We present the optical and infrared identifications of the 266 radio sources detected at 20cm with the Very Large Array in the Chandra Deep Field-South. Using deep i-band Advanced Camera for Surveys, R-band Wide Field Imager, K-band SOFI NTT, K-band ISAAC VLT and Spitzer imaging data, we are able to find reliable counterparts for 254 (~95%) VLA sources. Twelve radio sources remain unidentified, and three of them are "empty fields". Using literature and our own data we are able to assign redshifts to 186 (~70%) radio sources: 108 are spectroscopic redshifts and 78 are reliable photometric redshifts. Based on the rest-frame colors and morphological distributions of the host galaxies, we find evidences for a change in the submillijansky radio source population: (1) above ~0.08mJy early-type galaxies are dominating and (2) at flux densities below ~0.08mJy, starburst galaxies become dominant.
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).
We observed 60 fields towards 57 Abell and one Zwicky cluster of galaxies using the Very Large Array (VLA) with scaled arrays at 1.5 and 4.9 GHz. The source catalogue contains radio and optical parameters for 994 sources up to a lower flux limit of 1.0 mJy at 1.5 GHz and comprises a complete sample above 2.5 mJy. The combined sky area within the half-power circle on the maps is 3.5x10^-3^ sr, and the cluster fields are distributed between +35 deg and -30 deg declination. The source catalogue list positions, angular size, spectral index and optical identification, magnitude and morphology, if available.
We report 20 and 6cm VLA deep observations of the CDF-S including the Extended CDF-S. We discuss the radio properties of 266 cataloged radio sources, of which 198 are above a 20cm completeness level reaching down to 43uJy at the center of the field. Survey observations made at 6cm over a more limited region cover the original CDF-S to a comparable level of sensitivity as the 20cm observations. Of 266 cataloged radio sources, 52 have X-ray counterparts in the CDF-S and a further 37 have counterparts in the E-CDF-S area not covered by the 1Ms exposure. Using a wide range of material, we have found optical or infrared counterparts for 254 radio sources, of which 186 have either spectroscopic or photometric redshifts. Three radio sources have no apparent counterpart at any other wavelength. Measurements of the 20cm radio flux density at the position of each CDF-S X-ray source detected a further 30 radio sources above a conservative 3{sigma} detection limit. X-ray and submillimeter observations have been traditionally used as a measure of AGN and star formation activity, respectively. These new observations probe the faint end of both the star formation and radio galaxy/AGN population, as well as the connection between the formation and evolution of stars and SMBHs.
We have conducted a deep survey (rms noise ~=17{mu}Jy) with the Very Large Array (VLA) at 1.4GHz, with a resolution of 6arcsec, of a 1{deg}^2^ region included in the VIRMOS VLT Deep Survey. In the same field we already have multiband photometry down to I_AB_=25, and spectroscopic observations will be obtained during the VIRMOS VLT survey. The homogeneous sensitivity over the whole field has allowed to derive a complete sample of 1054 radio sources (5{sigma} limit). We give a detailed description of the data reduction and of the analysis of the radio observations, with particular care to the effects of clean bias and bandwidth smearing, and of the methods used to obtain the catalogue of radio sources. To estimate the effect of the resolution bias on our observations we have modelled the effective angular-size distribution of the sources in our sample and we have used this distribution to simulate a sample of radio sources. Finally we present the radio count distribution down to 0.08mJy derived from the catalogue. Our counts are in good agreement with the best fit derived from earlier surveys, and are about 50% higher than the counts in the HDF. The radio count distribution clearly shows, with extremely good statistics, the change in the slope for the sub-mJy radio sources.
VLA/VLBA obscured radio-loud active galactic nuclei
Short Name:
J/AJ/151/74
Date:
21 Oct 2021
Publisher:
CDS
Description:
This is the second paper directed toward finding new highly redshifted atomic and molecular absorption lines at radio frequencies. To this end, we selected a sample of 80 candidates for obscured radio-loud active galactic nuclei (AGNs) and presented their basic optical/near-infrared (NIR) properties in Yan et al. 2012AJ....144..124Y. In this paper, we present both high-resolution radio continuum images for all of these sources and H I 21 cm absorption spectroscopy for a few selected sources in this sample. A-configuration 4.9 and 8.5 GHz Very Large Array continuum observations find that 52 sources are compact or have substantial compact components with size <0.5" and flux densities >0.1 Jy at 4.9 GHz. The 36 most compact sources were then observed with the Very Long Baseline Array at 1.4 GHz. One definite and 10 candidate Compact Symmetric Objects (CSOs) are newly identified, which is a detection rate of CSOs ~three times higher than the detection rate previously found in purely flux-limited samples. Based on possessing compact components with high flux densities, 60 of these sources are good candidates for absorption-line searches. Twenty-seven sources were observed for H I 21 cm absorption at their photometric or spectroscopic redshifts with only six detections (five definite and one tentative). However, five of these were from a small subset of six CSOs with pure galaxy optical/NIR spectra (i.e., any AGN emission is obscured) and for which accurate spectroscopic redshifts place the redshifted 21 cm line in a radio frequency intereference (RFI)-free spectral "window" (i.e., the percentage of H I 21 cm absorption-line detections could be as high as ~90% in this sample). It is likely that the presence of ubiquitous RFI and the absence of accurate spectroscopic redshifts preclude H I detections in similar sources (only 1 detection out of the remaining 22 sources observed, 13 of which have only photometric redshifts); that is, H I absorption may well be present but is masked by the RFI. Future searches for highly redshifted H I and molecular absorption can easily find more distant CSOs among bright, "blank field" radio sources, but will be severely hampered by an inability to determine accurate spectroscopic redshifts due to their lack of rest-frame UV continuum.
