Jy Radio Source Research Articles

SuperCLASS – II. Photometric redshifts and characteristics of spatially resolved μJy radio sources

ABSTRACT We present optical and near-infrared imaging covering a ∼1.53 deg2 region in the Super-Cluster Assisted Shear Survey (SuperCLASS) field, which aims to make the first robust weak lensing measurement at radio wavelengths. We derive photometric redshifts for ≈176 000 sources down to $i^\prime _{\rm AB}\sim 24$ and present photometric redshifts for 1.4 GHz expanded Multi-Element Radio Linked Interferometer Network (e-MERLIN) and Karl G. Jansky Very Large Array (VLA) detected radio sources found in the central 0.26 deg2. We compile an initial catalogue of 149 radio sources brighter than S1.4 > 75 μJy and find their photometric redshifts span 0 < zphot < 4 with radio luminosities between 1021 and 1025 W Hz−1, with medians of $\langle z \rangle \, =0.55$ and $\langle L_{1.4}\rangle \, =1.9\times 10^{23}$ W Hz−1, respectively. We find 95 per cent of the μJy radio source sample (141/149) have spectral energy distributions (SEDs) best fit by star-forming templates while 5 per cent (8/149) are better fit by active galactic nuclei (AGN). Spectral indices are calculated for sources with radio observations from the VLA and Giant Metrewave Radio Telescope (GMRT) at 325 MHz, with an average spectral slope of α = 0.59 ± 0.04. Using the full photometric redshift catalogue, we construct a density map at the redshift of the known galaxy clusters, z = 0.20 ± 0.08. Four of the five clusters are prominently detected at $\gt 7\, \sigma$ in the density map and we confirm the photometric redshifts are consistent with previously measured spectra from a few galaxies at the cluster centres.

A New Detection of Extragalactic Anomalous Microwave Emission in a Compact, Optically Faint Region of NGC 4725

Abstract We discuss the nature of a discrete, compact radio source (NGC 4725 B) located ≈1.9 kpc from the nucleus in the nearby star-forming galaxy NGC 4725, which we believe to be a new detection of extragalactic anomalous microwave emission (AME). Based on detections at 3, 15, 22, 33, and 44 GHz, NGC 4725 B is a microjansky radio source peaking at ≈33 GHz. While the source is not identified in optical (BVRI) photometry, we detect counterparts in the midinfrared Spitzer/IRAC bands (3.6, 4.5, 5.8, 8.0 μm) that appear to be associated with dust emission in the central region of NGC 4725. Consequently, we conclude that NGC 4725 B is a new detection of AME and is very similar to a recent detection of AME in an outer-disk star-forming region in NGC 6946. We find that models of electric dipole emission from rapidly rotating ultra-small grains are able to reproduce the radio spectrum for reasonable interstellar medium conditions. Given the lack of an optical counterpart and the shape of the radio spectrum, NGC 4725 B appears consistent with a nascent star-forming region in which young (≲3 Myr) massive stars are still highly enshrouded by their natal cocoons of gas and dust with insufficient supernovae occurring to produce a measurable amount of synchrotron emission.

A near-IR study of the host galaxies of 2 Jy radio sources at 0.03 ≲z≲ 0.5 - I. The data★

We present the results of a program of K- and Ks-band imaging of a sample of 2Jy radio galaxies with redshifts 0.03 < z < 0.5, for which the host galaxy morphologies and structural parameters (effective radius, Sersic index and unresolved nuclear point source contribution) have been determined using GALFIT. Two-thirds of our sample are best modelled as being hosted by massive elliptical galaxies with Sersic indices of n=4-6, with the remainder being better suited either by a mixture of morphological components (usually a bulge plus a small, less luminous, disk component) or by more disky galaxy models with n=1-2. Our measured galaxy sizes are generally in very good agreement with other imaging programs, both space- and ground-based. We also determine a slightly higher average nuclear point source contribution than similar HST-based programs. This is due to our inability to separate the AGN emission from compact circum-nuclear stellar emission, but does not bias our modelling of the remainder of the host galaxies and our results remain robust. We also observe that roughly half of the objects in our sample are either undergoing major or minor merger activity or are clearly morphologically disturbed.

