- ID:
- ivo://CDS.VizieR/J/A+A/557/A81
- Title:
- XMM-LSS field X-ray sources classification
- Short Name:
- J/A+A/557/A81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The XMM-Large Scale Structure survey (XMM-LSS), covering an area of 11.1 sq. deg., contains more than 6000 X-ray point-like sources detected with XMM-Newton to a flux of 3x10^-15^erg/s/cm^2^ in the [0.5-2]keV band. The vast majority of these sources have optical (CFHTLS), infrared (SWIRE IRAC and MIPS), near-infrared (UKIDSS) and/or ultraviolet (GALEX) counterparts. We wish to investigate the environmental properties of the different types of the XMM-LSS X-ray sources by defining their environment using the i'-band CFHTLS W1 catalog of optical galaxies to a magnitude limit of 23.5mag. We have classified 4435 X-ray selected sources on the basis of their spectra, SEDs, and X-ray luminosity, and estimated their photometric redshifts, which have a 4-11 band photometry with an accuracy of sigma_dz_/(1+z_sp_)=0.076 with 22.6% outliers for i'<26mag. We estimated the local overdensities of 777 X-ray sources that have spectro-z or photo-z calculated by using more than seven bands (accuracy of sigma_dz_/(1+z_sp_)=0.061 with 13.8% outliers) within the volume-limited region defined by 0.1<z<0.85 and -23.5<M_i'_<-20. Although X-ray sources may be found in variety of environments, a high fraction (~55-60%), as verified by comparing with the random expectations, reside in overdense regions. The galaxy overdensities within which X-ray sources reside show a positive recent redshift evolution (at least for the range studied; z<0.85). We also find that X-ray selected galaxies, when compared to AGN, inhabit significantly higher galaxy overdensities, although their spatial extent appear to be smaller than that of AGN. Hard AGN (HR>-0.2) are located in more overdense regions than soft AGN (HR<-0.2), which is clearly seen in both redshift ranges, although it appears to be stronger in the higher redshift range (0.55<z<0.85). Furthermore, the galaxy overdensities (with {delta}>1.5) within which soft AGN are embedded appear to evolve more rapidly compared to the corresponding overdensities around hard AGN.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/474/473
- Title:
- XMM-LSS survey: AGN classifications
- Short Name:
- J/A+A/474/473
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Our goal is to characterize AGN populations by comparing their X-ray and optical classifications within the framework of the standard orientation-based unified scheme. We present a sample of 99 spectroscopically identified (R<=22mag) X-ray selected point sources in the XMM-LSS survey which are significantly detected (>=3{sigma}) in the [2-10]keV band with fluxes between 8x10^-15^ and 8x10^-14^erg/s/cm^2^, and which have more than 80 counts. We have compared their X-ray and optical classifications. To this end, we performed an X-ray spectral analysis for all of these 99 X-ray sources in order to assess whether they are intrinsically absorbed or not. The X-ray classification is based on the measured intrinsic column density. The optical classification is based on the measured FWHM of the permitted emission lines, the absence of broad lines being due to obscuration within the framework of the standard AGN unified scheme.
- ID:
- ivo://CDS.VizieR/J/MNRAS/352/91
- Title:
- XMM-Newton/2dF survey. IV.
- Short Name:
- J/MNRAS/352/91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of the X-ray spectral properties of 61 hard X-ray (2-8keV) selected sources from the bright XMM-Newton/2dF (f(2-8keV)>10^-14^erg/cm^2^/s) survey. This comprises nine XMMNewton pointings in the North Galactic Pole region (~1.6deg^2^) and overlaps with the SDSS, 2QZ and 2dFGRS surveys. Our sources contribute about 50 per cent of the 2-10keV X-ray background down to the flux limit of 10^-14^erg/cm^2^/s. The hardness ratio distribution of the sample suggests a deficit of heavily absorbed sources. Spectroscopic identifications exist for 34 sources.
