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841. Velocity dispersion in AGN
ID:
ivo://CDS.VizieR/J/ApJ/585/647
Title:
Velocity dispersion in AGN
Short Name:
J/ApJ/585/647
Date:
21 Oct 2021
Publisher:
CDS
Description:
It has been proposed that the width of the narrow [O III] {lambda}5007 emission line can be used as a surrogate for the stellar velocity dispersion in active galaxies. This proposition is tested using the Sloan Digital Sky Survey (SDSS) Early Data Release (EDR) spectra of 107 low-redshift radio-quiet QSOs and Seyfert 1 galaxies by investigating the correlation between black hole mass, as determined from H{beta} FWHM and optical luminosity, and [O III] FWHM. The correlation is real, but the scatter is large. Without additional information or selection criteria, the [O III] width can predict the black hole mass to a factor of 5.
842. Velocity dispersions in active galaxies
ID:
ivo://CDS.VizieR/J/ApJS/201/29
Title:
Velocity dispersions in active galaxies
Short Name:
J/ApJS/201/29
Date:
21 Oct 2021
Publisher:
CDS
Description:
We derive spatially resolved stellar kinematics for a sample of 84 out of 104 observed local (0.02<z<0.09) galaxies hosting type-1 active galactic nuclei (AGNs), based on long-slit spectra obtained at the 10m W. M. Keck-1 Telescope. In addition to providing central stellar velocity dispersions, we measure major axis rotation curves and velocity dispersion profiles using three separate wavelength regions, including the prominent Ca H&K, MgIb, and CaII NIR stellar features. In this paper, we compare kinematic measurements of stellar velocity dispersion obtained for different apertures, wavelength regions, and signal-to-noise ratios, and provide recipes to cross-calibrate the measurements reducing systematic effects to the level of a few percent. We also provide simple recipes based on readily observable quantities such as global colors and Ca H&K equivalent width that will allow observers of high-redshift AGN hosts to increase the probability of obtaining reliable stellar kinematic measurements from unresolved spectra in the region surrounding the Ca H&K lines.
843. VIMOS VLT Deep Survey: faint type-1 AGN sample
ID:
ivo://CDS.VizieR/J/A+A/457/79
Title:
VIMOS VLT Deep Survey: faint type-1 AGN sample
Short Name:
J/A+A/457/79
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the type-1 active galactic nuclei (AGN) sample extracted from the VIMOS VLT Deep Survey's first observations of 21000 spectra in 1.75{deg}^2^. This sample, which is purely magnitude-limited and free of morphological or color-selection biases, contains 130 broad-line AGN (BLAGN) spectra with redshift up to 5. Our data are divided into a wide (I_AB_<=22.5) and a deep (I_AB_<=24) subsample containing 56 and 74 objects, respectively. Because of its depth and selection criteria, this sample is uniquely suited for studying the population of faint type-1 AGN. Our measured surface density (~472+/-48 BLAGN per square degree with I_AB_<=24) is significantly higher than that of any other optically selected sample of BLAGN with spectroscopic confirmation. By applying a morphological and color analysis to our AGN sample, we find that (1) ~23% of the AGN brighter than I_AB_=22.5 are classified as extended, and this percentage increases to ~42 for those with z<1.6; (2) a non-negligible fraction of our BLAGN are lying close to the color-space area occupied by stars in the u*-g' versus g'-r' color-color diagram. This leads us to the conclusion that the classical optical-ultraviolet preselection technique, if employed at such deep magnitudes (I_AB_=22.5) in conjuction with a preselection of point-like sources, can miss up to ~35% of the AGN population. Finally, we present a composite spectrum of our sample of objects. While the continuum shape is very similar to that of the SDSS composite at short wavelengths, it is much redder than that of the SDSS composite at {lambda}>=3000{AA}. We interpret this as due to significant contamination from emission of the host galaxies, as expected from the faint absolute magnitudes sampled by our survey.
844. VLA-COSMOS 3 GHz Large Project. II.
ID:
ivo://CDS.VizieR/J/A+A/602/A2
Title:
VLA-COSMOS 3 GHz Large Project. II.
