On the apparent absence of broad iron lines in Seyfert galaxies

We present an analysis of XMM-Newton observations of eleven Seyfert galaxies that appear to be missing a broad iron K alpha line. These objects represent a challenge to the established paradigm for active galactic nuclei, where a relatively cold accretion disc feeds the central black hole. In that paradigm, X-ray illumination of the accretion disc should lead to continuum and fluorescence emission from iron which is broadened and shifted by relativistic effects close the hole. We extend the work of Nandra et al. (2007), who found no evidence for such a component in an earlier analysis of these objects, by testing a variety of more complex relativistic reflection models. Specifically, we consider the possibility that the disc is highly ionised, and/or that the the reflection is heavily blurred by strong relativistic effects in a Kerr geometry. We find that in 8/11 of the observations with no apparent broad iron line, the fit is significantly improved when an ionised or strongly blurred reflector is included, and that all 11 observations allow for such a component. The disc inclinations are found generally to be around 60 degrees, which when combined with a steep emissivity profile results in strong relativistic blurring of the reflection, rendering the K alpha line difficult to distinguish from the underlying continuum. Nevertheless, relativistic reflection does appear to be present, and the strength of the smeared reflection is similar to that expected from a flat disc illuminated by a point source. Such blurred reflection and the associated steep radial emissivity profiles are consistent with the gravitational light bending of the continuum photons close to the black hole.Comment: 9 pages, 2 figures. Accepted for publication in MNRA

Chandra detection of the intracluster medium around 3C294 at z=1.786

We present a Chandra observation of the powerful radio galaxy 3C294 showing clear evidence for a surrounding intracluster medium. At a redshift of 1.786 this is the most distant cluster of galaxies yet detected in X-rays. The radio core is detected as a point source, which has a spectrum consistent with a heavily-absorbed power law implying an intrinsic 2-10 keV luminosity of ~10^45 erg/s. A small excess of emission is associated with the southern radio hotspots. The soft, diffuse emission from the intracluster medium is centred on the radio source. It has an hour-glass shape in the N-S direction, extending to radii of at least 100 kpc, well beyond the radio source. The X-ray spectrum of this extended component is fit by a thermal model with temperature ~5 keV, or by gas cooling from above 7 keV at rates of ~400-700 Msolar/yr. The rest-frame 0.3-10 keV luminosity of the cluster is ~4.5x10^44 erg/s. The existence of such a cluster is consistent with a low density universe.Comment: 5 pages, 6 figures, accepted by MNRA

A Multiwavelength Study of a Sample of 70 micron Selected Galaxies in the COSMOS Field I: Spectral Energy Distributions and Luminosities

We present a large robust sample of 1503 reliable and unconfused 70microm selected sources from the multiwavelength data set of the Cosmic Evolution Survey (COSMOS). Using the Spitzer IRAC and MIPS photometry, we estimate the total infrared luminosity, L_IR (8--1000 microns), by finding the best fit template from several different template libraries. The long wavelength 70 and 160 micron data allow us to obtain a reliable estimate of L_IR, accurate to within 0.2 and 0.05 dex, respectively. The 70 micron data point enables a significant improvement over the luminosity estimates possible with only a 24 micron detection. The full sample spans a wide range in L_IR, L_IR ~ 10^8-10^14 L_sun, with a median luminosity of 10^11.4 L_sun. We identify a total of 687 luminous, 303 ultraluminous, and 31 hyperluminous infrared galaxies (LIRGs, ULIRGs, and HyLIRGs) over the redshift range 0.01<z<3.5 with a median redshift of 0.5. Presented here are the full spectral energy distributions for each of the sources compiled from the extensive multiwavelength data set from the ultraviolet (UV) to the far-infrared (FIR). Using SED fits we find possible evidence for a subset of cooler ultraluminous objects than observed locally. However, until direct observations at longer wavelengths are obtained, the peak of emission and the dust temperature cannot be well constrained. We use these SEDs, along with the deep radio and X-ray coverage of the field, to identify a large sample of candidate active galactic nuclei (AGN). We find that the fraction of AGN increases strongly with L_IR, as it does in the local universe, and that nearly 70% of ULIRGs and all HyLIRGs likely host a powerful AGN.Comment: 31 pages including 31 figures and 6 tables. Accepted for publication in ApJ. The full resolution version is available here: http://www.ifa.hawaii.edu/~jeyhan/paperI/Kartaltepe_70mic_PaperI.pd

Inferring Compton-thick AGN candidates at z>2 with Chandra using the >8 keV restframe spectral curvature

