- ID:
- ivo://CDS.VizieR/J/A+A/519/A17
- Title:
- X-ray/UV ratio of 2XMM AGN
- Short Name:
- J/A+A/519/A17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The observed relation between the X-ray radiation from active galactic nuclei, originating in the corona, and the optical/UV radiation from the disk is usually described by the anticorrelation between the UV to X-ray slope {alpha}_ox_ and the UV luminosity. Many factors can affect this relation, including: i) enhanced X-ray emission associated with the jets of radio-loud AGNs, ii) X-ray absorption associated with the UV broad absorption line (BAL) outflows, iii) other X-ray absorption not associated with BALs, iv) intrinsic X-ray weakness, v) UV and X-ray variability, and non-simultaneity of UV and X-ray observations. The separation of these effects provides information about the intrinsic {alpha}_ox_-L_UV_ relation and its dispersion, constraining models of disk-corona coupling. We use simultaneous UV/X-ray observations to remove the influence of non-simultaneous measurements from the {alpha}_ox_-L_UV_ relation.
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- ID:
- ivo://CDS.VizieR/J/ApJ/685/773
- Title:
- X-ray-UV relations in SDSS DR5 QSOs
- Short Name:
- J/ApJ/685/773
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze archived Chandra and XMM-Newton X-ray observations of 536 Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) quasars (QSOs) at 1.7<=z<=2.7 in order to characterize the relative UV and X-ray spectral properties of QSOs that do not have broad UV absorption lines (BALs). We constrain the fraction of X-ray-weak, non-BAL QSOs and find that such objects are rare; for example, sources underluminous by a factor of 10 comprise <~2% of optically selected SDSS QSOs. X-ray luminosities vary with respect to UV emission by a factor of <~2 over several years for most sources. UV continuum reddening and the presence of narrow-line absorbing systems are not strongly associated with X-ray weakness in our sample. X-ray brightness is significantly correlated with UV emission-line properties, so that relatively X-ray-weak, non-BAL QSOs generally have weaker, blueshifted CIV {lambda}1549 emission and broader CIII] {lambda}1909 lines. The CIV emission-line strength depends on both UV and X-ray luminosity, suggesting that the physical mechanism driving the global Baldwin effect is also associated with X-ray emission.
- ID:
- ivo://CDS.VizieR/J/A+A/654/A132
- Title:
- X-shooter spectra of AGN and inactive galaxies
- Short Name:
- J/A+A/654/A132
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The relation between nuclear (<~50pc) star formation and nuclear galactic activity is still elusive; theoretical models predict a link between the two, but it is unclear whether active galactic nuclei (AGNs) should appear at the same time, before, or after nuclear star formation activity. We present a study of this relation in a complete, volume-limited sample of nine of the most luminous (log_L14-195keV_>10^42.5^erg/s) local AGNs (the LLAMA sample), including a sample of 18 inactive control galaxies (six star-forming; 12 passive) that are matched by Hubble type, stellar mass (9.5<~logM*/M_{sun}_<~10.5), inclination, and distance. This allows us to calibrate our methods on the control sample and perform a differential analysis between the AGN and control samples. We performed stellar population synthesis on VLT/X-shooter spectra in an aperture corresponding to a physical radius of ~150pc. We find young (<~30Myr) stellar populations in seven out of nine AGNs and in four out of six star-forming control galaxies. In the non-star-forming control population, in contrast, only two out of 12 galaxies show such a population. We further show that these young populations are not indicative of ongoing star formation, providing evidence for models that see AGN activity as a consequence of nuclear star formation. Based on the similar nuclear star formation histories of AGNs and star-forming control galaxies, we speculate that the latter may turn into the former for some fraction of their time. Under this assumption, and making use of the volume completeness of our sample, we infer that the AGN phase lasts for about 5% of the nuclear starburst phase.
- ID:
- ivo://CDS.VizieR/J/A+A/628/A61
- Title:
- X-shooter spectra of 43 metal-poor M dwarfs
- Short Name:
- J/A+A/628/A61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of the project is to define metallicity/gravity/temperature scales for different spectral types of metal-poor M dwarfs. We obtained intermediate-resolution ultraviolet (UVB), optical (VIS), and near-infrared (NIR) spectra of 43 metal-poor M dwarfs (16 sdMs, 16 esdMs, and 12 usdMs with the ESO VLT X-shooter spectrograph. We compared our atlas of spectra to the BT-Settl synthetic spectral energy distribution over a wide range of metallicities, gravities, and effective temperatures to infer the physical properties for the whole M dwarf sequence at sub-solar metallicities and constrain the latest atmospheric models. The BT-Settl models accurately reproduce the observed spectra across the 450--2500 nm wavelength range except for a few regions. We find that the best fits for gravities of log(g)=5.0-5.5 for the three metal classes. We infer metallicities of [Fe/H]=-0.5, -1.5, and -2.0+/-0.5dex and effective temperatures of 3700-2600K, 3800-2900K, and 3700-2900K for sdMs, esdMs, and usdMs, respectively.
