Search

Start Over Subject quasars
651. QSO luminosity function at z~4
ID:
ivo://CDS.VizieR/J/ApJ/710/1498
Title:
QSO luminosity function at z~4
Short Name:
J/ApJ/710/1498
Date:
21 Oct 2021
Publisher:
CDS
Description:
The evolution of the quasar luminosity function (QLF) is one of the basic cosmological measures providing insight into structure formation and mass assembly in the universe. We have conducted a spectroscopic survey to find faint quasars (-26.0<M_1450_<-22.0) at redshifts z=3.8-5.2 in order to measure the faint end of the QLF at these early times. Using available optical imaging data from portions of the NOAO Deep Wide-Field Survey and the Deep Lens Survey, we have color-selected quasar candidates in a total area of 3.76deg^2^. Thirty candidates have R<=23mag. We conducted spectroscopic follow-up for 28 of our candidates and found 23 QSOs, 21 of which are reported here for the first time, in the 3.74<z<5.06 redshift range.
652. QSO MgII absorption line systems
ID:
ivo://CDS.VizieR/J/AJ/106/848
Title:
QSO MgII absorption line systems
Short Name:
J/AJ/106/848
Date:
21 Oct 2021
Publisher:
CDS
Description:
The results of a large R-band imaging survey of 71 bright (m(V)<18) quasars are presented. The quasars were chosen from published samples which have intermediate resolution optical spectroscopy available, so the presence of low redshift Mg II absorption lines can be determined. We have searched our data for galaxies close to the line-of-sight to the quasars, which we might be able to identify with the absorption systems. We find a high coincidence between galaxies very near the line-of-sight and quasars showing absorption systems in their spectra, a result consistent with other studies. These galaxies have a mean luminosity of 0.5L_star_ (assuming they lie at the absorption redshift). The distribution of impact parameters between the galaxies and the quasars extends with a flat distribution to large radii (>30h^-1^kpc). This suggests that the absorption systems may not be gravitationally bound to the observed galaxies, but may be part of larger extended systems. We also find a significant number of galaxies near the line-of-sight to the quasar where no absorption is seen in the quasar spectrum. The selection of our quasars is unbiased with respect to galaxies near the line-of-sight, so we can compare the observed number of absorption systems to that predicted by a simple model with a constant covering factor in Mg II absorbing gas within a maximum radius of each detected galaxy. The model is consistent with a covering factor of unity, but allowing for incompleteness in the detection of galaxies, the covering factor is less than unity. The redshifts of the galaxies are required to confirm this result.
653. QSO 2237+0305 photometry and light curves
ID:
ivo://CDS.VizieR/J/A+A/637/A89
Title:
QSO 2237+0305 photometry and light curves
Short Name:
J/A+A/637/A89
Date:
21 Oct 2021
Publisher:
CDS
Description:
Quasar microlensing offers a unique opportunity to resolve tiny sources in distant active galactic nuclei and study compact object populations in lensing galaxies. We therefore searched for microlensing-induced variability of the gravitationally lensed quasar QSO 2237+0305 (Einstein Cross) using 4374 optical frames taken with the 2.0m Liverpool Telescope and the 1.5m Maidanak Telescope. These gVrRI frames over the 2006-2019 period were homogeneously processed to generate accurate long-term multi-band light curves of the four quasar images A-D. Through difference light curves, we found strong microlensing signatures. We then focused on the analytical modelling of two putative caustic-crossing events in image C, finding compelling evidence that this image experienced a double caustic crossing. Additionally, our overall results indicate that a standard accretion disc accounts reasonably well for the brightness profile of UV continuum emission sources and for the growth in source radius when the emission wavelength increases: R_{lambda}_{prop.to}{lambda}^{alpha}^, {alpha}=1.33+/-0.09. However, we caution that numerical microlensing simulations are required before firm conclusions can be reached on the UV emission scenario because the VRI-band monitoring during the first caustic crossing and one of our two {alpha} indicators lead to a few good solutions with {alpha}~~1.
