Search

Start Over Subject quasars
751. Redshift catalog of HE 0435-1223 field-of-view
ID:
ivo://CDS.VizieR/J/MNRAS/470/4838
Title:
Redshift catalog of HE 0435-1223 field-of-view
Short Name:
J/MNRAS/470/4838
Date:
21 Oct 2021
Publisher:
CDS
Description:
Galaxies located in the environment or along the line of sight towards gravitational lenses can significantly affect lensing observables, and can lead to systematic errors on the measurement of H_0_ from the time-delay technique. We present the results of a systematic spectroscopic identification of the galaxies in the field of view of the lensed quasar HE 0435-1223 using the W.M. Keck, Gemini and ESO-Very Large telescopes. Our new catalogue triples the number of known galaxy redshifts in the direct vicinity of the lens, expanding to 102 the number of measured redshifts for galaxies separated by less than 3 arcmin from the lens. We complement our catalogue with literature data to gather redshifts up to 15 arcmin from the lens, and search for galaxy groups or clusters projected towards HE 0435-1223. We confirm that the lens is a member of a small group that includes at least 12 galaxies, and find 8 other group candidates near the line of sight of the lens. The flexion shift, namely the shift of lensed images produced by high-order perturbation of the lens potential, is calculated for each galaxy/group and used to identify which objects produce the largest perturbation of the lens potential. This analysis demonstrates that (i) at most three of the five brightest galaxies projected within 12 arcsec of the lens need to be explicitly used in the lens models, and (ii) the groups can be treated in the lens model as an external tidal field (shear) contribution.
752. Redshift dependence of BAL QSOs
ID:
ivo://CDS.VizieR/J/MNRAS/410/860
Title:
Redshift dependence of BAL QSOs
Short Name:
J/MNRAS/410/860
Date:
21 Oct 2021
Publisher:
CDS
Description:
We describe the application of non-negative matrix factorization to generate compact reconstructions of quasar spectra from the Sloan Digital Sky Survey (SDSS), with particular reference to broad absorption line quasars (BALQSOs). BAL properties are measured for SiIV{lambda}1400, CIV{lambda}1550, AlIII{lambda}1860 and MgII{lambda}2800, resulting in a catalogue of 3547 BALQSOs. Two corrections, based on extensive testing of synthetic BALQSO spectra, are applied in order to estimate the intrinsic fraction of CIV BALQSOs. First, the probability of an observed BALQSO spectrum being identified as such by our algorithm is calculated as a function of redshift, signal-to-noise ratio and BAL properties. Secondly, the different completenesses of the SDSS target selection algorithm for BALQSOs and non-BAL quasars are quantified.
753. Redshifts for X-ray selected AGNs
ID:
ivo://CDS.VizieR/J/A+A/434/475
Title:
Redshifts for X-ray selected AGNs
Short Name:
J/A+A/434/475
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present photometric redshift estimates for X-ray selected sources detected in the XMM/2dF survey. 5-band photometry for 193 sources has been obtained from the SDSS. We exclude 10 sources associated with Galactic stars. The tabulated data include the optical coordinate of all sources in our sample, their photometric redshift estimate, their r-band magnitude and g-r colour as well as their morphological classification (these optical parameters have been used in the discussion of our results). Spectroscopic redshifts are available only for a sub-sample of our data and are included in Table 1 together with the survey from which they have been obtained.
754. Redshifts in the SFQS survey
ID:
ivo://CDS.VizieR/J/AJ/131/2788
Title:
Redshifts in the SFQS survey
Short Name:
J/AJ/131/2788
Date:
21 Oct 2021
Publisher:
CDS
Description:
In this paper we present the first results of a deep spectroscopic survey of faint quasars in the Sloan Digital Sky Survey (SDSS) Southern Survey, a deep survey carried out by repeatedly imaging a 270{deg}^2^ area. Quasar candidates were selected from the deep data with good completeness over 0<z<5 and 2-3mag fainter than the SDSS main survey. Spectroscopic follow-up was carried out on the 6.5m MMT with Hectospec. The preliminary sample of this SDSS faint quasar survey (SFQS) covers ~3.9{deg}^2^, contains 414 quasars, and reaches g=22.5.
755. Redshifts of damped Lyman{alpha} absorbers
ID:
ivo://CDS.VizieR/J/MNRAS/346/1103
Title:
Redshifts of damped Lyman{alpha} absorbers
Short Name:
J/MNRAS/346/1103
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a study of the evolution of the column density distribution, f(N,z), and total neutral hydrogen mass in high column density quasar absorbers using candidates from a recent high-redshift survey for damped Lyman{alpha} (DLA) and Lyman-limit system (LLS) absorbers.
756. Redshift survey in 15 quasar fields
ID:
ivo://CDS.VizieR/J/MNRAS/367/1261
Title:
Redshift survey in 15 quasar fields
Short Name:
J/MNRAS/367/1261
Date:
21 Oct 2021
Publisher:
CDS
Description:
We investigate the relative distribution of the gaseous contents of the Universe (as traced by a sample of Ly{alpha} absorbers), and the luminous baryonic matter (as traced by a redshift survey of galaxies in the same volume searched for Ly{alpha} absorbers), along 16 lines of sight (LOS) between redshifts 0 and 1. Our galaxy redshift survey was made with the multi-object spectrograph on the Canada-France-Hawaii Telescope and, when combined with galaxies from the literature in the same LOS, gives us a galaxy sample of 636 objects. By combining this with an absorption-line sample of 406 absorbing systems drawn from published works, we are able to study the relationship between gas and galaxies over the latter half of the age of the Universe.
