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621. Position difference vectors and of the jets
ID:
ivo://CDS.VizieR/J/A+A/651/A64
Title:
Position difference vectors and of the jets
Short Name:
J/A+A/651/A64
Date:
22 Feb 2022
Publisher:
CDS
Description:
We aim to study the relative positions of quasar emission centers at different wavelengths in order to help link the various realizations of the International Celestial Reference System (ICRS), and to unveil systematic uncertainties and individual source behavior at different wavelengths. We based our study on four catalogs representing the ICRS, the ICRF3 positions in the three VLBI bands X, K, and Ka, and the Gaia EDR3 catalog in optical wavelengths. We complemented radio source positions with jet kinematics results from the MOJAVE team, allowing us to obtain jet directions on the sky. A six-parameter deformation model was used to remove systematic uncertainties present in the different catalogs. For a set of 194 objects common to the four catalogs and to the objects whose jet kinematics was studied by the MOJAVE team, we computed the orientation between positions at the different wavelengths and with respect to the directions of the jets. We find that the majority of these objects have their radio-to-optical vector along the jet, with the optical centroid downstream from the radio centroids, and that the K and Ka centroids are preferably upstream in the jet with respect to the X centroid, which is consistent with the paradigm of a simple core-jet model. For a population of multiwavelength positions aligned along the jet, astrometric information can therefore be used to measure the direction of the jet independently of imaging. In addition, we find several sources for which the optical centroid coincides with stationary radio features with a relatively high fraction of polarization, indicating optical emission dominated by a synchrotron process in the jet.
622. Positions of 790 AGNs
ID:
ivo://CDS.VizieR/J/A+AS/115/97
Title:
Positions of 790 AGNs
Short Name:
J/A+AS/115/97
Date:
21 Oct 2021
Publisher:
CDS
Description:
From the measurement on the Digitized Sky Survey of the optical position of 153 QSOs with an accurate VLBI position, we have determined that the r.m.s. uncertainties of these measurements is about 0.6 arcsec in both coordinates over the whole sky, except for objects located near the edge of the plates. We have measured the optical position of 790 AGNs (or AGNs candidates). For many of these objects, the accuracy of the published optical position was one arcminute or worst.
623. Positions of high-redshift luminous quasars
ID:
ivo://CDS.VizieR/VII/149
Title:
Positions of high-redshift luminous quasars
Short Name:
VII/149
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present finding charts and J2000 positions accurate to ~1" for the 528 high-redshift (z>1), luminous (M_v_<-25.5) quasars investigated in the Hubble Space Telescope Snapshot Survey. The information was produced with the Space Telescope Science Institute's Astrometric Support Program.
624. Principal Component Analysis of QSO UV spectra
ID:
ivo://CDS.VizieR/J/A+A/530/A50
Title:
Principal Component Analysis of QSO UV spectra
Short Name:
J/A+A/530/A50
Date:
21 Oct 2021
Publisher:
CDS
Description:
From a principal component analysis (PCA) of 78 z~3 high-quality quasar spectra in the SDSS-DR7 we derive the principal components that characterize the QSO continuum over the full available wavelength range. The shape of the mean continuum is similar to that measured at low-z (z~1), but the equivalent width of the emission lines is larger at low redshift. We calculate the correlation between fluxes at different wavelengths and find that the emission line fluxes in the red part of the spectrum are correlated with those in the blue part. We construct a projection matrix to predict the continuum in the Lyman{alpha} forest from the red part of the spectrum.
625. Proper motions of 555 quasars from VLBI
ID:
ivo://CDS.VizieR/J/A+A/529/A91
Title:
Proper motions of 555 quasars from VLBI
Short Name:
J/A+A/529/A91
Date:
21 Oct 2021
Publisher:
CDS
Description:
While analyzing decades of very long baseline interferometry (VLBI) data, we detected the secular aberration drift of the extragalactic radio source proper motions caused by the rotation of the Solar System barycenter around the Galactic center. Our results agree with the predicted estimate to be 4-6 micro arcseconds per year (uas/yr) towards RA=266{deg} and DE=-29{deg}. In addition, we tried to detect the quadrupole systematics of the velocity field. The analysis method consisted of three steps. First, we analyzed geodetic and astrometric VLBI data to produce radio source coordinate time series. Second, we fitted proper motions of 555 sources with long observational histories over the period 1990-2010 to their respective coordinate time series. Finally, we fitted vector spherical harmonic components of degrees 1 and 2 to the proper motion field.
