Table of contents

X-ray observations of several active galactic nuclei (AGNs) show prominent iron K-shell fluorescence lines that are sculpted due to special and general relativistic effects. These observations are important because they probe the spacetime geometry close to distant black holes. However, the intrinsic distribution of Fe line strengths in the cosmos has never been determined. This uncertainty has contributed to the controversy surrounding the relativistic interpretation of the emission feature. Now, by making use of the latest multi-wavelength data, we show theoretical predictions of the cosmic density of relativistic Fe lines as a function of their equivalent width (EW) and line flux. We are able to show unequivocally that the most common relativistic iron lines in the universe will be produced by neutral iron fluorescence in Seyfert galaxies and have EWs <100 eV. Thus, the small number of very intense lines that have been discovered are just the bright end of a distribution of line strengths. In addition to validating the current observations, the predicted distributions can be used for planning future surveys of relativistic Fe lines. Finally, the predicted sky density of EWs indicates that the X-ray source in AGNs cannot, on average, lie on the axis of the black hole.

We present evidence that the spectroscopically identified bipolar jets of the pre-main sequence binary KH 15D (P = 48.4 d, ∼ 0.6, periastron separation ∼18 R_A, M_A = 0.6 M_☉, M_B = 0.7 M_☉) are a common product of the whole binary system, rather than being launched from either star individually. They may be launched from the innermost part of the circumbinary disk (CBD) or may result from the merging of two outflows driven by the individual stars. This evidence is based on high-resolution Hα and [O i]λ6300 line profiles obtained during eclipse phases of this nearly edge-on system. The occultation of star A (the only currently visible star) by the disk strongly suppresses the stellar Hα and continuum emission and allows one to study the faint redshifted and blueshifted emission components of the bipolar jets. The strongest evidence for jet production by the whole binary system comes from the observed radial velocity symmetry of the two jet components relative to the systemic velocity of the binary in combination with current accretion models from the CBD onto a binary system.

Any multivariate distribution can be uniquely decomposed into marginal (one-point) distributions, and a function called the copula, which contains all of the information on correlations between the distributions. The copula provides an important new methodology for analyzing the density field in large-scale structure. We derive the empirical two-point copula for the evolved dark matter density field. We find that this empirical copula is well approximated by a Gaussian copula. We consider the possibility that the full n-point copula is also Gaussian and describe some of the consequences of this hypothesis. Future directions for investigation are discussed.

We make an inventory of the baryonic and gravitating mass in structures ranging from the smallest galaxies to rich clusters of galaxies. We find that the fraction of baryons converted to stars reaches a maximum between M₅₀₀ = 10¹² and 10¹³ M_☉, suggesting that star formation is most efficient in bright galaxies in groups. The fraction of baryons detected in all forms deviates monotonically from the cosmic baryon fraction as a function of mass. On the largest scales of clusters, most of the expected baryons are detected, while in the smallest dwarf galaxies, fewer than 1% are detected. Where these missing baryons reside is unclear.

The atomic carbon emission C i line feature at 1657 Å (³P⁰_J–³P_J) in the upper atmosphere of Titan is first identified from the airglow spectra obtained by the Cassini Ultra-violet Imaging Spectrograph. A one-dimensional photochemical model of Titan is used to study the photochemistry of atomic carbon on Titan. Reaction between CH and atomic hydrogen is the major source of atomic carbon, and reactions with hydrocarbons (C₂H₂ and C₂H₄) are the most important loss processes. Resonance scattering of sunlight by atomic carbon is the dominant emission mechanism. The emission intensity calculations based on model results show good agreement with the observations.

A set of H i sources extracted from the north Galactic polar region by the ongoing ALFALFA survey has properties that are consistent with the interpretation that they are associated with isolated minihalos in the outskirts of the Local Group (LG). Unlike objects detected by previous surveys, such as the compact high-velocity clouds of Braun & Burton, the H i clouds found by ALFALFA do not violate any structural requirements or halo scaling laws of the ΛCDM structure paradigm, nor would they have been detected by extant H i surveys of nearby galaxy groups other than the LG. At a distance of d Mpc, their H i masses range between 5 × 10⁴d² and 10⁶d² M_☉ and their H i radii between <0.4d and 1.6d kpc. If they are parts of gravitationally bound halos, the total masses would be on the order of 10⁸–10⁹ M_☉, their baryonic content would be significantly smaller than the cosmic fraction of 0.16 and present in a ionized gas phase of mass well exceeding that of the neutral phase. This study does not however prove that the minihalo interpretation is unique. Among possible alternatives would be that the clouds are shreds of the Leading Arm of the Magellanic Stream.