- ID:
- ivo://CDS.VizieR/J/MNRAS/456/4488
- Title:
- XQ-100 survey neutral gas
- Short Name:
- J/MNRAS/456/4488
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a sample of 38 intervening damped Lyman {alpha} (DLA) systems identified towards 100 z>3.5 quasars, observed during the XQ-100 survey. The XQ-100 DLA sample is combined with major DLA surveys in the literature. The final combined sample consists of 742 DLAs over a redshift range approximately 1.6<z_abs_<5.0. We develop a novel technique for computing {Omega}_HI_^DLA^ as a continuous function of redshift, and we thoroughly assess and quantify the sources of error therein, including fitting errors and incomplete sampling of the high column density end of the column density distribution function. There is a statistically significant redshift evolution in {Omega}_HI_^DLA^ (>=3{sigma}) from z~2 to z~5. In order to make a complete assessment of the redshift evolution of {Omega}_HI_, we combine our high-redshift DLA sample with absorption surveys at intermediate redshift and 21-cm emission line surveys of the local universe. Although {Omega}_HI_^DLA^, and hence its redshift evolution, remains uncertain in the intermediate-redshift regime (0.1<z_abs_<1.6), we find that the combination of high-redshift data with 21-cm surveys of the local universe all yield a statistically significant evolution in {Omega}_HI_ from z~0 to z~5 (>=3{sigma}). Despite its statistical significance, the magnitude of the evolution is small: a linear regression fit between {Omega}_HI_ and z yields a typical slope of ~0.17x10^-3^, corresponding to a factor of ~4 decrease in {Omega}_HI_ between z=5 and z=0.
- ID:
- ivo://CDS.VizieR/J/MNRAS/462/3285
- Title:
- XQ-100. X-shooter quasar spectra
- Short Name:
- J/MNRAS/462/3285
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We statistically study the physical properties of a sample of narrow absorption line (NAL) systems looking for empirical evidences to distinguish between intrinsic and intervening NALs without taking into account any a priori definition or velocity cut-off. We analyse the spectra of 100 quasars with 3.5<z_em_<4.5, observed with X-shooter/Very Large Telescope in the context of the XQ-100 Legacy Survey. We detect an ~8{sigma} excess in the CIV number density within 10000km/s of the quasar emission redshift with respect to the random occurrence of NALs. This excess does not show a dependence on the quasar bolometric luminosity and it is not due to the redshift evolution of NALs. It extends far beyond the standard 5000km/s cut-off traditionally defined for associated absorption lines. We propose to modify this definition, extending the threshold to 10000km/s when weak absorbers (equivalent width <0.2{AA}) are also considered. We infer NV is the ion that better traces the effects of the quasar ionization field, offering the best statistical tool to identify intrinsic systems. Following this criterion, we estimate that the fraction of quasars in our sample hosting an intrinsic NAL system is 33 per cent. Lastly, we compare the properties of the material along the quasar line of sight, derived from our sample, with results based on close quasar pairs investigating the transverse direction. We find a deficiency of cool gas (traced by C II) along the line of sight connected to the quasar host galaxy, in contrast with what is observed in the transverse direction.
- ID:
- ivo://CDS.VizieR/J/AJ/126/2209
- Title:
- X-ray AGN from RASS and SDSS
- Short Name:
- J/AJ/126/2209
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe the initial results of a new program aimed to ultimately yield ~10^4^ fully characterized X-ray source identifications - a sample about an order of magnitude larger than earlier efforts. The technique is detailed and employs X-ray data from the ROSAT All-Sky Survey (RASS, Cat. <IX/10>, <IX/29>) and optical imaging and spectroscopic follow-up from the Sloan Digital Sky Survey (SDSS, <J/AJ/123/567>); these two surveys prove to be serendipitously very well matched in sensitivity. As part of the SDSS software pipelines, optical objects in the SDSS photometric catalogs are automatically positionally cross-correlated with RASS X-ray sources. Then priorities for follow-on SDSS optical spectra of candidate counterparts are automatically assigned using an algorithm based on the known ratios of fX/fopt for various classes of X-ray emitters at typical RASS fluxes of 10^-13^ergs/cm^2^/s. SDSS photometric parameters for optical morphology, magnitude, and colors, plus FIRST radio information, serve as proxies for object class.
- ID:
- ivo://CDS.VizieR/J/ApJ/747/10
- Title:
- X-ray and multiwavelength properties of 11 WLQs
- Short Name:
- J/ApJ/747/10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the X-ray and multiwavelength properties of 11 radio-quiet quasars with weak or no emission lines identified by the Sloan Digital Sky Survey (SDSS) with redshift z=0.4-2.5. Our sample was selected from the Plotkin et al. catalog (2010, Cat. J/AJ/139/390) of radio-quiet, weak-featured active galactic nuclei (AGNs). The distribution of relative X-ray brightness for our low-redshift weak-line quasar (WLQ) candidates is significantly different from that of typical radio-quiet quasars, having an excess of X-ray weak sources, but it is consistent with that of high-redshift WLQs. Over half of the low-redshift WLQ candidates are X-ray weak by a factor of >~5, compared to a typical SDSS quasar with similar UV/optical luminosity. These X-ray weak sources generally show similar UV emission-line properties to those of the X-ray weak quasar PHL 1811 (weak and blueshifted high-ionization lines, weak semiforbidden lines, and strong UV Fe emission); they may belong to the notable class of PHL 1811 analogs. The average X-ray spectrum of these sources is somewhat harder than that of typical radio-quiet quasars.
