LOFAR/H-ATLAS: the low-frequency radio luminosity–star formation rate relation

Abstract

Radio emission is a key indicator of star formation activity in galaxies, but the radio luminositystar formation relation has to date been studied almost exclusively at frequencies of 1.4 GHz or above. At lower radio frequencies, the effects of thermal radio emission are greatly reduced, and so we would expect the radio emission observed to be completely dominated by synchrotron radiation from supernova-generated cosmic rays. As part of the LOFAR Surveys Key Science project, the Herschel-ATLAS NGP field has been surveyed with LOFAR at an effective frequency of 150 MHz. We select a sample from the MPA-JHU catalogue of Sloan Digital Sky Survey galaxies in this area: the combination of Herschel, optical and mid-infrared data enable us to derive star formation rates (SFRs) for our sources using spectral energy distribution fitting, allowing a detailed study of the low-frequency radio luminosity-star formation relation in the nearby Universe. For those objects selected as star-forming galaxies (SFGs) using optical emission line diagnostics, we find a tight relationship between the 150 MHz radio luminosity (L 150 ) and SFR. Interestingly, we find that a single power-law relationship between L 150 and SFR is not a good description of all SFGs: a broken power-law model provides a better fit. This may indicate an additional mechanism for the generation of radio-emitting cosmic rays. Also, at given SFR, the radio luminosity depends on the stellar mass of the galaxy. Objects that were not classified as SFGs have higher 150-MHz radio luminosity than would be expected given their SFR, implying an important role for low-level active galactic nucleus activity.

Revisiting the Fanaroff–Riley dichotomy and radio-galaxy morphology with the LOFAR Two-Metre Sky Survey (LoTSS)

“…We have used the rough population divisions of Mingo et al (2016) to identify sources with hosts that are likely to be elliptical galaxies (bottom-left), star-forming galaxies (bottom-centre), starburst/ultra-luminous infrared galaxies (ULIRG, bottom-right and top-right), and AGNdominated (top-centre and top-right). Given that our sample uses the selection criteria of Hardcastle et al (2019) and Gürkan et al (2018), the sparsity of starburst/ULIRG hosts is expected, as we only retain sources for which the radio emission is in significant excess to that expected from star formation. The relative gap between AGN and host-dominated sources (around W1-W2∼ 0.4 − 0.6) can be explained through a combination of selection (Hardcastle et al 2019) and evolutionary effects (Assef et al 2010(Assef et al , 2013.…”

Fundamental differences in the radio properties of red and blue quasars: insight from the LOFAR Two-metre Sky Survey (LoTSS)

“…In this context, one may expect rQSOs to be commonly found in hosts with very high levels of SF. Since this SF is also capable of producing low-frequency radio emission (e.g., Calistro Rivera et al 2017;Gürkan et al 2018;Wang et al 2019), it is valuable to test whether the higher incidence of compact radio sources among rQSOs may be produced by an underlying population of extreme starbursts that boost their radio power.…”

Ruling out 3 keV warm dark matter using 21 cm EDGES data

“…We model the excess radio background by assuming that early galaxies produce radio frequency radiation whose strength is proportional to the SFR. The local radio-SFR (LR −Ṁ * ) relation at 150 MHz is given by Gürkan et al (2018)…”