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721. 87 radio loud quasars (RLS) with 3.6<=z<=4.4
ID:
ivo://CDS.VizieR/J/MNRAS/449/2818
Title:
87 radio loud quasars (RLS) with 3.6<=z<=4.4
Short Name:
J/MNRAS/449/2818
Date:
21 Oct 2021
Publisher:
CDS
Description:
We obtain a sample of 87 radio-loud quasi-stellar objects (QSOs) in the redshift range 3.6<=z<=4.4 by cross-correlating sources in the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) radio survey (S_1.4GHz_>1mJy) with star-like objects having r<20.2 in Sloan Digital Sky Survey (SDSS) Data Release 7. Of these 87 QSOs, 80 are spectroscopically classified in previous work (mainly SDSS), and form the training set for a search for additional such sources. We apply our selection to 2916 FIRST-DR7 pairs and find 15 likely candidates. Seven of these are confirmed as high-redshift quasars, bringing the total to 87. The candidates were selected using a neural-network, which yields 97 percent completeness (fraction of actual high-z QSOs selected as such) and an efficiency (fraction of candidates which are high-z QSOs) in the range of 47-60 percent. We use this sample to estimate the binned optical luminosity function (LF) of radio-loud QSOs at z~4, and also the LF of the total QSO population and its comoving density. Our results suggest that the radio-loud fraction at high z is similar to that at low z and that other authors may be underestimating the fraction at high z. Finally, we determine the slope of the optical LF and obtain results consistent with previous studies of radio-loud QSOs and of the whole population of QSOs. The evolution of the LF with redshift was for many years interpreted as a flattening of the bright-end slope, but has recently been re-interpreted as strong evolution of the break luminosity for high-z QSOs, and our results, for the radio-loud population, are consistent with this.
722. Radio luminosity function of FSRQs
ID:
ivo://CDS.VizieR/J/ApJ/842/87
Title:
Radio luminosity function of FSRQs
Short Name:
J/ApJ/842/87
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the radio luminosity function (LF) of flat-spectrum radio quasars (FSRQ), using the largest and most complete sample to date. Cross-matching between the FIRST 20cm and GB6 6cm radio surveys, we find 638 flat-spectrum radio sources above 220mJy at 1.4GHz; of these, 327 are classified and verified using optical spectroscopy data, mainly from Sloan Digital Sky Survey Data Release 12. We also considered flat-spectrum radio sources that lack both literature references and optical spectroscopy, and we identified 12 out of the 43 such sources to potentially be FSRQs, using their WISE colors. From the fully identified sample of 242 FSRQs, we derived the radio LF and cosmic evolution of blazars at 1.4GHz, finding good agreement with previous work at 5GHz. The number density of FSRQs increases dramatically to a redshift of z~2 and then declines for higher redshifts. Furthermore, the redshift at which the quasar density peaks is clearly dependent on luminosity, with more luminous sources peaking at higher redshifts. The approximate best-fit LF for a luminosity-dependent evolutionary model is a broken power-law with slopes ~0.7 and ~1.7 below and above the break luminosity, logL_1.4_~43.8erg/s, respectively.
723. Radio observations of the HDFS region. I
ID:
ivo://CDS.VizieR/J/AJ/130/1358
Title:
Radio observations of the HDFS region. I
Short Name:
J/AJ/130/1358
Date:
21 Oct 2021
Publisher:
CDS
Description:
This paper is the first of a series describing the results of the Australia Telescope Hubble Deep Field-South radio survey. The survey was conducted at four wavelengths, 20, 11, 6, and 3cm, over a 4 year period and achieves an rms sensitivity of about 10{mu}Jy at each wavelength. We describe the observations and data reduction processes and present data on radio sources close to the center of the Hubble Deep Field-South. We discuss in detail the properties of a subset of these sources. The sources include both starburst galaxies and galaxies powered by an active galactic nucleus and range in redshift from 0.1 to 2.2. Some of them are characterized by unusually high radio-to-optical luminosities, presumably caused by dust extinction.
