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We made two new sensitive (rms noise μJy beam−1) high-resolution (θ = 3.″0 and θ = 0.″66 FWHM) S-band (2 < ν < 4 GHz) images covering a single JVLA primary beam (FWHM ≈ 14′) centered on J2000 , δ = +59°01′ in the Lockman Hole. These images yielded a catalog of 792 radio sources, 97.7 ± 0.8% of which have infrared counterparts stronger than S ≈ 2 μJy at λ = 4.5 μm. About 91% of the radio sources found in our previously published, comparably sensitive low-resolution (θ = 8″ FWHM) image covering the same area were also detected at 0.″66 resolution, so most radio sources with S(3 GHz) ≳ 5 μJy have angular structure ϕ ≲ 0.″66. The ratios of peak brightness in the 0.″66 and 3″ images have a distribution indicating that most μJy radio sources are quite compact, with a median Gaussian angular diameter FWHM and an rms scatter σϕ ≲ 0.″3 of individual sizes. Most of our μJy radio sources obey the tight far-infrared/radio correlation, indicating that they are powered by star formation. The median effective angular radius enclosing half the light emitted by an exponential disk is , so the median effective radius of star-forming galaxies at redshifts z ∼ 1 is . [ABSTRACT FROM AUTHOR]

We report the appearance of a new radio source at a projected offset of 460 pc from the nucleus of Cygnus A. The flux density of the source (which we designate Cygnus A-2) rose from an upper limit of <0.5 mJy in 1989 to 4 mJy in 2016 (ν = 8.5 GHz), but is currently not varying by more than a few percent per year. The radio luminosity of the source is comparable to the most luminous known supernovae, it is compact in Very Long Baseline Array observations down to a scale of 4 pc, and it is coincident with a near-infrared point source seen in pre-existing adaptive optics and HST observations. The most likely interpretation of this source is that it represents a secondary supermassive black hole in a close orbit around the Cygnus A primary, though an exotic supernova model cannot be ruled out. The gravitational influence of a secondary SMBH at this location may have played an important role in triggering the rapid accretion that has powered the Cygnus A radio jet over the past 107 years. [ABSTRACT FROM AUTHOR]

We discuss 6 GHz JVLA observations covering a volume-limited sample of 178 low-redshift () optically selected quasi-stellar objects (QSOs). Our 176 radio detections fall into two clear categories: (1) about 20% are radio-loud QSOs (RLQs) with spectral luminosities of that are primarily generated in the active galactic nucleus (AGN) responsible for the excess optical luminosity that defines a bona fide QSO; and (2) the remaining 80% that are radio-quiet QSOs (RQQs) that have and radio sizes , and we suggest that the bulk of their radio emission is powered by star formation in their host galaxies. “Radio-silent” QSOs () are rare, so most RQQ host galaxies form stars faster than the Milky Way; they are not “red and dead” ellipticals. Earlier radio observations did not have the luminosity sensitivity of that is needed to distinguish between such RLQs and RQQs. Strong, generally double-sided radio emission spanning was found to be associated with 13 of the 18 RLQ cores with peak flux densities of (). The radio luminosity function of optically selected QSOs and the extended radio emission associated with RLQs are both inconsistent with simple “unified” models that invoke relativistic beaming from randomly oriented QSOs to explain the difference between RLQs and RQQs. Some intrinsic property of the AGNs or their host galaxies must also determine whether or not a QSO appears radio-loud. [ABSTRACT FROM AUTHOR]

The Planck mission detected thousands of extragalactic radio sources at frequencies from 28 to 857 GHz. Planck's calibration is absolute (in the sense that it is based on the satellite’s annual motion around the Sun and the temperature of the cosmic microwave background), and its beams are well characterized at sub-percent levels. Thus, Planck's flux density measurements of compact sources are absolute in the same sense. We have made coordinated Very Large Array (VLA) and Australia Telescope Compact Array (ATCA) observations of 65 strong, unresolved Planck sources in order to transfer Planck's calibration to ground-based instruments at 22, 28, and 43 GHz. The results are compared to microwave flux density scales currently based on planetary observations. Despite the scatter introduced by the variability of many of the sources, the flux density scales are determined to 1%–2% accuracy. At 28 GHz, the flux density scale used by the VLA runs 2%–3% ± 1.0% below Planck values with an uncertainty of at 43 GHz, the discrepancy increases to 5%–6% ± 1.4% for both ATCA and the VLA. [ABSTRACT FROM AUTHOR]