- ID:
- ivo://CDS.VizieR/J/ApJ/783/119
- Title:
- z~1 Ly{alpha} emitters. I. 135 candidates from GALEX
- Short Name:
- J/ApJ/783/119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We construct a flux-limited sample of 135 candidate z~1 Ly{alpha} emitters (LAEs) from Galaxy Evolution Explorer (GALEX) grism data using a new data cube search method. These LAEs have luminosities comparable to those at high redshifts and lie within a 7Gyr gap present in existing LAE samples. We use archival and newly obtained optical spectra to verify the UV redshifts of these LAEs. We use the combination of the GALEX UV spectra, optical spectra, and X-ray imaging data to estimate the active galactic nucleus (AGN) fraction and its dependence on Ly{alpha} luminosity. We remove the AGNs and compute the luminosity function (LF) from 60 z~1 LAE galaxies. We find that the best-fit LF implies a luminosity density increase by a factor of ~1.5 from z~0.3 to z~1 and ~20 from z~1 to z~2. We find a z~1 volumetric Ly{alpha} escape fraction of 0.7%+/-0.4%.
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- ID:
- ivo://CDS.VizieR/J/ApJ/661/88
- Title:
- Zn measurements in sub-DLAs and DLAs QSOs
- Short Name:
- J/ApJ/661/88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observations of low mean metallicity of damped Ly{alpha} (DLA) quasar absorbers at all redshifts studied appear to contradict the predictions for the global mean interstellar metallicity in galaxies from cosmic chemical evolution models. On the other hand, a number of metal-rich sub-DLA systems have been identified recently, and the fraction of metal-rich sub-DLAs appears to be considerably larger than that of metal-rich DLAs, especially at z<1.5. In view of this, here we investigate the evolution of metallicity in sub-DLAs. We find that the mean Zn metallicity of the observed sub-DLAs may be higher than that of the observed DLAs, especially at low redshifts, reaching a near-solar level at z<~1. This trend does not appear to be an artifact of sample selection, the use of Zn, the use of N_HI_ weighting, or observational sensitivity.
- ID:
- ivo://CDS.VizieR/J/ApJ/833/19
- Title:
- 0.02<z<1.4 post-starburst SDSS galaxies
- Short Name:
- J/ApJ/833/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Post-starburst galaxies are in the transitional stage between blue, star-forming galaxies and red, quiescent galaxies and therefore hold important clues for our understanding of galaxy evolution. In this paper, we systematically searched for and identified a large sample of post-starburst galaxies from the spectroscopic data set of the Sloan Digital Sky Survey (SDSS) Data Release 9. In total, we found more than 6000 objects with redshifts between z~0.05 and z~1.3, making this the largest sample of post-starburst galaxies in the literature. We calculated the luminosity function of the post-starburst galaxies using two uniformly selected subsamples: the SDSS main galaxy sample and the Baryon Oscillation Spectroscopic Survey CMASS sample. The luminosity functions are reasonably fit by half-Gaussian functions. The peak magnitudes shift as a function of redshift from M~-23.5 at z~0.8 to M~-20.3 at z~0.1. This is consistent with the downsizing trend, whereby more massive galaxies form earlier than low-mass galaxies. We compared the mass of the post-starburst stellar population found in our sample to the decline of the global star formation rate and found that only a small amount (~1%) of all star formation quenching in the redshift range z=0.2-0.7 results in post-starburst galaxies in the luminosity range our sample is sensitive to. Therefore, luminous post-starburst galaxies are not the place where most of the decline in the star formation rate of the universe is happening.
