Star Formation Rates as a function of the Environment Using MeerKAT Observations

This study presents the study of star formation rates (SFR) in clusters using dust-unbiased radio luminosities from the MeerKAT Galaxy Clusters Legacy Survey (MGCLS). Probing the star formation (SF) activity of cluster galaxies paves an important path towards our understanding of cluster evolution. Our MeerKAT data is complemented by optical data from the Dark Energy Camera Legacy Survey (DECaLS), for photometric redshifts, and Sunyaev-Zel'dovich (SZ) effect-derived cluster masses from the Atacama Cosmology Telescope (ACT). We present the first statistical study of SFR in clusters using MeerKAT-detected galaxies. We take advantage of the large field of view coverage by MeerKAT to investigate the relation between SFR and the environment in clusters of different dynamical states. Using radio diffuse emission in the form of haloes and relics as a proxy for cluster merger activity, we divide our cluster sample between disturbed/merger clusters and relaxed clusters. We observe a higher fraction of star-forming galaxies (fSF) in disturbed clusters than in relaxed clusters. Disturbed clusters also have higher masses (M200) and total SFR (∑SFR) in contrast to relaxed clusters. On analysing the redshift evolution of mass-normalised ∑SFR, we observe a ≅ 4 times decline in SF activity from redshift of 0.35 to 0.15, corresponding to ≅ 2 Gyr in look-back time. Our result is roughly consistent with cluster studies using infrared-derived SFR (≅ 5 times decline) at a similar redshift slice as our sample. We use a subsample of double relic-hosting clusters to investigate the relation between cluster SF activity and the time that has passed since the merger started (t_merger) estimated from the relic distances from cluster cores. We observe an anti-correlation between ∑SFR and t_merger$, suggesting that younger mergers have a higher SF activity. However, we see no clear correlation in the mass-normalised ∑SFR with t_merger.