Short Name:
J/A+A/602/A2
Date:
21 Oct 2021
Publisher:
CDS
Description:
We study the composition of the faint radio population selected from the VLA-COSMOS 3GHz Large Project, a radio continuum survey performed at 10 cm wavelength. The survey covers a 2.6 square degree area with a mean rms of ~2.3uJy/beam, cataloging 10,830 sources above 5sigma, and enclosing the full 2 square degree COSMOS field. By combining these radio data with optical, near-infrared (UltraVISTA), and mid-infrared (Spitzer/IRAC) data, as well as X-ray data (Chandra), we find counterparts to radio sources for ~93% of the total radio sample (in the unmasked areas of the COSMOS field, i.e., those not affected by saturated or bright sources in the optical to NIR bands), reaching out to z~6. We further classify the sources as star forming galaxies or AGN based on various criteria, such as X-ray luminosity, observed MIR color, UV-FIR spectral-energy distribution, rest-frame NUV-optical color corrected for dust extinction, and radio-excess relative to that expected from the hosts' star-formation rate. We separate the AGN into sub-samples dominated by low-to-moderate and moderate-to-high radiative luminosity AGN, candidates for high- redshift analogues to local low- and high-excitation emission line AGN, respectively. We study the fractional contributions of these sub-populations down to radio flux levels of ~11uJy at 3GHz (or ~20uJy at 1.4GHz assuming a spectral index of -0.7). We find that the dominant fraction at 1.4GHz flux densities above ~200uJy is constituted of low-to-moderate radiative luminosity AGN. Below densities of ~100uJy the fraction of star-forming galaxies increases to ~60%, followed by the moderate-to-high radiative luminosity AGN (~20%), and low-to-moderate radiative luminosity AGN (~20%). Based on this observational evidence, we extrapolate the fractions down to sensitivities of the Square Kilometer Array (SKA). Our estimates suggest that at the faint flux limits to be reached by the (Wide, Deep, and UltraDeep) SKA1 surveys, a selection based only on radio flux limits can provide a simple tool to efficiently identify samples highly (>75%) dominated by star-forming galaxies.
845. VLA double-double radio galaxy candidates images
ID:
ivo://CDS.VizieR/J/A+A/622/A13
Title:
VLA double-double radio galaxy candidates images
Short Name:
J/A+A/622/A13
Date:
21 Oct 2021
Publisher:
CDS
Description:
Double-double radio galaxies (DDRGs) represent a short but unique phase in the life-cycle of some of the most powerful radio-loud active galactic nuclei (RLAGN). These galaxies display large-scale remnant radio plasma in the intergalactic medium left behind by a past episode of active galactic nuclei (AGN) activity, and meanwhile, the radio jets have restarted in a new episode. The knowledge of what causes the jets to switch off and restart is crucial to our understanding of galaxy evolution, while it is important to know if DDRGs form a host galaxy dichotomy relative to RLAGN. The sensitivity and field of view of LOFAR enables the observation of DDRGs on a population basis rather than single-source observations. Using statistical comparisons with a control sample of RLAGN, we may obtain insights into the nature of DDRGs in the context of their host galaxies, where physical differences in their hosts compared to RLAGN as a population may allow us to infer the conditions that drive restarting jets. We utilised the LOFAR Two-Metre Sky Survey (LoTSS) DR1, using a visual identification method to compile a sample of morphologically selected candidate DDRGs, showing two pairs of radio lobes. To confirm the restarted nature in each of the candidate sources, we obtained follow-up observations with the Karl. G. Jansky Very Large Array (VLA) at higher resolution to observe the inner lobes or restarted jets, the confirmation of which created a robust sample of 33 DDRGs.We created a comparison sample of 777 RLAGN, matching the luminosity distribution of the DDRG sample, and compared the optical and infrared magnitudes and colours of their host galaxies. We find that there is no statistically significant difference in the brightness of the host galaxies between double-doubles and single-cycle RLAGN. The DDRG and RLAGN samples also have similar distributions in WISE mid-infrared colours, indicating similar ages of stellar populations and dust levels in the hosts of DDRGs. We conclude that DDRGs and 'normal' RLAGN are hosted by galaxies of the same type, and that DDRG activity is simply a normal part of the life cycle of RLAGN. Restarted jets, particularly for the class of low-excitation radio galaxies, rather than being a product of a particular event in the life of a host galaxy, must instead be caused by smaller scale changes, such as in the accretion system surrounding the black hole.