- ID:
- ivo://CDS.VizieR/J/ApJ/768/105
- Title:
- z~5 QSO luminosity function from SDSS Stripe 82
- Short Name:
- J/ApJ/768/105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a measurement of the Type I quasar luminosity function at z=5 using a large sample of spectroscopically confirmed quasars selected from optical imaging data. We measure the bright end (M_1450_<-26) with Sloan Digital Sky Survey (SDSS) data covering ~6000deg^2^, then extend to lower luminosities (M_1450_<-24) with newly discovered, faint z~5 quasars selected from 235deg^2^ of deep, coadded imaging in the SDSS Stripe 82 region (the celestial equator in the Southern Galactic Cap). The faint sample includes 14 quasars with spectra obtained as ancillary science targets in the SDSS-III Baryon Oscillation Spectroscopic Survey, and 59 quasars observed at the MMT and Magellan telescopes. We construct a well-defined sample of 4.7<z<5.1 quasars that is highly complete, with 73 spectroscopic identifications out of 92 candidates. Our color selection method is also highly efficient: of the 73 spectra obtained, 71 are high-redshift quasars. These observations reach below the break in the luminosity function (M_1450_^*^~-27). The bright-end slope is steep ({beta}<~-4), with a constraint of {beta}<-3.1 at 95% confidence. The break luminosity appears to evolve strongly at high redshift, providing an explanation for the flattening of the bright-end slope reported previously. We find a factor of ~2 greater decrease in the number density of luminous quasars (M_1450_<-26) from z=5 to z=6 than from z=4 to z=5, suggesting a more rapid decline in quasar activity at high redshift than found in previous surveys. Our model for the quasar luminosity function predicts that quasars generate ~30% of the ionizing photons required to keep hydrogen in the universe ionized at z=5.
- ID:
- ivo://CDS.VizieR/J/MNRAS/435/1198
- Title:
- z~6 QSOs CIV doublet absorption systems
- Short Name:
- J/MNRAS/435/1198
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of observations taken with the X-shooter spectrograph devoted to the study of quasars at z~6. This paper focuses on the properties of metals at high redshift traced, in particular, by the CIV doublet absorption systems. Six objects were observed with resolutions =~27 and 34km/s in the visual, and 37.5 and 53.5km/s in the near-infrared. We detected 10^2^ CIV lines in the range: 4.35<z<6.2 of which 27 are above z~5. Thanks to the characteristics of resolution and spectral coverage of X-shooter, we could also detect 25 SiIV doublets associated with the CIV at z>~5. The column density distribution function of the CIV line sample is observed to evolve in redshift for z>~5.3, with respect to the normalization defined by low-redshift (1.5<z<4) CIV lines. This behaviour is reflected in the redshift evolution of the CIV cosmic mass density, {Omega}_CIV_, of lines with column density in the range 13.4<logN(CIV)<15, which is consistent with a drop of a factor of ~2 for z>~5.3. Considering only the stronger CIV lines (13.8<logN(CIV)<15), {Omega}_CIV_ gently rises by a factor of ~10 between z=~6.2 and z=~1.5 with a possible flattening towards z~0. The increase is well fitted by a power law: {Omega}_CIV=(2+/-1)x10^-8^[(1+z)/4]^-3.1+/-0.1^. An insight into the properties of the CIV absorbers and their evolution with redshift is obtained by comparing the observed column densities of associated CIV, SiIV and CII absorptions with the output of a set of cloudy photoionization models. As already claimed by cosmological simulations, we find that CIV is a good tracer of the metallicity in the low-density intergalactic medium (IGM) gas at z~5-6 while at z~3 it arises in gas with overdensity {delta}~100.
