- ID:
- ivo://CDS.VizieR/J/MNRAS/472/1850
- Title:
- Detecting damped Ly{alpha} absorbers
- Short Name:
- J/MNRAS/472/1850
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We develop an automated technique for detecting damped Ly{alpha} absorbers (DLAs) along spectroscopic lines of sight to quasi-stellar objects (QSOs or quasars). The detection of DLAs in large-scale spectroscopic surveys such as SDSS III sheds light on galaxy formation at high redshift, showing the nucleation of galaxies from diffuse gas. We use nearly 50000 QSO spectra to learn a novel tailored Gaussian process model for quasar emission spectra, which we apply to the DLA detection problem via Bayesian model selection. We propose models for identifying an arbitrary number of DLAs along a given line of sight. We demonstrate our method's effectiveness using a large-scale validation experiment, with excellent performance. We also provide a catalogue of our results applied to 162858 spectra from SDSS-III data release 12.
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Search Results
202. Dislodged AGNs
- ID:
- ivo://CDS.VizieR/J/ApJ/835/L30
- Title:
- Dislodged AGNs
- Short Name:
- J/ApJ/835/L30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate a sample of 2293 ICRF2 extragalactic radio-loud sources with accurate positions determined by VLBI, mostly active galactic nuclei (AGNs) and quasars, which are cross-matched with optical sources in the first Gaia release (Gaia DR1). The distribution of offsets between the VLBI sources and their optical counterparts is strongly non-Gaussian, with powerful wings extending beyond 1 arcsec. Limiting our analysis to only high-confidence difference detections, we find (and publish) a list of 188 objects with normalized variances above 12 and offsets below 1 arcsec. Pan-STARRS stacked and monochromatic images resolve some of these sources, indicating the presence of double sources, confusion sources, or pronounced extended structures. Some 89 high-quality objects, however, do not show any perturbations and appear to be star-like single sources, yet they are displaced by multiples of the expected error from the radio-loud AGN. We conclude that a fraction of luminous AGNs (more than 4%) can be physically dislodged from the optical centers of their parent galaxies.
- ID:
- ivo://CDS.VizieR/J/MNRAS/464/L56
- Title:
- DLA properties and EW of 36 QSOs
- Short Name:
- J/MNRAS/464/L56
- Date:
- 02 Feb 2022 07:22:02
- Publisher:
- CDS
- Description:
- The XQ-100 survey provides optical and near-infrared coverage of 36 blindly selected, intervening damped Lyman {alpha} systems (DLAs) at 2<z_abs_<4, simultaneously covering the MgII doublet at {lambda}{lambda}2796,2803{AA}, and the Ly{alpha} transition. Using the XQ-100 DLA sample, we investigate the completeness of selecting DLA absorbers based on their MgII rest-frame equivalent width (W_0_^2796^) at these redshifts. Of the 29 DLAs with clean Mg II profiles, we find that six (20 per cent of DLAs) have W_0_^2796^<0.6{AA}. The DLA incidence rate of W_0_^2796^<0.6{AA} absorbers is a factor of ~5 higher than what is seen in z~1 samples, indicating a potential evolution in the MgII properties of DLAs with redshift. All of the W_0_^2796^<0.6{AA} DLAs have low metallicities (-2.5<[M/H]<-1.7), small velocity widths (v_90_<50km/s), and tend to have relatively low N(HI). We demonstrate that the exclusion of these low W_0_^2796^ DLAs results in a higher mean N(HI) which in turn leads to an ~7 per cent increase in the cosmological gas density of HI of DLAs at 2<z_abs_<4; and that this exclusion has a minimal effect on the HI-weighted mean metallicity.
- ID:
- ivo://CDS.VizieR/J/A+A/611/A76
- Title:
- DLAS dust-corrected metallicity
- Short Name:
- J/A+A/611/A76
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Interpreting abundances of damped Ly-{alpha} absorbers (DLAs) from absorption-line spectroscopy has typically been a challenge because of the presence of dust. Nevertheless, because DLAs trace distant gas-rich galaxies regardless of their luminosity, they provide an attractive way of measuring the evolution of the metallicity of the neutral gas with cosmic time. This has been done extensively so far, but typically not taking proper dust corrections into account. The aims of this paper are to: (i) provide a simplified way of calculating dust corrections, based on a single observed [X/Fe], (ii) assess the importance of dust corrections for DLA metallicities and their evolution, and (iii) investigate the cosmic evolution of iron for a large DLA sample. We have derived dust corrections based on the observed [Zn/Fe], [Si/Fe], or [S/Fe], and confirmed their robustness. We present dust-corrected metallicities in a scale of [Fe/H]tot for 236 DLAs over a broad range of z, and assess the extent of dust corrections for different metals at different metallicities. Dust corrections in DLAs are important even for Zn (typically of 0.1-0.2, and up to 0.5dex), which is often neglected. Finally, we study the evolution of the dust-corrected metallicity with z. The DLA metallicities decrease with redshift, by a factor of 50-100 from today to ~12.6 billion years ago (z=5). When including dust corrections, the average DLA metallicities are 0.4-0.5dex higher than without corrections. The upper envelope of the relation between metallicity and z reaches solar metallicity at z<~0.5, although some systems can have solar metallicity already out to z~3.