We study the Spitzer Infrared Array Camera (IRAC) mid-infrared (rest-frame optical) fluxes of 14 newly WFC3/IR-detected z ∼ 7 z₈₅₀-dropout galaxies and 5z ∼ 8 Y₁₀₅-dropout galaxies. The WFC3/IR depth and spatial resolution allow accurate removal of contaminating foreground light, enabling reliable flux measurements at 3.6 μm and 4.5 μm. None of the galaxies are detected to [3.6] ≈ 26.9 (AB, 2σ), but a stacking analysis reveals a robust detection for the z₈₅₀-dropouts and an upper limit for the Y₁₀₅-dropouts. We construct average broadband spectral energy distributions using the stacked Advanced Camera for Surveys (ACS), WFC3, and IRAC fluxes and fit stellar population synthesis models to derive mean redshifts, stellar masses, and ages. For the z₈₅₀-dropouts, we find z = 6.9^+0.1_−0.1, (U − V)_rest ≈ 0.4, reddening A_V = 0, stellar mass 〈M*〉 = 1.2^+0.3_−0.6 × 10⁹ M_☉ (Salpeter initial mass function). The best-fit ages ∼300 Myr, M/L_V ≈ 0.2, and SSFR ∼1.7 Gyr⁻¹ are similar to values reported for luminous z ∼ 7 galaxies, indicating the galaxies are smaller but not much younger. The sub-L* galaxies observed here contribute significantly to the stellar mass density and under favorable conditions may have provided enough photons for sustained reionization at 7 < z < 11. In contrast, the z = 8.3^+0.1_−0.2 Y₁₀₅-dropouts have stellar masses that are uncertain by 1.5 dex due to the near-complete reliance on far-UV data. Adopting the 2σ upper limit on the M/L(z = 8), the stellar mass density to M_UV,AB < −18 declines from ρ*(z = 7) = 3.7^+1.4_−1.8 × 10⁶ M_☉ Mpc⁻³ to ρ*(z = 8) < 8 × 10⁵ M_☉ Mpc⁻³, following ∝(1 + z)⁻⁶ over 3 < z < 8. Lower masses at z = 8 would signify more dramatic evolution, which can be established with deeper IRAC observations, long before the arrival of the James Webb Space Telescope.

We use 10 orbits of Advanced Camera for Surveys observations to reach the end of the white dwarf (WD) cooling sequence in the solar-metallicity open cluster NGC 2158. Our photometry and completeness tests show that the end falls at magnitude m_F606W = 27.5 ± 0.15, which implies an age between ∼1.8 and ∼2.0 Gyr, consistent with the age of 1.9 ± 0.2 Gyr obtained from fits to the main-sequence turn-off. The faintest WDs show a clear turn toward bluer colors, as predicted by theoretical isochrones.

Submillimeter galaxies (SMGs) represent a dust-obscured high-redshift population undergoing massive star formation activity. Their properties and space density have suggested that they may evolve into spheroidal galaxies residing in galaxy clusters. In this Letter, we report the discovery of compact (∼10''–20'') galaxy overdensities centered at the position of three SMGs detected with the Max-Planck millimeter bolometer camera in the COSMOS field. These associations are statistically significant. The photometric redshifts of galaxies in these structures are consistent with their associated SMGs; all of them are between z = 1.4and2.5, implying projected physical sizes of ∼170 kpc for the overdensities. Our results suggest that about 30% of the radio-identified bright SMGs in that redshift range form in galaxy density peaks in the crucial epoch when most stars formed.

We present, for the first time, a clear N-body (NB) realization of the strong mass segregation solution for the stellar distribution around a massive black hole (MBH). We compare our NB results with those obtained by solving the orbit-averaged Fokker–Planck (FP) equation in energy space. The NB segregation is slightly stronger than in the FP solution, but both confirm the robustness of the regime of strong segregation when the number fraction of heavy stars is a (realistically) small fraction of the total population. In view of recent observations revealing a dearth of giant stars in the sub-parsec region of the Milky Way, we show that the timescales associated with cusp re-growth are not longer than (0.1 − 0.25) × T_rlx(r_h). These timescales are shorter than a Hubble time for black holes masses M_• ≲ 4 × 10⁶M_☉ and we conclude that quasi-steady, mass-segregated, stellar cusps may be common around MBHs in this mass range. Since extreme mass ratio inspirals detection rates by Laser Interferometer Space Antenna are expected to peak for M_• ∼ 4 × 10⁵–10⁶ M_☉, a good fraction of these events should originate from strongly segregated stellar cusps.

Quasi-periodic pulsations (QPPs) of gamma-ray emission with a period of about 40 s are found in a single loop X-class solar flare on 2005 January 1 at photon energies up to 2–6 MeV with the SOlar Neutrons and Gamma-rays (SONG) experiment aboard the CORONAS-F mission. The oscillations are also found to be present in the microwave emission detected with the Nobeyama Radioheliograph, and in the hard X-ray and low energy gamma-ray channels of RHESSI. Periodogram and correlation analysis shows that the 40 s QPPs of microwave, hard X-ray, and gamma-ray emission are almost synchronous in all observation bands. Analysis of the spatial structure of hard X-ray and low energy (80–225 keV) gamma-ray QPP with RHESSI reveals synchronous while asymmetric QPP at both footpoints of the flaring loop. The difference between the averaged hard X-ray fluxes coming from the two footpoint sources is found to oscillate with a period of about 13 s for five cycles in the highest emission stage of the flare. The proposed mechanism generating the 40 s QPP is a triggering of magnetic reconnection by a kink oscillation in a nearby loop. The 13 s periodicity could be produced by the second harmonics of the sausage mode of the flaring loop.