724. Radio observations of the HDFS region. II
ID:
ivo://CDS.VizieR/J/AJ/130/1373
Title:
Radio observations of the HDFS region. II
Short Name:
J/AJ/130/1373
Date:
21 Oct 2021
Publisher:
CDS
Description:
This paper is part of a series describing the results from the Australia Telescope Hubble Deep Field-South (ATHDFS) survey obtained with the Australia Telescope Compact Array. This survey consists of observations at 1.4, 2.5, 5.2, and 8.7GHz, all centered on the Hubble Deep Field-South. Here we present the first results from the extended observing campaign at 1.4GHz. A total of 466 sources have been cataloged to a local sensitivity of 5{sigma} (11{mu}Jy rms). A source extraction technique is developed that (1) successfully excludes spurious sources from the final source catalogs and (2) accounts for the nonuniform noise in our image. A source catalog is presented, and the general properties of the 1.4GHz image are discussed. We also present source counts derived from our ATHDFS 1.4GHz catalog.
725. Radio-optical scrutiny of compact AGN
ID:
ivo://CDS.VizieR/J/A+A/520/A62
Title:
Radio-optical scrutiny of compact AGN
Short Name:
J/A+A/520/A62
Date:
21 Oct 2021
Publisher:
CDS
Description:
We study the correlations between the VLBA (Very Long Baseline Array) radio emission at 15GHz, extended emission at 151MHz, and optical nuclear emission at 5100{AA} for a complete sample of 135 compact jets. We use the partial Kendall's tau correlation analysis to check the link between radio properties of parsec-scale jets and optical nuclear luminosities of host active galactic nuclei (AGN).
726. Radio polarimetry of CSS sources
ID:
ivo://CDS.VizieR/J/A+A/555/A4
Title:
Radio polarimetry of CSS sources
Short Name:
J/A+A/555/A4
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present multi-frequency VLA polarisation observations of compact steep spectrum (CSS) sources. About half of the sources are point-like even at the resolution of about 0.1x0.1 arcseconds. The remaining sources have double or triple structure. Low values for the percentage of polarised emission in CSS sources is confirmed. On the average, quasars are more polarised than galaxies. A wide range of RM values have been measured. There are clear indications of very large RMs up to about 5585rad/m^2^. CSS galaxies are characterized by RM values that are larger than CSS quasars. The majority of the objects show very large values of RM.
727. Radio properties of optically selected quasars
ID:
ivo://CDS.VizieR/J/ApJ/445/62
Title:
Radio properties of optically selected quasars
Short Name:
J/ApJ/445/62
Date:
21 Oct 2021
Publisher:
CDS
Description:
Approximately one-quarter (256 objects) of the Large Bright Quasar Survey (LBQS, Hewett et al., 1995, Cat. <J/AJ/109/1498>) has been observed with the VLA at 8.4GHz, resulting in 44 detections (17%) with a median 3{sigma} noise limit of 0.29mJy. Quasars with radio luminosity detectable at this limit are under-represented at faint absolute blue magnitudes (M_B_>=-24), an effect which cannot be explained by a potential LBQS selection bias against quasars which have large radio luminosities and small optical luminosities. The radio-loud (8GHz luminosity >10^25^W/Hz) fraction is observed to change as a function of redshift and MB, for M_B_<-24, although the causal variable is ambiguous. The description most consistent with the available data is that radio-loud fraction is approximately constant over the range -27.5<M_B_<-24 and increases at brighter absolute magnitudes. The radio-loud fraction as a function of redshift reaches a local maximum at z~1, and, aside from the effects of increased radio-loud fraction at bright M_B_, remains roughly constant to redshifts approaching 5. The log R_8.4_ distribution (radio-to-optical luminosity ratio) of the current LBQS sample may be bimodal, but the results of statistical tests are ambiguous, requiring a larger sample size to become definite.
