The LOFAR Two-metre Sky Survey: The nature of the faint source population and SFR-radio luminosity relation using PROSPECTOR

Spectral energy distribution (SED) fitting has been e xtensiv ely used to determine the nature of the faint radio source population. Recent efforts have combined fits from multiple SED-fitting codes to account for the host galaxy and an y activ e nucleus that may be present. We show that it is possible to produce similar-quality classifications using a single energy-balance SED fitting code, PROSPECTOR , to model up to 26 bands of UV-far-infrared aperture-matched photometry for ∼31 000 sources in the ELAIS-N1 field from the LOFAR Two-Metre Sky Survey (LoTSS) deep fields first data release. One of a new generation of SED-fitting codes, PROSPECTOR accounts for potential contributions from radiative active galactic nuclei (AGN) when estimating galaxy properties, including star formation rates (SFRs) derived using non-parametric star formation histories. Combining this information with radio luminosities, we classify 92 percent of the radio sources as a star-forming galaxy, high-/low-excitation radio galaxy, or radio-quiet AGN and study the population demographics as a function of 150 MHz flux density , luminosity , SFR, stellar mass, redshift, and apparent r -band magnitude. Finally, we use PROSPECTOR SED fits to investigate the SFR-150 MHz luminosity relation for a sample of ∼133 000 3.6 μm-selected z < 1 sources, finding that the stellar mass dependence is significantly weaker than previously reported, and may disappear altogether at log 10 ( SFR /M yr −1 ) > 0 . 5.