- ID:
- ivo://CDS.VizieR/J/other/Ap/63.166
- Title:
- AGN selected from an HRC/BHRC sample. II.
- Short Name:
- J/other/Ap/63.16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is a detailed spectral classification of 198 candidate active galactic nuclei (AGN) from a joint HRC/BHRC sample consisting of a combination of the HRC (Hamburg-ROSAT) and BHRC (Byurakan-ROSAT) catalogs. These objects have been identified as optical counterparts of ROSAT X-ray sources, but spectra for 198 of them are given in the SDSS without determinations of their spectral classification. They are studied using the SDSS spectra and detailed types of activity are found for them. For a more reliable classification, three diagnostic diagrams have been used, along with direct studies of the spectra. These sources were also identified in other wavelength ranges and their physical parameters have also been calculated.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/423/469
- Title:
- AGNs from RXTE 3-20keV All-Sky Survey
- Short Name:
- J/A+A/423/469
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We compiled a sample of 95 AGNs serendipitously detected in the 3-20keV band at Galactic latitude |b|>10deg during the RXTE slew survey (XSS, Revnivtsev et al., Cat. <J/A+A/418/927>), and utilize it to study the statistical properties of the local population of AGNs, including the X-ray luminosity function and absorption distribution. We find that among low X-ray luminosity (LX<10^43.5^erg/s) AGNs, the ratio of absorbed (characterized by intrinsic absorption in the range 10^22^cm^-2^<NH<10^24^cm^-2^) and unabsorbed (NH<10^22^cm^-2^) objects is 2:1, while this ratio drops to less than 1:5 for higher luminosity AGNs. The summed X-ray output of AGNs with LX>10^41^erg/s estimated here is smaller than the earlier estimated total X-ray volume emissivity in the local Universe, suggesting that a comparable X-ray flux may be produced together by lower luminosity AGNs, non-active galaxies and clusters of galaxies. Finally, we present a sample of 35 AGN candidates, composed of unidentified XSS sources.
- ID:
- ivo://CDS.VizieR/J/AJ/137/179
- Title:
- AGNs in the Extended Groth Strip Survey
- Short Name:
- J/AJ/137/179
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have employed a reliable technique of classification of active galactic nuclei (AGNs) based on the fit of well sampled spectral energy distributions (SEDs) with a complete set of AGN and starburst galaxy templates. We have compiled UV, optical, and IR data for a sample of 116 AGNs originally selected for their X-ray and mid-IR emissions (96 with single detections and 20 with double optical counterparts). This is the most complete compilation of multiwavelength data for such a large sample of AGN in the Extended Groth Strip. Through these SEDs, we are able to obtain highly reliable photometric redshifts and to distinguish between pure and host-dominated AGNs.
- ID:
- ivo://CDS.VizieR/J/A+A/564/A125
- Title:
- AGN Torus model comparison of AGN in the CDFS
- Short Name:
- J/A+A/564/A125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Active Galactic Nuclei are known to have complex X-ray spectra that depend on both the properties of the accreting supermassive black hole (e.g. mass, accretion rate) and the distribution of obscuring material in its vicinity (i.e. the "torus"). Often however, simple and even unphysical models are adopted to represent the X-ray spectra of AGN, which do not capture the complexity and diversity of the observations. In the case of blank field surveys in particular, this should have an impact on e.g. the determination of the AGN luminosity function, the inferred accretion history of the Universe and also on our understanding of the relation between AGN and their host galaxies. We develop a Bayesian framework for model comparison and parameter estimation of X-ray spectra. We take into account uncertainties associated with both the Poisson nature of X-ray data and the determination of source redshift using photometric methods. We also demonstrate how Bayesian model comparison can be used to select among ten different physically motivated X-ray spectral models the one that provides a better representation of the observations. This methodology is applied to X-ray AGN in the 4 Ms Chandra Deep Field South. For the ~350 AGN in that field, our analysis identifies four components needed to represent the diversity of the observed X-ray spectra: (1) an intrinsic power law, (2) a cold obscurer which reprocesses the radiation due to photo-electric absorption, Compton scattering and Fe-K fluorescence, (3) an unabsorbed power law associated with Thomson scattering off ionised clouds, and (4) Compton reflection, most noticeable from a stronger-than-expected Fe-K line. Simpler models, such as a photo-electrically absorbed power law with a Thomson scattering component, are ruled out with decisive evidence (B>100). We also find that ignoring the Thomson scattering component results in underestimation of the inferred column density, N_H_, of the obscurer. Regarding the geometry of the obscurer, there is strong evidence against both a completely closed (e.g. sphere), or entirely open (e.g. blob of material along the line of sight), toroidal geometry in favour of an intermediate case. Despite the use of low-count spectra, our methodology is able to draw strong inferences on the geometry of the torus. Simpler models are ruled out in favour of a geometrically extended structure with significant Compton scattering. We confirm the presence of a soft component, possibly associated with Thomson scattering off ionised clouds in the opening angle of the torus. The additional Compton reflection required by data over that predicted by toroidal geometry models, may be a sign of a density gradient in the torus or reflection off the accretion disk. Finally, we release a catalogue of AGN in the CDFS with estimated parameters such as the accretion luminosity in the 2-10keV band and the column density, N_H_, of the obscurer.
