- ID:
- ivo://CDS.VizieR/J/ApJ/755/89
- Title:
- Metallicities of damped Ly{alpha} systems
- Short Name:
- J/ApJ/755/89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present chemical abundance measurements for 47 damped Ly{alpha} (DLA) systems, 30 at z>4, observed with the Echellette Spectrograph and Imager and the High Resolution Echelle Spectrometer on the Keck telescopes. H I column densities of the DLAs are measured with Voigt profile fits to the Ly{alpha} profiles, and we find an increased number of false DLA identifications with Sloan Digital Sky Survey at z>4 due to the increased density of the Ly{alpha} forest. Ionic column densities are determined using the apparent optical depth method, and we combine our new metallicity measurements with 195 from previous surveys to determine the evolution of the cosmic metallicity of neutral gas. We find the metallicity of DLAs decreases with increasing redshift, improving the significance of the trend and extending it to higher redshifts, with a linear fit of -0.22+/-0.03 dex per unit redshift from z=0.09-5.06. The metallicity "floor" of {approx}1/600 solar continues out to z~5, despite our sensitivity for finding DLAs with much lower metallicities. However, this floor is not statistically different from a steep tail to the distribution. We also find that the intrinsic scatter of metallicity among DLAs of ~0.5dex continues out to z~5. In addition, the metallicity distribution and the {alpha}/Fe ratios of z>2 DLAs are consistent with being drawn from the same parent population with those of halo stars. It is therefore possible that the halo stars in the Milky Way formed out of gas that commonly exhibits DLA absorption at z>2.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/683/321
- Title:
- Metallicities of GRB, DLA, and Ly{alpha} galaxies
- Short Name:
- J/ApJ/683/321
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We test the hypothesis that the host galaxies of long-duration gamma-ray bursts (GRBs) as well as quasar-selected damped Ly{alpha} (DLA) systems are drawn from the population of UV-selected star-forming, high-z galaxies (generally referred to as Lyman break galaxies). Specifically, we compare the metallicity distributions of the GRB and DLA populations against simple models where these galaxies are drawn randomly from the distribution of star-forming galaxies according to their star formation rate and HI cross section, respectively. We find that it is possible to match both observational distributions assuming very simple and constrained relations between luminosity, metallicity, and HI sizes. The simple model can be tested by observing the luminosity distribution of GRB host galaxies and by measuring the luminosity and impact parameters of DLA-selected galaxies as a function of metallicity. Our results support the expectation that GRB and DLA samples, in contrast with magnitude-limited surveys, provide an almost complete census of z~3 star-forming galaxies that are not heavily obscured.
- ID:
- ivo://CDS.VizieR/J/ApJ/770/138
- Title:
- Metallicities of Lyman limit systems and DLA
- Short Name:
- J/ApJ/770/138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We assess the metal content of the cool (~10^4^K) circumgalactic medium (CGM) about galaxies at z<~1 using an H I-selected sample of 28 Lyman limit systems (LLS; defined here as absorbers with 16.2<~logN_HI_<~18.5) observed in absorption against background QSOs by the Cosmic Origins Spectrograph on board the Hubble Space Telescope. The N_HI_ selection avoids metallicity biases inherent in many previous studies of the low-redshift CGM. We compare the column densities of weakly ionized metal species (e.g., O II, Si II, Mg II) to N_HI_ in the strongest H I component of each absorber. We find that the metallicity distribution of the LLS (and hence the cool CGM) is bimodal with metal-poor and metal-rich branches peaking at [X/H]=~-1.6 and -0.3 (or about 2.5% and 50% solar metallicities). The cool CGM probed by these LLS is predominantly ionized. The metal-rich branch of the population likely traces winds, recycled outflows, and tidally stripped gas; the metal-poor branch has properties consistent with cold accretion streams thought to be a major source of fresh gas for star forming galaxies. Both branches have a nearly equal number of absorbers. Our results thus demonstrate there is a significant mass of previously undiscovered cold metal-poor gas and confirm the presence of metal enriched gas in the CGM of z<~1 galaxies.