654. QSO properties from SDSS-DR7
ID:
ivo://CDS.VizieR/J/ApJS/194/45
Title:
QSO properties from SDSS-DR7
Short Name:
J/ApJS/194/45
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a compilation of properties of the 105783 quasars in the Sloan Digital Sky Survey Data Release 7 (DR7) quasar catalog (Cat. VII/260). In this product, we compile continuum and emission line measurements around the H{alpha}, H{beta}, MgII, and CIV regions, as well as other quantities such as radio properties, and flags indicating broad absorption line quasars, disk emitters, etc. We also compile virial black hole mass estimates based on various calibrations. For the fiducial virial mass estimates we use the Vestergaard & Peterson (VP06; 2006ApJ...641..689V) calibrations for H{beta} and CIV, and our own calibration for MgII which matches the VP06 H{beta} masses on average. We describe the construction of this catalog and discuss its limitations.
655. QSOs and RR Lyrae in Pan-STARRS1 3{pi} Data
ID:
ivo://CDS.VizieR/J/ApJ/817/73
Title:
QSOs and RR Lyrae in Pan-STARRS1 3{pi} Data
Short Name:
J/ApJ/817/73
Date:
21 Oct 2021
Publisher:
CDS
Description:
In area and depth, the Pan-STARRS1 (PS1) 3{pi} survey is unique among many-epoch, multi-band surveys and has enormous potential for the all-sky identification of variable sources. PS1 has observed the sky typically seven times in each of its five bands (grizy) over 3.5 years, but unlike SDSS, not simultaneously across the bands. We developed a new approach for quantifying statistical properties of non-simultaneous, sparse, multi-color light curves through light curve structure functions, effectively turning PS1 into a {sim}35-epoch survey. We use this approach to estimate variability amplitudes and timescales for point sources brighter than r_P1_=21.5 mag in the survey. On this basis we provide a catalog of all likely variable point sources and likely QSOs in PS1.
656. QSOs at z~6 spectral cubes
ID:
ivo://CDS.VizieR/J/A+A/631/A78
Title:
QSOs at z~6 spectral cubes
Short Name:
J/A+A/631/A78
Date:
21 Oct 2021
Publisher:
CDS
Description:
Outflows in quasars during the early epochs of galaxy evolution are an important part of the feedback mechanisms potentially affecting the evolution of the host galaxy. However, systematic observations of outflows are only now becoming possible with the advent of sensitive mm telescopes. In this study we use spectral stacking methods to search for faint high velocity outflow signal in a sample of [CII] detected, z~6 quasars. We search for broad emission line signatures from high-velocity outflows for a sample of 26 z~6 quasars observed with ALMA, with a detection of the [CII] line. The observed emission lines of the sources are dominated by the host galaxy, and outflow emission is not detected for the individual sources. We use a spectral line stacking analysis developed for interferometric data to search for outflow emission. We stack both extracted spectra and the full spectral cubes. We also investigate the possibility that only a sub-set of our sample contributes to the stacked outflow emission. We find only a tentative detection of a broad emission line component in the stacked spectra. When taking a region of about 2 arcsec around the source central position of the stacked cubes, the stacked line shows an excess emission due to a broad component of 1.1-1.5 sigma, but the significance drops to 0.4-0.7 sigma when stacking the extracted spectra from a smaller region. The broad component can be characterised by a line width of full width half max FWHM > 700 km/s. Furthermore, we find a sub-sample of 12 sources the stack of which maximises the broad component emission. The stack of this sub-sample shows an excess emission due to a broad component of 1.2-2.5 sigma. The stacked line of these sources has a broad component of FWHM>775km/s. Deeper ALMA observations are necessary to confirm the presence of a broad component in the individual spectra.