We present the analysis of the radio jet evolution of the radio galaxy 3C 120 during a period of prolonged {gamma}-ray activity detected by the Fermi satellite between 2012 December and 2014 October. We find a clear connection between the {gamma}-ray and radio emission, such that every period of {gamma}-ray activity is accompanied by the flaring of the millimeter very long baseline interferometry (VLBI) core and subsequent ejection of a new superluminal component. However, not all ejections of components are associated with {gamma}-ray events detectable by Fermi. Clear {gamma}-ray detections are obtained only when components are moving in a direction closer to our line of sight. This suggests that the observed {gamma}-ray emission depends not only on the interaction of moving components with the millimeter VLBI core, but also on their orientation with respect to the observer. Timing of the {gamma}-ray detections and ejection of superluminal components locate the {gamma}-ray production to within ~0.13pc from the millimeter VLBI core, which was previously estimated to lie about 0.24pc from the central black hole. This corresponds to about twice the estimated extension of the broad line region, limiting the external photon field and therefore suggesting synchrotron self Compton as the most probable mechanism for the production of the {gamma}-ray emission. Alternatively, the interaction of components with the jet sheath can provide the necessary photon field to produced the observed {gamma}-rays by Compton scattering.
The canonical methods for gravitational wave detection are ground- and space- based laser interferometry, pulsar timing, and polarization of the cosmic microwave background. But as has been suggested by numerous investigators, astrometry offers an additional path to gravitational wave detection. Gravitational waves deflect light rays of extragalactic objects, creating apparent proper motions in a quadrupolar (and higher-order modes) pattern. Astrometry of extragalactic radio sources is sensitive to gravitational waves with frequencies between roughly 10^-18^ and 10^-8^Hz (H_0_ and 1/3yr^-1^), overlapping and bridging the pulsar timing and CMB polarization regimes. We present a methodology for astrometric gravitational wave detection in the presence of large intrinsic uncorrelated proper motions (i.e., radio jets). We obtain 95% confidence limits on the stochastic gravitational wave background using 711 radio sources, {Omega}_GW_<0.0064, and using 508 radio sources combined with the first Gaia data release: {Omega}_GW_<0.011. These limits probe gravitational wave frequencies 6x10^-18^Hz<~f<~1x10^-9^Hz. Using a WISE-Gaia catalog of 567721 AGN, we predict a limit expected from Gaia alone of {Omega}_GW_<0.0006, which is significantly higher than was originally forecast. Incidentally, we detect and report on 22 new examples of optical superluminal motion with redshifts 0.13-3.89.
A catalog containing milli-arcsecond-accurate positions of 1332 extragalactic radio sources distributed over the northern sky is presented - the Very Long Baseline Array Calibrator Survey (VCS1). The positions have been derived from astrometric analysis of dual-frequency 2.3 and 8.4 GHz VLBA snapshot observations; in a majority of cases, images of the sources are also available. These radio sources are suitable for use in geodetic and astrometric experiments, and as phase-reference calibrators in high-sensitivity astronomical imaging. The VCS1 is the largest high-resolution radio survey ever undertaken and triples the number of sources available to the radio astronomy community for VLBI applications. In addition to the astrometric role, this survey can be used in active galactic nuclei, Galactic, gravitational lens, and cosmological studies.
We used the Very Long Baseline Array and the European VLBI Network to perform phase-referenced very long baseline interferometry observations of the three most powerful maser transitions associated with the high-mass star-forming region G28.87+0.07: the 22.2GHz H_2_O, 6.7GHz CH_3_OH, and 1.665GHz OH lines. We also performed Very Large Array (VLA) observations of the radio continuum emission at 1.3 and 3.6cm and Subaru observations of the continuum emission at 24.5{mu}m. Two centimeter-continuum sources are detected and one of them (named hot molecular core (HMC)) is compact and placed at the center of the observed distribution of H_2_O, CH_3_OH, and OH masers. The bipolar distribution of line-of-sight velocities and the pattern of the proper motions suggest that the water masers are driven by a (proto)stellar jet interacting with the dense circumstellar gas. The same jet could both excite the centimeter-continuum source named HMC (interpreted as free-free emission from shocked gas) and power the molecular outflow observed at larger scales--although one cannot exclude that the free-free continuum is rather originating from a hypercompact H II region. At 24.5{mu}m, we identify two objects separated along the north-south direction, whose absolute positions agree with those of the two VLA continuum sources. We establish that ~90% of the luminosity of the region (~2x10^5^L_{sun}_) is coming from the radio source HMC, which confirms the existence of an embedded massive young stellar object exciting the masers and possibly still undergoing heavy accretion from the surrounding envelope.