757. Relativistic jets from black hole systems
ID:
ivo://CDS.VizieR/J/other/Sci/338.1445
Title:
Relativistic jets from black hole systems
Short Name:
J/other/Sci/338.
Date:
21 Oct 2021
Publisher:
CDS
Description:
Black holes generate collimated, relativistic jets, which have been observed in {gamma}-ray bursts (GRBs), microquasars, and at the center of some galaxies [active galactic nuclei (AGN)]. How jet physics scales from stellar black holes in GRBs to the supermassive ones in AGN is still unknown. Here, we show that jets produced by AGN and GRBs exhibit the same correlation between the kinetic power carried by accelerated particles and the {gamma}-ray luminosity, with AGN and GRBs lying at the low- and high-luminosity ends, respectively, of the correlation. This result implies that the efficiency of energy dissipation in jets produced in black hole systems is similar over 10 orders of magnitude in jet power, establishing a physical analogy between AGN and GRBs.
758. Relativistic jets in the RRFID database
ID:
ivo://CDS.VizieR/J/AJ/133/2357
Title:
Relativistic jets in the RRFID database
Short Name:
J/AJ/133/2357
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of an analysis of relativistic jet apparent speeds from VLBI images in the Radio Reference Frame Image Database (RRFID). The images are snapshot VLBI images at 8 and 2GHz using the VLBA, plus up to 10 additional antennas that provide global VLBI coverage. We have analyzed the 8GHz images from the first 5 years of the database (1994-1998), for all sources observed at three or more epochs during this time range. This subset comprises 966 images of 87 sources. The sources in this subset have an average of 11 epochs of observation over the years 1994-1998, with the best-observed sources having 19 epochs. About half of the sources in this RRFID kinematic survey have not been previously studied with multi-epoch VLBI observations. We have measured apparent speeds for a total of 184 jet components in 77 sources, of which the best-measured 94 component speeds in 54 sources are used in the final analysis.
759. Relativistic jets in the RRFID database. II. 10yr
ID:
ivo://CDS.VizieR/J/ApJ/758/84
Title:
Relativistic jets in the RRFID database. II. 10yr
Short Name:
J/ApJ/758/84
Date:
21 Oct 2021
Publisher:
CDS
Description:
We analyze blazar jet apparent speeds and accelerations from the RDV series of astrometric and geodetic very long baseline interferometry (VLBI) experiments. From these experiments, we have produced and analyzed 2753 global VLBI images of 68 sources at 8GHz with a median beam size of 0.9 milliarcseconds (mas) and a median of 43 epochs per source. From this sample, we analyze the motions of 225 jet components in 66 sources. The distribution of the fastest measured apparent speed in each source has a median of 8.3c and a maximum of 44c. Sources in the 2FGL Fermi LAT catalog display higher apparent speeds than those that have not been detected. On average, components farther from the core in a given source have significantly higher apparent speeds than components closer to the core; for example, for a typical source, components at ~3mas from the core (~15pc projected at z~0.5) have apparent speeds about 50% higher than those of components at ~1mas from the core (~5pc projected at z~0.5). We measure accelerations of components in orthogonal directions parallel and perpendicular to their average velocity vector. Parallel accelerations have significantly larger magnitudes than perpendicular accelerations, implying that observed accelerations are predominantly due to changes in the Lorentz factor (bulk or pattern) rather than projection effects from jet bending. Positive parallel accelerations are significantly more common than negative ones, so the Lorentz factor (bulk or pattern) tends to increase on the scales observed here. Observed parallel accelerations correspond to modest source frame increases in the bulk or pattern Lorentz factor.
760. REQUIEM survey. I. Ly{alpha} halos around QSOs
ID:
ivo://CDS.VizieR/J/ApJ/887/196
Title:
REQUIEM survey. I. Ly{alpha} halos around QSOs
Short Name:
J/ApJ/887/196
Date:
21 Oct 2021
Publisher:
CDS
Description:
The discovery of quasars a few hundred megayears after the Big Bang represents a major challenge to our understanding of black holes as well as galaxy formation and evolution. Quasars' luminosity is produced by extreme gas accretion onto black holes, which have already reached masses of M_BH_>10^9^M_{sun}_ by z~6. Simultaneously, their host galaxies form hundreds of stars per year, using up gas in the process. To understand which environments are able to sustain the rapid formation of these extreme sources, we started a Very Large Telescope/Multi-Unit Spectroscopic Explorer (MUSE) effort aimed at characterizing the surroundings of a sample of 5.7<z<6.6 quasars, which we have dubbed the Reionization Epoch QUasar InvEstigation with MUSE (REQUIEM) survey. We here present results of our searches for extended Ly{alpha} halos around the first 31 targets observed as part of this program. Reaching 5{sigma} surface brightness limits of 0.1-1.1x10^-17^erg/s/cm^2^/arcsec^2^ over a 1arcsec^2^ aperture, we were able to unveil the presence of 12 Ly{alpha} nebulae, eight of which are newly discovered. The detected nebulae show a variety of emission properties and morphologies with luminosities ranging from 8x10^42^ to 2x10^44^erg/s, FWHMs between 300 and 1700km/s, sizes <30pkpc, and redshifts consistent with those of the quasar host galaxies. As the first statistical and homogeneous investigation of the circumgalactic medium of massive galaxies at the end of the reionization epoch, the REQUIEM survey enables the study of the evolution of the cool gas surrounding quasars in the first 3Gyr of the universe. A comparison with the extended Ly{alpha} emission observed around bright (M_1450_<~-25mag) quasars at intermediate redshift indicates little variations on the properties of the cool gas from z~6 to z~3, followed by a decline in the average surface brightness down to z~2.