To fully understand cosmic black hole growth we need to constrain the population of heavily obscured active galactic nuclei (AGN) at the peak of cosmic black hole growth ($z\sim$1-3). Sources with obscuring column densities higher than $\mathrm{10^{24}}$ atoms $\mathrm{cm^{-2}}$, called Compton-thick (CT) AGN, can be identified by excess X-ray emission at $\sim$20-30 keV, called the "Compton hump". We apply the recently developed Spectral Curvature (SC) method to high-redshift AGN (2<z<5) detected with Chandra. This method parametrizes the characteristic "Compton hump" feature cosmologically redshifted into the X-ray band at observed energies <10 keV. We find good agreement in CT AGN found using the SC method and bright sources fit using their full spectrum with X-ray spectroscopy. In the Chandra deep field south, we measure a CT fraction of $\mathrm{17^{+19}_{-11}\%}$ (3/17) for sources with observed luminosity $\mathrm{>5\times 10^{43}}$ erg $\mathrm{s^{-1}}$. In the Cosmological evolution survey (COSMOS), we find an observed CT fraction of $\mathrm{15^{+4}_{-3}\%}$ (40/272) or $\mathrm{32\pm11 \%}$ when corrected for the survey sensitivity. When comparing to low redshift AGN with similar X-ray luminosities, our results imply the CT AGN fraction is consistent with having no redshift evolution. Finally, we provide SC equations that can be used to find high-redshift CT AGN (z>1) for current (XMM-Newton) and future (eROSITA and ATHENA) X-ray missions.Comment: 10 pages, 8 figure

Ultraluminous X-ray sources out to z~0.3 in the COSMOS field

Using Chandra observations we have identified a sample of seven off-nuclear X-ray sources, in the redshift range z=0.072-0.283, located within optically bright galaxies in the COSMOS Survey. Using the multi-wavelength coverage available in the COSMOS field, we study the properties of the host galaxies of these ULXs. In detail, we derived their star formation rate from H_alpha measurements and their stellar masses using SED fitting techniques with the aim to compute the probability to have an off-nuclear source based on the host galaxy properties. We divide the host galaxies in different morphological classes using the available ACS/HST imaging. We find that our ULXs candidates are located in regions of the SFR versus M$_star$ plane where one or more off-nuclear detectable sources are expected. From a morphological analysis of the ACS imaging and the use of rest-frame colours, we find that our ULXs are hosted both in late and early type galaxies. Finally, we find that the fraction of galaxies hosting a ULX ranges from ~0.5% to ~0.2% going from L[0.5-2 keV]=3 x 10^39 erg s^-1 to L[0.5-2 keV]= 2 x 10^40 erg s^-1.Comment: 10 pages, 9 figures, accepted for publication in Astronomy & Astrophysic

The First Release COSMOS Optical and Near-IR Data and Catalog

We present imaging data and photometry for the COSMOS survey in 15 photometric bands between 0.3um and 2.4um. These include data taken on the Subaru 8.3m telescope, the KPNO and CTIO 4m telescopes, and the CFHT 3.6m telescope. Special techniques are used to ensure that the relative photometric calibration is better than 1% across the field of view. The absolute photometric accuracy from standard star measurements is found to be 6%. The absolute calibration is corrected using galaxy spectra, providing colors accurate to 2% or better. Stellar and galaxy colors and counts agree well with the expected values. Finally, as the first step in the scientific analysis of these data we construct panchromatic number counts which confirm that both the geometry of the universe and the galaxy population are evolving.Comment: 19 pages, 13 figures, 14 tables, Accepted to ApJS for COSMOS speciall issu

Spectral Energy Distributions of Type 1 AGN in the COSMOS Survey I - The XMM-COSMOS Sample

The "Cosmic Evolution Survey" (COSMOS) enables the study of the Spectral Energy Distributions (SEDs) of Active Galactic Nuclei (AGN) because of the deep coverage and rich sampling of frequencies from X-ray to radio. Here we present a SED catalog of 413 X-ray (\xmm) selected type 1 (emission line FWHM$>2000$ km s$^{-1}$) AGN with Magellan, SDSS or VLT spectrum. The SEDs are corrected for the Galactic extinction, for broad emission line contributions, constrained variability, and for host galaxy contribution. We present the mean SED and the dispersion SEDs after the above corrections in the rest frame 1.4 GHz to 40 keV, and show examples of the variety of SEDs encountered. In the near-infrared to optical (rest frame $\sim 8\mu m$-- 4000\AA), the photometry is complete for the whole sample and the mean SED is derived from detections only. Reddening and host galaxy contamination could account for a large fraction of the observed SED variety. The SEDs are all available on-line.Comment: 22 pages, 22 figures, ApJ accepted, scheduled to be published October 20th, 2012, v75

