A new sample of southern radio galaxies: host-galaxy masses and star-formation rates

Abstract

ABSTRACT In this study we define a new sample of distant powerful radio galaxies in order to study their host galaxy properties and provide targets for future observations of H i absorption with new radio telescopes and to understand the fuelling and feedback from such sources. We have cross-matched the Sydney University Molonglo Sky Survey (SUMSS) radio catalogue at 843 MHz with the VISTA Hemisphere Survey (VHS) near-infrared catalogue using the likelihood ratio technique. Photometric redshifts from the Dark Energy Survey are then used to assign redshifts to the radio source counterparts. We found a total of 249 radio sources with photometric redshifts over a 148 deg2 region. By fitting the optical and near-infrared photometry with spectral synthesis models we determine the stellar mass and star formation rates of the radio sources, finding typical stellar masses of 1011–1012 M⊙ for the powerful high-redshift radio galaxies. We also find a population of low-mass blue galaxies. However, by comparing the derived star formation rates to the radio luminosity, we suggest that these sources are false positives in our likelihood ratio analysis. Follow-up, higher resolution (≲5 arcsec) radio imaging would help alleviate these mid-identifications, as the limiting factor in our cross-identifications is the low resolution (∼45 arcsec) of the SUMSS radio imaging.