- 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.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/336/339
- Title:
- VLA observations of ultracompact HII regions
- Short Name:
- J/A+A/336/339
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used the Very Large Array (VLA) to search for radio continuum emission towards a sample of 67 IRAS sources selected from a previous study. All observed sources are associated with high density molecular gas, exhibit an infrared spectral energy distribution characteristic of very cold young stellar objects and many of them are associated with H_2_O masers. The observed sample is divided into two groups of sources: High, with IRAS spectral energy distributions resembling those of ultracompact HII regions, and Low, for which previously collected evidence suggests that they may contain a higher fraction of protostellar objects than the High group; such objects might not have started hydrogen burning yet. Radio continuum emission was detected towards 37 sources (55%), although only in 22 cases an association with the IRAS source is established. Of the latter, 9 (24%) objects belong to the Low type and 13 (43%) to the High type. Thus, we find that 76% of Low and 57% of High sources are not associated with a radio counterpart. Because the majority of the sources have luminosities above ~10^4^L_{sun}_, corresponding to central stars of spectral type between B2 and O7, the lack of radio emission is interpreted as being due to the action of accreting matter that chokes off the expansion of the ionised gas. We show that this require s only moderate mass accretion rates, below ~10^-4^M_{sun}_/yr. Alternatively, dust absorption can also effectively absorb UV photons and the gas column density implied by our observations indicates values in excess of 10^22^cm^-2^. The physical properties of IRAS sources with associated radio counterpa rt derived from the present observations do not distinguish between High and Low sources. These sources are likely to be ZAMS stars with variable amounts of dust within the ionised region which acts as UV field absorber. The large majority of detected sources (75%) have spherical or unresolved morphology, while 15% are irregular or multiply peaked and only 10% have a core-halo structure. These results agree with the known properties of ultracompact HII regions, even though the average luminosity of the present sample is an order of magnitude lower than that in previous studies.
- ID:
- ivo://CDS.VizieR/J/ApJ/728/97
- Title:
- VLA rotation measures in the Galactic plane
- Short Name:
- J/ApJ/728/97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have determined 194 Faraday rotation measures (RMs) of polarized extragalactic radio sources using new, multi-channel polarization observations at frequencies around 1.4GHz from the Very Large Array in the Galactic plane at 17{deg}<=l<=63{deg} and 205{deg}<=l<=253{deg}. This catalog fills in gaps in the RM coverage of the Galactic plane between the Canadian Galactic Plane Survey (CGPS; Taylor et al. 2003, Cat. VI/128; Brown et al. 2003, Cat. J/ApJS/145/213) and Southern Galactic Plane Survey (SGPS; Haverkorn et al. 2006ApJS..167..230H; Brown et al. 2007, Cat. J/ApJ/663/258).
- ID:
- ivo://CDS.VizieR/J/ApJ/740/65
- Title:
- VLA search for 5GHz radio transients
- Short Name:
- J/ApJ/740/65
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a 5GHz survey with the Very Large Array (VLA) and the expanded VLA, designed to search for short-lived (<~1day) transients and to characterize the variability of radio sources at milli-Jansky levels. A total sky area of 2.66deg^2^, spread over 141 fields at low Galactic latitudes (b~6-8{deg}), was observed 16 times with a cadence that was chosen to sample timescales of days, months, and years. Most of the data were reduced, analyzed, and searched for transients in near real-time. Interesting candidates were followed up using visible light telescopes (typical delays of 1-2hr) and the X-ray Telescope on board the Swift satellite. The final processing of the data revealed a single possible transient with a peak flux density of f_{nu}_~2.4mJy. Furthermore, we use the data to measure the source variability on timescales of days to years, and we present the variability structure function of 5GHz sources.
- ID:
- ivo://CDS.VizieR/J/ApJS/255/30
- Title:
- VLASS QL Ep.1 Catalog, CIRADA version
- Short Name:
- J/ApJS/255/30
- Date:
- 09 Feb 2022 14:56:38
- Publisher:
- CDS
- Description:
- The Very Large Array Sky Survey (VLASS) is observing the entire sky north of -40{deg} in the S-band (2-4GHz), with the highest angular resolution (2.5") of any all-sky radio continuum survey to date. VLASS will cover its entire footprint over three distinct epochs, the first of which has now been observed in full. Based on Quick Look images from this first epoch, we have created a catalog of 1.9x10^6 reliably detected radio components. Due to the limitations of the Quick Look images, component flux densities are underestimated by ~15% at S>3mJy/beam and are often unreliable for fainter components. We use this catalog to perform statistical analyses of the 3GHz radio sky. Comparisons with the Faint Images of the Radio Sky at Twenty cm survey (FIRST) show the typical 1.4-3GHz spectral index to be -0.71. The radio color-color distribution of point and extended components is explored by matching with FIRST and the LOFAR Two Meter Sky Survey. We present the VLASS source counts, dN/dS, which are found to be consistent with previous observations at 1.4 and 3GHz. Resolution improvements over FIRST result in excess power in the VLASS two-point correlation function at angular scales <7", and in 18% of active galactic nuclei associated with a single FIRST component being split into multi-component sources by VLASS.