- ID:
- ivo://CDS.VizieR/J/A+A/545/A66
- Title:
- X-ray and radio emission of type 1 AGNs
- Short Name:
- J/A+A/545/A66
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- X-ray emission from Active Galactic Nuclei (AGN) is dominated by the accretion disk around a supermassive black hole. The radio luminosity, however, has not such a clear origin except in the most powerful sources where jets are evident. The origin (and even the very existence) of the local bi-modal distribution in radio-loudness is also a debated issue. By analysing X-ray, optical and radio properties of a large sample of type 1 AGN and quasars (QSOs) up to z>2, where the bulk of this population resides, we aim to explore the interplay between radio and X-ray emission in AGN, in order to further our knowledge on the origin of radio emission, and its relation to accretion. We analyse a large (~800 sources) sample of type 1 AGN and QSOs selected from the 2XMMi XMM-Newton X-ray source catalogue, cross-correlated with the SDSS DR7 spectroscopic catalogue, covering a redshift range from z~0.3 to z~2.3. Supermassive black hole masses are estimated from the Mg II emission line, bolometric luminosities from the X-ray data, and radio emission or upper limits from the FIRST catalogue. Most of the sources accrete close to the Eddington limit and the distribution in radio-loudness does not appear to have a bi-modal behaviour. We confirm that radio-loud AGN are also X-ray loud, with an X-ray-to-optical ratio up to twice that of radio-quiet objects, even excluding the most extreme strongly jetted sources. By analysing complementary radio-selected control samples, we find evidence that these conclusions are not an effect of the X-ray selection, but are likely a property of the dominant QSO population. Our findings are best interpreted in a context where radio emission in AGN, with the exception of a minority of beamed sources, arises from very close to the accretion disk and is therefore heavily linked to X-ray emission. We also speculate that the radio-loud/radio-quiet dichotomy might either be an evolutionary effect that developed well after the QSO peak epoch, or an effect of incompleteness in small samples.
- ID:
- ivo://CDS.VizieR/J/ApJ/657/116
- Title:
- X-ray and UV parameters of radio-quiet quasars
- Short Name:
- J/ApJ/657/116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report new Chandra observations of seven optically faint, z~4 radio-quiet quasars (RQQs). We have combined these new observations with previous Chandra observations of RQQs to create a sample of 174 sources. These sources have 0.1<z<4.7, and 10^44^ergs/s<{nu}L_{nu}_(2500{AA})<10^48^ergs/s. The X-ray detection fraction is 90%.
- ID:
- ivo://CDS.VizieR/J/PASJ/70/S36
- Title:
- X-ray-bright optically faint AGN
- Short Name:
- J/PASJ/70/S36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We construct a sample of X-ray-bright optically faint active galactic nuclei by combining Subaru Hyper Suprime-Cam, XMM-Newton, and infrared source catalogs. Fifty-three X-ray sources satisfying i-band magnitude fainter than 23.5mag and X-ray counts with the EPIC-PN detector larger than 70 are selected from 9.1 deg^2^, and their spectral energy distributions (SEDs) and X-ray spectra are analyzed. Forty-four objects with an X-ray to i-band flux ratio FX/Fi>10 are classified as extreme X-ray-to-optical flux sources. Spectral energy distributions of 48 among 53 are represented by templates of type 2 AGNs or star-forming galaxies and show the optical signature of stellar emission from host galaxies in the source rest frame. Infrared/optical SEDs indicate a significant contribution of emission from dust to the infrared fluxes, and that the central AGN is dust obscured. The photometric redshifts determined from the SEDs are in the range of 0.6-2.5. The X-ray spectra are fitted by an absorbed power-law model, and the intrinsic absorption column densities are modest (best-fit logNH=20.5-23.5cm^-2^ in most cases). The absorption-corrected X-ray luminosities are in the range of 6x10^42^-2x10^45^erg/s. Twenty objects are classified as type 2 quasars based on X-ray luminosity and NH. The optical faintness is explained by a combination of redshifts (mostly z>1.0), strong dust extinction, and in part a large ratio of dust/gas.
