- ID:
- ivo://CDS.VizieR/J/ApJS/217/21
- Title:
- XMM-Newton survey of local OVII absorbers
- Short Name:
- J/ApJS/217/21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Highly ionized, z=0 metal absorption lines detected in the X-ray spectra of background active galactic nuclei (AGNs) provide an effective method to probe the hot (T~10^6^K) gas and its metal content in and around the Milky Way. We present an all-sky survey of the K_{alpha}_ transition of the local OVII absorption lines obtained by Voigt-profile fitting archival XMM-Newton observations. A total of 43 AGNs were selected, among which 12 are BL Lac-type AGNs, and the rest are Seyfert 1 galaxies. At above the 3{sigma} level the local OVII absorption lines were detected in 21 AGNs, among which 7 were newly discovered in this work. The sky covering fraction, defined as the ratio between the number of detections and the sample size, increases from about 40% for all targets to 100% for the brightest targets, suggesting a uniform distribution of the OVII absorbers. We correlate the line equivalent width with the Galactic coordinates and do not find any strong correlations between these quantities. Some AGNs have warm absorbers that may complicate the analysis of the local X-ray absorber since the recession velocity can be compensated by the outflow velocity, especially for nearby targets. We discuss the potential impact of warm absorbers on our analysis.
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- ID:
- ivo://CDS.VizieR/J/ApJ/892/102
- Title:
- XMM X-ray data of Planck ESZ galaxy clusters
- Short Name:
- J/ApJ/892/102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the scaling relations derived by fitting the X-ray parameters determined from analyzing the XMM-Newton observations of 120 galaxy clusters in the Planck Early Sunyaev-Zel'dovich (SZ) sample spanning the redshift range of 0.059<z<0.546. We find that the slopes of all the investigated scaling relations significantly deviate from the self-similar predictions, if self-similar redshift evolution is assumed. When the redshift evolution is left free to vary, the derived slopes are more in agreement with the self-similar predictions. Relaxed clusters have on average ~30% higher X-ray luminosity than disturbed clusters at a given mass, a difference that, depending on the relative fraction of relaxed and disturbed clusters in the samples (e.g., SZ vs. X-ray selected), has a strong impact on the normalization obtained in different studies. Using the core-excised cluster luminosities reduces the scatter and brings into better agreement the L-M_tot_ and L-T relations determined for different samples. M_tot_-T, M_tot_-YX, and M_tot_-M_gas_ relations show little dependence on the dynamical state of the clusters, but the normalizations of these relations may depend on the mass range investigated. Although most of the clusters investigated in this work reside at relatively low redshift, the fits prefer values of {gamma}, the parameter accounting for the redshift evolution, different from the self-similar predictions. This suggests an evolution (<2{sigma} level, with the exception of the M_tot_-T relation) of the scaling relations. For the first time, we find significant evolution (>3{sigma}) of the M_tot_-T relation, pointing to an increase of the kinetic-to-thermal energy ratio with redshift. This is consistent with a scenario in which higher-redshift clusters are on average more disturbed than their lower-redshift counterparts.
- ID:
- ivo://CDS.VizieR/J/ApJ/815/129
- Title:
- X-ray AGNs with Subaru/FMOS NIR observations
- Short Name:
- J/ApJ/815/129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the Eddington ratio distribution of X-ray-selected broad-line active galactic nuclei (AGNs) in the redshift range 1.0<z<2.2, where the number density of AGNs peaks. Combining the optical and Subaru/Fiber Multi Object Spectrograph near-infrared spectroscopy, we estimate black hole masses for broad-line AGNs in the Chandra Deep Field South (CDF-S), Extended Chandra Deep Field South (E-CDF-S), and the XMM-Newton Lockman Hole (XMM-LH) surveys. AGNs with similar black hole masses show a broad range of AGN bolometric luminosities, which are calculated from X-ray luminosities, indicating that the accretion rate of black holes is widely distributed. We find a substantial fraction of massive black holes accreting significantly below the Eddington limit at z<~2, in contrast to what is generally found for luminous AGNs at high redshift. Our analysis of observational selection biases indicates that the "AGN cosmic downsizing" phenomenon can be simply explained by the strong evolution of the comoving number density at the bright end of the AGN luminosity function, together with the corresponding selection effects. However, one might need to consider a correlation between the AGN luminosity and the accretion rate of black holes, in which luminous AGNs have higher Eddington ratios than low-luminosity AGNs, in order to understand the relatively small fraction of low-luminosity AGNs with high accretion rates in this epoch. Therefore, the observed downsizing trend could be interpreted as massive black holes with low accretion rates, which are relatively fainter than less-massive black holes with efficient accretion.
- 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/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/ApJS/227/31
- Title:
- X-ray cavities from isolated gal. to clusters
- Short Name:
- J/ApJS/227/31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We perform a comprehensive study of X-ray cavities using a large sample of X-ray targets selected from the Chandra archive. The sample is selected to cover a large dynamic range including galaxy clusters, groups, and individual galaxies. Using {beta}-modeling and unsharp masking techniques, we investigate the presence of X-ray cavities for 133 targets that have sufficient X-ray photons for analysis. We detect 148 X-ray cavities from 69 targets and measure their properties, including cavity size, angle, and distance from the center of the diffuse X-ray gas. We confirm the strong correlation between cavity size and distance from the X-ray center similar to previous studies. We find that the detection rates of X-ray cavities are similar among galaxy clusters, groups and individual galaxies, suggesting that the formation mechanism of X-ray cavities is independent of environment.
