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25171. X-ray properties of BzK-selected galaxies
ID:
ivo://CDS.VizieR/J/MNRAS/428/3089
Title:
X-ray properties of BzK-selected galaxies
Short Name:
J/MNRAS/428/3089
Date:
21 Oct 2021
Publisher:
CDS
Description:
We investigate the X-ray properties of BzK-selected galaxies at z~2 using deep X-ray data in the Chandra Deep Field-South (CDFS) and Chandra Deep Field-North (CDFN). A subset of these BzK galaxies have been proposed as Compton-thick active galactic nucleus (AGN) candidates based on a high ratio of infrared (IR) to ultraviolet (UV) star formation rates (SFRs). With the benefit of deep 24{mu}m observations, our sample of these IR-excess galaxies is larger than previous studies and combined with the deepest X-ray data yield new insights into the population. We identify 701 and 534 star-forming BzK galaxies (sBzK galaxies) in the range z=1.2-3.0 in CDFS and CDFN, respectively. Of these we directly detect in X-rays 49 sBzK galaxies in CDFS and 32 sBzK galaxies in CDFN.
25172. X-ray properties of Carina OB1 association
ID:
ivo://CDS.VizieR/J/A+A/477/593
Title:
X-ray properties of Carina OB1 association
Short Name:
J/A+A/477/593
Date:
21 Oct 2021
Publisher:
CDS
Description:
X-ray properties of the stellar population in the Carina OB1 association are examined with special emphasis on early-type stars. Their spectral characteristics provide some clues to understanding the nature of X-ray formation mechanisms in the winds of single and binary early-type stars. A timing and spectral analysis of five observations with XMM-Newton is performed using various statistical tests and thermal spectral models. 235 point sources have been detected within the field of view. Several of these sources are probably pre-main sequence stars with characteristic short-term variability. Seven sources are possible background AGNs. Spectral analysis of twenty three sources of type OB and WR 25 was performed. We derived spectral parameters of the sources and their fluxes in three energy bands. Estimating the interstellar absorption for every source and the distance to the nebula, we derived X-ray luminosities of these stars and compared them to their bolometric luminosities. We discuss possible reasons for the fact that, on average, the observed X-ray properties of binary and single early type stars are not very different, and give several possible explanations.
25173. X-ray properties of Chandra red galaxies
ID:
ivo://CDS.VizieR/J/A+A/501/485
Title:
X-ray properties of Chandra red galaxies
Short Name:
J/A+A/501/485
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the X-ray properties of the extremely red objects (ERO) population observed by Chandra with three partially overlapping pointings (up to ~90ks) over an area of ~500arcmin^2^, down to a 0.5-8keV flux limit of ~10-15erg/cm^2^/s. We selected EROs using a multi-band photometric catalog down to a Ks-band magnitude of ~19.3 (Vega system); 14 EROs were detected in X-rays, corresponding to ~9% of the overall X-ray source population (149 X-ray sources) and to ~5% of the ERO population (288). The X-ray emission of all X-ray detected EROs is consistent with that of an active galactic nucleus (AGN) (>~3.5x10^42^erg/s at photometric redshifts z>1), in agreement with previous X-ray observations, with an indication of increasing absorption between the three X-ray brightest EROs and the 11 X-ray faintest EROs.
25174. X-ray properties of 3 EDisCS galaxy clusters
ID:
ivo://CDS.VizieR/J/MNRAS/371/1777
Title:
X-ray properties of 3 EDisCS galaxy clusters
Short Name:
J/MNRAS/371/1777
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present XMM-Newton observations of three optically selected z>0.6 clusters from the European Southern Observatory (ESO) Distant Cluster Survey (EDisCS), comprising the first results of a planned X-ray survey of the full EDisCS high-redshift sample. The EDisCS clusters were identified in the Las Campanas Distant Cluster Survey as surface brightness fluctuations in the optical sky and their masses and galaxy populations are well described by extensive photometric and spectroscopic observations. We detect two of the three clusters in the X-ray and place a firm upper limit on diffuse emission in the third cluster field. We are able to constrain the X-ray luminosity and temperature of the detected clusters and estimate their masses. We find that the X-ray properties of the detected EDisCS clusters are similar to those of X-ray-selected clusters of comparable mass and --- unlike other high-redshift, optically selected clusters --- are consistent with the T-sigma and L_X_-sigma relations determined from X-ray-selected clusters at low redshift. The X-ray determined mass estimates are generally consistent with those derived from weak-lensing and spectroscopic analyses. These preliminary results suggest that the novel method of optical selection used to construct the EDisCS catalogue may, like selection by X-ray luminosity, be well suited for identification of relaxed, high-redshift clusters whose intracluster medium is in place and stable by z=0.8.
