We present a unification model for a clumpy obscurer in active galactic nuclei (AGN) and investigate the properties of the resulting X-ray spectrum. Our model is constructed to reproduce the column ...density distribution of the AGN population and cloud eclipse events in terms of their angular sizes and frequency. We developed and released a generalised Monte Carlo X-ray radiative transfer code, XARS, to compute X-ray spectra of obscurer models. The geometry results in strong Compton scattering, causing soft photons to escape also along Compton-thick sight lines. This makes our model spectra very similar to our TORUS previous model. However, only if we introduce an additional Compton-thick reflector near the corona, we achieve good fits to NuSTAR spectra. This additional component in our model can be interpreted as part of the dust-free broad-line region, an inner wall or rim, or a warped disk. It cannot be attributed to a simple disk because the reflector must simultaneously block the line of sight to the corona and reflect its radiation. We release our model as an Xspec table model and present corresponding CLUMPY infrared spectra, paving the way for self-consistent multi-wavelength analyses.
Context.
The nuclear obscurer of active galactic nuclei (AGN) is poorly understood in terms of its origin, geometry, and dynamics.
Aims.
We investigate whether physically motivated geometries ...emerging from hydro-radiative simulations can be differentiated with X-ray reflection spectroscopy.
Methods.
For two new geometries, the radiative fountain model and a warped disk, we release spectral models produced with the ray tracing code XARS. We contrast these models with spectra of three nearby AGN taken by
NuSTAR
and
Swift
/BAT.
Results.
Along heavily obscured sightlines, the models present different 4−20 keV continuum spectra. These can be differentiated by current observations. Spectral fits of the Circinus Galaxy favour the warped disk model over the radiative fountain, and clumpy or smooth torus models.
Conclusions.
The necessary reflector (
N
H
≥ 10
25
cm
2
) suggests a hidden population of heavily Compton-thick AGN amongst local galaxies. X-ray reflection spectroscopy is a promising pathway to understand the nuclear obscurer in AGN.
We present the Data Release 12 Quasar catalog (DR12Q) from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey III. This catalog includes all SDSS-III/BOSS objects that ...were spectroscopically targeted as quasar candidates during the full survey and that are confirmed as quasars via visual inspection of the spectra, have luminosities Mi z = 2 < −20.5 (in a ΛCDM cosmology with H0 = 70 km s-1 Mpc-1, ΩM = 0.3, and ΩΛ = 0.7), and either display at least one emission line with a full width at half maximum (FWHM) larger than 500 km s-1 or, if not, have interesting/complex absorption features. The catalog also includes previously known quasars (mostly from SDSS-I and II) that were reobserved by BOSS. The catalog contains 297 301 quasars (272 026 are new discoveries since the beginning of SDSS-III) detected over 9376 deg2 with robust identification and redshift measured by a combination of principal component eigenspectra. The number of quasars with z > 2.15 (184 101, of which 167 742 are new discoveries) is about an order of magnitude greater than the number of z > 2.15 quasars known prior to BOSS. Redshifts and FWHMs are provided for the strongest emission lines (C iv, C iii, Mg ii). The catalog identifies 29 580 broad absorption line quasars and lists their characteristics. For each object, the catalog presents five-band (u, g, r, i, z) CCD-based photometry with typical accuracy of 0.03 mag together with some information on the optical morphology and the selection criteria. When available, the catalog also provides information on the optical variability of quasars using SDSS and Palomar Transient Factory multi-epoch photometry. The catalog also contains X-ray, ultraviolet, near-infrared, and radio emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra, covering the wavelength region 3600–10 500 Å at a spectral resolution in the range 1300 < R < 2500, can be retrieved from the SDSS Catalog Archive Server. We also provide a supplemental list of an additional 4841 quasars that have been identified serendipitously outside of the superset defined to derive the main quasar catalog.
