The LOFAR Two-metre Sky Survey - IV. First Data Release: Photometric redshifts and rest-frame magnitudes

Duncan, K.; Sabater, J.; Rottgering, H.; Jarvis, M.; Smith, D.J.B.; Best, P.N.; Callingham, J.R.; Cochrane, R.; Croston, J.H.; Mingo, B.; Morabito, L.; Nisbet, D.; Prandoni, I.; Shimwell, T. W.; Tasse, C.; White, G. J.; Williams, W. L.; Alegre, L.; Chyży, K. T.; Gürkan, G.; Hoeft, M.; Kondapally, R.; Mechev, A. P.; Miley, G. K.; Schwarz, D. J. and van Weeren, R. J. (2019). The LOFAR Two-metre Sky Survey - IV. First Data Release: Photometric redshifts and rest-frame magnitudes. Astronomy & Astrophysics, 622, article no. A3.

DOI: https://doi.org/10.1051/0004-6361/201833562

Abstract

The LOFAR Two-metre Sky Survey (LoTSS) is a sensitive, high-resolution 120-168 MHz survey of the Northern sky. The LoTSS First Data Release (DR1) presents 424 square degrees of radio continuum observations over the HETDEX Spring Field (10h45m00s < right ascension < 15h30m00s and 45^∘00′00′ < declination < 57^∘00′00′′) with a median sensitivity of 71μJy/beam and a resolution of 6′′. In this paper we present photometric redshifts (photo-z) for 94.4% of optical sources over this region that are detected in the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) 3π steradian survey. Combining the Pan-STARRS optical data with mid-infrared photometry from the Wide-field Infrared Survey Explorer, we estimate photo-zs using a novel hybrid photometric redshift methodology optimised to produce the best possible performance for the diverse sample of radio continuum selected sources. For the radio-continuum detected population, we find an overall scatter in the photo-z of 3.9% and an outlier fraction (|z_phot−z_spec|/(1+z_spec)>0.15) of 7.9%. We also find that, at a given redshift, there is no strong trend in photo-z quality as a function of radio luminosity. However there are strong trends as a function of redshift for a given radio luminosity, a result of selection effects in the spectroscopic sample and/or intrinsic evolution within the radio source population. Additionally, for the sample of sources in the LoTSS First Data Release with optical counterparts, we present rest-frame optical and mid-infrared magnitudes based on template fits to the consensus photometric (or spectroscopic when available) redshift.

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