Galaxy formation and evolution

Abstract:

Published by Oxford University Press on behalf of the Royal Astronomical Society. We have combined spectroscopic and photometric data from the Sloan Digital Sky Survey with 1.4 GHz radio observations, conducted as part of the Stripe 82 1-2 GHz Snapshot Survey using the Karl G. Jansky Very Large Array, which covers ~100 sq deg, to a flux limit of 88 μJy rms. Cross-matching the 11 768 radio source components with optical data via visual inspection results in a final sample of 4794 cross-matched objects, of which 1996 have spectroscopic redshifts and 2798 objects have photometric redshifts. Three previously undiscovered giant radio galaxies were found during the cross-matching process, which would have been missed using automated techniques. For the objects with spectroscopy, we separate radio-loud active galactic nuclei (AGN) and star-forming galaxies (SFGs) using three diagnostics and then further divide our radio-loud AGN into the high and low excitation radio galaxy (HERG and LERG) populations. A control-matched sample of HERGs and LERGs, matched on stellar mass, redshift, and radio luminosity, reveals that the host galaxies of LERGs are redder and more concentrated than HERGs. By combining with near-infrared data, we demonstrate that LERGs also follow a tight K - z relationship. These results imply the LERG populations are hosted by population ofmassive, passively evolving early-type galaxies. We go on to show that HERGs, LERGs, quasars, and SFGs in our sample all reside in different regions of aWide-field Infrared Survey Explorer colour-colour diagram. This cross-matched sample bridges the gap between previous 'wide but shallow' and 'deep but narrow' samples and will be useful for a number of future investigations.