- ID:
- ivo://CDS.VizieR/J/ApJS/173/538
- Title:
- XUV-Disk galaxies in the Local Universe
- Short Name:
- J/ApJS/173/538
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have initiated a search for extended ultraviolet disk (XUV-disk) galaxies in the local universe. Here we compare GALEX UV and visible-NIR images of 189 nearby (D<40Mpc) S0-Sm galaxies included in the GALEX Atlas of Nearby Galaxies (Gil de Paz et al. 2007, Cat. J/ApJS/173/185) and present the first catalog of XUV-disk galaxies. We find that XUV-disk galaxies are surprisingly common but have varied relative (UV/optical) extent and morphology. Type 1 objects (>~20% incidence) have structured, UV-bright/optically faint emission features in the outer disk, beyond the traditional star formation threshold. Type 2 XUV-disk galaxies (~10% incidence) exhibit an exceptionally large, UV-bright/optically low surface brightness (LSB) zone having blue UV-K_s_ outside the effective extent of the inner, older stellar population, but not reaching extreme galactocentric distance.
- ID:
- ivo://CDS.VizieR/J/ApJ/815/91
- Title:
- z<0.16 CIV absorbers from HST/COS QSOs spectra
- Short Name:
- J/ApJ/815/91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To investigate the evolution of metal-enriched gas over recent cosmic epochs as well as to characterize the diffuse, ionized, metal-enriched circumgalactic medium, we have conducted a blind survey for CIV absorption systems in 89 QSO sightlines observed with the Hubble Space Telescope Cosmic Origins Spectrograph. We have identified 42 absorbers at z<0.16, comprising the largest uniform blind sample size to date in this redshift range. Our measurements indicate an increasing CIV absorber number density per comoving path length (dN/dX=7.5+/-1.1) and modestly increasing mass density relative to the critical density of the universe ({Omega}_CIV_=10.0+/-1.5x10^-8^) from z~1.5 to the present epoch, consistent with predictions from cosmological hydrodynamical simulations. Furthermore, the data support a functional form for the column density distribution function that deviates from a single power law, also consistent with independent theoretical predictions. As the data also probe heavy element ions in addition to CIV at the same redshifts, we identify, measure, and search for correlations between column densities of these species where components appear to be aligned in velocity. Among these ion-ion correlations, we find evidence for tight correlations between CII and SiII, CII and SiIII, and CIV and SiIV, suggesting that these pairs of species arise in similar ionization conditions. However, the evidence for correlations decreases as the difference in ionization potential increases. Finally, when controlling for observational bias, we find only marginal evidence for a correlation (86.8% likelihood) between the Doppler line width b(CIV) and column density N(CIV).
- ID:
- ivo://CDS.VizieR/J/MNRAS/457/629
- Title:
- ZFOURGE catalogue of AGN candidates
- Short Name:
- J/MNRAS/457/629
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate active galactic nuclei (AGN) candidates within the FourStar Galaxy Evolution Survey (ZFOURGE) to determine the impact they have on star formation in their host galaxies. We first identify a population of radio, X-ray, and infrared-selected AGN by cross-matching the deep Ks-band imaging of ZFOURGE with overlapping multiwavelength data. From this, we construct a mass-complete (log(M*/M_{sun}_)>=9.75), AGN luminosity limited sample of 235 AGN hosts over z=0.2-3.2. We compare the rest-frame U-V versus V-J (UVJ) colours and specific star formation rates (sSFRs) of the AGN hosts to a mass-matched control sample of inactive (non-AGN) galaxies. UVJ diagnostics reveal AGN tend to be hosted in a lower fraction of quiescent galaxies and a higher fraction of dusty galaxies than the control sample. Using 160{mu}m Herschel PACS data, we find the mean specific star formation rate of AGN hosts to be elevated by 0.34-/-0.07dex with respect to the control sample across all redshifts. This offset is primarily driven by infrared-selected AGN, where the mean sSFR is found to be elevated by as much as a factor of ~5. The remaining population, comprised predominantly of X-ray AGN hosts, is found mostly consistent with inactive galaxies, exhibiting only a marginal elevation. We discuss scenarios that may explain these findings and postulate that AGN are less likely to be a dominant mechanism for moderating galaxy growth via quenching than has previously been suggested.
- ID:
- ivo://CDS.VizieR/J/ApJ/653/53
- Title:
- z~6 galaxies UV luminosity function
- Short Name:
- J/ApJ/653/53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have detected 506 i-dropouts (z~6 galaxies) in deep, wide-area HST ACS fields: HUDF, enhanced GOODS, and HUDF parallel ACS fields (HUDF-Ps). The contamination levels are <~8% (i.e., >~92% are at z~6). With these samples, we present the most comprehensive, quantitative analyses of z~6 galaxies yet and provide optimal measures of the UV luminosity function (LF) and luminosity density at z~6, and their evolution to z~3. We redetermine the size and color evolution from z~6 to z~3. Field-to-field variations (cosmic variance), completeness, flux, and contamination corrections are modeled systematically and quantitatively.