New generation TeV gamma-ray telescopes have discovered many new sources, including several enigmatic unidentified TeV objects. HESS J0632+057 is a particularly interesting unidentified TeV source since: it is a point source, it has a possible hard-spectrum X-ray counterpart and a positionally consistent Be star, it has evidence of long-term very high energy gamma-ray flux variability, and it is postulated to be a newly detected TeV/X-ray binary. We have obtained Swift X-ray telescope observations of this source from MJD 54857 to 54965, in an attempt to ascertain its nature and to investigate the hypothesis that it is a previously unknown X-ray/TeV binary. Variability and spectral properties similar to those of the other three known X-ray/TeV binaries have been observed, with measured flux increases by factors of ∼3. X-ray variability is present on multiple timescales including days to months; however, no clear signature of periodicity is present on the timescales probed by these data. If binary modulation is present and dominating the measured variability, then the period of the orbit is likely to be ⩾54 days (half of this campaign), or it has a shorter period with a variable degree of flux modulation on successive high states. If the two high states measured to date are due to binary modulation, then the favored period is approximately 35–40 days. More observations are required to determine if this object is truly a binary system and to determine the extent that the measured variability is due to inter-orbit flaring effects or periodic binary modulation.

NGC 1275, the central galaxy in the Perseus cluster, is the host of gigantic hot bipolar bubbles inflated by active galactic nucleus (AGN) jets observed in the radio as Perseus A. It presents a spectacular Hα-emitting nebulosity surrounding NGC 1275, with loops and filaments of gas extending to over 50 kpc. The origin of the filaments is still unknown, but probably correlates with the mechanism responsible for the giant buoyant bubbles. We present 2.5 and three-dimensional magnetohydrodynamical (MHD) simulations of the central region of the cluster in which turbulent energy, possibly triggered by star formation and supernovae (SNe) explosions, is introduced. The simulations reveal that the turbulence injected by massive stars could be responsible for the nearly isotropic distribution of filaments and loops that drag magnetic fields upward as indicated by recent observations. Weak shell-like shock fronts propagating into the intracluster medium (ICM) with velocities of 100–500 km s⁻¹ are found, also resembling the observations. The isotropic outflow momentum of the turbulence slows the infall of the ICM, thus limiting further starburst activity in NGC 1275. As the turbulence is subsonic over most of the simulated volume, the turbulent kinetic energy is not efficiently converted into heat and additional heating is required to suppress the cooling flow at the core of the cluster. Simulations combining the MHD turbulence with the AGN outflow can reproduce the temperature radial profile observed around NGC 1275. While the AGN mechanism is the main heating source, the SNe are crucial to isotropize the energy distribution.

We present a new maximum-light optical spectrum of the extremely low luminosity and exceptionally low-energy Type Ia supernova (SN Ia) 2008ha, obtained one week before the earliest published spectrum. Previous observations of SN 2008ha were unable to distinguish between a massive star and white dwarf (WD) origin for the SN. The new maximum-light spectrum, obtained one week before the earliest previously published spectrum, unambiguously shows features corresponding to intermediate mass elements, including silicon, sulfur, and carbon. Although strong silicon features are seen in some core-collapse SNe, sulfur features, which are a signature of carbon/oxygen burning, have always been observed to be weak in such events. It is therefore likely that SN 2008ha was the result of a thermonuclear explosion of a carbon–oxygen WD. Carbon features at maximum light show that unburned material is present to significant depths in the SN ejecta, strengthening the case that SN 2008ha was a failed deflagration. We also present late-time imaging and spectroscopy that are consistent with this scenario.

DP Leo is the first discovered eclipsing polar with a short period of 1.4967 hours. The period variation of the eclipsing binary was analyzed by using five new determined eclipse times together with those compiled from the literature. It is discovered that the O − C curve of DP Leo shows a cyclic variation with a period of 23.8 years and a semiamplitude of 31.5 s. The small-amplitude periodic change can be plausibly explained as the light-travel time effect due to the presence of a tertiary companion. The mass of the tertiary component is determined to be M₃sin i' = 0.00600(±0.00055) M_☉ = 6.28(±0.58) M_Jupiter when a total mass of 0.69 M_☉ is adopted. If the tertiary companion is coplanar to the eclipsing binary (i.e., i' = 795), it should be a giant extrasolar planet with a mass of 6.39 M_Jupiter at a distance of 8.6 astronomical units to the central binary. One of the most interesting things that we have learned about extrasolar planets over the last 17 years is that they can exist almost anywhere. The detection of a giant planet orbiting a polar would provide insight into the formation and evolution of circumbinary planets (planets orbiting both components of short-period binaries) as well as the late evolution of binary stars.