We present a WFC3 F160W (H-band) selected catalog in the CANDELS/GOODS-N field containing photometry from the ultraviolet (UV) to the far-infrared (IR), photometric redshifts, and stellar parameters ...derived from the analysis of the multiwavelength data. The catalog contains 35,445 sources over the 171 arcmin2 of the CANDELS F160W mosaic. The 5 detection limits (within an aperture of radius 0 17) of the mosaic range between H = 27.8, 28.2, and 28.7 in the wide, intermediate, and deep regions, which span approximately 50%, 15%, and 35% of the total area. The multiwavelength photometry includes broadband data from the UV (U band from KPNO and LBC), optical (HST/ACS F435W, F606W, F775W, F814W, and F850LP), near-to-mid IR (HST/WFC3 F105W, F125W, F140W, and F160W; Subaru/MOIRCS Ks; CFHT/Megacam K; and Spitzer/IRAC 3.6, 4.5, 5.8, and 8.0 m), and far-IR (Spitzer/MIPS 24 m, HERSCHEL/PACS 100 and 160 m, SPIRE 250, 350 and 500 m) observations. In addition, the catalog also includes optical medium-band data (R ∼ 50) in 25 consecutive bands, λ = 500-950 nm, from the SHARDS survey and WFC3 IR spectroscopic observations with the G102 and G141 grisms (R ∼ 210 and 130). The use of higher spectral resolution data to estimate photometric redshifts provides very high, and nearly uniform, precision from z = 0-2.5. The comparison to 1485 good-quality spectroscopic redshifts up to z ∼ 3 yields Δz/(1 + zspec) = 0.0032 and an outlier fraction of = 4.3%. In addition to the multiband photometry, we release value-added catalogs with emission-line fluxes, stellar masses, dust attenuations, UV- and IR-based star formation rates, and rest-frame colors.
In this paper we describe and publicly release a catalogue consisting of 8445 point-like X-ray sources detected in the XMM-XXL north survey. For the 2512 AGN which have reliable spectroscopy from ...SDSS-III/BOSS, we present the X-ray spectral fitting which has been computed with a Bayesian approach. We have also applied an X-ray spectral stacking method to different sub-samples, selected on the basis of the AGN physical properties (L
2−10 keV, z, M
BH, λEdd and N
H). We confirm the well-known Iwasawa–Taniguchi effect in our luminosity–redshift sub-samples, and argue that such an effect is due to a decrease in the covering factor of a distant obscuring ‘torus’ with increasing X-ray luminosity. By comparing the distribution of the reflection fraction, the ratio of the normalization of the reflected component to the direct radiation, we find that the low-luminosity, low-redshift sub-sample had systematically higher reflection fraction values than the high-redshift, high-luminosity one. On the other hand, no significant difference is found between samples having similar luminosity but different redshift, suggesting that the structure of the torus does not evolve strongly with redshift. Contrary to previous works, we do not find evidence for an increasing photon index at high Eddington ratio. This may be an indication that the structure of the accretion disc changes as the Eddington ratio approaches unity. Comparing our X-ray spectral analysis results with the optical spectral classification, we find that ∼20 per cent of optical type-1 AGN show an X-ray absorbing column density higher than 1021.5 cm− 2, and about 50 per cent of type-2 AGN have an X-ray absorbing column density less than 1021.5 cm− 2. We suggest that the excess X-ray absorption shown in the high-luminosity optical type-1 AGN can be due to small-scale dust-free gas within (or close to) the broad-line region, while in the low-luminosity ones it can be due to a clumpy torus with a large covering factor.
Abstract
This is the fifth paper in a series of investigations of the clustering properties of luminous, broad-emission-line active galactic nuclei (AGNs) identified in the ROSAT All-Sky Survey ...(RASS) and Sloan Digital Sky Survey (SDSS). In this work we measure the cross-correlation function (CCF) between RASS/SDSS Data Release 14 AGNs with the SDSS CMASS galaxy sample at 0.44 <
z
< 0.64. We apply halo occupation distribution (HOD) modeling to the CCF along with the autocorrelation function of the CMASS galaxies. We find that X-ray-selected and optically selected AGNs at 0.44 <
z
< 0.64 reside in statistically identical halos with a typical dark matter halo (DMH) mass of
M
DMH
typ
,
AGN
∼
10
12.7
h
−
1
M
⊙
. The acceptable HOD parameter space for these two broad-line AGN samples have only statistically marginal differences caused by small deviations of the CCFs in the one-halo-dominated regime on small scales. In contrast to optically selected AGNs, the X-ray AGN sample may contain a larger population of satellites at
M
DMH
∼ 10
13
h
−1
M
⊙
. We compare our measurements in this work with our earlier studies at lower independent redshift ranges, spanning a lookback time of 6 Gyr. The comparison over this wider redshift range of 0.07 <
z
< 0.64 reveals (i) no significant difference between the typical DMH masses of X-ray-selected and optically selected AGNs, (ii) weak positive clustering dependencies of
M
DMH
typ
,
AGN
with
L
X
and
M
BH
, (iii) no significant dependence of
M
DMH
typ
,
AGN
on Eddington ratio, and (iv) the same DMH masses host more-massive accreting black holes at high redshift than at low redshifts.