- ID:
- ivo://CDS.VizieR/J/ApJ/819/24
- Title:
- z>4.5 QSOs with SDSS and WISE. I. Opt. spectra
- Short Name:
- J/ApJ/819/24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High-redshift quasars are important tracers of structure and evolution in the early universe. However, they are very rare and difficult to find when using color selection because of contamination from late-type dwarfs. High-redshift quasar surveys based on only optical colors suffer from incompleteness and low identification efficiency, especially at z>~4.5. We have developed a new method to select 4.7<~z>~5.4 quasars with both high efficiency and completeness by combining optical and mid-IR Wide-field Infrared Survey Explorer (WISE) photometric data, and are conducting a luminous z~5 quasar survey in the whole Sloan Digital Sky Survey (SDSS) footprint. We have spectroscopically observed 99 out of 110 candidates with z-band magnitudes brighter than 19.5, and 64 (64.6%) of them are quasars with redshifts of 4.4<~z<~5.5 and absolute magnitudes of -29<~M_1450_<~-26.4. In addition, we also observed 14 fainter candidates selected with the same criteria and identified 8 (57.1%) of them as quasars with 4.7<z<5.4. Among 72 newly identified quasars, 12 of them are at 5.2<z<5.7, which leads to an increase of ~36% of the number of known quasars at this redshift range. More importantly, our identifications doubled the number of quasars with M_1450_<-27.5 at z>4.5, which will set strong constraints on the bright end of the quasar luminosity function. We also expand our method to select quasars at z>~5.7. In this paper we report the discovery of four new luminous z>~5.7 quasars based on SDSS-WISE selection.
- ID:
- ivo://CDS.VizieR/J/A+A/616/A158
- Title:
- z>1.5 QSO VLT-XSHOOTER spectra
- Short Name:
- J/A+A/616/A158
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study a sample of 17 z>1.5 absorbers selected based on the presence of strong neutral carbon (CI) absorption lines in Sloan Digital Sky Survey (SDSS) spectra and observed with the European Southern Observatory Very Large Telescope (ESO-VLT) spectrograph X-shooter. We derive metallicities, depletion onto dust, and extinction by dust, and analyse the absorption from MgII, MgI, CaII, and NaI that are redshifted into the near infrared wavelength range. We show that most of these CI absorbers have high metallicity and dust content. We detect nine CaII absorptions with W(CaI 3934)>0.23{AA} out of 14 systems where we have appropriate wavelength coverage. The observed equivalent widths are similar to what has been measured in other lower redshift surveys of CaII systems. We detect ten NaI absorptions in the 11 systems where we could observe this absorption. The median equivalent width (W(NaI 5891)=0.68{AA}) is larger than what is observed in local clouds with similar HI column densities but also in z<0.7 CaII systems detected in the SDSS. The systematic presence of NaI absorption in these CI systems strongly suggests that the gas is neutral and cold, maybe part of the diffuse molecular gas in the interstellar medium (ISM) of high-redshift galaxies. Most of the systems (12 out of 17) have W(MgII 2796)>2.5{AA} and six of them have logN(HI)<20.3, with the extreme case of J1341+1852 that has log N(HI)=18.18. The MgII absorptions are spread over more than {Delta}v~400km/s for half of the systems; three absorbers have {Delta}v>500km/s. The kinematics are strongly perturbed for most of these systems, which indicates that these systems probably do not arise in quiet disks and must be close to regions with intense star-formation activity and/or are part of interacting objects. All this suggests that a large fraction of the cold gas at high redshift arises in disturbed environments.
- ID:
- ivo://CDS.VizieR/J/ApJ/858/60
- Title:
- z~0.8 quiescent galaxy kinematics from LEGA-C
- Short Name:
- J/ApJ/858/60
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present stellar rotation curves and velocity dispersion profiles for 104 quiescent galaxies at z=0.6-1 from the Large Early Galaxy Astrophysics Census (LEGA-C) spectroscopic survey. Rotation is typically probed across 10-20kpc, or to an average of 2.7Re. Combined with central stellar velocity dispersions ({sigma}0) this provides the first determination of the dynamical state of a sample selected by a lack of star formation activity at large lookback time. The most massive galaxies (M_*_>2x10^11^M_{sun}_) generally show no or little rotation measured at 5 kpc (|V_5_|/{sigma}_0_<0.2 in eight of ten cases), while ~64% of less massive galaxies show significant rotation. This is reminiscent of local fast- and slow- rotating ellipticals and implies that low- and high-redshift quiescent galaxies have qualitatively similar dynamical structures. We compare |V_5_|/{sigma}_0_ distributions at z~0.8 and the present day by re-binning and smoothing the kinematic maps of 91 low-redshift quiescent galaxies from the Calar Alto Legacy Integral Field Area (CALIFA) survey and find evidence for a decrease in rotational support since z~1. This result is especially strong when galaxies are compared at fixed velocity dispersion; if velocity dispersion does not evolve for individual galaxies then the rotational velocity at 5kpc was an average of 94+/-22% higher in z~0.8 quiescent galaxies than today. Considering that the number of quiescent galaxies grows with time and that new additions to the population descend from rotationally supported star-forming galaxies, our results imply that quiescent galaxies must lose angular momentum between z~1 and the present, presumably through dissipationless merging, and/or that the mechanism that transforms star-forming galaxies also reduces their rotational support.