- ID:
- ivo://CDS.VizieR/J/A+A/602/A123
- Title:
- AGN vs. host galaxy properties in COSMOS field
- Short Name:
- J/A+A/602/A123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The coeval AGN and galaxy evolution and the observed local relations between SMBHs and galaxy properties suggest some connection or feedback between SMBH growth and galaxy build-up. We looked for correlations between properties of X-ray detected AGN and their FIR detected host galaxies, to find quantitative evidences for this connection, highly debated in the latest years. We exploit the rich multi-wavelength data set available in the COSMOS field for a large sample (692 sources) of AGN and their hosts, in the redshift range 0.1<z<4. We use X-ray data to select AGN and determine their properties (intrinsic luminosity and nuclear obscuration), and broad-band SED fitting to derive host galaxy properties (stellar mass M* and star formation rate SFR). We find that the AGN 2-10keV luminosity (LX) and the host 8-1000um star formation luminosity (LSFIR) are significantly correlated. However, the average host LSFIR has a flat distribution in bins of AGN LX, while the average AGN LX increases in bins of host LSFIR, with logarithmic slope of ~0.7, in the redshifts range 0.4<z<1.2. We also discuss the comparison between the distribution of these two quantities and the predictions from hydro-dynamical simulations. Finally we find that the average column density (NH) shows a positive correlation with the host M*, at all redshifts, but not with the SFR (or LSFIR). This translates into a negative correlation with specific SFR. Our results are in agreement with the idea that BH accretion and SF rates are correlated, but occur with different variability time scales. The presence of a positive correlation between NH and host M* suggests that the X-ray NH is not entirely due to the circum-nuclear obscuring torus, but may also include a contribution from the host galaxy.
- ID:
- ivo://CDS.VizieR/J/ApJS/176/355
- Title:
- AGN X-Ray emission and black holes
- Short Name:
- J/ApJS/176/355
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work we use a sample of 318 radio-quiet quasars (RQQs) to investigate the dependence of the ratio of optical/UV flux to X-ray flux, {alpha}_ox_, and the X-ray photon index, {Gamma}_X_, on black hole mass, UV relative to Eddington luminosity, and X-ray relative to Eddington luminosity. Our sample is drawn from the literature, with X-ray data from ROSAT and Chandra, and optical data mostly from the SDSS; 153 of these sources have estimates of {Gamma}_X_ from Chandra. We estimate M_BH_ using standard estimates derived from the H{beta}, MgII, and CIV broad emission lines. To date, this is the largest study of the dependence of RQQ X-ray parameters on black hole mass and related quantities, and the first to attempt to correct for the large statistical uncertainty in the broad-line mass estimates.
