- ID:
- ivo://CDS.VizieR/J/A+A/568/A46
- Title:
- High redshift cosmic web with quasar systems
- Short Name:
- J/A+A/568/A46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To understand the formation, evolution, and present-day properties of the cosmic web we need to study it at low and high redshifts. We trace the cosmic web at redshifts 1.0<z<1.8 using the quasar (QSO) data from in the SDSS DR7 QSO catalogue. We apply a friend-of-friend (FoF) algorithm to the quasar and random catalogues to determine systems at a series of linking length, and analyse richness and sizes of these systems. At the linking lengths l<=30Mpc/h, the number of quasar systems is larger than the number of systems detected in random catalogues, and the systems themselves have smaller diameters than random systems. The diameters of quasar systems are comparable to the sizes of poor galaxy superclusters in the local Universe. The richest quasar systems have four members. The mean space density of quasar systems is close to the mean space density of local rich superclusters. At intermediate linking lengths (40<=l<=70Mpc/h), the richness and length of quasar systems are similar to those derived from random catalogues. Quasar system diameters are similar to the sizes of rich superclusters and supercluster chains in the local Universe. The percolating system, which penetrate the whole sample volume appears in a quasar sample at a smaller linking length than in random samples (85Mpc/h). At the linking length 70Mpc/h, the richest systems of quasars have diameters exceeding 500Mpc. Quasar luminosities in systems are not correlated with the system richness. Quasar system catalogues in our web pages and at the Strasbourg Astronomical Data Center (CDS) serve as a database for searching for superclusters of galaxies and for tracing the cosmic web at high redshifts.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/761/112
- Title:
- High-redshift MgII absorption QSOs with FIRE
- Short Name:
- J/ApJ/761/112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present initial results from the first systematic survey for Mg II quasar absorption lines at z>2.5. Using infrared spectra of 46 high-redshift quasars, we discovered 111 Mg II systems over a path covering 1.9<z<6.3. Five systems have z>5, with a maximum of z=5.33 --the most distant Mg II system now known. The comoving Mg II line density for weaker systems (W_r_<1.0{AA}) is statistically consistent with no evolution from z=0.4 to 5.5, while that for stronger systems increases three-fold until z~3 before declining again toward higher redshifts. The equivalent width distribution, which fits an exponential, reflects this evolution by flattening as z-->3 before steepening again. The rise and fall of the strong absorbers suggests a connection to the star formation rate density, as though they trace galactic outflows or other byproducts of star formation. The weaker systems' lack of evolution does not fit within this interpretation, but may be reproduced by extrapolating low redshift scaling relations between host galaxy luminosity and absorbing halo radius to earlier epochs. For the weak systems, luminosity-scaled models match the evolution better than similar models based on Mg II occupation of evolving cold dark matter halo masses, which greatly underpredict dN/dz at early times unless the absorption efficiency of small halos is significantly larger at early times. Taken together, these observations suggest that the general structure of Mg II-bearing halos was put into place early in the process of galaxy assembly. Except for a transient appearance of stronger systems near the peak epoch of cosmic star formation, the basic properties of Mg II absorbers have evolved fairly little even as the (presumably) associated galaxy population grew substantially in stellar mass and half-light radius.
- ID:
- ivo://CDS.VizieR/J/ApJ/693/8
- Title:
- High-redshift QSOs in the COSMOS survey
- Short Name:
- J/ApJ/693/8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new measurement of the space density of high-redshift (z~3.0-4.5), X-ray-selected quasi-stellar objects (QSOs) obtained by exploiting the deep and uniform multiwavelength coverage of the COSMOS survey. We have assembled a large (40 objects), homogeneous sample of z>3 QSOs with X-ray flux F0.5-2keV>10^-15^erg/cm^2^/s, and available spectroscopic (22) or photometric (18) redshifts. We discuss their optical (color-color diagrams) and X-ray properties, their number counts and space densities and compare our findings with previous works and model predictions.
- ID:
- ivo://CDS.VizieR/J/ApJ/675/49
- Title:
- High-redshift QSOs in the SWIRE survey
- Short Name:
- J/ApJ/675/49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use a simple optical/infrared (IR) photometric selection of high-redshift QSOs that identifies a Lyman break in the optical photometry and requires a red IR color to distinguish QSOs from common interlopers. The search yields 100 z~3 (U-dropout) QSO candidates with 19<r'<22 over 11.7deg^2^ in the ELAIS-N1 (EN1) and ELAIS-N2 (EN2) fields of the Spitzer Wide-area Infrared Extragalactic (SWIRE) Legacy Survey. The z~3 selection is reliable, with spectroscopic follow-up of 10 candidates confirming that they are all QSOs at 2.83<z<3.44. We find that our z~4 (g'-dropout) sample suffers from both unreliability and incompleteness but present seven previously unidentified QSOs at 3.50<z<3.89.
- ID:
- ivo://CDS.VizieR/J/MNRAS/428/226
- Title:
- High-redshift quasar candidates
- Short Name:
- J/MNRAS/428/226
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Quasars with a high redshift (z) are important to understand the evolution processes of galaxies in the early Universe. However, only a few of these distant objects are known to this date. The costs of building and operating a 10-m class telescope limit the number of facilities and, thus, the available observation time. Therefore, an efficient selection of candidates is mandatory. This paper presents a new approach to select quasar candidates with high redshift (z>4.8) based on photometric catalogues. We have chosen to use the z>4.8 limit for our approach because the dominant Lyman {alpha} emission line of a quasar can only be found in the Sloan i- and z-band filters. As part of the candidate selection approach, a photometric redshift estimator is presented, too. Three of the 120000 generated candidates have been spectroscopically analysed in follow-up observations and a new z=5.0 quasar was found. This result is consistent with the estimated detection ratio of about 50% and we expect 60000 high-redshift quasars to be part of our candidate sample. The created candidates are available for download at MNRAS or at http://www.astro.rub.de/polsterer/quasar-candidates.csv.
- 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.
- 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.
- 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.
- 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.
- 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.