846. VLA fluxes for AT20G radio galaxies
ID:
ivo://CDS.VizieR/J/ApJ/732/45
Title:
VLA fluxes for AT20G radio galaxies
Short Name:
J/ApJ/732/45
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present flux densities and polarization percentages of 159 radio galaxies based on nearly simultaneous Very Large Array observations at four frequencies, 4.86, 8.46, 22.46, and 43.34GHz. This sample is selected from the high-frequency Australia Telescope 20GHz (AT20G) survey and consists of all sources with flux density S_20GHz_>40mJy in an equatorial field of the Atacama Cosmology Telescope (ACT) survey. For a subset of 25 of these sources, we used the Green Bank Telescope (GBT) to obtain 90GHz data. We find that, as expected, this sample consists of flatter spectrum and more compact or point-like sources than low-frequency-selected samples. In the K band, variability is typically <~20%, although there are exceptions. The higher frequency data are well suited to the detection of extreme gigahertz peak spectrum sources. The inclusion of the 43GHz data causes the relative fraction of inverted spectrum sources to go down and of peaked spectrum sources to go up when compared with the AT20G survey results. The trend largely continues with the inclusion of the 90GHz data, although ~10% of the sources with GBT data show a spectral upturn from 43GHz to 90GHz. The measured polarization fractions are typically <5%, although in some cases they are measured to be up to ~20%. For sources with detected polarized flux in all four bands, about 40% of the sample, the polarization fractions typically increase with frequency. This trend is stronger for steeper spectrum sources as well as for the lower flux density sources.
847. VLA 33GHz obs. of star-forming regions
ID:
ivo://CDS.VizieR/J/ApJS/234/24
Title:
VLA 33GHz obs. of star-forming regions
Short Name:
J/ApJS/234/24
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present 33GHz imaging for 112 pointings toward galaxy nuclei and extranuclear star-forming regions at ~2" resolution using the Karl G. Jansky Very Large Array (VLA) as part of the Star Formation in Radio Survey. A comparison with 33GHz Robert C. Byrd Green Bank Telescope single-dish observations indicates that the interferometric VLA observations recover 78%+/-4% of the total flux density over 25" regions (~kpc scales) among all fields. On these scales, the emission being resolved out is most likely diffuse non-thermal synchrotron emission. Consequently, on the ~30-300pc scales sampled by our VLA observations, the bulk of the 33GHz emission is recovered and primarily powered by free-free emission from discrete HII regions, making it an excellent tracer of massive star formation. Of the 225 discrete regions used for aperture photometry, 162 are extranuclear (i.e., having galactocentric radii rG>=250pc) and detected at >3{sigma} significance at 33GHz and in H{alpha}. Assuming a typical 33GHz thermal fraction of 90%, the ratio of optically-thin 33GHz to uncorrected H{alpha} star formation rates indicates a median extinction value on ~30-300pc scales of A_H{alpha}_~1.26+/-0.09mag, with an associated median absolute deviation of 0.87mag. We find that 10% of these sources are "highly embedded" (i.e., A_H{alpha}_>~3.3mag), suggesting that on average, HII regions remain embedded for <~1Myr. Finally, we find the median 33GHz continuum-to-H{alpha} line flux ratio to be statistically larger within rG<250pc relative to the outer disk regions by a factor of 1.82+/-0.39, while the ratio of 33GHz to 24{mu}m flux densities is lower by a factor of 0.45+/-0.08, which may suggest increased extinction in the central regions.