- ID:
- ivo://CDS.VizieR/J/MNRAS/452/4326
- Title:
- Metal-rich damped Ly{alpha} systems at z~2
- Short Name:
- J/MNRAS/452/4326
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using our sample of the most metal-rich damped Lyman {alpha} systems (DLAs) at z_abs_~2, and two literature compilations of chemical abundances in 341 DLAs and 2818 stars, we present an analysis of the chemical composition of DLAs in the context of the Local Group. The metal-rich sample of DLAs at z_abs~2 probes metallicities as high as the Galactic disc and the most metal-rich dwarf spheroidals (dSphs), permitting an analysis of many elements typically observed in DLAs (Fe, Zn, Cr, Mn, Si, and S) in comparison to stellar abundances observed in the Galaxy and its satellites (in particular dSphs). Our main conclusions are: (1) non-solar [Zn/Fe] abundances in metal-poor Galactic stars and in dSphs over the full metallicity range probed by DLAs, suggest that Zn is not a simple proxy for Fe in DLAs and therefore not a suitable indicator of dust depletion. After correcting for dust depletion, the majority of DLAs have subsolar [Zn/Fe] similar to dSphs; (2) at [Fe/H]~-0.5, a constant [Mn/Fe]~-0.5 and near-solar [{alpha}/Fe] (requiring an assumption about dust depletion) are in better agreement with dwarf galaxies than Galactic disc stars; (3) [{alpha}/Zn] is usually solar or subsolar in DLAs. However, although low ratios of [{alpha}/Fe] are usually considered more 'dwarf-like' than `Milky Way-like', subsolar [Zn/Fe] in Local Group dwarfs leads to supersolar [{alpha}/Zn] in the dSphs, in contrast with the DLAs. Therefore, whilst DLAs exhibit some similarities with the Local Group dwarf population, there are also notable differences.
- ID:
- ivo://CDS.VizieR/J/ApJ/763/37
- Title:
- Metals in SDSS QSOs. I. 1.5<z<4.5 CIV absorbers
- Short Name:
- J/ApJ/763/37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have vastly increased the CIV statistics at intermediate redshift by surveying the thousands of quasars in the Sloan Digital Sky Survey (SDSS) Data-Release 7. We visually verified over 16000 CIV systems with 1.46<z<4.55 - a sample size that renders Poisson error negligible. Detailed Monte Carlo simulations show that we are approximately 50% complete down to rest equivalent widths W_r_{approx}0.6{AA}. We analyzed the sample as a whole and in 10 small redshift bins with approximately 1500 doublets each. The equivalent width frequency distributions f(W_r_) were well modeled by an exponential, with little evolution in shape. In contrast with previous studies that modeled the frequency distribution as a single power law, the fitted exponential gives a finite mass density for the CIV ions. The comoving line density dN_CIV_/dX evolved smoothly with redshift, increasing by a factor of 2.37+/-0.09 from z=4.55-1.96, then plateauing at dN_CIV_/dX~0.34 for z=1.96-1.46. Comparing our SDSS sample with z<1 (ultraviolet) and z>5 (infrared) surveys, we see an approximately 10-fold increase in dN_CIV_/dX over z{approx}6->0, for W_r_>=0.6{AA}. This suggests a monotonic and significant increase in the enrichment of gas outside galaxies over the 12Gyr lifetime of the universe.
- ID:
- ivo://CDS.VizieR/J/PASP/118/1077
- Title:
- Metal-strong damped Ly{alpha} systems
- Short Name:
- J/PASP/118/1077
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have identified a metal-strong [logN(Zn+)>=13.15 or logN(Si^+^)>=15.95] damped Ly{alpha} (MSDLA) population from an automated quasar (QSO) absorber search in the Sloan Digital Sky Survey (SDSS) Data Release 3 quasar sample and find that MSDLAs comprise >>5% of the entire DLA population with z_abs_>=2.2 found in QSO sight lines with r<19.5. We have also acquired 27 Keck ESI (Echellete Spectrograph and Imager) follow-up spectra of metal strong candidates in order to evaluate our automated technique and examine the MSDLA candidates at higher resolution.
- ID:
- ivo://CDS.VizieR/J/MNRAS/353/211
- Title:
- Method for selection of quasars
- Short Name:
- J/MNRAS/353/211
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The application of supervised artificial neural networks (ANNs) for quasar selection from combined radio and optical surveys with photometric and morphological data is investigated, using the list of candidates and their classification from the work of White et al. (2000, Cat. J/ApJS/126/133>) Seven input parameters and one output, evaluated to 1 for quasars and 0 for non-quasars during the training, were used, with architectures 7: 1 and 7: 2: 1. Both models were trained on samples of 800 sources and yielded similar performance on independent test samples, with reliability as large as 87 per cent at 80 per cent completeness (or 90 to 80 per cent for completeness from 70 to 90 per cent). For comparison, the quasar fraction from the original candidate list was 56 per cent.