- ID:
- ivo://CDS.VizieR/J/ApJ/778/188
- Title:
- z<0.4 sources from Chandra/SDSS
- Short Name:
- J/ApJ/778/188
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Striking similarities have been seen between accretion signatures of Galactic X-ray binary (XRB) systems and active galactic nuclei (AGNs). XRB spectral states show a V-shaped correlation between X-ray spectral hardness and Eddington ratio as they vary, and some AGN samples reveal a similar trend, implying analogous processes at vastly larger masses and timescales. To further investigate the analogies, we have matched 617 sources from the Chandra Source Catalog (CSC) to Sloan Digital Sky Survey (SDSS) spectroscopy, and uniformly measured both X-ray and optical spectral characteristics across a broad range of AGN and galaxy types. We provide useful tabulations of X-ray spectral slope for broad- and narrow-line AGNs, star-forming and passive galaxies, and composite systems, also updating relationships between optical (H{alpha} and [OIII]) line emission and X-ray luminosity. We further fit broadband spectral energy distributions with a variety of templates to estimate bolometric luminosity. Our results confirm a significant trend in AGNs between X-ray spectral hardness and Eddington ratio expressed in X-ray luminosity, albeit with significant dispersion. The trend is not significant when expressed in the full bolometric or template-estimated AGN luminosity. We also confirm a relationship between the X-ray/optical spectral slope {alpha}_ox_ and Eddington ratio, but it may not follow the trend predicted by analogy with XRB accretion states.
- ID:
- ivo://CDS.VizieR/J/ApJ/822/42
- Title:
- z~3.3 star-forming galaxies NIR spectra
- Short Name:
- J/ApJ/822/42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the relationship between stellar mass, star formation rate (SFR), ionization state, and gas-phase metallicity for a sample of 41 normal star-forming galaxies at 3<~z<~3.7. The gas-phase oxygen abundance, ionization parameter, and electron density of ionized gas are derived from rest-frame optical strong emission lines measured on near-infrared spectra obtained with Keck/Multi-Object Spectrograph for Infra-Red Exploration. We remove the effect of these strong emission lines in the broadband fluxes to compute stellar masses via spectral energy distribution fitting, while the SFR is derived from the dust-corrected ultraviolet luminosity. The ionization parameter is weakly correlated with the specific SFR, but otherwise the ionization parameter and electron density do not correlate with other global galaxy properties such as stellar mass, SFR, and metallicity. The mass-metallicity relation (MZR) at z~3.3 shows lower metallicity by ~0.7dex than that at z=0 at the same stellar mass. Our sample shows an offset by ~0.3dex from the locally defined mass-metallicity-SFR relation, indicating that simply extrapolating such a relation to higher redshift may predict an incorrect evolution of MZR. Furthermore, within the uncertainties we find no SFR-metallicity correlation, suggesting a less important role of SFR in controlling the metallicity at high redshift. We finally investigate the redshift evolution of the MZR by using the model by Lilly et al. (2013ApJ...772..119L), finding that the observed evolution from z=0 to z~3.3 can be accounted for by the model assuming a weak redshift evolution of the star formation efficiency.
