A Quick Look at the 3 GHz Radio Sky. I. Source Statistics from the Very Large Array Sky Survey

Abstract

The Very Large Array Sky Survey (VLASS) is observing the entire sky north of −40° in the S band (2 GHz < ν < 4 GHz), 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 1.9 × 106 reliably detected radio components. Due to the limitations of the Quick Look images, component flux densities are underestimated by ∼15% at S peak > 3 mJy beam−1 and are often unreliable for fainter components. We use this catalog to perform statistical analyses of the ν ∼ 3 GHz radio sky. Comparisons with the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) survey show the typical 1.4–3 GHz spectral index, α, 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 3 GHz. 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 multicomponent sources by VLASS.

Search and identification of transient and variable radio sources using MeerKAT observations: a case study on the MAXI J1820+070 field

“…This bright variable source is associated with NVSS 181752+064638 with an NVSS flux density of 100.8±3.1 mJy at 1.4 GHz (Condon et al 1998). This source is also detected in the VLASS survey with a flux density of 73.0±0.3 mJy at 2-4 GHz (Gordon et al 2021). We find this source is on average 10% brighter in our MeerKAT observations.…”

“…First, we searched for associations within existing radio catalogues at 1.4 GHz, specifically NVSS (Condon et al 1998) and VLASS (Gordon et al 2021). We find that this source is associated with NVSS J181849+062843, and has flux densities of 2.2±0.4 mJy (1.4 GHz; FIRST) and 13.8±0.3 mJy (2-4 GHz; VLASS) respectively.…”

Structural and spectral properties of Galactic plane variable radio sources

“…The other eight sources have flat or steep spectra. Compared to the peak 𝛼 = −0.71 of the spectral index distribution found by Gordon et al (2021) in about half million radio sources between 1.4 and 3.0 GHz, these sources have relatively flatter spectra. Together with their compact morphology in the CORNISH images and their variability on decadal timescales, they would represent relatively young and compact radio AGN activity (e.g.…”

“…The ASKAP Variables and Slow Transients (VAST) pilot survey has revealed a highlypolarized transient point source (Wang et al 2021) and 28 highly variable sources including several pulsars and radio stars (Murphy et al 2021). The ongoing Karl G. Jansky Very Large Array Sky Survey (VLASS) at 2-4 GHz plans to have three epochs separated by 32 months (Lacy et al 2020;Gordon et al 2021). The VLASS at the first epoch has enabled the discoveries of a transient source consistent with a merger-triggered core collapse supernova (Dong et al 2021), a decades-long extragalactic radio transient (Law et al 2018), and a sample of quasars that brightened by a factor of 2-25 on decadal timescales (Nyland et al 2020).…”

On the Fast Radio Burst and Persistent Radio Source Populations

“…By number, PRSs are a small fraction (10 −5 -10 −3 ) of a typical radio catalog (e.g., VLASS epoch 1 catalog has 1.7×10 6 sources; Gordon et al 2021). Condon et al (2019) use radio and infrared emission to classify extragalactic radio sources in the local universe.…”