626. Properties of BAL quasars
ID:
ivo://CDS.VizieR/J/MNRAS/469/3163
Title:
Properties of BAL quasars
Short Name:
J/MNRAS/469/3163
Date:
21 Oct 2021
Publisher:
CDS
Description:
We investigate broad absorption line (BAL) disappearance and emergence using a 470 BAL-quasar sample over <=0.10-5.25 rest-frame years with at least three spectroscopic epochs for each quasar from the Sloan Digital Sky Survey. We identify 14 disappearing BALs over <=1.73-4.62 rest-frame years and 18 emerging BALs over <=1.46-3.66 rest-frame years associated with the CIV{lambda}{lambda}1548,1550 and/or SiIV{lambda}{lambda}1393,1402 doublets, and report on their variability behaviour. BAL quasars in our data set exhibit disappearing/emerging C IV BALs at a rate of 2.3^+0.9^_-0.7_ and 3.0^+1.0^_-0.8_ per cent, respectively, and the frequency for BAL to non-BAL quasar transitions is 1.7^+0.8^_-0.6_ per cent. We detect four re-emerging BALs over <=3.88 rest-frame years on average and three re-disappearing BALs over <=4.15 rest-frame years on average, the first reported cases of these types. We infer BAL lifetimes along the line of sight to be nominally <=100-1000yr using disappearing CIV BALs in our sample. Interpretations of (re-)emerging and (re-)disappearing BALs reveal evidence that collectively supports both transverse-motion and ionization-change scenarios to explain BAL variations. We constrain a nominal CIV/SiIV BAL-outflow location of <=100pc from the central source and a radial size of >=1x10^-7^pc (0.02au) using the ionization-change scenario, and constrain a nominal outflow location of <=0.5pc and a transverse size of ~0.01pc using the transverse-motion scenario. Our findings are consistent with previous work, and provide evidence in support of BALs tracing compact flow geometries with small filling factors.
627. Properties of BQS objects in the SDSS DR3 area
ID:
ivo://CDS.VizieR/J/AJ/130/873
Title:
Properties of BQS objects in the SDSS DR3 area
Short Name:
J/AJ/130/873
Date:
21 Oct 2021
Publisher:
CDS
Description:
We investigate the extent to which the Palomar-Green (PG) Bright Quasar Survey (BQS) is complete and representative of the general quasar population by comparing it with imaging and spectroscopy from the Sloan Digital Sky Survey (SDSS).
628. Properties of low z QSO absorption systems
ID:
ivo://CDS.VizieR/J/ApJS/122/355
Title:
Properties of low z QSO absorption systems
Short Name:
J/ApJS/122/355
Date:
21 Oct 2021
Publisher:
CDS
Description:
(Partial): We examine the clustering properties of low-redshift Ly{alpha} and heavy-element QSO absorption line systems seen in the spectra of 13 QSOs at the Galactic poles. This is the densest sample of ~1 degree separated QSOs observed spectroscopically with the Hubble Space Telescope to date. At the median redshift of the Ly{alpha} sample (z{=~}0.7), the QSO lines of sight are separated on transverse scales from about 15 to 200h^-1^Mpc (q_0_=0.5, H=100h.km/s/Mpc), allowing the three-dimensional clustering of the absorbers to be examined on those scales. The Galactic poles are also regions where relatively deep and wide-field galaxy redshift surveys have taken place, so the distributions of galaxies and Ly{alpha} systems can be compared within the same volume of space. There are 545 total absorption lines detected in the complete sample from 13 QSOs. We identify 307 Ly{alpha} systems, of which 18 contain heavy-element lines. We confirm the relatively slow redshift number density evolution for Ly systems at z{<=}1. There are also five likely C IV doublets in our sample, for which the Ly{alpha} line is not accessible.
629. Properties of radio-loud BAL quasars
ID:
ivo://CDS.VizieR/J/MNRAS/427/1135
Title:
Properties of radio-loud BAL quasars
Short Name:
J/MNRAS/427/1135
Date:
21 Oct 2021
Publisher:
CDS
Description:
We recently presented radio observations of a large sample of radio-loud broad absorption line (BAL) quasars from the Sloan Digital Sky Survey (SDSS) and Faint Images of the Radio Sky at Twenty-cm surveys, as well as a well matched sample of unabsorbed quasars, primarily to measure their radio spectral indices and estimate ensemble orientations. Here, we analyse the SDSS spectra of these samples and compare the rest-frame ultraviolet properties of radio-loud BAL and non-BAL quasars. Ultraviolet properties include the continuum shape, emission-line measurements of CIV, AlIII, CIII], FeII and MgII, and BAL properties including the balnicity index, absorption index and minimum and maximum outflow velocities. We find that radio-loud BAL quasars have similar ultraviolet properties compared to radio-loud non-BAL sources, though they do appear to have redder continua and stronger FeII emission, which is consistent with what is found for radio-quiet BAL sources. No correlations exist between outflow properties and orientation (radio spectral index), suggesting that BAL winds along any line of sight are driven by the same mechanisms. There are also few correlations between spectral index and other properties. We conclude that BAL outflows occur along all lines of sight with similar strengths and velocities.
630. Properties of SDSS QSOs in the ChaMP
ID:
ivo://CDS.VizieR/J/ApJ/690/644
Title:
Properties of SDSS QSOs in the ChaMP
Short Name:
J/ApJ/690/644
Date:
21 Oct 2021
Publisher:
CDS
Description:
We study the spectral energy distributions and evolution of a large sample of optically selected quasars from the Sloan Digital Sky Survey that were observed in 323 Chandra images analyzed by the Chandra Multiwavelength Project. Our highest-confidence matched sample includes 1135 X-ray detected quasars in the redshift range 0.2<z<5.4, representing some 36Msec of effective exposure. We provide catalogs of QSO properties, and describe our novel method of calculating X-ray flux upper limits and effective sky coverage. Spectroscopic redshifts are available for about 1/3 of the detected sample; elsewhere, redshifts are estimated photometrically. We detect 56 QSOs with redshift z>3, substantially expanding the known sample. We find no evidence for evolution out to z~5 for either the X-ray photon index {Gamma} or for the ratio of optical/UV to X-ray flux {alpha}_ox_.