tentative detection of the fundamental transition of para-D₂H⁺ (1_1,0-1_0,1) at the dust emission peak. Maps in N₂H⁺, N₂D⁺, HCO⁺, and DCO⁺ are used and interpreted with the aid of a spherically symmetric chemical model that predicts the column densities and abundances of these species as a function of radius. The correlation between the observed deuterium fractionation of H, N₂H⁺, and HCO⁺ and the observed integrated CO depletion factor across the core can be reproduced by this chemical model. In addition, a simpler model is used to study the H₂D⁺ ortho-to-para ratio. We conclude that, in order to reproduce the observed ortho-H₂D⁺ observations, the grain radius should be larger than 0.3 μm.

We present a detailed theoretical study of the isolated Bok globule CB 17 (L1389) based on spectral maps of CS, HCO⁺, C¹⁸O, C³⁴S, and H¹³CO⁺ lines. The intensity of the external UV field, the probability for molecules to stick onto dust grains, the core age, the infall, and rotation velocity all significantly affect the molecular line spectra. We demonstrate that these parameters are well constrained when results of the modeling are compared to observations in multiple lines of sight through the core. We use a detailed chemical model to compute the time-dependent abundances in a number of locations within the core. Both static and dynamically evolving cloud configurations are considered. These abundances are then used to simulate the spectral maps. We developed a general criterion that allows us to quantify the difference between observed and simulated spectral maps. By minimizing this difference, we isolate the model that represents a good approximation to the core chemical and kinematic structure. The chemical age of the core is about 2 Myr, while the most probable effective sticking probability value is 0.3-0.5. The spatial distribution of intensities and self-absorption features of optically thick lines is indicative of attenuated UV radiation of the core. The line asymmetry pattern in CB 17 is reproduced by a combination of infall, rotation, and turbulent motions with velocities of ~0.05, ~0.1, and ~0.1 km s^-1, respectively. These parameters correspond to energy ratios E_rot/E_grav ≈ 0.03, E_therm/E_grav ≈ 0.8, and E_turb/E_grav ≈ 0.05 (the rotation parameters are determined for i = 90^°). Based on the angular momentum value, we argue that the core is going to fragment, i.e., to form a binary (multiple) system.

We studied the collapse of rotating molecular cloud cores with inclined magnetic fields, based on three-dimensional numerical simulations. The numerical simulations start from a rotating Bonnor-Ebert isothermal cloud in a uniform magnetic field. The magnetic field is initially taken to be inclined from the rotation axis. As the cloud collapses, the magnetic field and rotation axis change their directions. When the rotation is slow and the magnetic field is relatively strong, the direction of the rotation axis changes to align with the magnetic field, as shown earlier by Matsumoto & Tomisaka. When the magnetic field is weak and the rotation is relatively fast, the magnetic field inclines to become perpendicular to the rotation axis. In other words, the evolution of the magnetic field and rotation axis depends on the relative strength of the rotation and magnetic field. Magnetic braking acts to align the rotation axis and magnetic field, while the rotation causes the magnetic field to incline through dynamo action. The latter effect dominates the former when the ratio of the angular velocity to the magnetic field is larger than a critical value Ω₀/B₀ > 0.39G^1/2c, where B₀, Ω₀, G, and c_s denote the initial magnetic field, initial angular velocity, gravitational constant, and sound speed, respectively. When the rotation is relatively strong, the collapsing cloud forms a disk perpendicular to the rotation axis and the magnetic field becomes nearly parallel to the disk surface in the high-density region. A spiral structure appears due to the rotation and the wound up magnetic field in the disk.

We present observations of 3.86 deg² of the Perseus molecular cloud complex with the Spitzer Space Telescope Infrared Array Camera (IRAC). The maps show strong extended emission arising from shocked H₂ in outflows and from polycyclic aromatic hydrocarbon features. More than 120,000 sources are extracted toward the cloud. Based on their IRAC colors and comparison to off-cloud and extragalactic fields, we identify 400 candidate young stellar objects. About two-thirds of these are associated with the young clusters IC 348 and NGC 1333, while the last third is distributed over the remaining cloud. The young stellar objects are classified according to the slope of their spectral energy distributions. Significant differences are found between the numbers of embedded Class I objects and more evolved Class II objects in IC 348, NGC 1333 and the remaining cloud, with the embedded Class I and "flat-spectrum" YSOs constituting 14%, 36% and 47% of the total number of YSOs identified in each of these regions. The high number of Class I objects in the extended cloud (61% of the Class I objects in the entire cloud) suggests that a significant fraction of the current star formation occurs outside the two main clusters. Finally, we discuss a number of outflows and identify their driving sources, including the deeply embedded Class 0 sources outside the two main clusters. The Class 0 objects are detected by Spitzer and have very red [3.6] - [4.5] colors, but they do not show similarly red [5.8] - [8.0] colors. The Class 0 objects are easily identifiable in color-color diagrams but are problematic to extract automatically due to the extended emission from shocked gas or scattered light in cavities related to the associated outflows.

The bipolar outflow from the massive star-forming cluster in DR 21 is one of the most powerful known, and in IRAC images the outflow stands out by virtue of its brightness at 4.5 μm (band 2). Indeed, IRAC images of many Galactic and extragalactic star formation regions feature prominent band 2 morphologies. We have analyzed archival ISO SWS spectra of the DR 21 outflow and compare them to updated H₂ shocked and UV excitation models. We find that H₂ line emission contributes about 50% of the flux of the IRAC bands at 3.6, 4.5, and 5.8 μm, and is a significant contributor to the 8.0 μm band as well, and confirm that the outflow contains multiple excitation mechanisms. Other potentially strong features, in particular Brα and CO emission, have been suggested as contributing to IRAC fluxes in outflows, but they are weak or absent in DR 21; surprisingly, there also is no evidence for strong PAH emission. The results imply that IRAC images can be a powerful detector of, and diagnostic for, outflows caused by massive star formation activity in our Galaxy, and in other galaxies as well. They also suggest that IRAC color-color diagnostic diagrams may need to take into account the possible influence of these strong emission lines. IRAC images of the general ISM in the region, away from the outflow, are in approximate, but not precise, agreement with theoretical models.

We have discovered an optically thick, edge-on circumstellar disk around a Herbig Ae star in the binary system PDS 144, providing the first intermediate-mass analog of HK Tau and similar T Tauri stars. This system consists of a V ~ 13 mag primary and a fainter companion, with the spectra of both stars showing evidence for circumstellar disks and accretion; both stars were classified as Herbig Ae by the Pico dos Dias Survey. In Lick adaptive optics polarimetry, we resolved extended polarized light scattered from dust around the northern star. Follow-up Keck adaptive optics and mid-infrared observations show that this star is entirely hidden by an optically thick disk at all wavelengths from 1.2 to 11.7 μm. The disk major axis subtends ~08 on the sky, corresponding to ~800 AU at a distance of 1000 pc. Bright "wings" extend 03 above and below the disk ansae, due most likely to scattering from the edges of an outflow cavity in a circumstellar envelope. We discuss the morphology of the disk and the spectral energy distributions of the two PDS 144 stars, present preliminary disk models, and identify a number of open questions regarding this fascinating system.

