- ID:
- ivo://CDS.VizieR/J/ApJS/247/57
- Title:
- Compact bright radio-loud AGNs. III. VLBA 43GHz
- Short Name:
- J/ApJS/247/57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results from the 43GHz Very Long Baseline Array (VLBA) observations of 124 compact radio-loud active galactic nuclei (AGNs) that were conducted between 2014 November and 2016 May. The typical dimensions of the restoring beam in each image are about 0.5masx0.2mas. The highest resolution of 0.2mas corresponds to a physical size of 0.02pc for the lowest redshift source in the sample. The 43GHz very long baseline interferometry (VLBI) images of 97 AGNs are presented for the first time. We study the source compactness on milliarcsecond and submilliarcsecond scales, and suggest that 95 sources in our sample are suitable for future space VLBI observations. By analyzing our data supplemented with other VLBA AGN surveys from the literature, we find that the core brightness temperature increases with increasing frequency below a break frequency ~7GHz, and decreases between ~7 and 240GHz but increases again above 240GHz in the rest frame of the sources. This indicates that the synchrotron opacity changes from optically thick to thin. We also find a strong statistical correlation between radio and {gamma}-ray flux densities. Our correlation is tighter than those in the literature derived from lower-frequency VLBI data, suggesting that the {gamma}-ray emission is produced more cospatially with the 43GHz VLBA core emission. This correlation can also be extrapolated to the unbeamed AGN population, implying that a universal {gamma}-ray production mechanism might be at work for all types of AGNs.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/408/2261
- Title:
- Compact steep spectrum new sample
- Short Name:
- J/MNRAS/408/2261
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new sample of compact steep spectrum (CSS) sources with radio luminosity below 10^26^W/Hz at 1.4GHz; these are called low-luminosity compact (LLC) objects. The sources have been selected from the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey and observed with the multi-element radio linked interferometer network (MERLIN) at the L and C bands. The main criterion used for selection was the luminosity of the objects, and approximately one-third of the CSS sources from the new sample have a value of radio luminosity comparable to Fanaroff-Riley type 1 sources (FR Is). About 80 per cent of the sources have been resolved and about 30 per cent have weak extended emission and disturbed structures when compared with the observations of higher-luminosity CSS sources. We have studied the correlation between radio power and linear size, and the redshift with a larger sample that also included published samples of compact objects and large-scale FR IIs and FR Is.
- ID:
- ivo://CDS.VizieR/J/ApJ/511/612
- Title:
- Comparison of Radio-loud and Quiet Quasars
- Short Name:
- J/ApJ/511/612
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have made radio observations of 87 optically selected quasars at 5 GHz with the VLA in order to measure the radio power for these objects and hence determine how the fraction of radio-loud quasars varies with redshift and optical luminosity. The sample has been selected from the recently completed Edinburgh Quasar Survey and covers a redshift range of 0.3{<=}z{<=}1.5 and an optical absolute magnitude range of (-26.5){<=}M_B_{<=}(-23.5) (h=1/2, q_o_=1/2). We have also matched other existing surveys with the Faint Images of the Radio Sky at Twenty Centimeters and NRAO VLA Sky Survey radio catalogs and combined these data so that the optical luminosity-redshift plane is now far better sampled than before. We have fitted a model to the probability of a quasar being radio-loud as a function of absolute magnitude and redshift, and from this model we infer the radio-loud and radio-quiet optical luminosity functions. The radio-loud optical luminosity function is featureless and flatter than the radio-quiet one. It evolves at a marginally slower rate if quasars evolve by density evolution, but the difference in the rate of evolutions of the two different classes is much less than was previously thought.
- ID:
- ivo://CDS.VizieR/J/other/RAA/19.29
- Title:
- Compilation of known QSOs for the Gaia mission
- Short Name:
- J/other/RAA/19.2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Quasars are essential for astrometric in the sense that they are spatial stationary because of their large distance from the Sun. The European Space Agency (ESA) space astrometric satellite Gaia is scanning the whole sky with unprecedented accuracy up to a few uas level. However, Gaia's two fields of view observations strategy may introduce a parallax bias in the Gaia catalog. Since it presents no significant parallax, quasar is perfect nature object to detect such bias. More importantly, quasars can be used to construct a Celestial Reference Frame in the optical wavelengths in Gaia mission. In this paper, we compile the most reliable quasars existing in literatures.The final compilation (designated as Known Quasars Catalog for Gaia mission, KQCG) contains 1842076 objects, among of them, 797632 objects are found in Gaia DR1 after cross-identifications. This catalog will be very useful in Gaia mission.