657. QSOs CaII absorbers
ID:
ivo://CDS.VizieR/J/A+A/528/A12
Title:
QSOs CaII absorbers
Short Name:
J/A+A/528/A12
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a systematic study of weak intervening CaII absorbers at low redshift (z<0.5), based on the analysis of archival high-resolution (R>=45000) optical spectra of 304 quasars and active galactic nuclei observed with VLT/UVES. Along a total redshift path of {DELTA}z~~100 we detected 23 intervening CaII absorbers in both the CaII H & K lines, with rest frame equivalent widths W_r,3934_=15-799m{AA} and column densities logN(CaII)=11.25-13.04 (obtained by fitting Voigt-profile components).
658. QSO selection based on photometric variability
ID:
ivo://CDS.VizieR/J/ApJ/728/26
Title:
QSO selection based on photometric variability
Short Name:
J/ApJ/728/26
Date:
21 Oct 2021
Publisher:
CDS
Description:
We develop a method for separating quasars from other variable point sources using Sloan Digital Sky Survey (SDSS) Stripe 82 light-curve data for ~10000 variable objects. To statistically describe quasar variability, we use a damped random walk (DRW) model parametrized by a damping timescale, {tau}, and an asymptotic amplitude (structure function), SF_{infinite}_. With the aid of an SDSS spectroscopically confirmed quasar sample, we demonstrate that variability selection in typical extragalactic fields with low stellar density can deliver complete samples with reasonable purity (or efficiency, E). Compared to a selection method based solely on the slope of the structure function, the inclusion of the {tau} information boosts E from 60% to 75% while maintaining a highly complete sample (98%) even in the absence of color information. For a completeness of C=90%, E is boosted from 80% to 85%. Conversely, C improves from 90% to 97% while maintaining E=80% when imposing a lower limit on {tau}. With the aid of color selection, the purity can be further boosted to 96%, with C=93%. Hence, selection methods based on variability will play an important role in the selection of quasars with data provided by upcoming large sky surveys, such as Pan-STARRS and the Large Synoptic Survey Telescope (LSST). In summary, given an adequate survey cadence, photometric variability provides an even better method than color selection for separating quasars from stars.
659. QSOs in 2MASS second incremental data release
ID:
ivo://CDS.VizieR/J/AJ/121/2843
Title:
QSOs in 2MASS second incremental data release
Short Name:
J/AJ/121/2843
Date:
21 Oct 2021
Publisher:
CDS
Description:
Using the 2MASS Second Incremental Data Release (Cat. <B/2mass>), we have searched for near-infrared counterparts to 13214 quasars from the Veron-Cetty & Veron (Cat. <VII/215>) catalog. We have detected counterparts within 4" for 2277 of the approximately 6320 quasars within the area covered by the 2MASS Second Incremental Data Release. Only 1.6% of these are expected to be chance coincidences. Though this sample is heterogeneous, we find that known radio-loud quasars are more likely to have large near-infrared-to-optical luminosity ratios than radio-quiet quasars are, at a statistically significant level. This is consistent with dust-reddened quasars being more common in radio-selected samples than in optically selected samples, due to stronger selection effects against dust-reddened quasars in the latter. We also find a statistically significant dearth of optically luminous quasars with large near-infrared-to-optical luminosity ratios. This can be explained in a dust obscuration model but not in a model where synchrotron emission extends from the radio into the near-infrared and creates such large ratios. We also find that selection of quasar candidates from the B-J/J-K color-color diagram, modeled on the V-J/J-K selection method of Warren, Hewett, & Foltz, is likely to be more sensitive to dust-obscured quasars than selection using only infrared-infrared colors.
660. QSOs in the M3 field
ID:
ivo://CDS.VizieR/J/A+A/392/851
Title:
QSOs in the M3 field
Short Name:
J/A+A/392/851
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results from a variability and proper motion (VPM) search for QSOs in the field around M3. The VPM search is demonstrated to be powerful technique for efficiently finding QSOs without major selection effects with regard to the spectral energy distribution. Remarkably, the properties of the VPM QSOs do not significantly differ from those of samples from more conventional optical search techniques. The lightcurves of the QSOs from the resulting sample provide an interesting data set for the statistical investigation of QSO long-term variability.