Using the Spitzer Space Telescope, we have observed 90 weak-line and classical T Tauri stars in the vicinity of the Ophiuchus, Lupus, Chamaeleon, and Taurus star-forming regions as part of the Cores to Disks (c2d) Spitzer Legacy project. In addition to the Spitzer data, we have obtained contemporaneous optical photometry to assist in constructing spectral energy distributions. These objects were specifically chosen as solar-type young stars with low levels of Hα emission, strong X-ray emission, and lithium absorption, i.e., weak-line T Tauri stars, most of which were undetected in the mid- to far-IR by the IRAS survey. Weak-line T Tauri stars are potentially extremely important objects in determining the timescale over which disk evolution may take place. Our objective is to determine whether these young stars are diskless or have remnant disks that are below the detection threshold of previous infrared missions. We find that only 5/83 weak-line T Tauri stars have detectable excess emission between 3.6 and 70 μm, which would indicate the presence of dust from the inner few tenths of an AU out to the planet-forming regions a few tens of AU from the star. Of these sources, two have small excesses at 24 μm consistent with optically thin disks; the others have optically thick disks already detected by previous IR surveys. All of the seven classical T Tauri stars show excess emission at 24 and 70 μm although their properties vary at shorter wavelengths. Our initial results show that disks are rare among young stars selected for their weak Hα emission.

The circumstellar dust disk of the Herbig Ae star AB Aur has been found to exhibit complex spiral-like structures in the near-IR image obtained with the Subaru Telescope. We present maps of the disk in both ¹²CO (3-2) and dust continuum at 345 GHz with the Submillimeter Array at an angular resolution of 10 × 07 (144 × 100 AU). The continuum emission traces a dust disk with a central depression and a maximum overall dimension of 450 AU (FWHM). This dust disk exhibits several distinct peaks that appear to coincide with bright features in the near-IR image, in particular the brightest inner spiral arm. The CO emission traces a rotating gas disk of size 530 × 330 AU with a deprojected maximum velocity of 2.8 km s^-1 at 450 AU. In contrast with the dust disk, the gas disk exhibits an intensity peak at the stellar position. Furthermore, the CO emission in several velocity channels traces the innermost spiral arm seen in the near-IR. We compare the observed spatial-kinematic structure of the CO emission to a simple model of a disk in Keplerian rotation and find that only the emission tracing the main spiral arm clearly lies outside the confines of our model. This emission has a net outward radial motion compared with the radial velocity predicted by the model at the location of the main spiral arms. The disk of AB Aur is therefore quite different from the Keplerian disks seen around many Herbig Ae stars. The spiral-like structures of the disk with non-Keplerian motions we revealed in ¹²CO (3-2), together with the central depression of the dust disk, could be explained to be driven by the possible existence of a giant planet forming in the disk.

Based on recent models of relativistic jet formation by thermal energy deposition around black hole-torus systems, the relation between the on- and off-axis appearance of short, hard gamma-ray bursts (GRBs) is discussed in terms of energetics, duration, average Lorentz factor, and probability of observation, assuming that the central engines are remnants of binary neutron star (NS+NS) or neutron star-black hole (NS+BH) mergers. As a consequence of the interaction with the torus matter at the jet base and the subsequent expansion of the jets into an extremely low density environment, the collimated ultrarelativistic outflows possess flat core profiles with only little variation of radially averaged properties and are bounded by very steep lateral edges. Owing to the rapid decrease of the isotropic equivalent energy near the jet edges, the probability of observing the lateral, lower Lorentz factor wings is significantly reduced, and most short GRBs should be seen with on-axis-like properties. Taking into account cosmological and viewing angle effects, theoretical predictions are made for the short-GRB distributions with redshift z, fluence, and isotropic equivalent energy. The observational data for short bursts with determined redshifts are found to be compatible with the predictions only if either the intrinsic GRB rate density drops rapidly at z ≳ 1 or a large number of events at z > 1 are missed, implying that the subenergetic GRB 050509b was an extremely rare low-fluence event with detectable photon flux only because of its proximity and shortness. It appears unlikely that GRB 050509b can be explained as an off-axis event. The detection of short GRBs with small Lorentz factors is statistically disfavored, suggesting a possible reason for the absence of soft short bursts in the duration-hardness diagram.

The unique capability of the Swift satellite to perform a prompt and autonomous slew to a newly detected gamma-ray burst (GRB) has yielded the discovery of interesting new properties of GRB X-ray afterglows, such as the steep early light-curve decay and the frequent presence of flares detected up to a few hours after the GRB trigger. We present observations of GRB 050607, the fourth case of a GRB discovered by Swift with flares superimposed on the overall fading X-ray afterglow. The flares of GRB 050607 were not symmetric as in previously reported cases, showing a very steep rise and a shallower decay, similar to the fast rise, exponential decay that are frequently observed in the gamma-ray prompt emission. The brighter flare had a flux increase by a factor of ~25, peaking for 30 s at a count rate of approximately 30 counts s^-1, and it presented hints of additional short-timescale activity during the decay phase. There is evidence of spectral evolution during the flares. In particular, at the onset of the flares the observed emission was harder, with a gradual softening as each flare decayed. The very short timescale and the spectral variability during the flaring activity are indicators of possible extended periods of energy emission by the GRB central engine. The flares were followed by a phase of shallow decay, during which the forward shock was being refreshed by a long-lived central engine or by shells of lower Lorentz factors, and by a steepening after approximately 12 ks to a decay slope considered typical of X-ray afterglows.

The gamma-ray burst GRB 031203 at a redshift z = 0.1055 revealed a highly reddened Type Ic supernova, SN 2003lw, in its afterglow light. This is the third well-established case of a link between a long-duration GRB and a Type Ic SN. The SN light curve is obtained by subtracting the galaxy contribution and is modeled together with two spectra at near-maximum epochs. A red VLT grism 150I spectrum of the SN near peak is used to extend the spectral coverage, and in particular to constrain the uncertain reddening, the most likely value for which is E_G+H(B - V) ≃ 1.07 ± 0.05. Accounting for reddening, SN 2003lw is ~0.3 mag brighter than the prototypical GRB-SN 1998bw. Light curve models yield a ⁵⁶Ni mass of ~0.55 M_☉. The optimal explosion model is somewhat more massive (M_ej ~ 13 M_☉) and more energetic (E ~ 6 × 10⁵² ergs) than the model for SN 1998bw, implying a massive progenitor (40-50 M_☉). The mass at high velocity is not very large (1.4 M_☉ above 30,000 km s^-1, but only 0.1 M_☉ above 60,000 km s^-1), but it is sufficient to cause the observed broad lines. The similarity of SNe 2003lw and 1998bw and the weakness of their related GRBs, GRB 031203 and GRB 980425, suggest that both GRBs may be normal events viewed slightly off-axis or a weaker but possibly more frequent type of GRB.