- ID:
- ivo://CDS.VizieR/J/ApJ/580/774
- Title:
- X-ray cluster of galaxies behind the Milky way
- Short Name:
- J/ApJ/580/774
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the design and status of the Clusters in the Zone of Avoidance (CIZA) project, the first systematic X-ray search for clusters of galaxies behind the Milky Way. Our project, Clusters in the Zone of Avoidance (CIZA), uses X-ray data from the RASS for the initial cluster candidate selection and subsequent optical and NIR observations to confirm or refute the cluster nature of all selected candidates. We demonstrate that an X-ray survey can find galaxy clusters at low Galactic latitude where optical searches are inefficient because of massive obscuration and extinction problems. We discuss the rationale for such a survey in the context of large-scale structure studies and describe in detail the combined X-ray/optical/NIR approach used by CIZA to identify clusters of galaxies at |b|<20{deg}, a region of the sky that has traditionally been excluded from earlier cluster catalogs. So far, CIZA has identified and spectroscopically confirmed 137 galaxy clusters in what used to be the zone of avoidance; additional clusters have been confirmed in imaging observations and await spectroscopic observation. We present a catalog of the 73 X-ray brightest CIZA clusters, 53 (73%) of which are new discoveries.
- ID:
- ivo://CDS.VizieR/J/A+A/420/61
- Title:
- X-ray clusters of galaxies
- Short Name:
- J/A+A/420/61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new method for a simultaneous search for clusters of galaxies in X-ray photon maps and optical galaxy maps is described. The method appears ideally suited for the analysis of the recently proposed wide-angle X-ray missions like DUO and ROSITA. As a first application, clusters are extracted from the 3rd version of the ROSAT All-Sky Survey (<IX/10>) and the Early Date Release of the Sloan Digital Sky Survey (SDSS, <J/AJ/123/567>). The time-consuming computations are performed within the German Astrophysical Virtual Observatory (GAVO). On a test area of 140 square degrees, 75 X-ray clusters are detected down to an X-ray flux limit of 3-5*10^-13^erg/s/cm^2^ in the ROSAT energy band 0.1-2.4keV. The clusters have redshifts z<0.5.
- ID:
- ivo://CDS.VizieR/J/A+A/542/A16
- Title:
- X-ray detection of radio-selected SF galaxies
- Short Name:
- J/A+A/542/A16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- X-ray surveys contain sizable numbers of star forming galaxies, beyond the AGN which usually make the majority of detections. Many methods to separate the two populations are used in the literature, based on X-ray and multiwavelength properties. We aim at a detailed test of the classification schemes and to study the X-ray properties of the resulting samples. We build on a sample of galaxies selected at 1.4GHz in the VLA-COSMOS survey, classified by Smolcic et al. (2008ApJS..177...14S) according to their optical colours and observed with Chandra. A similarly selected control sample of AGN is also used for comparison. We review some X-ray based classification criteria and check how they affect the sample composition. The efficiency of the classification scheme devised by Smolcic et al. (2008ApJS..177...14S) is such that ~30% of composite/misclassified objects are expected because of the higher X-ray brightness of AGN with respect to galaxies. The latter fraction is actually 50% in the X-ray detected sources, while it is expected to be much lower among X-ray undetected sources. Indeed, the analysis of the stacked spectrum of undetected sources shows, consistently, strongly different properties between the AGN and galaxy samples. X-ray based selection criteria are then used to refine both samples. The radio/X-ray luminosity correlation for star forming (SF) galaxies is found to hold with the same X-ray/radio ratio valid for nearby galaxies. Some evolution of the ratio may be possible for sources at high redshift or high luminosity, tough it is likely explained by a bias arising from the radio selection. Finally, we discuss the X-ray number counts of star forming galaxies from the VLA- and C-COSMOS surveys according to different selection criteria, and compare them to the similar determination from the Chandra Deep Fields. The classification scheme proposed here may find application in future works and surveys.
- ID:
- ivo://CDS.VizieR/J/ApJ/726/20
- Title:
- X-ray emission from quasars
- Short Name:
- J/ApJ/726/20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of an investigation into the X-ray properties of radio-intermediate and radio-loud quasars (RIQs and RLQs, respectively). We combine large, modern optical (e.g., SDSS) and radio (e.g., FIRST) surveys with archival X-ray data from Chandra, XMM-Newton, and ROSAT to generate an optically selected sample that includes 188 RIQs and 603 RLQs. This sample is constructed independently of X-ray properties but has a high X-ray detection rate (85%); it provides broad and dense coverage of the l-z plane, including at high redshifts (22% of objects have z=2-5), and it extends to high radio-loudness values (33% of objects have R*=3-5, using logarithmic units). We measure the "excess" X-ray luminosity of RIQs and RLQs relative to radio-quiet quasars (RQQs) as a function of radio loudness and luminosity, and parameterize the X-ray luminosity of RIQs and RLQs both as a function of optical/UV luminosity and also as a joint function of optical/UV and radio luminosity. RIQs are only modestly X-ray bright relative to RQQs; it is only at high values of radio loudness (R*>~3.5) and radio luminosity that RLQs become strongly X-ray bright.