468. MEXSAS catalogue
- ID:
- ivo://CDS.VizieR/J/A+A/593/A55
- Title:
- MEXSAS catalogue
- Short Name:
- J/A+A/593/A55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Most investigations of the X-ray variability of active galactic nuclei (AGN) have been concentrated on the detailed analyses of individual, nearby sources. A relatively small number of studies have treated the ensemble behaviour of the more general AGN population in wider regions of the luminosity-redshift plane. We want to determine the ensemble variability properties of a rich AGN sample, called Multi-Epoch XMM Serendipitous AGN Sample (MEXSAS), extracted from the fifth release of the XMM-Newton Serendipitous Source Catalogue (XMMSSC-DR5), with redshift between 0.1 and 5, and X-ray luminosities in the 0.5-4.5keV band between 10^42^ and 10^47^erg/s. We urge caution on the use of the normalised excess variance (NXS), noting that it may lead to underestimate variability if used improperly. We use the structure function (SF), updating our previous analysis for a smaller sample. We propose a correction to the NXS variability estimator, accounting for the light curve duration in the rest frame on the basis of the knowledge of the variability behaviour gained by SF studies. We find an ensemble increase of the X-ray variability with the rest-frame time lag tau, given by tau^0.12^. We confirm an inverse dependence on the X-ray luminosity, approximately as L_X^-0.19^. We analyse the SF in different X-ray bands, finding a dependence of the variability on the frequency as nu^-0.15^, corresponding to a softer when brighter trend. In turn, this dependence allows us to parametrically correct the variability estimated in observer-frame bands to that in the rest frame, resulting in a moderate shift upwards (V-correction). Ensemble X-ray variability of AGNs is best described by the structure function. An improper use of the normalised excess variance may lead to an underestimate of the intrinsic variability, so that appropriate corrections to the data or the models must be applied to prevent these effects.
- ID:
- ivo://CDS.VizieR/J/ApJ/748/131
- Title:
- MgII absorbers in SDSS-DR7 quasar catalog
- Short Name:
- J/ApJ/748/131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A few percent of quasars show strong associated Mg II absorption, with velocities (v_off_) lying within a few thousand km/s from the quasar systemic redshift. These associated absorption line (AAL) systems are usually interpreted as absorbers that are either intrinsic to the quasar and its host, or arising from external galaxies clustering around the quasar. Using composite spectra of ~1800 Mg II AAL quasars selected from SDSS DR7 at 0.4<~z<~2, we show that quasars with AALs with v_off_<1500km/s have a prominent excess in [OII]{lambda}3727 emission (detected at >7{sigma}) at rest relative to the quasar host, compared to unabsorbed quasars. We interpret this [OII] excess as due to enhanced star formation in the quasar host. Our results suggest that a significant fraction of AALs with v_off_<1500km/s are physically associated with the quasar and its host. AAL quasars also have dust reddening lying between normal quasars and the so-called dust-reddened quasars. We suggest that the unique properties of AAL quasars can be explained if they are the transitional population from heavily dust-reddened quasars to normal quasars in the formation process of quasars and their hosts. This scenario predicts a larger fraction of young bulges, disturbed morphologies, and interactions of AAL quasar hosts compared to normal quasars. The intrinsic link between associated absorbers and quasar hosts opens a new window to probe massive galaxy formation and galactic-scale feedback processes, and provides a crucial test of the evolutionary picture of quasars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/354/L25
- Title:
- MgII absorbers in SDSS QSOs
- Short Name:
- J/MNRAS/354/L25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the cross-correlation between 212 Mg II quasar absorption systems and ~20000 luminous red galaxies (LRGs) selected from the Sloan Digital Sky Survey Data Release 1 (Cat. <J/AJ/126/2579>) in the redshift range 0.4<=z<=0.8. The Mg II systems were selected to have {lambda}{lambda}2796 and 2803 rest-frame equivalent widths >=1.0{AA} and identifications confirmed by the Fe II {lambda}2600 or Mg I {lambda}2852 lines.