728. Radio properties of z < 0.3 quasars
ID:
ivo://CDS.VizieR/J/MNRAS/466/921
Title:
Radio properties of z < 0.3 quasars
Short Name:
J/MNRAS/466/921
Date:
21 Oct 2021
Publisher:
CDS
Description:
To better constrain the hypotheses proposed to explain why only a few quasars are radio loud (R_L_), we compare the characteristics of 1958 nearby (z<=0.3) SDSS (Sloan Digital Sky Survey) quasars, covered by the FIRST (Faint Images of the Radio Sky at Twenty Centimeters) and NVSS (NRAO VLA Sky Survey) radio surveys. Only 22 per cent are R_L_ with log(L_1.4GHz_)>=22.5W/Hz, the majority being compact (C), weak radio sources (WRS), with log(L_1.4GHz_)<24.5W/Hz. 15 per cent of the RL quasars have extended radio morphologies: 3 per cent have a core and a jet (J), 2 per cent have a core with one lobe (L), and 10 per cent have a core with two lobes (T), the majority being powerful radio sources (PRS), with log(L_1.4GHz_)>=24.5W/Hz. In general, RL quasars have higher bolometric luminosities and ionization powers than radio-quiet (RQ) quasars. The WRS have comparable black hole (BH) masses as the RQ quasars, but higher accretion rates or radiative efficiencies. The PRS have higher BH masses than the WRS, but comparable accretion rates or radiative efficiencies. The WRS also have higher FWHM_{[OIII]} than the PRS, consistent with a coupling of the spectral characteristics of the quasars with their radio morphologies. Inspecting the SDSS images and applying a neighbour search algorithm reveal no difference between the RQ and RL quasars of their host galaxies, environments, and interaction. Our results prompt the conjecture that the phenomenon that sparks the RL phase in quasars is transient, intrinsic to the active galactic nuclei, and stochastic, due to the chaotic nature of the accretion process of matter on to the BHs.
729. Radio-Quiet BAL quasars sample
ID:
ivo://CDS.VizieR/J/MNRAS/444/2498
Title:
Radio-Quiet BAL quasars sample
Short Name:
J/MNRAS/444/2498
Date:
21 Oct 2021
Publisher:
CDS
Description:
Studies of radio-loud (RL) broad absorption line (BAL) quasars indicate that popular orientation-based BAL models fail to account for all observations. Are these results extendable to radio-quiet (RQ) BAL quasars? Comparisons of RL and RQ BAL quasars show that many of their properties are quite similar. Here, we extend these analyses to the rest-frame ultraviolet (UV) spectral properties, using a sample of 73 RL and 473 RQ BAL quasars selected from the Sloan Digital Sky Survey. Each RQ quasar is individually matched to an RL quasar in both redshift (over the range 1.5<z<3.5) and continuum luminosity. We compare several continuum, emission line, and absorption line properties, as well as physical properties derived from these measurements. Most properties in the samples are statistically identical, though we find slight differences in the velocity structure of the BALs that cause apparent differences in C iv emission line properties. Differences in the velocities may indicate an interaction between the radio jets and the absorbing material. We also find that UV FeII emission is marginally stronger in RL BAL quasars. All of these differences are subtle, so in general we conclude that RL and RQ BAL QSOs are not fundamentally different objects, except in their radio properties. They are therefore likely to be driven by similar physical phenomena, suggesting that results from samples of RL BAL quasars can be extended to their RQ counterparts.
730. Radio source J1402+5347 1.4GHz light curves
ID:
ivo://CDS.VizieR/J/A+A/641/L4
Title:
Radio source J1402+5347 1.4GHz light curves
Short Name:
J/A+A/641/L4
Date:
21 Oct 2021
Publisher:
CDS
Description:
Propagation of the radio waves from distant compact radio sources through turbulent interstellar plasma in our Galaxy leads to twinkling of these sources, a phenomenon called interstellar scintillation. Such scintillations are a unique probe of the micro-arcsecond structure of radio sources as well as of the sub-AU-scale structure of the Galactic interstellar medium. Weak scintillations (i.e. intensity modulation of a few per cent) on timescales of a few days or longer are commonly seen at centimetre wavelengths and are thought to result from the line-of-sight integrated turbulence in the Milky Way's interstellar plasma. So far, only three sources were known that show more extreme variations, with modulations at the level of tens of per cent on timescales less than an hour. This requires propagation through nearby (d<~10pc) anomalously dense (n_e_>10^2^cm^3^) plasma clouds. Here we report the discovery with Apertif of a source (J1402+5347) showing extreme (~50%) and rapid variations on a timescale of just 6.5 minutes in the decimetre band (1.4GHz). The spatial scintillation pattern is highly anisotropic with a semi-minor axis of about 20,000 km. Canonical theory of refractive scintillation constrains the scattering plasma to be within the Oort cloud. The sight-line to J1402+5347 however passes unusually close to the B3 star Alkaid (eta UMa) at a distance of 32pc. If the scintillations are associated with Alkaid, then the angular size of J1402+5347 along the minor-axis of the scintels must be smaller than 10 microarcseconds yielding an apparent brightness temperature for an isotropic source of >10^14^K.