- ID:
- ivo://CDS.VizieR/J/MNRAS/435/482
- Title:
- DLA system from SDSS DR5
- Short Name:
- J/MNRAS/435/482
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the chemical abundance measurements of the first large, medium-resolution, uniformly selected damped Lyman {alpha} system (DLA) survey. The sample contains 99 DLAs towards 89 quasars selected from the SDSS DR5 DLA sample in a uniform way. We analyse the metallicities and kinematic diagnostics, including the velocity width of 90 percent of the optical depth, {Delta}V_90_, and the equivalent widths of the SiII {lambda}1526 (W}{lambda}1526), CIV {lambda}1548 and MgII {lambda}2796 transitions. To avoid strong line-saturation effects on the metallicities measured in medium-resolution spectra (FWHM~71km/s), we derived metallicities from metal transitions which absorbed at most 35 percent of the quasar continuum flux. We find the evolution in cosmic mean metallicity of the sample, <Z>=(-0.04+/-0.13)z-(1.06+/-0.36), consistent with no evolution over the redshift range z~[2.2, 4.4], but note that the majority of our sample falls at z~[2.2, 3.5]. The apparent lack of metallicity evolution with redshift is also seen in a lack of evolution in the median {Delta}V_90_ and W{lambda}1526 values. While this result may seem to conflict with other large surveys that have detected significant metallicity evolution, such as Rafelski et al. who found <Z>=(-0.22+/-0.03)z-(0.65+/-0.09) over z~[0, 5], several tests show that these surveys are not inconsistent with our new result. However, over the smaller redshift range covered by our uniformly selected sample, the true evolution of the cosmic mean metallicity in DLAs may be somewhat flatter than the Rafelski et al. (2012ApJ...755...89R, Cat. J/ApJ/755/89) estimate.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/131/666
- Title:
- Double-lobed radio quasars from the SDSS
- Short Name:
- J/AJ/131/666
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have combined a sample of 44,984 quasars selected from the Sloan Digital Sky Survey (SDSS) Data Release 3 (Cat. <II/259>) with the FIRST radio survey (Cat. <VIII/71>). Using a novel technique in which the optical quasar position is matched to the complete radio environment within 450", we are able to characterize the radio morphological make-up of what is essentially an optically selected quasar sample, regardless of whether the quasar (nucleus) itself has been detected in the radio.
- ID:
- ivo://CDS.VizieR/J/ApJ/693/1554
- Title:
- Double QSOs: merger scenarios
- Short Name:
- J/ApJ/693/1554
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze the available sample of double quasars, and investigate their physical properties. Our sample comprises 85 pairs, selected from the Sloan Digital Sky Survey (SDSS). We derive physical parameters for the engine and the host, and model the dynamical evolution of the pair. First, we compare different scaling relationships between massive black holes and their hosts (bulge mass, velocity dispersion, and their possible redshift dependences), and discuss their consistency. We then compute dynamical friction timescales for the double quasar systems to investigate their frequency and their agreement with the "merger driven" scenario for quasar triggering.
- ID:
- ivo://CDS.VizieR/J/ApJ/697/182
- Title:
- Dust emission from unobscured AGN
- Short Name:
- J/ApJ/697/182
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use mid-infrared (MIR) spectroscopy of unobscured active galactic nuclei (AGNs) to reveal their native dusty environments. We concentrate on Seyfert 1 galaxies, observing a sample of 31 with the Infrared Spectrograph aboard the Spitzer Space Telescope, and compare them with 21 higher luminosity quasar counterparts.
- ID:
- ivo://CDS.VizieR/J/A+A/591/A130
- Title:
- Dynamic SEDs of southern blazars - DSSB
- Short Name:
- J/A+A/591/A130
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Simultaneous broadband spectral and temporal studies of blazars are an important tool for investigating active galactic nuclei (AGN) jet physics. We study the spectral evolution between quiescent and flaring periods of 22 radio-loud AGN through multiepoch, quasi-simultaneous broadband spectra. For many of these sources these are the first broadband studies. We use a Bayesian block analysis of Fermi/LAT light curves to determine time ranges of constant flux for constructing quasi-simultaneous spectral energy distributions (SEDs). The shapes of the resulting 81 SEDs are described by two logarithmic parabolas and a blackbody spectrum where needed.
- ID:
- ivo://CDS.VizieR/J/ApJ/657/706
- Title:
- EGRET blazar gamma-ray spectrum
- Short Name:
- J/ApJ/657/706
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma-Ray Observatory (CGRO) discovered gamma-ray emission from more than 67 blazars during its 9yr lifetime. We conducted an exhaustive search of the EGRET archives and selected all the blazars that were observed multiple times and were bright enough to enable a spectral analysis using standard power-law models. The sample consists of 18 flat-spectrum radio quasars (FSRQs), 6 low-frequency peaked BL Lac objects (LBLs) and 2 high-frequency peaked BL Lac objects (HBLs). We do not detect any clear pattern in the variation of spectral index with flux. Some of the blazars do not show any statistical evidence for spectral variability.
