- 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.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/854/158
- Title:
- z<0.5 PG quasars IR energy distributions
- Short Name:
- J/ApJ/854/158
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The interstellar medium is crucial to understanding the physics of active galaxies and the coevolution between supermassive black holes and their host galaxies. However, direct gas measurements are limited by sensitivity and other uncertainties. Dust provides an efficient indirect probe of the total gas. We apply this technique to a large sample of quasars, whose total gas content would be prohibitively expensive to measure. We present a comprehensive study of the full (1 to 500{mu}m) infrared spectral energy distributions of 87 redshift <0.5 quasars selected from the Palomar-Green sample, using photometric measurements from 2MASS, WISE, and Herschel, combined with Spitzer mid-infrared (5-40{mu}m) spectra. With a newly developed Bayesian Markov Chain Monte Carlo fitting method, we decompose various overlapping contributions to the integrated spectral energy distribution, including starlight, warm dust from the torus, and cooler dust on galaxy scales. This procedure yields a robust dust mass, which we use to infer the gas mass, using a gas-to-dust ratio constrained by the host galaxy stellar mass. Most (90%) quasar hosts have gas fractions similar to those of massive, star-forming galaxies, although a minority (10%) seem genuinely gas-deficient, resembling present-day massive early-type galaxies. This result indicates that "quasar mode" feedback does not occur or is ineffective in the host galaxies of low-redshift quasars. We also find that quasars can boost the interstellar radiation field and heat dust on galactic scales. This cautions against the common practice of using the far-infrared luminosity to estimate the host galaxy star formation rate.
- 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/826/114
- Title:
- z~3-6 protoclusters in the CFHTLS deep fields
- Short Name:
- J/ApJ/826/114
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the discovery of three protoclusters at z~3-4 with spectroscopic confirmation in the Canada-France-Hawaii Telescope Legacy Survey Deep Fields. In these fields, we investigate the large-scale projected sky distribution of z~3-6 Lyman-break galaxies and identify 21 protocluster candidates from regions that are overdense at more than 4{sigma} overdensity significance. Based on cosmological simulations, it is expected that more than 76% of these candidates will evolve into a galaxy cluster of at least a halo mass of 10^14^ M_{sun}_ at z=0. We perform follow-up spectroscopy for eight of the candidates using Subaru/FOCAS, Keck II/DEIMOS, and Gemini-N/GMOS. In total we target 462 dropout candidates and obtain 138 spectroscopic redshifts. We confirm three real protoclusters at z=3-4 with more than five members spectroscopically identified and find one to be an incidental overdense region by mere chance alignment. The other four candidate regions at z~5-6 require more spectroscopic follow-up in order to be conclusive. A z=3.67 protocluster, which has 11 spectroscopically confirmed members, shows a remarkable core-like structure composed of a central small region (<0.5 physical Mpc) and an outskirts region (~1.0 physical Mpc). The Ly{alpha} equivalent widths of members of the protocluster are significantly smaller than those of field galaxies at the same redshift, while there is no difference in the UV luminosity distributions. These results imply that some environmental effects start operating as early as at z~4 along with the growth of the protocluster structure. This study provides an important benchmark for our analysis of protoclusters in the upcoming Subaru/HSC imaging survey and its spectroscopic follow-up with the Subaru/PFS that will detect thousands of protoclusters up to z~6.