- ID:
- ivo://CDS.VizieR/J/A+A/398/901
- Title:
- VLA survey at 6 cm in the Lockman Hole
- Short Name:
- J/A+A/398/901
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A deep radio image was obtained with the Very Large Array at 6cm in the Lockman Hole, during three runs of eleven hours each on January 16, 17 and 19, 1999 at 4835 and 4885MHz with a bandwidth of 50MHz in C configuration. From these data a catalogue of 63 radio sources was extracted, having a maximum distance of 10arcmin from the field center and a peak flux density greater than 4.5 times the local rms noise. The noise level in the central part of the field is ~11{mu}Jy.
- ID:
- ivo://CDS.VizieR/J/ApJ/831/155
- Title:
- VLA survey for faint compact radio sources in ONC
- Short Name:
- J/ApJ/831/155
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Karl G. Jansky Very Large Array 1.3, 3.6, and 6cm continuum maps of compact radio sources in the Orion Nebular Cluster (ONC). We mosaicked 34arcmin^2^ at 1.3cm, 70arcmin^2^ at 3.6cm and 109arcmin^2^ at 6cm, containing 778 near-infrared detected young stellar objects and 190 Hubble Space Telescope-identified proplyds (with significant overlap between those characterizations). We detected radio emission from 175 compact radio sources in the ONC, including 26 sources that were detected for the first time at these wavelengths. For each detected source, we fitted a simple free-free and dust emission model to characterize the radio emission. We extrapolate the free-free emission spectrum model for each source to ALMA bands to illustrate how these measurements could be used to correctly measure protoplanetary disk dust masses from submillimeter flux measurements. Finally, we compare the fluxes measured in this survey with previously measured fluxes for our targets, as well as four separate epochs of 1.3cm data, to search for and quantify the variability of our sources.
- ID:
- ivo://CDS.VizieR/J/ApJS/80/501
- Title:
- VLA survey of Abell clusters. II.
- Short Name:
- J/ApJS/80/501
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present radio contour maps, models, and optical identifications for 130 radio galaxies in Abell clusters of galaxies.
- ID:
- ivo://CDS.VizieR/J/AJ/109/853
- Title:
- VLA survey of Abell clusters. IV.
- Short Name:
- J/AJ/109/853
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the fourth in a series of papers describing an in depth study of a large statistical sample of radio galaxies in Abell clusters. This sample forms the basis of a detailed optical and radio study of the host galaxy properties, environments, and evolutionary models for radio galaxies as a class of objects. In this paper, we examine the radio detection statistics as a function of cluster morphological type, galaxy richness, and spatial location within the cluster galaxy distribution. These relationships are also parametrized as a function of radio power. The spatial distributions of the radio sources as a function of distance from the cluster center indicate that radio galaxies are preferentially located at small radii from the center of the cluster potential. This is observed as a factor of 2-3 excess over that predicted by a King-model surface-density distribution. The excess is higher in the upper radio power bin. This result is easily explained, however, from the spatial distribution of the brightest galaxies and the relationship between radio and optical luminosity. The sample is divided into richness classes 0, 1, and 2, according to Abell's criterion, and in two radio power ranges. While simple counting shows that richer clusters have more radio galaxies in both radio power bins, when the detections are scaled to the number of galaxies surveyed in each cluster, no significant correlations are found. This result implies that the number of radio galaxies detected simply scales with the number of galaxies surveyed. The higher galaxy density (and presumably higher ICM gas density) in richer clusters does not appear to affect the rate of radio source formation. The clusters are divided into Rood-Sastry and Bautz-Morgan morphological types. While it would appear that the more regular clusters have higher radio detection rates, when the classes are normalized to the number of galaxies, the radio detection rates are found to be identical regardless of cluster morphology. In conclusion, it is the optical properties of the host galaxy which most influence both the radio detection rate and the radio source properties. The cluster properties, galaxy density, and spatial location of the galaxy do not significantly affect the observed radio statistics.
- ID:
- ivo://CDS.VizieR/J/AJ/98/64
- Title:
- VLA survey of Abell clusters of galaxies I.
- Short Name:
- J/AJ/98/64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of a VLA survey at 20cm of a complete sample of nearby Abell clusters (D<=3). We have compiled an extensive catalog of cluster radio sources with S_20_>10mJy from a combination of our VLA observations and observations of similar resolution with the Westerbork Synthesis Radio Telescope (WSRT). Using these radio data and X-ray data from the Einstein observatory, we have analyzed the properties of these clusters. Unlike that previously suggested, no significant correlation is found between 20cm radio power and X-ray luminosity. There is weak evidence that richer clusters have a higher probability of radio emission. Based on Rood-Sastry morphological types of clusters, we do not find any strong evidence that regular-type clusters are statistically more likely to be radio loud than irregular-type clusters. However, Bautz-Morgan types I and II-III are found to have comparable radio-detection rates; but Bautz-Morgan Type III clusters are likely to have a lower radio-detection rate. A weak correlation between X-ray-cooling mass-accretion rates and radio powers was found for central, dominant galaxies in cooling-flow clusters. This might suggest that either cooling accretion directly fuels the central engine and/or cooling flows strongly interact with (e.g., confine) the radio plasma. In addition, radio sources associated with central dominant galaxies in cooling-flow clusters tend to be small in comparison with those in non-cooling-flow clusters. This might suggest that cooling flows tend to obstruct the propagation of radio jets from central, dominant galaxies.
