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

Abstract

We present optical and near-infrared imaging covering a ∼1.53 deg 2 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 AB ∼ 24 and present photometric redshifts for 1.4 GHz e-MERLIN and VLA detected radio sources found in the central 0.26 deg 2 . We compile an initial catalog of 149 radio sources brighter than S 1.4 > 75 µJy and find their photometric redshifts span 0 < z phot < 4 with radio luminosities between 10 21 − 10 25 W Hz −1 , with medians of z = 0.55 and L 1.4 = 1.9 × 10 23 W Hz −1 respectively. We find 95% of the µJy radio source sample (141/149) have SEDs best fit by star-forming templates while 5% (8/149) are better fit by AGN. Spectral indices are calculated for sources with radio observations from VLA and GMRT at 325 MHz, with an average spectral slope of α = 0.59 ± 0.04. Using the full photometric redshift catalog 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 > 7 σ in the density map and we confirm the photometric redshifts are consistent with previously measured spectra from a few galaxies at the cluster centers.

Intrinsic alignments of the extended radio continuum emission of galaxies in the EAGLE simulations

“…In principle, ho we ver, shear measurements can also be made using the extended radio continuum emission of the interstellar medium. To date, deep radio surv e ys such as the VLA-COSMOS (Smol či ć et al 2017 ) and the SuperCLuster Assisted Shear Surv e y (SuperCLASS; Battye et al 2020 ;Harrison et al 2020 ;Manning et al 2020 ) have yielded insufficient source counts of galaxies ( ࣠ 1 arcmin −2 o v er a few square degrees) to enable meaningful shear measurements, but surv e ys conducted with the forthcoming Square Kilometer Array (SKA) have the potential to yield competitive measurements. The first phase (SKA1) is forecast to achieve galaxy source counts of 2.27 arcmin −2 o v er 5000 deg 2 (Square Kilometre Array Cosmology Science Working Group et al 2020 ), while Brown et al ( 2015 ) suggest that the most optimistic second phase (SKA2) implementation would deliver 30 galaxies arcmin −2 o v er 3 π steradians.…”

Intrinsic alignments of the extended radio continuum emission of galaxies in the EAGLE simulations

“…In principle, however, shear measurements can also be made using the extended radio continuum emission of the interstellar medium. To date, deep radio surveys such as the VLA-COSMOS (Smolčić et al 2017) and the SuperCLuster Assisted Shear Survey (SuperCLASS; Battye et al 2020;Harrison et al 2020;Manning et al 2020) have yielded insufficient source counts of galaxies ( 1 arcmin −2 over a few square degrees) to enable meaningful shear measurements, but surveys conducted with the forthcoming Square Kilometer Array (SKA) have the potential to yield competitive measurements. The first phase (SKA1) is forecast to achieve galaxy source counts of 2.27 arcmin −2 over 5000 deg 2 (Square Kilometre Array Cosmology Science Working Group et al 2020), while Brown et al (2015) suggest that the most optimistic second phase (SKA2) implementation would deliver 30 galaxies arcmin −2 over 3𝜋 steradians.…”