Cosmic evolution of low-excitation radio galaxies in the LOFAR two-metre sky survey deep fields

• Published in: Monthly notices of the Royal Astronomical Society 2022-05, Vol.513 (3), p.3742-3767
• Main Authors: Kondapally, Rohit, Best, Philip N, Cochrane, Rachel K, Sabater, José, Duncan, Kenneth J, Hardcastle, Martin J, Haskell, Paul, Mingo, Beatriz, Röttgering, Huub J A, Smith, Daniel J B, Williams, Wendy L, Bonato, Matteo, Calistro Rivera, Gabriela, Gao, Fangyou, Hale, Catherine L, Małek, Katarzyna, Miley, George K, Prandoni, Isabella, Wang, Lingyu
• Format: Article
• Language: English
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stac1128

ABSTRACT Feedback from low-excitation radio galaxies (LERGs) plays a key role in the lifecycle of massive galaxies in the local Universe; their evolution, and the impact of these active galactic nuclei on early galaxy evolution, however, remain poorly understood. We use a sample of 10 481 LERGs from the first data release of the LOFAR two-metre Sky Survey Deep Fields, covering ∼25 deg2, to present the first measurement of the evolution of the radio luminosity function (LF) of LERGs out to z ∼ 2.5; this shows relatively mild evolution. We split the LERGs into those hosted by quiescent and star-forming galaxies, finding a new dominant population of LERGs hosted by star-forming galaxies at high redshifts. The incidence of LERGs in quiescent galaxies shows a steep dependence on stellar mass out to z ∼ 1.5, consistent with local Universe measurements of accretion occurring from cooling of hot gas haloes. The quiescent-LERGs dominate the LFs at z < 1, showing a strong decline in space density with redshift, tracing that of the available host galaxies, while there is an increase in the characteristic luminosity. The star-forming LERG LF increases with redshift, such that this population dominates the space densities at most radio-luminosities by z ∼ 1. The incidence of LERGs in star-forming galaxies shows a much weaker stellar-mass dependence, and increases with redshift, suggesting a different fuelling mechanism compared to their quiescent counterparts, potentially associated with the cold gas supply present in the star-forming galaxies.