- 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/A+A/636/A12
- Title:
- 1.4<=z<=5.0 QSOs luminosity function
- Short Name:
- J/A+A/636/A12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an estimate of the optical luminosity function (OLF) of LOFAR radio-selected quasars (RSQs) at 1.4<z<5.0 in the 9.3deg^2^ NOAO Deep Wide-field survey (NDWFS) of the Bootes field. The selection was based on optical and mid-infrared photometry used to train three different machine learning (ML) algorithms (Random forest, SVM, Bootstrap aggregation). Objects taken as quasars by the ML algorithms are required to be detected at >=5{sigma} significance in deep radio maps to be classified as candidate quasars. The optical imaging came from the Sloan Digital Sky Survey and the Pan-STARRS1 3{PI} survey; mid-infrared photometry was taken from the Spitzer Deep, Wide-Field Survey; and radio data was obtained from deep LOFAR imaging of the NDWFS-Bootes field. The requirement of a 5{sigma} LOFAR detection allowed us to reduce the stellar contamination in our sample by two orders of magnitude. The sample comprises 130 objects, including both photometrically selected candidate quasars (47) and spectroscopically confirmed quasars (83). The spectral energy distributions calculated using deep photometry available for the NDWFS-Bootes field confirm the validity of the photometrically selected quasars using the ML algorithms as robust candidate quasars. The depth of our LOFAR observations allowed us to detect the radio-emission of quasars that would be otherwise classified as radio-quiet. Around 65% of the quasars in the sample are fainter than M_1450_=-24.0, a regime where the OLF of quasars selected through their radio emission, has not been investigated in detail. It has been demonstrated that in cases where mid-infrared wedge-based AGN selection is not possible due to a lack of appropriate data, the selection of quasars using ML algorithms trained with optical and infrared photometry in combination with LOFAR data provides an excellent approach for obtaining samples of quasars. The OLF of RSQs can be described by pure luminosity evolution at z<2.4, and a combined luminosity and density evolution at z>2.4. The faint-end slope, {alpha}, becomes steeper with increasing redshift. This trend is consistent with previous studies of faint quasars (M_1450_<=-22.0). We demonstrate that RSQs show an evolution that is very similar to that exhibited by faint quasars. By comparing the spatial density of RSQs with that of the total (radio-detected plus radio-undetected) faint quasar population at similar redshifts, we find that RSQs may compose up to ~20% of the whole faint quasar population. This fraction, within uncertainties, is constant with redshift. Finally, we discuss how the compactness of the RSQs radio-morphologies and their steep spectral indices could provide valuable insights into how quasar and radio activity are triggered in these systems.
- 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/AJ/155/131
- Title:
- z~5 quasar luminosity function from the CFHTLS
- Short Name:
- J/AJ/155/131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from a spectroscopic survey of z~5 quasars in the CFHT Legacy Survey (Cat. II/317). Using both optical color selection and a likelihood method, we select 97 candidates over an area of 105 deg^2^ to a limit of i_AB_<23.2, and 7 candidates in the range 23.2<i_AB_<23.7 over an area of 18.5 deg^2^. Spectroscopic observations for 43 candidates were obtained with Gemini, MMT, and Large Binocular Telescope, of which 37 are z>4 quasars. This sample extends measurements of the quasar luminosity function ~1.5 mag fainter than our previous work in Sloan Digital Sky Survey Stripe 82. The resulting luminosity function is in good agreement with our previous results, and suggests that the faint end slope is not steep. We perform a detailed examination of our survey completeness, particularly the impact of the Ly{alpha} emission assumed in our quasar spectral models, and find hints that the observed Ly{alpha} emission from faint z~5 quasars is weaker than for z~3 quasars at a similar luminosity. Our results strongly disfavor a significant contribution of faint quasars to the hydrogen-ionizing background at z=5.
- ID:
- ivo://CDS.VizieR/J/ApJ/755/169
- Title:
- 3<z<5 quasar luminosity function in the COSMOS
- Short Name:
- J/ApJ/755/169
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the high-redshift quasar luminosity function (QLF) down to an apparent magnitude of I_AB_=25 in the Cosmic Evolution Survey (COSMOS). Careful analysis of the extensive COSMOS photometry and imaging data allows us to identify and remove stellar and low-redshift contaminants, enabling a selection that is nearly complete for type-1 quasars at the redshifts of interest. We find 155 likely quasars at z>3.1, 39 of which have prior spectroscopic confirmation. We present our sample in detail and use these confirmed and likely quasars to compute the rest-frame UV QLF in the redshift bins 3.1<z<3.5 and 3.5<z<5. The space density of faint quasars decreases by roughly a factor of four from z~3.2 to z~4, with faint-end slopes of {beta}~-1.7 at both redshifts. The decline in space density of faint optical quasars at z>3 is similar to what has been found for more luminous optical and X-ray quasars. We compare the rest-frame UV luminosity functions found here with the X-ray luminosity function at z>3, and find that they evolve similarly between z~3.2 and z~4; however, the different normalizations imply that roughly 75% of X-ray bright active galactic nuclei (AGNs) at z~3-4 are optically obscured. This fraction is higher than found at lower redshift and may imply that the obscured, type-2 fraction continues to increase with redshift at least to z~4. Finally, the implications of the results derived here for the contribution of quasars to cosmic reionization are discussed.
- 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.