A fully 3D Monte Carlo scheme is applied to compute optical bolometric light curves for aspherical (jetlike) supernova explosion models. Density and abundance distributions are taken from hydrodynamic explosion models, with the energy varied as a parameter to explore the dependence. Our models show initially a very large degree (~4 depending on model parameters) of boosting luminosity toward the polar (z) direction relative to the equatorial (r) plane, which decreases as the time of the peak is approached. After the peak, the factor of the luminosity boost remains almost constant (~1.2) until the supernova enters the nebular phase. This behavior is due mostly to the aspherical ⁵⁶Ni distribution in the earlier phase and to the disklike inner low-velocity structure in the later phase. In addition, the aspherical models yield an earlier peak date than the spherical models, especially if viewed from near the z-axis. Aspherical models with an ejecta mass of ~10 M_☉ are examined, and one with a kinetic energy of expansion of ~(2 ± 0.5) × 10⁵² ergs and a mass of ⁵⁶Ni of ~0.4 M_☉ yields a light curve in agreement with the observed light curve of SN 1998bw (the prototypical hyperenergetic supernova). The aspherical model is also at least qualitatively consistent with evolution of photospheric velocities, showing large velocities near the z-axis. In addition, a late-phase nebular spectrum is well explained. The viewing angle is close to the z-axis, strengthening the case for the association of SN 1998bw with the gamma-ray burst GRB 980425.

We deduce new constraints on the entropy per baryon (s/k), dynamical timescale (τ_dyn), and electron fraction (Y_e) consistent with heavy-element nucleosynthesis in the r-process. We show that the previously neglected reaction flow through the reaction sequence ⁴He(t, γ)⁷Li(n, γ)⁸Li(α, n)¹¹B significantly enhances the production of seed nuclei. We analyze the r-process nucleosynthesis in the context of a schematic exponential wind model. We show that fewer neutrons per seed nucleus implies that the entropy per baryon required for successful r-process nucleosynthesis must be more than a factor of 2 higher than previous estimates. This places new constraints on dynamical models for the r-process.

We calculate evolution, collapse, explosion, and nucleosynthesis of Population III very massive stars with 500 and 1000 M_☉. Presupernova evolution is calculated in spherical symmetry. Collapse and explosion are calculated by a two-dimensional code, based on the bipolar jet models. We compare the results of nucleosynthesis with the abundance patterns of intracluster matter, hot gases in M82, and extremely metal-poor stars in the Galactic halo. It was found that both 500 and 1000 M_☉ models enter the region of pair instability but continue to undergo core collapse. In the presupernova stage, silicon-burning regions occupy a large fraction, more than 20% of the total mass. For moderately aspherical explosions, the patterns of nucleosynthesis match the observational data of both the intracluster medium and M82. Our results suggest that explosions of Population III core-collapse very massive stars contribute significantly to the chemical evolution of gases in clusters of galaxies. For Galactic halo stars our [O/Fe] ratios are smaller than the observational abundances. However, our proposed scenario is naturally consistent with this outcome. The final black hole masses are ~230 and ~500 M_☉ for the 500 and 1000 M_☉ models, respectively. This result may support the view that Population III very massive stars are responsible for the origin of intermediate-mass black holes, which were recently reported to be discovered.

In this paper we use high-quality X-ray observations from XMM-Newton and Chandra to gain new insights into the explosion that originated Tycho's supernova 433 yr ago. We perform a detailed comparison between the ejecta emission from the spatially integrated X-ray spectrum of the supernova remnant and current models for Type Ia supernova explosions. We use a grid of synthetic X-ray spectra based on hydrodynamic models of the evolution of the supernova remnant and nonequilibrium ionization calculations for the state of the shocked plasma. We find that the fundamental properties of the X-ray emission in Tycho are well reproduced by a one-dimensional delayed detonation model with a kinetic energy of ~1.2 × 10⁵¹ ergs. All the other paradigms for Type Ia explosions that we have tested, including one-dimensional deflagrations, pulsating delayed detonations, and sub-Chandrasekhar explosions, as well as deflagration models calculated in three dimensions, fail to provide a good approximation of the observed ejecta emission. Our results require that the supernova ejecta retain some degree of chemical stratification, with Fe peak elements interior to intermediate-mass elements. This strongly suggests that a supersonic burning front (i.e., a detonation) must be involved at some stage in the physics of Type Ia supernova explosions.

We investigate the quantity and composition of unburned material in the outer layers of three normal Type Ia supernovae (SNe Ia): 2000dn, 2002cr, and 2004bw. Pristine matter from a white dwarf progenitor is expected to be a mixture of oxygen and carbon in approximately equal abundance. Using near-infrared (NIR, 0.7-2.5 μm) spectra, we find that oxygen is abundant, while carbon is severely depleted with low upper limits in the outer third of the ejected mass. Strong features from the O I line at λ_rest = 0.7773 μm are observed through a wide range of expansion velocities ≈ × 10³ km s^-1. This large velocity domain corresponds to a physical region of the supernova with a large radial depth. We show that the ionization of C and O will be substantially the same in this region. C I lines in the NIR are expected to be 7-50 times stronger than those from O I, but there is only marginal evidence of C I in the spectra and none of C II. We deduce that for these three normal SNe Ia, oxygen is more abundant than carbon by factors of 10²-10³. Mg II is also detected in a velocity range similar to that of O I. The presence of O and Mg combined with the absence of C indicates that for these SNe Ia, nuclear burning has reached all but the extreme outer layers; any unburned material must have expansion velocities greater than 18 × 10³ km s^-1. This result favors deflagration to detonation transition (DD) models over pure deflagration models for SNe Ia.

