- ID:
- ivo://CDS.VizieR/J/A+A/658/A10
- Title:
- 3C295 LOFAR, MERLIN and VLA images
- Short Name:
- J/A+A/658/A10
- Date:
- 02 Feb 2022 13:43:44
- Publisher:
- CDS
- Description:
- 3C295 is a bright, compact steep spectrum source with a well-studied integrated radio spectral energy distribution (SED) from 132MHz to 15GHz. However, spatially resolved spectral studies have been limited due to a lack of high resolution images at low radio frequencies. These frequencies are crucial for measuring absorption processes, and anchoring the overall spectral modelling of the radio SED. In this paper, we use International LOw-Frequency ARray (LOFAR) Telescope (ILT) observations of 3C295 to study its spatially resolved spectral properties with sub-arcsecond resolution at 132MHz. Combining our new 132MHz observation with archival data at 1.6GHz, 4.8GHz, and 15GHz, we are able to carryout a resolved radio spectral analysis. The spectral properties of the hotspots provides evidence for low frequency flattening. In contrast, the spectral shape across the lobes is consistent with a Jaffe-Perola spectral ageing model. Usingthe integrated spectral information for each component, we then fitted low-frequency absorption models to the hotspots,finding that both free-free absorption and synchrotron self-absorption models provide a better fit to the data than a standard power law. Although we can say there is low-frequency absorption present in the hot spots of 3C295, future observations with the Low Band Antenna of the ILT at 55MHz may allow us to distinguish the type of absorption.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/133/2222
- Title:
- Clustering of high-redshift QSOs from SDSS
- Short Name:
- J/AJ/133/2222
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the two-point correlation function of a uniformly selected sample of 4426 luminous optical quasars with redshift 2.9<=z<=5.4 selected over 4041deg^2^ from the Fifth Data Release of the Sloan Digital Sky Survey. We fit a power-law to the projected correlation function w_p_(r_p_) to marginalize over redshift-space distortions and redshift errors.
- ID:
- ivo://CDS.VizieR/J/A+A/478/701
- Title:
- Color excess of SDSS quasars with DLA systems
- Short Name:
- J/A+A/478/701
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyzed the spectroscopic and photometric database of the 5th data release of the Sloan Digital Sky Survey (SDSS) to search for evidence of the quasar reddening produced by dust embedded in intervening damped Ly{alpha} (DLA) systems. From a list of 5164 quasars in the interval of emission redshift 2.25<=z_e_<=3.5 and SDSS spectra with signal-to-noise ratio SNR>~4, we built up an "absorption sample" of 248 QSOs with a single DLA system in the interval of absorption redshift 2.2<z_a_<=3.5 and a "pool" of 1959 control QSOs without DLA systems or strong metal systems. For each QSO of the absorption sample we extracted from the pool a subset of control QSOs that are closest in redshift and magnitude.
- ID:
- ivo://CDS.VizieR/J/ApJ/883/78
- Title:
- Column densities of CGM absorption lines
- Short Name:
- J/ApJ/883/78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the geometric distribution of gas metallicities in the circumgalactic medium (CGM) around 47, z<0.7 galaxies from the "Multiphase Galaxy Halos" Survey. Using a combination of quasar spectra from Hubble Space Telescope (HST)/COS and from Keck/HIRES or Very Large Telescope/UVES, we measure column densities of, or determine limits on, CGM absorption lines. We then use a Markov Chain Monte Carlo approach with Cloudy to estimate the metallicity of cool (T~10^4^K) CGM gas. We also use HST images to determine host-galaxy inclination and quasar-galaxy azimuthal angles. Our sample spans a HI column density range of 13.8cm^-2^<logN_HI_<19.9cm^-2^. We find (1) while the metallicity distribution appears bimodal, a Hartigan dip test cannot rule out a unimodal distribution (0.4{sigma}). (2) CGM metallicities are independent of halo mass, spanning three orders of magnitude at a fixed halo mass. (3) The CGM metallicity does not depend on the galaxy azimuthal and inclination angles regardless of HI column density, impact parameter, and galaxy color. (4) The ionization parameter does not depend on azimuthal angle. We suggest that the partial Lyman limit metallicity bimodality is not driven by a spatial azimuthal bimodality. Our results are consistent with simulations where the CGM is complex and outflowing, accreting, and recycled gas are well-homogenized at z<0.7. The presence of low-metallicity gas at all orientations suggests that cold streams of accreting filaments are not necessarily aligned with the galaxy plane at low redshifts or intergalactic transfer may dominate. Finally, our results support simulations showing that strong metal absorption can mask the presence of low-metallicity gas in integrated line-of-sight CGM metallicities.
- 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.
- 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/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/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.