- ID:
- ivo://CDS.VizieR/J/ApJ/671/1355
- Title:
- EGRET blazars in VIPS
- Short Name:
- J/ApJ/671/1355
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine the radio properties of EGRET-detected blazars observed as part of the VLBA Imaging and Polarimetry Survey (VIPS). VIPS has a flux limit roughly an order of magnitude below the MOJAVE survey and most other samples that have been used to study the properties of EGRET blazars. At lower flux levels, radio flux density does not directly correlate with gamma-ray flux density. We do find that the EGRET-detected blazars tend to have higher brightness temperatures, greater core fractions, and possibly larger than average jet opening angles. A weak correlation is also found with jet length and with polarization. All of the well-established trends can be explained by systematically larger Doppler factors in the gamma-ray-loud blazars, consistent with the measurements of higher apparent velocities found in monitoring programs carried out at radio frequencies above 10 GHz.
- ID:
- ivo://CDS.VizieR/J/ApJS/92/53
- Title:
- Einstein database of quasars. I.
- Short Name:
- J/ApJS/92/53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first volume of the Einstein quasar database. The database includes estimates of the X-ray count rates, fluxes, and luminosities for 514 quasars and Seyfert 1 galaxies observed with the Imaging Proportional Counter (IPC) aboard the Einstein Observatory. All were previously known optically selected or radio-selected objects, and most were targets of the X-ray observations. The X-ray properties of the AGNs have been derived by reanalyzing the IPC data in a systematic manner to provide a uniform database for general use by the astronomical community. We use the database to extend earlier quasar luminosity studies which were made using only a subset of the currently available data. The database can be accessed on Internet via the SAO Einstein on-line system ("Einline") and is available in ASCII format on magnetic tape and DOS diskette.
- ID:
- ivo://CDS.VizieR/IX/22
- Title:
- Einstein extended deep survey
- Short Name:
- IX/22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Einstein Deep Survey program (EDS) consists of very deep X-ray exposures in selected regions of the sky at high galactic latitude. The main purposes of the survey are to investigate the nature of the extragalactic X-ray background through direct source counts at very low flux levels and to study the nature of the very faint X-ray sources which comprise a significant fraction, if not all, of the soft X-ray background. The survey includes 9 IPC observations and 34 HRI observations, which, in general, cover the central 32'x32' regions of the IPC fields. In total, 178 IPC sources and 202 HRI sources were detected above thresholds set to allow ~1 false source per observation. Data from all IPC energy bands and all HRI detect cells are included. The data are largely the result of standard Einstein Rev. 1 HRI and Rev. 1B IPC reprocessing; however, minor corrections to IPC count rates, fluxes, and flux significances have been made to account for different column densities toward various fields and small systematic errors in the IPC analysis of count rates and significances for long exposures. For further details please refer to the paper referenced above. The HRI field parameters have been determined from standard processing and from other information contained in the HRI .SDF file. For information on HRI sources, see the table "hsrc.dat"; for information on individual IPC fields, see the table "ifield.dat".
- ID:
- ivo://CDS.VizieR/J/ApJ/871/258
- Title:
- ELQS in SDSS. III. The full ELQS quasar catalog
- Short Name:
- J/ApJ/871/258
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have designed the Extremely Luminous Quasar Survey (ELQS) to provide a highly complete census of unobscured UV-bright quasars during the cosmic noon, z=2.8-5.0. Here we report the discovery of 70 new quasars in the ELQS South Galactic Cap (ELQS-S) quasar sample, doubling the number of known extremely luminous quasars in 4237.3deg^2^ of the Sloan Digital Sky Survey footprint. These observations conclude the ELQS and we present the properties of the full ELQS quasar catalog, containing 407 quasars over 11838.5deg^2^. Our novel ELQS quasar selection strategy resulted in unprecedented completeness at the bright end and allowed us to discover 109 new quasars in total. This marks an increase of ~36% (109/298) in the known population at these redshifts and magnitudes, while we further are able to retain a selection efficiency of ~80%. On the basis of 166 quasars from the full ELQS quasar catalog, which adhere to the uniform criteria of the Two Micron All Sky Survey point source catalog, we measure the bright-end quasar luminosity function (QLF) and extend it one magnitude brighter than previous studies. Assuming a single power law with exponential density evolution for the functional form of the QLF, we retrieve the best-fit parameters from a maximum likelihood analysis. We find a steep bright-end slope of {beta}~-4.1, and we can constrain the bright-end slope to {beta}<=-3.4 with 99% confidence. The density is well modeled by the exponential redshift evolution, resulting in a moderate decrease with redshift ({gamma}~-0.4).
