MeerKAT observations of starburst galaxies and AGNs within the core of XMMXCS J2215.9−1738 at z  = 1.46

Abstract

We present the first detailed radio study of the galaxy cluster XMMXCS J2215.9-1738 at z = 1.46 using MeerKAT L-band (1.3 GHz) observations. We combine our radio observation with archival optical and infrared data to investigate the star formation and AGN population within R200 (R = 0.8 Mpc) of the cluster centre. Using three selection criteria; the radio luminosity, the far-infrared radio ratio (qIR) and the mid-infrared colour, we distinguish galaxies with radio emission predominantly powered by star formation from that powered by AGNs. We selected 24 cluster members within R200 in the MeerKAT image based on either their photometric or spectroscopic redshift. We classified 12/24 (50 %) as galaxies whose radio emission is dominated by star-formation activity, 6/24 (25 %) as intermediate star-forming galaxies and 6/24 (25 %) as AGN-dominated galaxies. Using the radio continuum luminosities of the star-forming cluster galaxies, we estimated an integrated star formation rate (SFR) value of 1700 ± 330 M⊙yr−1 within R200. We derived a mass-normalized integrated SFR value of (570 ± 110) × 10−14 yr−1. This supports previous observational and theoretical studies that indicated a rapid increase in star formation activity within the core of high-redshift clusters. We also show that the high AGN fraction within the cluster core is consistent with previous cluster observations at z > 1.5.