- ID:
- ivo://CDS.VizieR/J/ApJ/748/124
- Title:
- AGN X-ray variability in the 4Ms catalog
- Short Name:
- J/ApJ/748/124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The 4 Ms Chandra Deep Field-South (CDF-S) and other deep X-ray surveys have been highly effective at selecting active galactic nuclei (AGNs). However, cosmologically distant low-luminosity AGNs (LLAGNs) have remained a challenge to identify due to significant contribution from the host galaxy. We identify long-term X-ray variability (~month-years, observed frame) in 20 of 92 CDF-S galaxies spanning redshifts z{approx}0.08-1.02 that do not meet other AGN selection criteria. We show that the observed variability cannot be explained by X-ray binary populations or ultraluminous X-ray sources, so the variability is most likely caused by accretion onto a supermassive black hole (SMBH). The variable galaxies are not heavily obscured in general, with a stacked effective power-law photon index of {Gamma}_stack_{approx}1.93+/-0.13, and are therefore likely LLAGNs. The LLAGNs tend to lie a factor of {approx}6-80 below the extrapolated linear variability-luminosity relation measured for luminous AGNs.
- ID:
- ivo://CDS.VizieR/J/ApJ/815/33
- Title:
- A Hubble diagram for quasars
- Short Name:
- J/ApJ/815/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new method to test the {Lambda}CDM cosmological model and to estimate cosmological parameters based on the nonlinear relation between the ultraviolet and X-ray luminosities of quasars. We built a data set of 1138 quasars by merging several samples from the literature with X-ray measurements at 2keV and SDSS photometry, which was used to estimate the extinction-corrected 2500{AA} flux. We obtained three main results: (1) we checked the nonlinear relation between X-ray and UV luminosities in small redshift bins up to z~6, confirming that the relation holds at all redshifts with the same slope; (2) we built a Hubble diagram for quasars up to z~6, which is well matched to that of supernovae in the common z=0-1.4 redshift interval and extends the test of the cosmological model up to z~6; and (3) we showed that this nonlinear relation is a powerful tool for estimating cosmological parameters. Using the present data and assuming a {Lambda}CDM model, we obtain {Omega}_M_=0.22_-0.08_^+0.10^ and {Omega}_{Lambda}_=0.92-0.30_^+0.18^ ({Omega}=0.28+/-0.04 and {Omega}_{Lambda}_=0.73+/-0.08 from a joint quasar-SNe fit). Much more precise measurements will be achieved with future surveys. A few thousand SDSS quasars already have serendipitous X-ray observations from Chandra or XMM-Newton, and at least 100000 quasars with UV and X-ray data will be made available by the extended ROentgen Survey with an Imaging Telescope Array all-sky survey in a few years. The Euclid, Large Synoptic Survey Telescope, and Advanced Telescope for High ENergy Astrophysics surveys will further increase the sample size to at least several hundred thousand. Our simulations show that these samples will provide tight constraints on the cosmological parameters and will allow us to test for possible deviations from the standard model with higher precision than is possible today.
49. A2125 in X-ray
- ID:
- ivo://CDS.VizieR/J/ApJ/611/821
- Title:
- A2125 in X-ray
- Short Name:
- J/ApJ/611/821
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an 82ks Chandra ACIS-I observation of a large-scale hierarchical complex, which consists of various clusters/groups of galaxies and low surface brightness X-ray emission at z=0.247. This high-resolution Chandra observation allows us for the first time to separate unambiguously the X-ray contributions from discrete sources and large-scale diffuse hot gas. We detect 99 X-ray sources in a 17{arcmin}x17{arcmin} field.
- ID:
- ivo://CDS.VizieR/IX/48
- Title:
- Allsky cross-matched 3XMMe catalogue
- Short Name:
- IX/48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- ARCHES (Astronomical Resource Cross-matching for High Energy Studies) is a FP7-Space funded project whose aim is to provide the astronomical community with well-characterised multi-wavelength data in the form of spectral energy distributions (SEDs) for large samples of objects extracted from the 3XMM DR5 X-ray catalogue of serendipitous sources. The project has developed new tools implementing fully probabilistic simultaneous cross-correlation of several catalogues for unresolved sources. A cleaned and enhanced version of the 3XMM DR5 catalogue (the 3XMMe catalogue) has been cross-correlated using the ARCHES tool with a number of selected multi-wavelength archival catalogues. These catalogues cover wavelengths ranging from UV to far IR. They provide probabilities of associations, magnitude and fluxes from which spectral energy distributions can be extracted.