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25081. X-ray bright AGN in massive galaxy clusters
ID:
ivo://CDS.VizieR/J/MNRAS/446/2709
Title:
X-ray bright AGN in massive galaxy clusters
Short Name:
J/MNRAS/446/2709
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of a new analysis of the X-ray selected active galactic nuclei (AGN) population residing in and behind 135 of the most massive galaxy clusters in the redshift range of 0.2<z<0.9 observed with Chandra. With a sample of more than 11000 X-ray point sources, we are able to measure, for the first time, evidence for evolution in the cluster AGN population beyond the expected evolution of field AGN. Our analysis shows that overall number density of cluster AGN scales with the cluster mass as ~M_500_-1.2. There is no evidence for the overall number density of cluster member X-ray AGN depending on the cluster redshift in a manner different than field AGN, nor is there any evidence that the spatial distribution of cluster AGN (given in units of the cluster overdensity radius r_500_) strongly depends on the cluster mass or redshift. The M^-1.2+/-0.7^ scaling relation we measure is consistent with theoretical predictions of the galaxy merger rate in clusters, which is expected to scale with the cluster velocity dispersion, {sigma}, as ~{sigma}^-3^ or ~M^-1^. This consistency suggests that galaxy mergers may be an important contributor to the cluster AGN population, a result that is further corroborated by visual inspection of Hubble images for 23 spectroscopically confirmed cluster member AGN in our sample. A merger-driven scenario for the triggering of X-ray AGN is not strongly favoured by studies of field galaxies, however, suggesting that different mechanisms may be primarily responsible for the triggering of cluster and field X-ray AGN.
25082. X-ray-bright optically faint AGN
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.
25083. X-ray bursting neutron star atmos. models. II
ID:
ivo://CDS.VizieR/J/A+A/545/A120
Title:
X-ray bursting neutron star atmos. models. II
Short Name:
J/A+A/545/A120
Date:
21 Oct 2021
Publisher:
CDS
Description:
Theoretical spectra of X-ray bursting neutron star (NS) model atmospheres are widely used for determination of the NS basic parameters such as their masses and radii. Compton scattering, that plays an important role in spectra formation at high luminosities, is often accounted for using the differential Kompaneets operator, while in other models a more general, integral operator for the Compton scattering kernel is used. We construct here accurate NS atmosphere models using exact treatment of Compton scattering with the integral relativistic kinetic equation and exact relativistic angle-dependent redistribution function.
25084. X-ray bursting neutron star atmosphere models
ID:
ivo://CDS.VizieR/J/A+A/527/A139
Title:
X-ray bursting neutron star atmosphere models
Short Name:
J/A+A/527/A139
Date:
21 Oct 2021
Publisher:
CDS
Description:
X-ray bursting neutron stars in low mass X-ray binaries constitute an appropriate source class to constrain masses and radii of neutron stars, but a sufficiently extended set of corresponding model atmospheres is necessary for these investigations. Methods. We computed such a set of model atmospheres and emergent spectra in a plane-parallel, hydrostatic, and LTE approximation with Compton scattering taken into account.
25085. X-ray catalog of Eagle Nebula
ID:
ivo://CDS.VizieR/J/ApJ/753/117
Title:
X-ray catalog of Eagle Nebula
Short Name:
J/ApJ/753/117
Date:
21 Oct 2021
Publisher:
CDS
Description:
Mechanisms regulating the origin of X-rays in young stellar objects and the correlation with their evolutionary stage are under debate. Studies of the X-ray properties in young clusters allow us to understand these mechanisms. One ideal target for this analysis is the Eagle Nebula (M16), with its central cluster NGC 6611. At 1750pc from the Sun, it harbors 93 OB stars, together with a population of low-mass stars from embedded protostars to disk-less Class III objects, with age <=3Myr. We study an archival 78ks Chandra/ACIS-I observation of NGC 6611 and two new 80ks observations of the outer region of M16, one centered on the Column V and the other on a region of the molecular cloud with ongoing star formation. We detect 1755 point sources with 1183 candidate cluster members (219 disk-bearing and 964 disk-less). We study the global X-ray properties of M16 and compare them with those of the Orion Nebula Cluster. We also compare the level of X-ray emission of Class II and Class III stars and analyze the X-ray spectral properties of OB stars. Our study supports the lower level of X-ray activity for the disk-bearing stars with respect to the disk-less members. The X-ray luminosity function (XLF) of M16 is similar to that of Orion, supporting the universality of the XLF in young clusters. Eighty-five percent of the O stars of NGC 6611 have been detected in X-rays. With only one possible exception, they show soft spectra with no hard components, indicating that mechanisms for the production of hard X-ray emission in O stars are not operating in NGC 6611.