Stellar atmosphere models of ionized accretion disks have generally neglected the contribution of magnetic fields to the vertical hydrostatic support, although magnetic fields are widely believed to play a critical role in the transport of angular momentum. Simulations of magnetorotational turbulence in a vertically stratified shearing box geometry show that magnetic pressure support can be dominant in the upper layers of the disk. We present calculations of accretion disk spectra that incorporate vertical magnetic pressure and dissipation profiles derived from the radiation magnetohydrodynamical simulation of Hirose, Krolik, & Stone. Magnetic pressure support generically produces a more vertically extended disk atmosphere with a larger density scale height. This acts to harden the spectrum compared to models that neglect magnetic pressure support. We estimate the significance of this effect on disk-integrated spectra by calculating an illustrative disk model for a stellar mass black hole, assuming that similar magnetic pressure support exists at all radii.

Fast and slow magnetosonic shock formation is presented for stationary and axisymmetric magnetohydrodynamic (MHD) accretion flows onto a black hole. The shocked black hole accretion solution must pass through magnetosonic points at some locations outside and inside the shock location. We analyze critical conditions at the magnetosonic points and the shock conditions. Then, we show the restrictions on the flow parameters for strong shocks. We also show that a very hot shocked plasma is obtained for a very high energy inflow with a small number density. Such a MHD shock can appear very close to the event horizon and can be expected as a source of high-energy emissions. Examples of shocked MHD accretion flows are presented in the Schwarzschild case.

We report on the emission properties of PSR B1929+10 and its putative trail from a multiwavelength study performed using optical, X-ray, and radio data. XMM-Newton observations confirm the existence of the diffuse emission with a trail morphology lying in a direction opposite to the transverse motion of the pulsar. The trail spectrum is nonthermal and produced by electron-synchrotron emission in the shock between the pulsar wind and the surrounding medium. Radio data from the Effelsberg 11 cm radio continuum survey show an elongated feature that roughly coincides with the X-ray trail. Three not fully resolved radio sources seen in the NVSS survey data at 1.4 GHz match with part of the elongated radio feature seen at 11 cm. The emission properties observed from PSR B1929+10 are in excellent agreement with a nonthermal, and thus magnetospheric-radiation-dominated, emission scenario. The pulsar's X-ray spectrum is best described by a single power-law model with a photon index of 2.72. A flux contribution from the thermal emission of heated polar caps of at most ~7% is inferred from a best-fitting composite Planckian and power-law spectral model. A pure thermal emission spectrum consisting of two Planckian spectra is regarded as unlikely. A broken power-law spectral model with E_break = 0.83 keV and the photon indexes α₁ = 1.12 and α₂ = 2.48 can describe the optical and X-ray data entirely in terms of a nonthermal magnetospheric origin. The X-ray pulse profile observed in the 0.2-10 keV band is found to be markedly different from the broad sinusoidal pulse profile seen in the low statistic Röntgensatellit (ROSAT) data. Fitting Gaussians to the X-ray light curve indicates the possible existence of three pulse components. A small narrow pulse, characterized by energies greater than 1 keV, is found to lead the radio main pulse by ~20°. The fraction of pulsed photons in the 0.2-10 keV band is 32% ± 4%. For the subbands 0.2-1.0 and 1.0-2.1 keV the pulsed fraction is 24% ± 5% and 44% ± 6%, respectively, indicating a mild energy dependence at a ~2 σ level. Simulations in the framework of an outer gap emission model are able to reproduce the observed X-ray pulse profile and its phase shift relative to the radio pulse.

We demonstrate a new Bayesian technique to invert color-magnitude diagrams of main-sequence and white dwarf stars to reveal the underlying cluster properties of age, distance, metallicity, and line-of-sight absorption, as well as individual stellar masses. The advantages our technique has over traditional analyses of color-magnitude diagrams are objectivity, precision, and explicit dependence on prior knowledge of cluster parameters. Within the confines of a given set of often-used models of stellar evolution, a single mapping of initial to final masses, and white dwarf cooling, and assuming photometric errors that one could reasonably achieve with the Hubble Space Telescope, our technique yields exceptional precision for even modest numbers of cluster stars. For clusters with 50-400 members and one to a few dozen white dwarfs, we find typical internal errors of σ([Fe/H]) ≤ 0.03 dex, σ(m - M_V) ≤ 0.02 mag, and σ(A_V) ≤ 0.01 mag. We derive cluster white dwarf ages with internal errors of typically only 10% for clusters with only three white dwarfs and almost always ≤5% with 10 white dwarfs. These exceptional precisions will allow us to test white dwarf cooling models and standard stellar evolution models through observations of white dwarfs in open and globular clusters.

In the light of the recent results of the stellar interferometry, we examine the nature of the extra molecular layer outside the photosphere of red supergiant stars, so far studied mostly with the use of the infrared spectra. Although the visibility data are more direct probes of the spatial structure of the outer atmosphere, it is essential that they are analyzed in combination with the spectral data. In the case of the M2 supergiant μ Cephei, several sets of data, both spectra and visibilities, strongly suggested the presence of an extra molecular layer (which we referred to as "MOLsphere" for simplicity), and the basic parameters of the MOLsphere are estimated to be excitation temperature T_ex ≈ 1600 K, column densities of CO and H₂O molecules N_col ≈ 3.0 × 10²⁰ cm^-2, and located at about one stellar radius above the photosphere or R_in ≈ 2.0R_*. The result shows reasonable agreement with the one based on the infrared spectra alone, and the model inferred from the spectra is now fully supported with the recent visibility data. In the case of the M2 supergiant α Orionis, the infrared spectra and visibilities show a consistent picture in that its MOLsphere is closer to the photosphere (R_in ≈ 1.3R_*) with higher gas temperature (T_ex ≈ 2250 K) and lower gas column density (N_col ≈ 10²⁰ cm^-2), compared with that of μ Cep. Some controversy on the interpretation of the mid-infrared data of α Orionis can be reconciled. Given that the presence of the extra molecular layer is reasonably well established, the major unsolved problem is how to understand the origin of such a rather warm and dense layer in the outer atmosphere.

We present the results of an observational campaign for the long-period variable subdwarf B star PG 1338+481. Seven continuous weeks of observing time at the Steward Observatory 1.55 m Kuiper telescope on Mount Bigelow, Arizona, and the 1.3 m MDM telescope at Kitt Peak rendered ~250 hr of simultaneous U/R time series photometry, as well as an extra ~70 hr of R-band-only data. The analysis of the combined light curves resulted in the extraction of 13 convincing periodicities in the 2100-7200 s range, with amplitudes up to ~0.3% and ~0.2% in the U and R, respectively. Comparing the ratios of amplitudes in the two wave bands to those predicted from theory suggests the presence of dipole modes, a notion that is further supported by the period spacing between the highest amplitude peaks. If confirmed, this poses a challenge to current nonadiabatic theory. At the quantitative level, we find that the distribution of the observed period spectrum is highly nonuniform and much sparser than that predicted from a representative model. We provide a possible interpretation in the text. The asteroseismological analysis attempted for PG 1338+481 on the basis of six observed periodicities believed to constitute consecutive dipole modes renders encouraging results. Fixing the effective temperature and surface gravity to the spectroscopic estimates, we successfully isolate just one family of optimal models that can reproduce the measured periods to better than 1%. While the stellar parameters thus inferred must be regarded as preliminary, the achieved fit bodes well for future asteroseismic analyses of long-period variable subdwarf B stars.

