- 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.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/639/A5
- Title:
- X-ray absorption in INTEGRAL AGN
- Short Name:
- J/A+A/639/A5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work the INTEGRAL hard X-ray selected sample of AGN has been used to investigate the possible contribution of absorbing material distributed within the host galaxies to the total amount of NH measured in the X-ray band. We collected all the available axial ratio measurements of the galaxies hosting our AGN together with their morphological information and find that also for our hard X-ray selected sample a deficit of edge-on galaxies hosting type 1 AGN is present. We estimate that in our hard X-ray selected sample there is a deficit of 24% (+/-5%) of type 1 AGN. Possible bias in redshift has been excluded, as we found the same effect in a well determined range of z where the number and the distributions of the two classes are statistically the same. Our findings clearly indicate that material located in the host galaxy on scales of hundreds of parsecs and not aligned with the putative absorbing torus of the AGN can contribute to the total amount of column density. This galactic absorber can be large enough to hide the broad line region of some type 1 AGN causing their classification as type 2 objects and giving rise to the deficiency of type 1 in edge-on galaxies.
- ID:
- ivo://CDS.VizieR/J/A+A/648/A121
- Title:
- X-ray activity and accretion in the ONC
- Short Name:
- J/A+A/648/A121
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Recent works highlight the importance of stellar X-rays on the evolution of the circumstellar disks of young stellar objects, especially for disk photoevaporation. A signature of this process may be seen in the so far tentatively observed dependence of stellar accretion rates on X-ray luminosities. According to models of X-ray driven photoevaporation, stars with higher X-ray luminosities should show lower accretion rates, on average, in a sample with similar masses and ages. To this aim, we have analyzed X-ray properties of young stars in the Orion Nebula Cluster determined with Chandra during the COUP observation as well as accretion data obtained from the photometric catalog of the HST Treasury Program. With these data, we have performed a statistical analysis of the relation between X-ray activity and accretion rates using partial linear regression analysis. The initial anticorrelation found with a sample of 332 young stars is considerably weaker compared to previous studies. However, excluding flaring activity or limiting the X-ray luminosity to the soft band (0.5-2.0keV) leads to a stronger anticorrelation, which is statistically more significant. Furthermore, we have found a weak positive correlation between the higher component of the plasma temperature gained in the X-ray spectral fitting and the accretion rates, indicating that the hardness of the X-ray spectra may influence the accretion process. There is evidence for a weak anticorrelation, as predicted by theoretical models, suggesting that X-ray photoevaporation modulates the accretion rate through the inner disk at late stages of disk evolution, leading to a phase of photoevaporation-starved accretion.
- ID:
- ivo://CDS.VizieR/J/other/RAA/19.98
- Title:
- X-ray activity from different types of stars
- Short Name:
- J/other/RAA/19.9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- X-ray emission is an important indicator of stellar activity. In this paper, we study stellar X-ray activity using the XMM-Newton and LAMOST data for different types of stars. We provide a sample including 1259 X-ray-emitting stars, of which 1090 have accurate stellar parameter estimations. Our sample size is much larger than those used in previous works. We find a bimodal distribution of the X-ray to optical flux ratio (log(fX/fV)) for G and K stars. We interpret that this bimodality is due to two subpopulations with different coronal heating rates. Furthermore, using the full widths at half maxima calculated from H{alpha} and H{beta} lines, we show that these stars in the inactive peaks have smaller rotational velocities. This is consistent with the magnetic dynamo theory that presumes stars with low rotational velocities have low levels of stellar activity. We also examine the correlation between log(fX/fV) and luminosity of the excess emission in the H{alpha} line, and find a tight relation between the coronal and chromospheric activity indicators.
