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341. High-redshift quasars in SDSS
ID:
ivo://CDS.VizieR/J/AJ/121/31
Title:
High-redshift quasars in SDSS
Short Name:
J/AJ/121/31
Date:
21 Oct 2021
Publisher:
CDS
Description:
This is the third paper in a series aimed at finding high-redshift quasars from five-color (u'g'r'i'z') imaging data taken along the celestial equator by the Sloan Digital Sky Survey (SDSS) during its commissioning phase. In this paper, we first present the observations of 14 bright, high-redshift quasars (3.66<=z<=4.77, i*<~20) discovered in the SDSS fall equatorial stripe, and the SDSS photometry of two previously known high-redshift quasars in the same region of the sky. Combined with the quasars presented in Paper I (1999AJ....118....1F) and by Schneider et al. (2001AJ....121.1232S), we define a color-selected flux-limited sample of 39 quasars at 3.6<z<5.0 and i*<~20, covering a total effective area of 182deg^2^. From this sample, we estimate the average spectral power-law slope in the rest-frame UV for quasars at z~4 to be -0.79 with a standard deviation of 0.34, and the average rest-frame equivalent width of the Ly{alpha}+N V emission line to be 69{AA} with a standard deviation of 18{AA}. Based on observations obtained with the Sloan Digital Sky Survey, with the Apache Point Observatory 3.5m telescope.
342. High-Redshift Quasars (z>=2.2) in SGP and F401
ID:
ivo://CDS.VizieR/VII/182
Title:
High-Redshift Quasars (z>=2.2) in SGP and F401
Short Name:
VII/182
Date:
21 Oct 2021
Publisher:
CDS
Description:
(Paper I) We provide details of a multicolor ( u, b_j_, v, or, r, i), wide-field, faint magnitude survey for high-redshift (z >= 2.2 ) quasars. The survey extends over the magnitude range 16<=m_or_<=20 and covers a total area of 58.6 square degrees. Sources of incompleteness in the photometric catalog are quantified, giving the survey an effective area of 45.7 square degrees. Particular attention is paid to the details of the plate-matching and image-classification procedures used in the generation of the photometric catalog from which quasars are selected, in order that the number of spurious quasar candidates be kept to an absolute minimum. The selection of candidates incorporates a number of novel features, including treating the multicolor information as low-resolution spectra, adopting a quantitative candidate identification algorithm that employs all the available information, and requiring only that objects be detected in the or passband. We describe how model quasar spectra are used to calculate the selection function for the survey, and we present the computed sample completeness, as a function of redshift and magnitude, for a range of representative quasar types. The spectroscopic results of the survey are reported in a companion paper and the derivation of the quasar luminosity function at high redshift will be reported in a third paper. (Paper II; see also documentation files "doc.tex" or "doc.txt") In a wide-field multicolor survey (45.7 deg^2^, 16.0<=m_or_<=20.0) we have discovered 130 new quasars, of which 100 are of redshift z>=2.2. There are 49 new quasars of redshift z>=3.0 including three of z>=4.0. We provide spectra, coordinates, redshifts, broad-band magnitudes (u, b_j_, v, or, r, i), line-equivalent widths for Lyman-{alpha}/NV and CIV, FWHM CIV, and continuum spectral indices for all the new quasars. The sample includes 96 quasars selected according to the rigid criteria detailed in the companion paper by Warren, Hewett, Irwin, and Osmer. These are combined with 14 previously known quasars in one of our fields, which also meet these selection criteria, to form a complete sample. The median equivalent width for Lyman-{alpha}/NV for the complete sample is 67A, and for CIV is 31{AA}. The median FWHM CIV is 35{AA} and the median spectral index is {alpha}=-0.60. The complete sample contains at least five broad absorption-line quasars. We have obtained spectra of a total of 473 multicolor selected candidates. The proportion of quasars found, including previously known quasars, of all redshifts, is 30%. The proportion of quasars of redshift z>=2.2 in the list of candidates that satisfy the selection criteria of the complete sample is 43%. Finally we limit the sample to the 85 objects of redshift z>=2.2 in the complete sample, and summarize the relevant observational data input to the calculation of the luminosity function, comprising the redshift versus magnitude distribution and the distribution of the spectral properties. The analysis of the luminosity function will be presented in a forthcoming paper.
343. High-redshift SDSS-DR5 QSOs
ID:
ivo://CDS.VizieR/J/ApJ/699/782
Title:
High-redshift SDSS-DR5 QSOs
Short Name:
J/ApJ/699/782
Date:
21 Oct 2021
Publisher:
CDS
Description:
We identify a sample of 74 high-redshift quasars (z>3) with weak UV emission lines from the Fifth Data Release of the Sloan Digital Sky Survey and present infrared, optical, and radio observations of a subsample of four objects at z>4. These weak emission-line quasars (WLQs) constitute a prominent tail of the Ly{alpha}+NV equivalent width distribution, and we compare them to quasars with more typical emission-line properties and to low-redshift active galactic nuclei with weak/absent emission lines, namely BL Lac objects. We find that WLQs exhibit hot (T~1000K) thermal dust emission and have rest-frame 0.1-5um spectral energy distributions that are quite similar to those of normal quasars. The variability, polarization, and radio properties of WLQs are also different from those of BL Lacs, making continuum boosting by a relativistic jet an unlikely physical interpretation.