- ID:
- ivo://CDS.VizieR/J/ApJ/475/469
- Title:
- Composite HST Spectrum of Quasars
- Short Name:
- J/ApJ/475/469
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We construct a composite quasar spectrum from 284 HST FOS spectra of 101 quasars with redshifts z>0.33. The spectrum covers the wavelengths between 350 and 3000A in the rest frame, with a peak S/N level of ~130 per A at ~1200A. Since ~90% of the sample quasars have redshift z<1.5, the spectrum is suitable for studying the wavelength region shortward of Ly{alpha} without large effects from intervening Ly{alpha} forest absorption. Data in the waveband between 350 and 600A are mainly from the spectra of z>1.5 quasars, for which significant corrections for the accumulated Lyman-series line and continuum absorption have been applied. There is a significant steepening of the continuum slope around 1050A. The continuum between 1050 and 2200A can be modeled as a power law f_{nu} proportional to {nu}_{alpha}_ with {alpha}=-0.99+/-0.05. For the full sample the power-law index in the extreme ultraviolet (EUV) between 350 and 1050A is {alpha}=-1.96+/-0.15. For the radio-loud subsample (60 objects), the EUV spectral index is {alpha}~=-2.2, while for the radio-quiet subsample (41 objects) it is {alpha}~=-1.8. The continuum flux in the wavelengths near the Lyman limit shows a depression of ~10%. The break in the power-law index and the slight depression of the continuum near the Lyman limit are features expected in Comptonized accretion-disk spectra. Comptonization produces a power-law tail in the wavelength band shortward of 1000A and smears out the Lyman-limit edge of the intrinsic accretion-disk spectrum. In the EUV waveband, we detect several possible emission features, including one around 690A that may be O III + N III produced by the Bowen fluorescence effect. Comparing our composite spectrum with one made at higher redshifts by Francis et al. (1991ApJ...373..465F), we find that the equivalent widths of Ly{alpha} and high-ionization emission lines are larger in our sample, reflecting a known luminosity dependence. The equivalent widths of low-ionization lines do not exhibit such a dependence, suggesting that the quasar EUV continuum above ~50eV is steeper at higher luminosity. Radio-quiet quasars appear to show a slightly harder continuum and lower ionization levels in their emission lines.
- ID:
- ivo://CDS.VizieR/J/ApJ/849/53
- Title:
- Composite SEDs of type 1 and type 2 QSOs
- Short Name:
- J/ApJ/849/53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present observed mid-infrared and optical colors and composite spectral energy distributions (SEDs) of type 1 (broad-line) and 2 (narrow-line) quasars selected from Sloan Digital Sky Survey (SDSS) spectroscopy. A significant fraction of powerful quasars are obscured by dust and are difficult to detect in optical photometric or spectroscopic surveys. However, these may be more easily identified on the basis of mid-infrared (MIR) colors and SEDs. Using samples of SDSS type 1 and 2 matched in redshift and [OIII] luminosity, we produce composite rest-frame 0.2-15{mu}m SEDs based on SDSS, UKIDSS, and Wide-field Infrared Survey Explorer photometry and perform model fits using simple galaxy and quasar SED templates. The SEDs of type 1 and 2 quasars are remarkably similar, with the differences explained primarily by the extinction of the quasar component in the type 2 systems. For both types of quasar, the flux of the active galactic nucleus (AGN) relative to the host galaxy increases with AGN luminosity (L_[OIII]_) and redder observed MIR color, but we find only weak dependencies of the composite SEDs on mechanical jet power as determined through radio luminosity. We conclude that luminous quasars can be effectively selected using simple MIR color criteria similar to those identified previously (W1-W2>0.7; Vega), although these criteria miss many heavily obscured objects. Obscured quasars can be further identified based on optical-IR colors (for example, (u-W3[AB]>1.4(W1-W2[Vega])+3.2). These results illustrate the power of large statistical studies of obscured quasars selected on the basis of MIR and optical photometry.
- ID:
- ivo://CDS.VizieR/J/ApJ/836/186
- Title:
- Continuum-band lags in SDSS QSOs from PS1 obs.
