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331. High frequency peakers. The faint sample
ID:
ivo://CDS.VizieR/J/AN/330/223
Title:
High frequency peakers. The faint sample
Short Name:
J/AN/330/223
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a sample of sources with convex radio spectra peaking at frequencies above a few GHz, known as "High Frequency Peakers" (HFPs). A "bright" sample with a flux density limit of 300mJy at 5GHz has been presented by Dallacasa et al. (2000, Cat. J/A+A/363/887). Here we present the "faint" sample with flux density between 50 and 300mJy at 5GHz, restricted to the area around the North Galactic Cap, where the FIRST catalogue is available. The candidates have been observed with the VLA at several frequencies ranging from 1.4 to 22GHz, in order to derive a simultaneous radio spectrum. The final list of confirmed HFP sources consists of 61 objects.
332. High-frequency polarization of Kuehr sources
ID:
ivo://CDS.VizieR/J/A+A/415/549
Title:
High-frequency polarization of Kuehr sources
Short Name:
J/A+A/415/549
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have observed 250 of the 258 southern sources in the complete 5GHz 1Jy sample by Kuehr et al. (1981, Cat. <VIII/5>) using the Australia Telescope Compact Array (ATCA) at 18.5GHz. This paper focuses on the polarization properties of this sample, while other properties will be addressed in a future paper.
333. Highly Accreting Quasars: SDSS Low z Catalog
ID:
ivo://CDS.VizieR/J/A+A/620/A118
Title:
Highly Accreting Quasars: SDSS Low z Catalog
Short Name:
J/A+A/620/A118
Date:
21 Oct 2021
Publisher:
CDS
Description:
The most highly accreting quasars are of special interest in studies of the physics of active galactic nuclei (AGNs) and host galaxy evolution. Quasars accreting at high rates (L/LEdd~1) hold promise for use as "standard candles": distance indicators detectable at very high redshift. However, their observational properties are still largely unknown. We seek to identify a significant number of extreme accretors. A large sample can clarify the main properties of quasars radiating near L/LEdd~1 (in this paper they are designated as extreme Population A quasars or simply as extreme accretors) in the H{beta} spectral range for redshift <~0.8. We use selection criteria derived from four-dimensional Eigenvector 1 (4DE1) studies to identify and analyze spectra for a sample of 334 candidate sources identified from the SDSS DR7 database. The source spectra were chosen to show a ratio R_FeII_ between the FeII emission blend at {lambda}4570 and H{beta}, R_FeII_ > 1. Composite spectra were analyzed for systematic trends as a function of FeII strength, line width, and [OIII] strength. We introduced tighter constraints on the signal-to-noise ratio (S/N) and R_FeII_ values that allowed us to isolate sources most likely to be extreme accretors. We provide a database of detailed measurements. Analysis of the data allows us to confirm that H{beta} shows a Lorentzian function with a full width at half maximum (FWHM) of H{beta}<=4000km/s. We find no evidence for a discontinuity at 2000km/s in the 4DE1, which could mean that the sources below this FWHM value do not belong to a different AGN class. Systematic [OIII] blue shifts, as well as a blueshifted component in H{beta} are revealed. We interpret the blueshifts as related to the signature of outflowing gas from the quasar central engine. The FWHM of H{beta} is still affected by the blueshifted emission; however, the effect is non-negligible if the FWHM H{beta} is used as a "virial broadening estimator" (VBE). We emphasize a strong effect of the viewing angle on H{beta} broadening, deriving a correction for those sources that shows major disagreement between virial and concordance cosmology luminosity values. The relatively large scatter between concordance cosmology and virial luminosity estimates can be reduced (by an order of magnitude) if a correction for orientation effects is included in the FWHM H{beta} value; outflow and sample definition yield relatively minor effects.
334. High probability quasar candidates
ID:
ivo://CDS.VizieR/J/A+AS/119/265
Title:
High probability quasar candidates
Short Name:
J/A+AS/119/265
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Automated Quasar Detection (AQD) technique has been applied to six connected fields near the South Galactic Pole. A comparison with the Veron & Veron catalogue (1993) <VII/188> and the Cristiani et al. compilation (1995A&AS..112..347C) shows that AQD rediscovered ~75% of the known quasars with non-overlapping objective-prism spectra present in these fields (~40% if considering only the high degree candidates). A list of 1592 high grade candidates is given, including the results of cross-correlation with X-ray and radio catalogues.
335. 142 high-redshift blazars at the cosmic dawn
ID:
ivo://CDS.VizieR/J/ApJ/897/177
Title:
142 high-redshift blazars at the cosmic dawn
Short Name:
J/ApJ/897/177
Date:
11 Mar 2022
Publisher:
CDS
Description:
The uncharted territory of the high-redshift (z>~3) universe holds the key to understanding the evolution of quasars. In an attempt to identify the most extreme members of the quasar population, that is, blazars, we have carried out a multiwavelength study of a large sample of radio-loud quasars beyond z=3. Our sample consists of nine {gamma}-ray-detected blazars and 133 candidate blazars selected based on the flatness of their soft X-ray spectra (0.3-10keV photon index <~1.75), including 15 with Nuclear Spectroscopic Telescope Array (NuSTAR) observations. The application of the likelihood profile stacking technique reveals that the high-redshift blazars are faint {gamma}-ray emitters with steep spectra. The high-redshift blazars host massive black holes (<logM_BH,M{odot}_>>9) and luminous accretion disks (<L_disk_>>10^46^erg/s). Their broadband spectral energy distributions are found to be dominated by high-energy radiation, indicating their jets are among the most luminous ones. Focusing on the sources exhibiting resolved X-ray jets (as observed with the Chandra satellite), we find the bulk Lorentz factor to be larger with respect to other z>3 blazars, indicating faster moving jets. We conclude that the presented list of high-redshift blazars may act as a reservoir for follow-up observations, such as with NuSTAR, to understand the evolution of relativistic jets at the dawn of the universe.
336. High redshift cosmic web with quasar systems
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.
337. High-redshift MgII absorption QSOs with FIRE
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.
338. High-redshift QSOs in the COSMOS survey
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.
339. High-redshift QSOs in the SWIRE survey
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.
340. High-redshift quasar candidates
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.