344. High-z MgII absorption QSOs with FIRE. II.
ID:
ivo://CDS.VizieR/J/ApJ/764/9
Title:
High-z MgII absorption QSOs with FIRE. II.
Short Name:
J/ApJ/764/9
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a detailed study of HI and metals for 110 MgII absorption systems discovered at 1.98<=z<=5.33 in the infrared spectra of high-redshift QSOs. Using new measurements of rest-frame UV lines from optical spectra of the same targets, we compare the high-redshift sample with carefully constructed low-redshift control samples from the literature to study evolutionary trends from z=0-->5.33 (>12Gyr). We observe a significant strengthening in the characteristic N(HI) for fixed MgII equivalent width as one moves toward higher redshift. Indeed, at our sample's mean <Z>=3.402, all MgII systems are either damped Ly{alpha} absorbers (DLAs) or sub-DLAs, with 40.7% of systems exceeding the DLA threshold (compared to 16.7% at <Z>=0.927). We set lower limits on the metallicity of the MgII systems where we can measure HI; these results are consistent with the full DLA population. The classical MgII systems (W({lambda}2796)_0_=0.3-1.0{AA}), which preferentially associate with sub-DLAs, are quite metal rich at ~0.1 solar. We applied quantitative classification metrics to our absorbers to compare with low-redshift populations, finding that weak systems are similar to classic MgII absorbers at low redshift. The strong systems either have very large MgII and FeII velocity spreads implying non-virialized dynamics or are more quiescent DLAs. There is tentative evidence that the kinetically complex systems evolve in similar fashion to the global star formation rate. We speculate that if weaker MgII systems represent accreting gas as suggested by recent studies of galaxy-absorber inclinations, then their high metal abundance suggests re-accretion of recently ejected material rather than first-time infall from the metal-poor intergalactic medium, even at early times.
345. HI photoionization rate at z<0.5 for 79 QSOs
ID:
ivo://CDS.VizieR/J/MNRAS/467/3172
Title:
HI photoionization rate at z<0.5 for 79 QSOs
Short Name:
J/MNRAS/467/3172
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have developed a parallel code called the VoIgt profile Parameter Estimation Routine (VIPER) for automatically fitting the HI Ly{alpha} forest seen in the spectra of quasi-stellar objects (QSOs). We obtained the HI column density distribution function (CDDF) and linewidth (b) parameter distribution for z<0.45 using spectra of 82 QSOs obtained using the Cosmic Origins Spectrograph and VIPER. The consistency of these with existing measurements in the literature validates our code. By comparing this CDDF with those obtained from hydrodynamical simulations, we constrain the H I photoionization rate ({Gamma}_HI_) at z<0.45 in four redshift bins. VIPER, together with the Code for Ionization and Temperature Evolution (CITE), which we developed for GADGET-2, allows us to explore parameter space and perform {chi}^2^ minimization to obtain {Gamma}_HI_. We notice that the b parameters from the simulations are smaller than those derived from observations. We show that the observed b parameter distribution and b versus logNHI scatter can be reproduced in simulations by introducing subgrid-scale turbulence. However, it has very little influence on the derived {Gamma}_HI_. The {Gamma}_HI_(z) obtained here, (3.9+/-0.1)x10^-14^(1+z)^4.98+/-0.11^s^-1^, is in good agreement with the values derived by us using flux-based statistics in a previous article. These values are consistent with the hydrogen ionizing ultraviolet (UV) background being dominated mainly by QSOs, without needing any contribution from non-standard sources of UV photons.
346. HI-selected-Lyman limit system metallicities
ID:
ivo://CDS.VizieR/J/ApJ/833/270
Title:
HI-selected-Lyman limit system metallicities
Short Name:
J/ApJ/833/270
Date:
21 Oct 2021
Publisher:
CDS
Description:
We measured metallicities for 33 z=3.4-4.2 absorption line systems drawn from a sample of HI-selected-Lyman limit systems (LLSs) identified in Sloan Digital Sky Survey (SDSS) quasar spectra and stratified based on metal line features. We obtained higher-resolution spectra with the Keck Echellette Spectrograph and Imager, selecting targets according to our stratification scheme in an effort to fully sample the LLS population metallicity distribution. We established a plausible range of HI column densities and measured column densities (or limits) for ions of carbon, silicon, and aluminum, finding ionization-corrected metallicities or upper limits. Interestingly, our ionization models were better constrained with enhanced {alpha}-to-aluminum abundances, with a median abundance ratio of [{alpha}/Al]=0.3. Measured metallicities were generally low, ranging from [M/H]=-3 to -1.68, with even lower metallicities likely for some systems with upper limits. Using survival statistics to incorporate limits, we constructed the cumulative distribution function (CDF) for LLS metallicities. Recent models of galaxy evolution propose that galaxies replenish their gas from the low-metallicity intergalactic medium (IGM) via high-density HI "flows" and eject enriched interstellar gas via outflows. Thus, there has been some expectation that LLSs at the peak of cosmic star formation (z~3) might have a bimodal metallicity distribution. We modeled our CDF as a mix of two Gaussian distributions, one reflecting the metallicity of the IGM and the other representative of the interstellar medium of star-forming galaxies. This bimodal distribution yielded a poor fit. A single Gaussian distribution better represented the sample with a low mean metallicity of [M/H]~-2.5.