Atomic X-ray Spectroscopy of Accreting Black Holes

Current astrophysical research suggests that the most persistently luminous objects in the Universe are powered by the flow of matter through accretion disks onto black holes. Accretion disk systems are observed to emit copious radiation across the electromagnetic spectrum, each energy band providing access to rather distinct regimes of physical conditions and geometric scale. X-ray emission probes the innermost regions of the accretion disk, where relativistic effects prevail. While this has been known for decades, it also has been acknowledged that inferring physical conditions in the relativistic regime from the behavior of the X-ray continuum is problematic and not satisfactorily constraining. With the discovery in the 1990s of iron X-ray lines bearing signatures of relativistic distortion came the hope that such emission would more firmly constrain models of disk accretion near black holes, as well as provide observational criteria by which to test general relativity in the strong field limit. Here we provide an introduction to this phenomenon. While the presentation is intended to be primarily tutorial in nature, we aim also to acquaint the reader with trends in current research. To achieve these ends, we present the basic applications of general relativity that pertain to X-ray spectroscopic observations of black hole accretion disk systems, focusing on the Schwarzschild and Kerr solutions to the Einstein field equations. To this we add treatments of the fundamental concepts associated with the theoretical and modeling aspects of accretion disks, as well as relevant topics from observational and theoretical X-ray spectroscopy.Comment: 63 pages, 21 figures, Einstein Centennial Review Article, Canadian Journal of Physics, in pres

NGC 5548: Lack of a Broad Fe K Line and Constraints on the Location of the Hard X-ray Source

We present an analysis of the co-added and individual 0.7-40 keV spectra from seven Suzaku observations of the Sy 1.5 galaxy NGC 5548 taken over a period of eight weeks. We conclude that the source has a moderately ionized, three-zone warm absorber, a power-law continuum, and exhibits contributions from cold, distant reflection. Relativistic reflection signatures are not significantly detected in the co-added data, and we place an upper limit on the equivalent width of a relativistically broad Fe K line at EW \leq 26 eV at 90% confidence. Thus NGC 5548 can be labeled an "weak" type-1 AGN in terms of its observed inner disk reflection signatures, in contrast to sources with very broad, strong iron lines such as MCG-6-30-15, which are likely much fewer in number. We compare physical properties of NGC 5548 and MCG-6-30-15 that might explain this difference in their reflection properties. Though there is some evidence that NGC 5548 may harbor a truncated inner accretion disk, this evidence is inconclusive, so we also consider light bending of the hard X-ray continuum emission in order to explain the lack of relativistic reflection in our observation. If the absence of a broad Fe K line is interpreted in the light-bending context, we conclude that the source of the hard X-ray continuum lies at <100 gravitational radii. We note, however, that light-bending models must be expanded to include a broader range of physical parameter space in order to adequately explain the spectral and timing properties of average AGN, rather than just those with strong, broad iron lines.Comment: 42 pages (preprint format), 8 figures. Accepted by Ap

Suzaku Monitoring of the Iron K Emission Line in the Type 1 Active Galactic Nucleus Ngc 5548

We present seven sequential weekly observations of NGC 5548 conducted in 2007 with the Suzaku X-ray Imaging Spectrometer (XIS) in the 0.2–12 keV band and Hard X-ray Detector (HXD) in the 10–600 keV band. The iron Kα line is well detected in all seven observations and Kβ line is also detected in four observations. In this paper, we investigate the origin of the Fe K lines using both the width of the line and the reverberation mapping method. With the co-added XIS and HXD spectra, we identify Fe Kα and Kβ line at 6.396+0.009 −0.007 keV and 7.08+0.05 −0.05 keV, respectively. The width of line obtained from the co-added spectra is 38+16 −18 eV (FWHM = 4200+1800 −2000 km s−1) which corresponds to a radius of 20+50 −10 light days, for the virial production of 1.220 × 107 M in NGC 5548. To quantitatively investigate the origin of the narrow Fe line by the reverberation mapping method, we compare the observed light curves of Fe Kα line with the predicted ones, which are obtained by convolving the continuum light curve with the transfer functions in a thin shell and an inclined disk. The best-fit result is given by the disk case with i = 30◦ which is better than a fit to a constant flux of the Fe K line at the 92.7% level (F-test). However, the results with other geometries are also acceptable (P > 50%). We find that the emitting radius obtained from the light curve is 25–37 light days, which is consistent with the radius derived from the Fe K line width. Combining the results of the line width and variation, the most likely site for the origin of the narrow iron lines is 20–40 light days away from the central engine, though other possibilities are not completely ruled out. This radius is larger than the Hβ emitting parts of the broad-line region at 6–10 light days (obtained by the simultaneous optical observation), and smaller than the inner radius of the hot dust in NGC 5548 (at about 50 light days).Astronom