25086. X-ray catalog of Galactic O stars
ID:
ivo://CDS.VizieR/J/A+A/620/A89
Title:
X-ray catalog of Galactic O stars
Short Name:
J/A+A/620/A89
Date:
21 Oct 2021
Publisher:
CDS
Description:
The X-ray emission of O-type stars was first discovered in the early days of the Einstein satellite. Since then many different surveys have confirmed that the ratio of X-ray to bolometric luminosity in O-type stars is roughly constant, but there is a paucity of studies that account for detailed information on spectral and wind properties of O-stars. Recently a significant sample of O stars within our Galaxy was spectroscopically identified and presented in the Galactic O-Star Spectroscopic Survey (GOSS). At the same time, a large high-fidelity catalog of X-ray sources detected by the XMM-Newton X-ray telescope was released. Here we present the X-ray catalog of O stars with known spectral types and investigate the dependence of their X-ray properties on spectral type as well as stellar and wind parameters.We find that, among the GOSS sample, 127 O-stars have a unique XMM-Newton source counterpart and a Gaia data release 2 (DR2) association. Terminal velocities are known for a subsample of 35 of these stars.We confirm that the X-ray luminosities of dwarf and giant O stars correlate with their bolometric luminosity. For the subsample of O stars with measure terminal velocities we find that the X-ray luminosities of dwarf and giant O stars also correlate with wind parameters. However, we find that these correlations break down for supergiant stars. Moreover, we show that supergiant stars are systematically harder in X-rays compared to giant and dwarf O-type stars. We find that the X-ray luminosity depends on spectral type, but seems to be independent of whether the stars are single or in a binary system. Finally, we show that the distribution of log(LX/Lbol) in our sample stars is non-Gaussian, with the peak of the distribution at log(LX/Lbol)~=-6.6.
25087. X-ray cavities from isolated gal. to clusters
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.
25088. X-ray classification of young star clusters
ID:
ivo://CDS.VizieR/J/ApJ/659/585
Title:
X-ray classification of young star clusters
Short Name:
J/ApJ/659/585
Date:
21 Oct 2021
Publisher:
CDS
Description:
A large volume of low signal-to-noise, multidimensional data is available from the CCD imaging spectrometers aboard the Chandra X-Ray Observatory and the X-Ray Multimirror Mission (XMM-Newton). To make progress analyzing this data, it is essential to develop methods to sort, classify, and characterize the vast library of X-ray spectra in a nonparametric fashion (complementary to current parametric model fits). We have developed a spectral classification algorithm that handles large volumes of data and operates independently of the requirement of spectral model fits. We use proven multivariate statistical techniques including principal component analysis and an ensemble classifier consisting of agglomerative hierarchical clustering and K-means clustering applied for the first time for spectral classification. The algorithm positions the sources in a multidimensional spectral sequence and then groups the ordered sources into clusters based on their spectra. These clusters appear more distinct for sources with harder observed spectra. The apparent diversity of source spectra is reduced to a three-dimensional locus in principal component space, with spectral outliers falling outside this locus. The algorithm was applied to a sample of 444 strong sources selected from the 1616 X-ray emitting sources detected in deep Chandra imaging spectroscopy of the Orion Nebula Cluster.
25089. X-ray cluster of galaxies behind the Milky way
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.
25090. X-ray clusters from XMM
ID:
ivo://CDS.VizieR/J/MNRAS/423/3561
Title:
X-ray clusters from XMM
Short Name:
J/MNRAS/423/3561
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have processed 2774 high galactic observations from the XMM archive (as of 2010 May) and extracted a serendipitous catalogue of some 850 clusters of galaxies based on purely X-ray criteria, following the methodology developed for the XMM-Large-Scale Survey. Restricting the sample to the highest signal-to-noise ratio objects (347 clusters), we perform a cosmological analysis using only the X-ray information. The analysis consists in the modelling of the observed colour-magnitude [count rate and hardness ratio (CR-HR)] diagram constructed from cluster instrumental count rates measured in the [0.5-2], [1-2] and [0.5-1] keV bands. A Monte Carlo Markov chain procedure simultaneously fits the cosmological parameters, the evolution of the cluster scaling laws and the selection effects.

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