The reliability of detecting source variability in sparsely and irregularly sampled X-ray light curves is investigated. This is motivated by the unprecedented survey capabilities of eROSITA on board ...the Spektrum-Roentgen-Gamma observatory, providing light curves for many thousand sources in its final-depth equatorial deep-field survey. Four methods for detecting variability are evaluated: excess variance, amplitude maximum deviations, Bayesian blocks, and a new Bayesian formulation of the excess variance. We judge the false-detection rate of variability based on simulated Poisson light curves of constant sources, and calibrate significance thresholds. Simulations in which flares are injected favour the amplitude maximum deviation as most sensitive at low false detections. Simulations with white and red stochastic source variability favour Bayesian methods. The results are applicable also for the million sources expected in the eROSITA all-sky survey.
The properties (temperature, density, chemical composition, velocity) of hot astrophysical plasma and the physical processes affecting them (heating/cooling, turbulence, shocks, acceleration) can be ...probed by high‐resolution X‐ray spectroscopy, to be complemented by high‐spatial‐resolution imaging. The paper presents the status of the European Space Agency's Advanced Telescope for High Energy Astrophysics (Athena) mission, particularly focusing on the science performance of its two focal‐plane instruments for studies of extended X‐ray sources: the wide‐field imager and the X‐ray integral field unit. This paper then provides a brief summary of the breakthroughs expected with Athena on the astrophysics of hot plasma, building on the vast heritage of the discoveries and revolutionary results obtained by Chandra and XMM‐Newton in this field. As of November 12, 2019, Athena successfully concluded its feasibility study, and has since then moved into the definition phase, with a launch date scheduled in the early 2030s.
Multiwavelength surveys covering large sky volumes are necessary to obtain an accurate census of rare objects such as high-luminosity and/or high-redshift active galactic nuclei (AGNs). Stripe 82X is ...a 31.3 X-ray survey with Chandra and XMM-Newton observations overlapping the legacy Sloan Digital Sky Survey Stripe 82 field, which has a rich investment of multiwavelength coverage from the ultraviolet to the radio. The wide-area nature of this survey presents new challenges for photometric redshifts for AGNs compared to previous work on narrow-deep fields because it probes different populations of objects that need to be identified and represented in the library of templates. Here we present an updated X-ray plus multiwavelength matched catalog, including Spitzer counterparts, and estimated photometric redshifts for 5961 (96% of a total of 6181) X-ray sources that have a normalized median absolute deviation, , and an outlier fraction, = 13.7%. The populations found in this survey and the template libraries used for photometric redshifts provide important guiding principles for upcoming large-area surveys such as eROSITA and 3XMM (in X-ray) and the Large Synoptic Survey Telescope (optical).
On the nature of unabsorbed Seyfert 2 galaxies Brightman, Murray; Nandra, Kirpal
Monthly notices of the Royal Astronomical Society,
November 2008, Letnik:
390, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We present an analysis of six 12 μm selected Seyfert 2 galaxies that have been reported to be unabsorbed in the X-ray. By comparing the luminosities of these galaxies in the mid-infrared (12 μm), ...optical (O iii) and hard X-ray (2–10 keV), we show that they are all underluminous in the 2–10 keV X-ray band. Four of the objects exhibit X-ray spectra indicative of a hard excess, consistent with a heavily obscured X-ray component and hence a hidden nucleus. In these objects, the softer X-rays may be dominated by a strong soft scattered continuum or contamination from the host galaxy, which is responsible for the unabsorbed X-ray spectra observed, and accounts for the anomalously low 2–10 keV X-ray luminosity. We confirm this assertion in NGC 4501 with a Chandra observation, which shows hard X-ray emission coincident with the nucleus, consistent with heavy absorption, and a number of contaminating softer sources which account for the bulk of the softer emission. We point out that such ‘Compton thick’ sources need not necessarily present iron Kα emission of high equivalent width. An example in our sample is IRASF 01475–0740, which we know must host an obscured active galactic nucleus (AGN) as it hosts a hidden broad line region (BLR) seen in scattered light. The X-ray spectrum is nonetheless relatively unobscured and the iron Kα line only moderate in strength (∼160 eV). These observations can be reconciled if the hidden nuclear emission is dominated by transmitted, rather than reflected X-rays, which can then be weak compared to the soft scattered light or galactic emission even at 6.4 keV. Despite these considerations, we conclude that two sources, NGC 3147 and 3660, may intrinsically lack a BLR, confirming the recent results of Bianchi et al. in the case of NGC 3147. Neither X-ray spectrum shows signs of hidden hard emission and both sources exhibit X-ray variability leading us to believe that we are viewing the nucleus directly.
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