We report the discovery of LEHPM 2-59 as the coolest extreme M subdwarf (esdM) found to date. Optical and near-infrared spectroscopy demonstrate that this source is of later spectral type than the esdM7 APMPM J0559-2903, with the presence of strong alkali lines (including Rb I), VO absorption at 7400 Å, and H₂O absorption at 1.4 μm. Current optical classification schemes yield a spectral type of esdM8, making LEHPM 2-59 one of only two ultracool esdMs known. The substantial space velocity of this object (V_galactic ≈ -180 km s^-1) identifies it as a halo star. Spectral model fits to the optical and near-infrared spectral data for this and four other late-type esdMs indicate that LEHPM 2-59 is the coolest esdM currently known, with T_eff = 2800-3000 K and -1.5 ≲ [M/H] ≲ -2.0. Comparison of T_eff determinations for M dwarfs and esdMs based on spectral model fits from this study and the literature demonstrate a divergence in T_eff scales beyond spectral types ~M5/esdM5, as large as 600-800 K by types M8/esdM8. While this divergence is likely an artifact of the underlying classification scheme, it may lead to systematic errors in the derived properties of intermediate metallicity subdwarfs. We comment on the future of ultracool subdwarf classification and suggest several ideas for addressing shortcomings in current (largely extrapolated) schemes.

We have carried out sensitive 1.3 mm observations of 20 young brown dwarfs in the Taurus star-forming region, representing the largest sample of young substellar objects targeted in a deep millimeter-continuum survey to date. Under standard assumptions, the masses of brown dwarf disks range from ≲0.4 to several Jupiter masses. Their relative disk masses are comparable to those derived for coeval low-mass stars; most of them are in the ≲1%-5% range, and there is no clear change of relative disk mass with object mass from 0.015 to 3 M_☉. Specifically, we do not find evidence for disk truncation, as would be expected in the ejection scenario for brown dwarf origin, although the signature of ejection may be hidden in our nondetections. We use the millimeter fluxes, complemented by mid-infrared data from the Spitzer Space Telescope to construct spectral energy distributions (SEDs) for six of our sources, and model those SEDs with a Monte Carlo radiative transfer code. We find that the SEDs in the mid-infrared often exhibit lower flux levels than predicted by hydrostatic models, implying dust settling to the disk midplane. What is more, at least 25% of our targets are likely to have disks with radii >10 AU; models with smaller disks cannot reproduce the millimeter fluxes. This result is in contrast to the results of some simulations of the ejection scenario for brown dwarf formation that suggest only ~5% of ejected objects would harbor disks larger than 10 AU. Our findings imply that ejection is probably not the dominant formation process, but may still be relevant for some brown dwarfs.

The large eccentricities of many giant extrasolar planets may represent the endpoint of gravitational scattering in initially more crowded systems. If so, the early evolution of the giant planets is likely to be more restrictive of terrestrial planet formation than would be inferred from the current, dynamically quiescent configurations. Here we study statistically the extent of the anticorrelation between giant planets and terrestrial planets expected in a scattering model. We use marginally stable systems of three giant planets, with a realistic range of planetary masses, as a simple model for the initial conditions prior to scattering, and we show that after scattering the surviving planets reproduce well the known extrasolar planet eccentricities beyond a > 0.5 AU. By tracking the minimum periastron values of all planets during the evolution, we derive the distribution of orbital radii across which strong perturbations (from crossing orbits) are likely to affect low-mass planet formation. We find that scattering affects inner planet formation at orbital separations less than 50% of the final periastron distance, q_fm, of the innermost massive planet in approximately 30% of the realizations and can occasionally influence planet formation at orbital separations less than 20% of q_fm. The domain of influence of the scattering massive planets increases as the mass differential between the massive planets decreases. Observational study of the correlation between massive and terrestrial extrasolar planets in the same system has the potential to constrain the origin of planetary eccentricity.

The 1998 September 9 solar particle event was a ³He-rich solar particle event that showed a strong increase of Fe ionization states in the energy range below 1 MeV nucleon^-1. We have investigated this event by fitting Wind and ACE observations using a model of acceleration and stripping near the Sun, followed by particle transport in the interplanetary medium taking into account particle focusing, pitch-angle scattering, adiabatic deceleration, and convection. The simulation provides a reconstruction of the injection function of the energetic particles released from the Sun and their time, energy, and charge dependence. We find that electrons and Fe ions are injected almost impulsively, whereas the injection of protons takes place on a much longer timescale or even consists of two distinct injection processes. We are able to obtain good overall fits to the observations. This suggests that our model can be used to obtain information about the conditions in the acceleration region such as density, temperature, and the timescales of the acceleration process, if sufficiently accurate modeling of the particle transport in the solar wind is possible.

In this paper we investigate the thermal and dynamic properties of dynamic structures in and around a prominence channel observed on the limb on 2003 April 17. Observations were taken with the Solar and Heliospheric Observatory's Solar Ultraviolet Measurements of Emitted Radiation (SOHO SUMER) in lines formed at temperatures from 80,000 K to 1.6 MK. The instrument was pointed to a single location and took a series of 90 s exposures. Two-dimensional context was provided by the Transition Region and Coronal Explorer (TRACE) in the UV and EUV and the Kanzelhöhe Solar Observatory in Hα. Two dynamic features were studied in depth: an activated prominence and repeated motions in a loop near the prominence. We calculated three-dimensional geometries and trajectories, differential emission measures, and limits on the mass, pressure, average density, and kinetic and thermal energies. These observations provide important tests for models of dynamics in prominences and cool (~10⁵ K) loops, which will ultimately lead to a better understanding of the mechanism(s) leading to energy and mass flow in these solar features.

We simulate the two-dimensional transport of the open magnetic flux on the surface of the Sun. The temporal evolution of the flux density depends on the advective motions due to solar differential rotation and poleward meridional flow and on an effective spatial diffusive motion. The latter is a result of the uniform diffusion of field line footpoints in the network lanes and a nonuniform diffusion of field lines due to reconnection of open field lines with closed loops on the solar surface. The gradient of the diffusion coefficient represents an effective velocity in addition to the advective velocity. We investigate the behavior of the steady state solution for solar minimum and solar maximum conditions with spatially uniform and nonuniform diffusion coefficients. We find that for solar minimum conditions, the effect of spatial diffusion resulting from reconnection processes enhances the poleward meridional flow due to the large-scale preferred direction in the gradient of the diffusion coefficient. For solar maximum conditions, the net effect of spatial diffusion is minimal because of the isotropic and local gradients of the diffusion coefficient. Our simulation demonstrates that magnetic reconnection processes on the solar surface can be a mechanism to vary motions on the photosphere, in particular, poleward meridional flow.