347. HI-selected Lyman limit systems metallicities
ID:
ivo://CDS.VizieR/J/ApJ/833/283
Title:
HI-selected Lyman limit systems metallicities
Short Name:
J/ApJ/833/283
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the first results from our KODIAQ Z survey aimed at determining the metallicity distribution and physical properties of the z>~2 partial and full Lyman limit systems (pLLSs and LLSs; 16.2<=logN_HI_<19), which are probed of the interface regions between the intergalactic medium (IGM) and galaxies. We study 31 HI-selected pLLSs and LLSs at 2.3<z<3.3 observed with Keck/HIRES in absorption against background QSOs. We compare the column densities of metal ions to HI and use photoionization models to assess the metallicity. The metallicity distribution of the pLLSs/LLSs at 2.3<z<3.3 is consistent with a unimodal distribution peaking at [X/H]~-2. The metallicity distribution of these absorbers therefore evolves markedly with z since at z<~1 it is bimodal with peaks at [X/H]~-1.8 and -0.3. There is a substantial fraction (25%-41%) of pLLSs/LLSs with metallicities well below those of damped Ly{alpha} absorbers (DLAs) at any studied z from z<~1 to z~2-4, implying reservoirs of metal-poor, cool, dense gas in the IGM/galaxy interface at all z. However, the gas probed by pLLSs and LLSs is rarely pristine, with a fraction of 3%-18% for pLLSs/LLSs with [X/H]<=-3. We find C/{alpha} enhancement in several pLLSs and LLSs in the metallicity range -2<~[X/H]<~-0.5, where C/{alpha} is 2-5 times larger than observed in Galactic metal-poor stars or high-redshift DLAs at similar metallicities. This is likely caused by preferential ejection of carbon from metal-poor galaxies into their surroundings.
348. Historic light curves of 3 known blazars
ID:
ivo://CDS.VizieR/J/AJ/139/2425
Title:
Historic light curves of 3 known blazars
Short Name:
J/AJ/139/2425
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the historic photographic light curves of three little known blazars (two BL Lac objects and one FSRQ), GB6 J1058+5628, GB6 J1148+5254, and GB6 J1209+4119, spanning a time interval of about 50 years, mostly built using the Asiago plate archive. All objects show evident long-term variability, over which short-term variations are superposed. One source, GB6 J1058+5628, showed a marked quasi-periodic variability of 1mag on timescale of about 6.3 years, making it one of the few BL Lac objects with a quasi-periodic behavior.
349. Hopkins Ultraviolet Telescope
ID:
ivo://archive.stsci.edu/hut
Title:
Hopkins Ultraviolet Telescope
Short Name:
HUT
Date:
22 Jul 2020 21:30:05
Publisher:
Space Telescope Science Institute Archive
Description:
The Hopkins Ultraviolet Telescope (HUT) was a shuttle-borne instrument used to obtain ultraviolet spectra in the far ultraviolet region of the spectrum. It was part of the ASTRO payload complement of three co-mounted instruments that flew in December 1990 and March 1995 as Space Shuttle missions. More than 650 spectra were obtained of 340 targets. In April, 2013, the HUT data was reprocessed to improve calibration, expand metadata, add new data products, and update file formats. The current cone service uses the metadata from these reprocessed files.
350. Host galaxies of 2MASS-QSOs with z<=3
ID:
ivo://CDS.VizieR/J/AJ/126/63
Title:
Host galaxies of 2MASS-QSOs with z<=3
Short Name:
J/AJ/126/63
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present and discuss optical imaging of 76 active galactic nuclei (AGNs) that represent the selected Two Micron All Sky Survey (2MASS) sample for z<0.3, from a full list of 243. They are found to have dust-obscured nuclei, residing in host galaxies that show a high fraction (greater than 70%) of tidal interactions. The derived luminosities of the AGNs and host galaxies are similar to traditionally selected AGNs, and they may comprise some 40% of the total AGN population at low redshift. We have measured a number of host galaxy properties and discuss their distributions and interrelations. We compare the 2MASS AGNs with optically selected samples and the IRAS-selected galaxy samples and discuss the differences in terms of merger processes and initial conditions.