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Over 700 bright millisecond-duration radio transients, known as fast radio bursts (FRBs), have been identified to date. Nevertheless, the origin of FRBs remains unknown. Two repeating FRBs (FRB 20121102A and FRB 20190520B) have been verified to be associated with persistent radio sources (PRSs), making them the best candidates to study the nature of FRBs. Monitoring the variability in PRSs is essential for understanding their physical nature. We conducted 22 observations of the PRSs linked to FRB 20121102A and FRB 20190520B using the Karl G. Jansky Very Large Array, to study their variability. We have observed significant flux variability for the PRSs of FRB 20121102A and FRB 20190520B, with a confidence level exceeding 99.99%, based on the observations covering the longest timescale recorded to date. The observed variability of the two PRSs exhibits no significant difference in amplitude across both short and long timescales. We found that the radio-derived star formation rates of the two FRB hosts are significantly higher than those measured by the optical H α emissions, indicating that their host galaxies are highly obscured or most radio emissions are not from star formation processes. The observed timescale of PRS flux evolution constrained the magnetic field of FRB 20121102A with B ∥ ≳ 1 mG and FRB 20190520B with B ∥ ≳ 0.1 mG. [ABSTRACT FROM AUTHOR]

The nearby elliptical galaxy IC 4296 has produced a large (510 kpc) low-luminosity radio source with typical FR i core/jet/lobe morphology. The unprecedented combination of brightness sensitivity, dynamic range, and angular resolution of a new 1.28 GHz MeerKAT continuum image reveals striking new morphological features, which we call threads, ribbons, and rings. The threads are faint narrow emission features originating where helical Kelvin–Helmholtz instabilities disrupt the main radio jets. The ribbons are smooth regions between the jets and the lobes, and they appear to be relics of jets powered by earlier activity that have since come into pressure equilibrium. Vortex rings in the outer portions of the lobes and their backflows indicate that the straight outer jets and ribbons are inclined by from the line of sight, in agreement with photometric, geometric, and gas-dynamical estimates of inclination angles near the nucleus. [ABSTRACT FROM AUTHOR]

We matched the 1.4 GHz local luminosity functions of star-forming galaxies (SFGs) and active galactic nuclei to the 1.4 GHz differential source counts from 0.25 μJy to 25 Jy using combinations of luminosity and density evolution. We present the most robust and complete local far-infrared (FIR)/radio luminosity correlation to date in a volume-limited sample of ≈4.3 × 103 nearby SFGs, finding that it is very tight but distinctly sublinear:. If the local FIR/radio correlation does not evolve, the evolving 1.4 GHz luminosity function of SFGs yields the evolving star formation rate density (SFRD) ψ(M⊙ yr−1 Mpc−3) as a function of time since the Big Bang. The SFRD measured at 1.4 GHz grows rapidly at early times, peaks at "cosmic noon" when t ≈ 3 Gyr and z ≈ 2, and subsequently decays with an e-folding timescale τ = 3.2 Gyr. This evolution is similar to, but somewhat stronger than, SFRD evolution estimated from UV and FIR data. [ABSTRACT FROM AUTHOR]

The Frontier Fields project is an observational campaign targeting six galaxy clusters, with the intention of using the magnification provided by gravitational lensing to study galaxies that are extremely faint or distant. We used the Karl G. Jansky Very Large Array (VLA) at 3 and 6 GHz to observe three Frontier Fields: MACS J0416.1−2403 (z = 0.396), MACS J0717.5+3745 (z = 0.545), and MACS J1149.5+2223 (z = 0.543). The images reach noise levels of ∼1 μJy beam−1 with subarcsecond resolution (∼2.5 kpc at z = 3), providing a high-resolution view of high-z star-forming galaxies that is unbiased by dust obscuration. We generate dual-frequency continuum images at two different resolutions per band, per cluster, and derive catalogs totaling 1966 compact radio sources. Components within the areas of Hubble Space Telescope and Subaru observations are cross-matched, providing host galaxy identifications for 1296 of them. We detect 13 moderately lensed (2.1 < μ < 6.5) sources, one of which has a demagnified peak brightness of 0.9 μJy beam−1, making it a candidate for the faintest radio source ever detected. There are 66 radio sources exhibiting complex morphologies, and 58 of these have host galaxy identifications. We reveal that MACS J1149.5+2223 is not a cluster with a double relic, as the western candidate relic is resolved as a double-lobed radio galaxy associated with a foreground elliptical at z = 0.24. The VLA Frontier Fields project is a public legacy survey. The image and catalog products from this work are freely available. [ABSTRACT FROM AUTHOR]

We present high spatial and frequency resolution images of the SiO masers in Stokes /, Q, U, and V around the asymptotic giant branch star IK Tau and describe and exploit a new technique for making accurate calibration of Stokes V. This technique also resulted in improved images of Stokes /. An evaluation of the results suggests that the circular polarization is neither the result of Zeeman splitting nor an alternate propagation effect. The pattern of circular and linear polarization across the maser lines shows no tendency toward that expected for simple Zeeman splitting. The fractional circular polarization greatly exceeds that expected from the alternate mechanism. The overall shape of the masing ring has changed from the elliptical form repeatedly observed over the last decade and a half. [ABSTRACT FROM AUTHOR]

We used the Karl G. Jansky Very Large Array to image one primary beam area at 3 GHz with 8″ FWHM resolution and 1.0 μJy beam–1 rms noise near the pointing center. The P(D) distribution from the central 10 arcmin of this confusion-limited image constrains the count of discrete sources in the 1 < S(μJy) < 10 range. At this level, the brightness-weighted differential count S2n(S) is converging rapidly, as predicted by evolutionary models in which the faintest radio sources are star-forming galaxies; and ≈96% of the background originating in galaxies has been resolved into discrete sources. About 63% of the radio background is produced by active galactic nuclei (AGNs), and the remaining 37% comes from star-forming galaxies that obey the far-infrared (FIR)/radio correlation and account for most of the FIR background at λ ≈ 160 μm. Our new data confirm that radio sources powered by AGNs and star formation evolve at about the same rate, a result consistent with AGN feedback and the rough correlation of black hole and stellar masses. The confusion at centimeter wavelengths is low enough that neither the planned Square Kilometre Array nor its pathfinder ASKAP EMU survey should be confusion limited, and the ultimate source detection limit imposed by “natural” confusion is ⩽0.01 μJy at ν = 1.4 GHz. If discrete sources dominate the bright extragalactic background reported by ARCADE 2 at 3.3 GHz, they cannot be located in or near galaxies and most are ⩽0.03 μJy at 1.4 GHz. [ABSTRACT FROM AUTHOR]