We search for a relation between flows below active regions and flare events occurring in those active regions. For this purpose, we determine the subsurface flows from high-resolution Global Oscillation Network Group (GONG) and Michelson Doppler Imager (MDI) Dynamics Program data using the ring-diagram technique. We then calculate the vorticity of the flows associated with active regions and compare it with a proxy of the total X-ray flare intensity of these regions using data from the Geostationary Operation Environmental Satellite (GOES). We have analyzed 408 active regions with X-ray flare activity from GONG and 159 active regions from MDI data. Both data sets lead to similar results. The maximum unsigned zonal and meridional vorticity components of active regions are correlated with the total flare intensity; this behavior is most apparent at values greater than 3.2 × 10^-5 W m^-2. These vorticity components show a linear relation with the logarithm of the flare intensity that is dependent on the maximum unsigned magnetic flux; vorticity values are proportional to the product of total flare intensity and maximum unsigned magnetic flux for flux values greater than about 36 G. Active regions with strong flare intensity show a dipolar pattern in the zonal and meridional vorticity component that reverses at depths between ~2 and 5 Mm. A measure of this pattern shows the same kind of relation with total flare intensity as the vorticity components. The vertical vorticity component shows no clear relation to flare activity.

We discuss the theory of the Bracewell nulling interferometer and explicitly demonstrate that the phase of the "white light" null fringe is the same as the phase of the bright output from an ordinary stellar interferometer. As a consequence, a "closure phase" exists for a nulling interferometer with three or more telescopes. We calculate the phase offset as a function of baseline length for an Earth-like planet around the Sun at 10 pc, with a contrast ratio of 10^-6 at 10 μm. The magnitude of the phase due to the planet is ~10^-6 radians, assuming the star is at the phase center of the array. Although this is small, this phase may be observable in a three-telescope nulling interferometer that measures the closure phase. We propose a simple nonredundant three-telescope nulling interferometer that can perform this measurement. This configuration is expected to have improved characteristics compared to other nulling interferometer configurations, such as a relaxation of path length tolerances, through the use of the "ratio of wavelengths" technique, a closure phase, and better discrimination between extrasolar zodiacal dust and planets.

A simple model, based on fitting experimental energy term values, has been developed to calculate the line oscillator strengths (f) of N ₂b' ¹Σ(1), c¹Σ(0), b¹Π(4), b¹Π(5), and c₃¹Π(0)-X¹Σ(0) bands. The strong rovibronic coupling among these states leads to quantum interference in the transition dipole matrix elements and results in anomalous P/R branch oscillator strength ratios. The calculated line oscillator strengths are in very good agreement with experimental values. The calculated values can be used for modeling atmospheric emission. Calculated line oscillator strengths for J' up to 30 are provided.

Accurate measurements of the angular power spectrum of cosmic microwave background (CMB) radiation have lead to a marked improvement in the estimates of different cosmological parameters. This has required removal of foreground contamination as well as detector noise bias with reliability and precision. We present the estimation of the CMB angular power spectrum from the multifrequency observations of the Wilkinson Microwave Anisotropy Probe (WMAP) using a novel model-independent method. The primary results of WMAP are the observations of the CMB in 10 independent difference assemblies (DAs) that have uncorrelated noise. Our method utilizes the maximum information available within the WMAP data by linearly combining all the DA maps in order to remove foreground contamination and by estimating the power spectrum from cross-power spectra of clean maps with independent noise. We compute 24 cross-power spectra that are the basis of the final power spectrum. The binned average power matches the WMAP team's published power spectrum closely. A small systematic difference at large multipoles is accounted for by the correction for the expected residual power from unresolved point sources. The correction is small and significantly tempered. Previous estimates have depended on foreground templates built using extraneous observational input. This is the first demonstration that the CMB angular spectrum can be reliably estimated with precision from a self-contained analysis of the WMAP data.

We explore the possibility of subsequent star formation after a first star forms in a Population III object, by focusing on the radiation-hydrodynamic (RHD) feedback caused by ionizing photons, as well as H₂-dissociating photons. For this purpose, we perform three-dimensional RHD simulations in which the radiative transfer of ionizing photons and H₂-dissociating photons from a first star is self-consistently coupled with hydrodynamics based on a smoothed particle hydrodynamics method. It is shown that density peaks above a threshold density can keep collapsing, owing to the shielding of H₂-dissociating radiation by an H₂ shell formed ahead of a D-type ionization front. But, below the threshold density an M-type ionization front with a shock propagates, and density peaks are radiation-hydrodynamically evaporated by the shock. The threshold density depends on the distance from the source star and is ≈10² cm^-3 for a source distance of 30 pc. Taking into consideration that the extent of a Population III object is ≈100 pc and the density peaks within it have densities of 10²-10⁴ cm^-3, it is concluded that secondary star formation is possible in the broad regions of a Population III object.

We present ~3'' resolution imaging of the z = 4.7 QSO BR 1202-0725 at 900 μm from the Submillimeter Array. The two submillimeter continuum components are clearly resolved from each other, and the positions are consistent with previous lower frequency images. In addition, we detect [C II] line emission from the northern component at L = 4.5 × 10⁹L_☉. The ratio of [C II] to far-infrared luminosity is 0.04% for the northern component, and an upper limit of <0.03% is obtained for the southern component. These ratios are similar to the low values found in local ultraluminous galaxies, indicating that the excitation conditions are different from those found in local field galaxies. X-ray emission is detected by Chandra from the southern component at L_{0.5-2 keV} = 3 × 10⁴⁵ ergs s^-1 and, at 99.6% confidence, from the northern component at L_{0.5-2 keV} ~ 3 × 10⁴⁴ ergs s^-1, supporting the idea that BR 1202-0725 is a pair of interacting galaxies at z = 4.7 and that each harbors an active nucleus.

We present VLT long-slit optical spectroscopy of the luminous BL Lacertae object PKS 2005-489. The high signal-to-noise ratio and the good spatial resolution of the data allow us to detect the signatures of ongoing star formation in an extended rotating ring, at ~4 kpc from the nucleus. We find that the ring is almost perpendicular to the radio axis, and its total star formation rate is ≃1 M_☉ yr^-1. We briefly discuss the concomitant presence of recent star formation and nuclear activity.