- ID:
- ivo://CDS.VizieR/J/MNRAS/422/2024
- Title:
- X-ray-age relation and exoplanet evaporation
- Short Name:
- J/MNRAS/422/2024
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the relationship between coronal X-ray emission and stellar age for late-type stars, and the variation of this relationship with spectral type. We select 717 stars from 13 open clusters and find that the ratio of X-ray to bolometric luminosity during the saturated phase of coronal emission decreases from 10^-3.1^ for late K-dwarfs to 10^-4.3^ for early F-type stars (across the range 0.29<(B-V)_0_<1.41). Our determined saturation timescales vary between 10^7.6^ and 10^8.3^ years, though with no clear trend across the whole FGK range. We apply our X-ray emission - age relations to the investigation of the evaporation history of 121 known transiting exoplanets using a simple energy -limited model of evaporation and taking into consideration Roche lobe effects and different heating/evaporation efficiencies. We confirm that a linear cut-off of the planet distribution in the M^2^/R^3^ versus a^-2^ plane is an expected result of population modification by evaporation and that the known transiting exoplanets display such a cut-off. We find that for an evaporation efficiency of 25 percent we expect around 1 in 5 of the known transiting exoplanets to have lost >10 percent of their mass since formation. In addition we provide estimates of the minimum formation mass for which a planet could be expected to survive for 4Gyrs for a range of stellar and planetary parameters. We emphasise the importance of the earliest periods of a planet's life for its evaporation history with 75 percent expect to occur within the first Gyr. This raises the possibility of using evaporation histories to distinguish different migration mechanisms. For planets with spin-orbit angles available from measurements of the Rossiter-McLaughlin effect no difference is found between the distributions of planets with misaligned orbits and those with aligned orbits. This suggests that dynamical effects accounting for misalignment occur early in the life of a planetary system, although additional data is required to test this.
- ID:
- ivo://CDS.VizieR/J/A+A/281/355
- Title:
- X-ray AGN content of Molonglo 408MHz survey
- Short Name:
- J/A+A/281/355
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The cross-correlation of a source list from the ROSAT All-Sky Survey with the Molonglo 408MHz survey (MRC) yields to a catalogue of 549 sources. The majority of the objects are quasars and radio galaxies with known optical counterparts; more than one third of the objects are optically unidentified.
21697. X-ray AGN from RASS and SDSS
- 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/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/743/166
- Title:
- X-ray and infra-red study of RCW 38
- Short Name:
- J/ApJ/743/166
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the structure of the high-mass star-forming region RCW 38 and the spatial distribution of its young stellar population. Spitzer Infrared Array Camera (IRAC) photometry (3-8um) is combined with Two Micron All Sky Survey near-IR data to identify young stellar objects (YSOs) by IR-excess emission from their circumstellar material. Chandra X-ray data are used to identify class III pre-main-sequence stars lacking circumstellar material. We identify 624 YSOs: 23 class 0/I and 90 flat spectrum protostars, 437 class II stars, and 74 class III stars. We also identify 29 (27 new) O star candidates over the IRAC field. Seventy-two stars exhibit IR-variability, including 7 class 0/I and 12 flat spectrum YSOs. A further 177 tentative candidates are identified by their location in the IRAC [3.6] versus [3.6]-[5.8] color-magnitude diagram. We find strong evidence of subclustering in the region.
- ID:
- ivo://CDS.VizieR/J/ApJ/715/671
- Title:
- X-ray and IR emission from YSOs
- Short Name:
- J/ApJ/715/671
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on a multiwavelength study of a partially embedded region of star formation centered on the Herbig Be star LkH{alpha} 101. Using two 40ks Chandra observations, we detect 213 X-ray sources in the ~17'x17' ACIS-I field. We combine the X-ray data with Two Micron All Sky Survey near-IR observations and Spitzer IRAC and MIPS 24um observations to obtain a complete picture of the cluster. A total of 158 of the X-ray sources have infrared counterparts. Of these, we find nine protostars, 48 Class II objects, five transition objects, and 72 Class III objects. From the Spitzer data we identify an additional 10 protostars, 53 Class II objects, and four transition disk candidates which are not detected by Chandra. We obtained optical spectra of a sample of both X-ray-detected and non-X-ray-detected objects. Combining the X-ray, Spitzer, and spectral data, we obtain independent estimates of cluster distance and the total cluster size -excluding protostars. We obtain consistent distance estimates of 510^+100^_-40_pc and a total cluster size of 255^+50^_-25_ stars. We find the Class II:III ratio is about 5:7 with some evidence that the Class III sources are spatially more dispersed. The cluster appears very young with three sites of active star formation and a median age of about 1Myr.