205. DLAs in SDSS-DR7
- ID:
- ivo://CDS.VizieR/J/A+A/505/1087
- Title:
- DLAs in SDSS-DR7
- Short Name:
- J/A+A/505/1087
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the evolution of the cosmological mass density of neutral gas using a fully automatic search for Damped Lyman-alpha systems in the Sloan Digital Sky Survey II Data Release 7.
- ID:
- ivo://CDS.VizieR/J/MNRAS/435/482
- Title:
- DLA system from SDSS DR5
- Short Name:
- J/MNRAS/435/482
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the chemical abundance measurements of the first large, medium-resolution, uniformly selected damped Lyman {alpha} system (DLA) survey. The sample contains 99 DLAs towards 89 quasars selected from the SDSS DR5 DLA sample in a uniform way. We analyse the metallicities and kinematic diagnostics, including the velocity width of 90 percent of the optical depth, {Delta}V_90_, and the equivalent widths of the SiII {lambda}1526 (W}{lambda}1526), CIV {lambda}1548 and MgII {lambda}2796 transitions. To avoid strong line-saturation effects on the metallicities measured in medium-resolution spectra (FWHM~71km/s), we derived metallicities from metal transitions which absorbed at most 35 percent of the quasar continuum flux. We find the evolution in cosmic mean metallicity of the sample, <Z>=(-0.04+/-0.13)z-(1.06+/-0.36), consistent with no evolution over the redshift range z~[2.2, 4.4], but note that the majority of our sample falls at z~[2.2, 3.5]. The apparent lack of metallicity evolution with redshift is also seen in a lack of evolution in the median {Delta}V_90_ and W{lambda}1526 values. While this result may seem to conflict with other large surveys that have detected significant metallicity evolution, such as Rafelski et al. who found <Z>=(-0.22+/-0.03)z-(0.65+/-0.09) over z~[0, 5], several tests show that these surveys are not inconsistent with our new result. However, over the smaller redshift range covered by our uniformly selected sample, the true evolution of the cosmic mean metallicity in DLAs may be somewhat flatter than the Rafelski et al. (2012ApJ...755...89R, Cat. J/ApJ/755/89) estimate.
- ID:
- ivo://CDS.VizieR/J/AJ/131/666
- Title:
- Double-lobed radio quasars from the SDSS
- Short Name:
- J/AJ/131/666
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have combined a sample of 44,984 quasars selected from the Sloan Digital Sky Survey (SDSS) Data Release 3 (Cat. <II/259>) with the FIRST radio survey (Cat. <VIII/71>). Using a novel technique in which the optical quasar position is matched to the complete radio environment within 450", we are able to characterize the radio morphological make-up of what is essentially an optically selected quasar sample, regardless of whether the quasar (nucleus) itself has been detected in the radio.
- ID:
- ivo://CDS.VizieR/J/ApJ/693/1554
- Title:
- Double QSOs: merger scenarios
- Short Name:
- J/ApJ/693/1554
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze the available sample of double quasars, and investigate their physical properties. Our sample comprises 85 pairs, selected from the Sloan Digital Sky Survey (SDSS). We derive physical parameters for the engine and the host, and model the dynamical evolution of the pair. First, we compare different scaling relationships between massive black holes and their hosts (bulge mass, velocity dispersion, and their possible redshift dependences), and discuss their consistency. We then compute dynamical friction timescales for the double quasar systems to investigate their frequency and their agreement with the "merger driven" scenario for quasar triggering.
- ID:
- ivo://CDS.VizieR/J/ApJ/697/182
- Title:
- Dust emission from unobscured AGN
- Short Name:
- J/ApJ/697/182
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use mid-infrared (MIR) spectroscopy of unobscured active galactic nuclei (AGNs) to reveal their native dusty environments. We concentrate on Seyfert 1 galaxies, observing a sample of 31 with the Infrared Spectrograph aboard the Spitzer Space Telescope, and compare them with 21 higher luminosity quasar counterparts.
- ID:
- ivo://CDS.VizieR/J/A+A/591/A130
- Title:
- Dynamic SEDs of southern blazars - DSSB
- Short Name:
- J/A+A/591/A130
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Simultaneous broadband spectral and temporal studies of blazars are an important tool for investigating active galactic nuclei (AGN) jet physics. We study the spectral evolution between quiescent and flaring periods of 22 radio-loud AGN through multiepoch, quasi-simultaneous broadband spectra. For many of these sources these are the first broadband studies. We use a Bayesian block analysis of Fermi/LAT light curves to determine time ranges of constant flux for constructing quasi-simultaneous spectral energy distributions (SEDs). The shapes of the resulting 81 SEDs are described by two logarithmic parabolas and a blackbody spectrum where needed.