We present the results of a search for metal absorption lines in the spectra of background QSOs whose sight lines pass close to foreground QSOs. We detect Mg II λλ2796, 2803 absorption in Sloan Digital Sky Survey (SDSS) spectra of four z > 1.5 QSOs whose lines of sight pass within 26-98 h kpc of lower redshift (z ≃ 0.5-1.5) QSOs. The 100% detection rate (four out of four pairs) of Mg II in the background QSOs is clearly at odds with the incidence of associated z_abs ≃ z_em systems—absorbers that exist toward only a few percent of QSOs. Although the quality of our foreground QSO spectra is not as high as the SDSS data, absorption seen toward one of the background QSOs clearly does not show up at the same strength in the spectrum of the corresponding foreground QSO. This implies that the absorbing gas is distributed inhomogeneously around the QSO, presumably as a direct consequence of the anisotropic emission from the central active galactic nucleus. We discuss possible origins for the Mg II lines, including absorption by gas from the foreground QSO host galaxy, companion galaxies fueling the QSO through gravitational interactions, and tidal debris left by galaxy mergers or interactions that initiated the QSO activity. No single explanation is entirely satisfactory, and we may well be seeing a mixture of phenomena.

Using the Swift data of GRB 050315, we are making progress toward understanding the uniqueness of our theoretically predicted gamma-ray burst (GRB) structure, which is composed of a proper GRB (P-GRB), emitted at the transparency of an electron-positron plasma with suitable baryon loading, and an afterglow comprising the so-called prompt emission due to external shocks. Thanks to the Swift observations, the P-GRB is identified, and for the first time we can theoretically fit detailed light curves for selected energy bands on a continuous timescale ranging over 10⁶ s. The theoretically predicted instantaneous spectral distribution over the entire afterglow is presented, confirming a clear hard-to-soft behavior encompassing, continuously, the "prompt emission" all the way to the latest phases of the afterglow.

We present SMARTS consortium optical/IR light curves of SN 2006aj, associated with GRB 060218. We find that this event is broadly similar to two previously observed events, SN 1998bw/GRB 980425 and SN 2003lw/GRB 031203. In particular, all of these events are greatly underluminous in gamma rays compared with typical long-duration GRBs. We find that the observation by Swift of even one such event implies a large enough true event rate to create difficulties in interpreting these events as typical GRBs observed off-axis. Thus, these events appear to be intrinsically different from and much more common than high-luminosity GRBs, which have been observed in large numbers out to a redshift of at least 6.3. The existence of a range of intrinsic energies of GRBs may present challenges to using GRBs as standard candles.

A new Chandra observation of SNR 0506-68.0 (also called N23) reveals a complex, highly structured morphology in the low-energy X-ray band and an isolated compact central object in the high-energy band. Spectral analysis indicates that the X-ray emission overall is dominated by thermal gas whose composition is consistent with swept-up ambient material. There is a strong gradient in ambient density across the diameter of the remnant. Toward the southeast, near a prominent star cluster, the emitting density is 10-23 cm^-3, while toward the northwest it has dropped to a value of only 1 cm^-3. The total extent of the X-ray remnant is 100'' × 120'' (24 × 29 pc for a distance of 50 kpc), somewhat larger than previously known. The remnant's age is estimated to be ~4600 yr. One part of the remnant shows evidence for enhanced O, Ne, and perhaps Mg abundances, which is interpreted as evidence for ejecta from a massive star core collapse supernova. The compact central object has a luminosity of a few times 10³³ ergs s^-1 and no obvious radio or optical counterpart. It does not show an extended nebula or pulsed emission as expected from a young energetic pulsar, but resembles the compact central objects seen in other core collapse SNe, such as Cas A.

The study of the propagation of ultra-high-energy cosmic rays (UHECRs) is a key step to unveiling the secret of their origin. Up to now only the influence of the galactic and extragalactic magnetic fields was considered. In this article we focus our analysis on the influence of the magnetic field of the galaxies standing between possible UHECR sources and us. Our main approach is to start from the well-known galaxy distribution up to 120 Mpc. We use the most complete galaxy catalog: the LEDA catalog. Inside a sphere of 120 Mpc, we extract 60,130 galaxies with known positions. In our simulations we assign a halo dipole magnetic field (HDMF) to each galaxy. The code developed is able to retro-propagate a charged particle from the arrival points of UHECR data across our galaxy sample. We present simulations in the case of the Virgo Cluster and show that there is a nonnegligible deviation in the case of protons of 7 × 10¹⁹ eV, even if the B value is conservative. Then special attention is devoted to the AGASA triplet, where we find that NGC 3998 and NGC 3992 could be possible source candidates.

Cosmic-ray interactions with interstellar gas produce both ⁶Li, which accumulates in the interstellar medium (ISM), and π⁰ mesons, which decay to gamma rays that propagate throughout the cosmos. Local ⁶Li abundances and extragalactic gamma rays thus have a common origin that tightly links them. We exploit this connection to use gamma-ray observations to infer the contribution to ⁶ Li nucleosynthesis by standard Galactic cosmic-ray (GCR) interactions with the ISM. Our calculation uses a carefully propagated cosmic-ray spectrum and accounts for ⁶Li production from both fusion reactions (αα → ⁶Li) as well as spallation channels (p, α + CNO → ⁶Li). We find that, although extreme assumptions yield a consistent picture, more realistic ones indicate that solar ⁶Li cannot be produced by standard GCRs alone without overproducing the hadronic gamma rays. Implications for the primordial ⁶Li production by decaying dark matter and cosmic rays from cosmological structure formation are discussed. Upcoming gamma-ray observations by the Gamma-Ray Large Area Space Telescope will be crucial for determining the resolution of this problem.

We show that Fermi acceleration at an ultrarelativistic shock wave cannot operate on a particle for more than 1 Fermi cycles (i.e., u → d → u → d) if the particle's Larmor radius is much smaller than the coherence length of the magnetic field on both sides of the shock, as is usually assumed. This conclusion proves to be in excellent agreement with recent numerical simulations. We thus argue that efficient Fermi acceleration at ultrarelativistic shock waves requires significant nonlinear processing of the far-upstream magnetic field with strong amplification of the small-scale magnetic power. The streaming or transverse Weibel instabilities are likely to play a key role in this respect.

Gravitational waves (GWs) from the inspiral of compact remnants (CRs) into massive black holes (MBHs) will be observable to cosmological distances. While a CR spirals in, two-body scattering by field stars may cause it to fall into the central MBH before reaching a short-period orbit that would give an observable signal. As a result, only CRs very near (~0.01 pc) the MBH can spiral in successfully. In a multimass stellar population, the heaviest objects sink to the center, where they are more likely to slowly spiral into the MBH without being swallowed prematurely. We study how mass segregation modifies the stellar distribution and the rate of GW events. We find that the inspiral rate per galaxy is 30 Gyr^-1 for white dwarfs, 6 Gyr^-1 for neutron stars, and 250 Gyr^-1 for 10 M_☉ stellar black holes (SBHs). The high rate for SBHs is due to their extremely steep density profile, n_BH(r) ∝ r^-2. The GW detection rate will be dominated by SBHs.

