The LOFAR Two-metre Sky Survey Deep Fields

Abstract

In this paper, we investigate the relationship between 150 MHz luminosity and the star-formation rate – the SFR-L150 MHz relation – using 150 MHz measurements for a near-infrared selected sample of 118 517 z < 1 galaxies. New radio survey data offer compelling advantages over previous generation surveys for studying star formation in galaxies, including huge increases in sensitivity, survey speed, and resolution, while remaining impervious to extinction. The LOFAR Surveys Key Science Project is transforming our understanding of the low-frequency radio sky, with the 150 MHz data over the European Large Area Infrared Space Observatory Survey-North 1 field reaching an rms sensitivity of 20 μJy beam−1 over 10 deg2 at 6 arcsec resolution. All of the galaxies studied have SFR and stellar mass estimates that were derived from energy balance spectral energy distribution fitting using redshifts and aperture-matched forced photometry from the LOFAR Two-metre Sky Survey (LoTSS) Deep Fields data release. The impact of active galactic nuclei (AGN) is minimised by leveraging the deep ancillary data in the LoTSS data release, alongside median-likelihood methods that we demonstrate are resistant to AGN contamination. We find a linear and non-evolving SFR-L150 MHz relation, apparently consistent with expectations based on calorimetric arguments, down to the lowest SFRs < 0.01M⊙ yr−1. However, we also recover compelling evidence for stellar mass dependence in line with previous work on this topic, in the sense that higher mass galaxies have a larger 150 MHz luminosity at a given SFR, suggesting that the overall agreement with calorimetric arguments may be a coincidence. We conclude that, in the absence of AGN, 150 MHz observations can be used to measure accurate galaxy SFRs out to z = 1 at least, but it is necessary to account for stellar mass in the estimation in order to obtain 150 MHz-derived SFRs accurate to better than 0.5 dex. Our best-fit relation is log10(L150 MHz ∕W Hz−1) = (0.90 ± 0.01)log10(ψ∕M⊙ yr−1) + (0.33 ± 0.04)log10(M∕1010M⊙) + 22.22 ± 0.02.

The LOFAR Two-metre Sky Survey Deep fields

“…To investigate how the FIRC depends on redshift and stellar mass we need to construct mass complete samples. We use the magphys SED fits from Smith et al (2021) in ELAIS-N1 to construct a mass complete sample. Smith et al (2021) used magphys to measure the SED for galaxies in the LOFAR catalogues with 2021) SED fits.…”

“…We use the magphys SED fits from Smith et al (2021) in ELAIS-N1 to construct a mass complete sample. Smith et al (2021) used magphys to measure the SED for galaxies in the LOFAR catalogues with 2021) SED fits. The red contours show the distribution for galaxies with a detection at 150MHz and the grey histogram shows the distribution for the galaxies without a detection at 150MHz.…”

“…They also found that galaxies not classified as SF had a greater radio luminosity than would be predicted from their SFR, implying low level AGN activity. This work was expanded on by Read et al (2018); Smith et al (2021) which found the FIRC to explicitly vary with stellar mass and redshift. A redshift evolution was also found by Calistro Rivera et al ( 2017) using a radio-selected sample from LOFAR data at 150MHz in Boötes.…”

“…In particular, the high mass, low redshift galaxies (z<0.4) have a higher normalisation than the higher redshift (z>0.4) galaxies. In addition, using the LoTSS deep field data in ELAIS-N1, Smith et al (2021) found that the radio luminosity -SFR relation is mass dependant i.e for a given radio luminosity a higher mass galaxy will have a lower SFR than a galaxy with a lower stellar mass. Smith et al (2014) and Read et al (2018) showed that as dust temperature increases the FIRC decreases for monochromatic fluxes (fluxes were measured at 100, 160, 250, 350 and 500 µm).…”

The GLEAM 200-MHz local radio luminosity function for AGN and star-forming galaxies

“…Condon, 1992). Smith et al (2021) studied the relationship between 150-MHz luminosity and SFR using LOFAR measurements at 150 MHz for a near-infrared selected sample of z < 1 galaxies. We derive SFRs for the SF galaxies in our sample using their best-fit relation, which where ϒ K is the mass-to-light ratio in the K-band and M K, abs, Sun is the absolute K-band magnitude of the Sun.…”