848. VLA imaging of IRAS 1 Jy ULIRG sample
ID:
ivo://CDS.VizieR/J/A+A/409/115
Title:
VLA imaging of IRAS 1 Jy ULIRG sample
Short Name:
J/A+A/409/115
Date:
21 Oct 2021
Publisher:
CDS
Description:
This paper presents the results of a high resolution radio imaging survey of 83 of the 118 ultraluminous infrared galaxies (ULIRGs) in the IRAS 1Jy ULIRG sample (Kim & Sanders, 1998ApJS..119...41K, Veilleux et al., 2002, Cat. <J/ApJS/143/315>). We have observed these ULIRGs at 15-GHz with the Very Large Array (VLA). We find that ~75% of Seyferts (both type 1 and 2) and LINERs have radio nuclei which are compact at our 150mas resolution. The detection rate of HII nuclei is significantly lower (32%); the detections among these are preferentially HII+LINER/Seyfert composite nuclei. Among ULIRGs with multiple optical or near-IR nuclei our observations detected only one (or no) nucleus; in these the radio detection is typically towards the brightest near-IR nucleus. The compactness of the radio sources, the higher detection rates in AGN-type nuclei than HII nuclei, the preferential detection of nuclei with unresolved point sources in the near-IR, the low soft X-ray to nuclear radio luminosity ratio (arguing against thermal emission powering the radio nuclei), and the lack of correlation between radio power and H{alpha} luminosity, all support an origin of the detected radio nuclei in AGN related activity. This result is especially interesting for LINER ULIRGs for which signatures of AGNs have often been ambiguous in other wavebands. Such a high incidence of AGN would provide, for the first time, a large sample in which to study the interplay between AGN, starbursts, and galaxy mergers.
849. VLA 352MHz image of the Bootes field. I.
ID:
ivo://CDS.VizieR/J/MNRAS/450/1477
Title:
VLA 352MHz image of the Bootes field. I.
Short Name:
J/MNRAS/450/1477
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a 324.5MHz image of the NOAO Bootes field that was made using Very Large Array (VLA) P-band observations. The image has a resolution of 5.6"x5.1", a radius of 2.05 degrees and a central noise of ~0.2mJy/beam. Both the resolution and noise of the image are an order of magnitude better than what was previously available at this frequency and will serve as a valuable addition to the already extensive multiwavelength data that are available for this field. The final source catalogue contains 1370 sources and has a median 325 to 1400MHz spectral index of -0.72. Using a radio colour-colour diagram of the unresolved sources in our catalogue, we identify 33 megahertz peaked-spectrum (MPS) sources. Based on the turnover frequency linear size relation for the gigahertz peaked-spectrum (GPS) and compact steep-spectrum (CSS) sources, we expect that the MPS sources that are compact on scales of tens of milliarcseconds should be young radio loud active galactic nuclei at high (z>2) redshifts. Of the 33 MPS sources, we were able to determine redshifts for 24, with an average redshift of 1.3. Given that five of the sources are at z>2, that the four faint sources for which we could not find redshifts are likely at even higher redshifts and that we could only select sources that are compact on a scale of ~5", there is encouraging evidence that the MPS method can be used to search for high-redshift sources.
850. VLA survey of CDF-S. III.
ID:
ivo://CDS.VizieR/J/ApJ/698/740
Title:
VLA survey of CDF-S. III.
Short Name:
J/ApJ/698/740
Date:
21 Oct 2021
Publisher:
CDS
Description:
We discuss the X-ray properties of the radio sources detected in a deep 1.4 and 5GHz VLA Radio survey of the Extended Chandra Deep Field-South (E-CDFS). Among the 266 radio sources detected, we find 89 sources (1/3 of the total) with X-ray counterparts in the catalog of the 1Ms exposure of the central 0.08deg^2^ or in the catalog of the 250ks exposure of the 0.3deg^2^ E-CDFS field. For 76 (85%) of these sources, we have spectroscopic or photometric redshifts, and therefore we are able to derive their intrinsic properties from X-ray spectral analysis, namely intrinsic absorption and total X-ray luminosities. We find that the population of submillijansky radio sources with X-ray counterparts is composed of a mix of roughly 1/3 star-forming galaxies and 2/3 active galactic nuclei (AGNs).