Ketenimine (CH₂CNH) has been detected in absorption toward the star-forming region Sagittarius B2(N) with the 100 m Green Bank Telescope by means of three rotational transitions: 7₁₆-8₀₈ at 41.5 GHz, 8₁₉-9₀₉ at 23.2 GHz, and 9₁₈-10_{0, 10} at 4.9 GHz. Ketenimine has a sparse rotational spectrum below 50 GHz. From transition line strength arguments, the spectral lines found are the ones most likely to be detected, and they occur in spectral regions that have little possibility of confusion with other molecular species. Partially resolved hyperfine structure is apparent in the 4.9 GHz transition, which has energy levels ~50 K above the ground-state level; the absorption seen in this transition appears to be emanating from gas in close proximity to the LMH hot core that has a systemic LSR velocity of +64 km s^-1. By comparison, the 41.5 and 23.2 GHz transitions have lower energy levels of ~33 and ~41 K, respectively, and show absorption against the two star-forming Sgr B2(N) hot cores with systematic LSR velocities of +64 (the LMH) and +82 km s^-1. These ketenimine data show that the hot core at +82 km s^-1 is cooler than the hot core at +64 km s^-1. Ketenimine is likely formed directly from its isomer methyl cyanide (CH₃CN) by tautomerization driven by shocks that pervade the star-forming region.

The anomalous microwave emission detected in the Perseus molecular complex by Watson et al. has been observed at 11 GHz through dual orthogonal polarizations with the COSMOSOMAS experiment. Stokes U and Q maps were obtained at a resolution of ~09 for a 30° × 30° region including the Perseus molecular complex. Faint polarized emission has been measured; we find Q = -0.2% ± 1.0% and U = -3.4%, both at the 95% confidence level, with a systematic uncertainty estimated to be lower than 1% determined from tests of the instrumental performance using unpolarized sources in our map as null hypothesis. The resulting total polarization level is Π = 3.4%. These are the first constraints on the polarization properties of an anomalous microwave emission source. The low level of polarization seems to indicate that the particles responsible for this emission in the Perseus molecular complex are not significantly aligned in a common direction over the whole region, as a consequence of either a high structural symmetry in the emitting particle or a low-intensity magnetic field. Our weak detection is fully consistent with predictions from electric dipole emission and resonance relaxation at this frequency.

We study the role of spin-down in driving quark deconfinement in the high-density cores of isolated neutron stars. Assuming spin-down to be solely due to magnetic braking, we obtain typical timescales to quark deconfinement for neutron stars that are born with Keplerian frequencies. Employing different equations of state (EOSs), we determine the minimum and maximum neutron star masses that will allow for deconfinement via spin-down only. We find that the time to reach deconfinement is strongly dependent on the magnetic field and that this time is least for EOSs that support the largest minimum mass at zero spin, unless rotational effects on stellar structure are large. For a fiducial critical density of 5ρ₀ for the transition to the quark phase (ρ₀ = 2.5 × 10¹⁴ g cm^-3 is the saturation density of nuclear matter), we find that neutron stars lighter than 1.5 M_☉ cannot reach a deconfined phase. Depending on the EOS, neutron stars of more than 1.5 M_☉ can enter a quark phase only if they are spinning faster than about 3 ms as observed now, whereas larger spin periods imply either that they are already quark stars or that they will never become them.

The recently discovered RRAT sources are characterized by very bright radio bursts that, while being periodically related, occur infrequently. We find bursts with the same characteristics for the known pulsar B0656+14. These bursts represent pulses from the bright end of an extended smooth pulse-energy distribution and are shown to be unlike giant pulses, giant micropulses, or the pulses of normal pulsars. The extreme peak fluxes of the brightest of these pulses indicate that PSR B0656+14, were it not so near, could only have been discovered as an RRAT source. Longer observations of the RRATs may reveal that they, like PSR B0656+14, emit weaker emission in addition to the bursts.

LP 714-37 was identified by Phan-Bao et al. as one of the very few wide pairs of very low mass (VLM) stars known to date, with a separation of 33 AU. Here we present adaptive optics imaging that resolves the secondary of the wide pair into a tighter binary, with a projected angular separation of 036, or 7 AU. The estimated spectral types of LP 714-37B and LP 714-37C are M8.0 and M8.5, respectively. We discuss the implications of this finding for brown dwarf formation scenarios.

Observations of nonthermal X-ray sources are critical to the study of electron acceleration and transport in solar flares. Strong thermal emission radiated from the preheated plasma before the flare impulsive phase often makes it difficult to detect low-energy X-ray sources that are produced by relatively low-energy nonthermal electrons. Knowledge of the distribution of these low-energy nonthermal electrons is particularly important in determining the total nonthermal electron energy in solar flares. We report on an "early impulsive flare" in which impulsive hard X-ray emission was seen early in the flare before the soft X-ray emission had risen significantly, indicating limited plasma preheating. Early in the flare, RHESSI <25 keV images show coronal sources that moved first downward and then upward along the legs of a flare loop. In particular, the 3-6 keV source appeared as a single coronal source at the start of the flare, and then it evolved into two coronal sources moving down along the two legs of the loop. After nearly reaching the two footpoints at the hard X-ray peak, the two sources moved back up to the looptop again. RHESSI images and light curves all indicate that nonthermal emission dominated at energies as low as 3-6 keV. We suggest that the evolution of both the spectral index and the low-energy cutoff of the injected electron distribution could result in the accelerated electrons reaching a lower altitude along the legs of the dense flare loop and hence result in the observed downward and upward motions of the nonthermal sources.

We present clear evidence of the formation of three-dimensional (3D) plasmoids in the current sheet between two magnetic flux systems in a 3D numerical experiment of flux emergence into the solar atmosphere and study their properties and time evolution. Plasmoids are most likely the result of resistive tearing mode instabilities. They adopt the shape of a solenoid contained within the current sheet: the solenoid is tightly wound when the field in the two flux systems is close to antiparallel. The plasmoids are expelled to the sides of the sheet as a result of a reconnection imbalance between the two x-lines on their sides. We show the complex, 3D field line geometry in various plasmoids: individual plasmoid field lines have external linkages to the flux system on either side of the current sheet; we also find field lines that go through a few plasmoids in succession, probably indicating that the field line has resulted from multiple reconnection events.