A catalogue of Jy radio sources in northern legacy fields

We present catalogues of faint 1.4-GHz radio sources from extremely deep Very Large Array pointings in the Lockman Hole, the Hubble Deep Field-North (HDF-N) and the European Large Area ISO Survey (ELAIS) N2 field. Our analysis of the HDF-N data has produced maps that are significantly deeper than those previously published, and we have used these to search for counterparts to submillimetre sources. For each of the fields, we have derived normalized differential source counts and in the case of the HDF-N find no evidence for the previously reported underdensity of sources; our counts are entirely consistent with those found for the majority of other fields. The catalogues are available as an online supplement to this paper and the maps are also available for download.

Neutral Hydrogen 21 Centimeter Absorption at Redshift 0.673 toward 1504+377

We detect the 21 cm line of neutral hydrogen in absorption at a redshift of 0.673 toward the 1 Jy radio source 1504+377. The 1504+377 radio source is located toward the center of what appears to be an inclined disk galaxy at z = 0.674. The 21 cm absorption line shows multiple velocity components over a velocity range of about 100 km s-1, with a total H I column density of N(H I) = 3.8 × 1019(Ts/f) cm-2. The velocity-integrated optical depth of this system is the largest yet seen for redshifted H I 21 cm absorption-line systems. The 21 cm absorption line is coincident in redshift with a previously detected broad molecular absorption line system. We do not detect H I 21 cm absorption associated with the narrow molecular absorption line system at z = 0.67150, nor do we detect absorption at these redshifts by the 18 cm lines of OH, nor by the 2 cm transition of H2CO. There is no evidence for a bright optical active galactic nucleus (AGN) in 1504+377, suggesting significant obscuration through the disk—a hypothesis supported by the strong absorption observed. The 1504+377 system resembles the red quasar PKS 1413+135, which has been modeled as an optically obscured AGN with a very young radio jet in the center of a gas-rich disk galaxy. The presence of very bright radio jets at the centers of these two disk galaxies presents a challenge to unification schemes for extragalactic radio sources and to models for the formation of radio-loud AGNs.

The Canada–France Redshift Survey – VII. Optical counterparts of microjansky radio sources

Deep imaging and spectroscopy have been carried out for optical counterparts of a complete sample of S$>$16 $\mu$Jy radiosources during the course of the Canada-France Redshift Survey (CFRS). All 36 sources but two have been optically identified, and spectra have been obtained for 23 of them. The objects brighter than $I_{AB}<$22.5 for which we have spectra reveal three populations dominating the $\mu$Jy radio counts: z$>$0.7 early-type galaxies with radio emission powered by an AGN, intermediate redshift post-starburst galaxies, and lower redshift blue emission-line objects. From their radio and optical properties, it is argued that the 11 objects fainter than $I_{AB}>$22.5 are mostly at z$>$1, and one half of them are probably early-type galaxies. We conclude that $\sim$40 per cent of the $\mu$Jy sources are likely to be at z $>$1. Between one third and one half of the luminous ellipticals in this field beyond z = 0.7 show moderately powerful radio emission (P $\sim$ 5 10$^{23}$ W Hz$^{-1}$) which is at least 10 times more powerful than seen in local samples, and probably reflects evolution of the activity in their nuclei. Only one classical starburst galaxy is identified in the sample; the rest of the blue emission-line objects show optical and radio activity more typical of low power AGNs than starbursts. The number of post-starbursts at $\mu$Jy levels is considerably higher than the surface density of mJy starburst galaxies, suggesting the latter are the parent population of the former. While starburst galaxies are considered to be major contributors to the mJy radiosources counts, the majority of the $\mu$Jy radio sources appear to be related to AGN activity rather than to normal star