25175. X-ray properties of 26 high-luminosity quasars
ID:
ivo://CDS.VizieR/J/MNRAS/504/5556
Title:
X-ray properties of 26 high-luminosity quasars
Short Name:
J/MNRAS/504/5556
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present an investigation of the interdependence of the optical-to-X-ray spectral slope (aox), the HeII equivalent-width (EW), and the monochromatic luminosity at 2500{AA} (L2500). The values of {alpha}_ox_ and HeII EW are indicators of the strength/shape of the quasar ionizing continuum, from the ultraviolet (UV; 1500-2500{AA}), through the extreme ultraviolet (EUV;300-50{AA}), to the X-ray (2keV) regime. For this investigation, we measure the HeII EW of 206 radio-quiet quasars devoid of broad absorption lines that have high-quality spectral observations of the UV and 2keV X-rays. The sample spans wide redshift (z~0.13-3.5) and luminosity (logL_2500_~29.2-32.5erg/s/Hz) ranges. We recover the well-known {alpha}_ox_-L_2500_ and HeII EW-L_2500_ anti-correlations, and we find a similarly strong correlation between {alpha}_ox_ and HeII EW, and thus the overall spectral shape from the UV, through the EUV, to the X-ray regime is largely set by luminosity. A significant {alpha}_ox_-HeII EW correlation remains after removing the contribution of L_2500_ from each quantity, and thus the emission in the EUV and the X-rays are also directly tied. This set of relations is surprising, since the UV, EUV, and X-ray emission are expected to be formed in three physically distinct regions. Our results indicate the presence of a redshift-independent physical mechanism that couples the continuum emission from these three different regions, and thus controls the overall continuum shape from the UV to the X-ray regime.
25176. X-ray properties of HM1 and IC2944/2948
ID:
ivo://CDS.VizieR/J/A+A/555/A83
Title:
X-ray properties of HM1 and IC2944/2948
Short Name:
J/A+A/555/A83
Date:
21 Oct 2021
Publisher:
CDS
Description:
Using XMM-Newton data, we study for the first time the X-ray emission of HM1 and IC2944/2948. Low-mass, pre-main sequence objects with an age of a few Myr are detected, as well as a few background or foreground objects. Most massive stars in both clusters display the usual high-energy properties of that kind of objects, though with log(Lx/Lbol) apparently lower in HM1 than in IC2944/2948. Comparing with studies of other clusters, it seems that low S/N at soft energies, due to the high extinction, may the main cause of this difference. In HM1, the two Wolf-Rayet stars show contrasting behaviours: WR89 is extremely bright, but much softer than WR87. It remains to be seen whether wind-wind collisions or magnetically confined winds can explain such emissions. In IC2944/2948, the X-ray sources concentrate around HD101205; a group of massive stars to the north of this object appears rather isolated, suggesting that there exist two subclusters in the field-of-view.
25177. X-ray properties of NGC 300. I.
ID:
ivo://CDS.VizieR/J/A+A/443/103
Title:
X-ray properties of NGC 300. I.
Short Name:
J/A+A/443/103
Date:
21 Oct 2021
Publisher:
CDS
Description:
X-ray properties of NGC 300 point sources, extracted from 66ks of XMM-Newton data taken in 2000 December and 2001 January. A total of 163 sources were detected in the energy range of 0.3-6kev. We report on the global properties of the sources detected inside the D_25_ optical disk, such as the hardness ratio and X-ray fluxes, and on the properties of their optical counterparts found in B, V, and R images from the 2.2m MPG/ESO telescope. Furthermore, we cross-correlate the X-ray sources with SIMBAD, the USNO-A2.0 catalog, and radio catalogues.