- Short Name:
- J/ApJ/836/186
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the time lags between the continuum emission of quasars at different wavelengths, based on more than four years of multi-band (g, r, i, z) light curves in the Pan-STARRS Medium Deep Fields. As photons from different bands emerge from different radial ranges in the accretion disk, the lags constrain the sizes of the accretion disks. We select 240 quasars with redshifts of z~1 or z~0.3 that are relatively emission-line free. The light curves are sampled from day to month timescales, which makes it possible to detect lags on the scale of the light crossing time of the accretion disks. With the code JAVELIN, we detect typical lags of several days in the rest frame between the g band and the riz bands. The detected lags are ~2-3 times larger than the light crossing time estimated from the standard thin disk model, consistent with the recently measured lag in NGC 5548 and microlensing measurements of quasars. The lags in our sample are found to increase with increasing luminosity. Furthermore, the increase in lags going from g-r to g-i and then to g-z is slower than predicted in the thin disk model, particularly for high-luminosity quasars. The radial temperature profile in the disk must be different from what is assumed. We also find evidence that the lags decrease with increasing line ratios between ultraviolet Fe II lines and Mg II, which may point to changes in the accretion disk structure at higher metallicity.
- ID:
- ivo://CDS.VizieR/J/A+A/590/A10
- Title:
- 3C 279 optical photometry and polarimetry
- Short Name:
- J/A+A/590/A10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Over the past few years, several occasions of large, continuous rotations of the electric vector position angle (EVPA) of linearly polarized optical emission from blazars have been reported. These events are often coincident with high energy gamma-ray flares and they have attracted considerable attention, as they could allow one to probe the magnetic field structure in the gamma-ray emitting region of the jet. The flat-spectrum radio quasar 3C 279 is one of the most prominent examples showing this behaviour. Our goal is to study the observed EVPA rotations and to distinguish between a stochastic and a deterministic origin of the polarization variability. We have combined multiple data sets of R-band photometry and optical polarimetry measurements of 3C 279, yielding exceptionally well-sampled flux density and polarization curves that cover a period of 2008-2012. Several large EVPA rotations are identified in the data. We introduce a quantitative measure for the EVPA curve smoothness, which is then used to test a set of simple random walk polarization variability models against the data. 3C 279 shows different polarization variation characteristics during an optical low-flux state and a flaring state. The polarization variation during the flaring state, especially the smooth approx. 360 deg. rotation of the EVPA in mid-2011, is not consistent with the tested stochastic processes. We conclude that during the two different optical flux states, two different processes govern the polarization variation, possibly a stochastic process during the low-brightness state and a deterministic process during the flaring activity.
- ID:
- ivo://CDS.VizieR/J/A+A/407/899
- Title:
- Core dominance in extragalactic radio sources
- Short Name:
- J/A+A/407/899
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, based on a paper by Liu and Zhang (2002, Cat. <J/A+A/381/757>), we have chosen a sample of 542 extragalactic sources (27 BL Lac objects, 300 galaxies (radio galaxies and Seyfert galaxies), and 215 quasars), for which we have calculated the core-dominance parameters and investigated the relation between core-dominance parameter and the core and extended luminosities. The core-dominance parameter of galaxies is smaller than that in quasars, which is smaller than that in BL Lac objects.
- ID:
- ivo://CDS.VizieR/J/MNRAS/465/2120
- Title:
- Correcting CIV-based virial black hole masses
- Short Name:
- J/MNRAS/465/2120
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The CIV{lambda}{lambda}1498,1501 broad emission line is visible in optical spectra to redshifts exceeding z~5. CIV has long been known to exhibit significant displacements to the blue and these 'blueshifts' almost certainly signal the presence of strong outflows. As a consequence, single-epoch virial black hole (BH) mass estimates derived from CIV velocity widths are known to be systematically biased compared to masses from the hydrogen Balmer lines. Using a large sample of 230 high-luminosity (L_Bol_=10^45.5^-10^48^erg/s), redshift 1.5<z<4.0 quasars with both CIV and Balmer line spectra, we have quantified the bias in CIV BH masses as a function of the CIV blueshift. CIV BH masses are shown to be a factor of 5 larger than the corresponding Balmer-line masses at C IV blueshifts of 3000km/s and are overestimated by almost an order of magnitude at the most extreme blueshifts, ?=5000km/s. Using the monotonically increasing relationship between the CIV blueshift and the mass ratio BH(CIV)/BH(H{alpha}), we derive an empirical correction to all CIV BH masses. The scatter between the corrected CIV masses and the Balmer masses is 0.24dex at low CIV blueshifts (~0km/s) and just 0.10dex at high blueshifts (~3000km/s), compared to 0.40dex before the correction. The correction depends only on the CIV line properties - i.e. full width at half-maximum and blueshift - and can therefore be applied to all quasars where CIV emission line properties have been measured, enabling the derivation of unbiased virial BH-mass estimates for the majority of high-luminosity, high-redshift, spectroscopically confirmed quasars in the literature.