25178. X-ray properties of O and B stars in Carina
ID:
ivo://CDS.VizieR/J/ApJS/194/7
Title:
X-ray properties of O and B stars in Carina
Short Name:
J/ApJS/194/7
Date:
21 Oct 2021
Publisher:
CDS
Description:
The key empirical property of the X-ray emission from O stars is a strong correlation between the bolometric and X-ray luminosities. In the framework of the Chandra Carina Complex Project, 129 O and B stars have been detected as X-ray sources; 78 of those, all with spectral type earlier than B3, have enough counts for at least a rough X-ray spectral characterization. This leads to an estimate of the L_X-L_BOL ratio for an exceptional number of 60 O stars belonging to the same region and triples the number of Carina massive stars studied spectroscopically in X-rays. The derived log(L_X/L_BOL) is 7.26 for single objects, with a dispersion of only 0.21dex. Using the properties of hot massive stars listed in the literature, we compare the X-ray luminosities of different types of objects. In the case of O stars, the L_X-L_BOL ratios are similar for bright and faint objects, as well as for stars of different luminosity classes or spectral types. Binaries appear only slightly harder and slightly more luminous in X-rays than single objects; the differences are not formally significant (at the 1% level), except for the L_X-L_BOL ratio in the medium (1.0-2.5keV) energy band. Weak-wind objects have similar X-ray luminosities but they display slightly softer spectra compared with "normal" O stars with the same bolometric luminosity. Discarding three overluminous objects, we find a very shallow trend of harder emission in brighter objects. The properties of the few B stars bright enough to yield some spectral information appear to be different overall (constant X-ray luminosities, harder spectra), hinting that another mechanism for producing X-rays, besides wind shocks, might be at work. However, it must be stressed that the earliest and X-ray brightest among these few detected objects are similar to the latest O stars, suggesting a possibly smooth transition between the two processes.
25179. X-ray properties of optically selected ETGs
ID:
ivo://CDS.VizieR/J/MNRAS/422/494
Title:
X-ray properties of optically selected ETGs
Short Name:
J/MNRAS/422/494
Date:
21 Oct 2021
Publisher:
CDS
Description:
We study the X-ray properties of 393 optically selected early-type galaxies (ETGs) over the redshift range of z~~0.0-1.2 in the Chandra Deep Fields (CDFs). To measure the average X-ray properties of the ETG population, we use X-ray stacking analyses with a subset of 158 passive ETGs (148 of which were individually undetected in X-ray). This ETG subset was constructed to span the redshift ranges of z=0.1-1.2 in the ~~4Ms CDF-South and ~~2Ms CDF-North and z=0.1-0.6 in the ~~250ks Extended-CDF-South where the contribution from individually undetected active galactic nuclei (AGN) is expected to be negligible in our stacking.
25180. X-ray properties of PHL1811 analogs and WLQs
ID:
ivo://CDS.VizieR/J/ApJ/805/122
Title:
X-ray properties of PHL1811 analogs and WLQs
Short Name:
J/ApJ/805/122
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present an X-ray and multiwavelength study of 33 weak emission-line quasars (WLQs) and 18 quasars that are analogs of the extreme WLQ, PHL1811, at z~0.5-2.9. New Chandra 1.5-9.5ks exploratory observations were obtained for 32 objects while the others have archival X-ray observations. Significant fractions of these luminous type 1 quasars are distinctly X-ray weak compared to typical quasars, including 16 (48%) of the WLQs and 17 (94%) of the PHL 1811 analogs with average X-ray weakness factors of 17 and 39, respectively. We measure a relatively hard ({Gamma}=1.16^+0.37^_-0.32_) effective power-law photon index for a stack of the X-ray weak subsample, suggesting X-ray absorption, and spectral analysis of one PHL 1811 analog, J1521+5202, also indicates significant intrinsic X-ray absorption. We compare composite Sloan Digital Sky Survey spectra for the X-ray weak and X-ray normal populations and find several optical-UV tracers of X-ray weakness, e.g., FeII rest-frame equivalent width (REW) and relative color. We describe how orientation effects under our previously proposed "shielding-gas" scenario can likely unify the X-ray weak and X-ray normal populations. We suggest that the shielding gas may naturally be understood as a geometrically thick inner accretion disk that shields the broad line region from the ionizing continuum. If WLQs and PHL 1811 analogs have very high Eddington ratios, the inner disk could be significantly puffed up (e.g., a slim disk). Shielding of the broad emission-line region by a geometrically thick disk may have a significant role in setting the broad distributions of CIV REW and blueshift for quasars more generally.

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