The MeerKAT Galaxy Clusters Legacy Survey: star formation in massive clusters at 0.15 < z < 0.35

TL;DR

This study uses radio data from MeerKAT to analyze star formation rates in massive galaxy clusters at redshifts 0.15 to 0.35, revealing environmental effects and differences related to radio halo presence.

Contribution

It provides the first dust-unbiased radio-based analysis of star formation in clusters at this redshift range, highlighting the impact of merger activity on star formation.

Findings

Star-forming galaxy fraction decreases towards cluster centers.

Clusters with radio haloes and relics have higher star formation activity.

Total star formation rate per cluster mass is higher in clusters with radio haloes and relics.

Abstract

We investigate dust-unbiased star formation rates (SFR) as a function of the environment in 20 massive clusters ($M_{200}>4\times10^{14} {\rm M}_{\odot}$) between $0.15<z<0.35$ using radio luminosities ($L_{\rm 1.4GHz}$) from the recently released MeerKAT Galaxy Cluster Legacy Survey catalogue. We use optical data from the Dark Energy Camera Legacy Survey to estimate photo-$z$s and assign cluster membership. We observe a steady decline in the fraction ($f_{\rm SF}$) of star-forming galaxies from $2R_{200}$ to the cluster centres in our full cluster sample, but notice a significant difference in $f_{\rm SF}$ gradients between clusters hosting large-scale extended radio emission in the form of haloes and relics (associated with ongoing merger activity) and non-radio-halo/relic hosting clusters. For star-forming galaxies within $R_{200}$, the $f_{\rm SF}$ in clusters hosting radio haloes and relics ($0.148\pm0.016$) is $\approx23\%$ higher than in non-radio-halo/relic hosting clusters ($0.120\pm0.011$). We observe a $3\sigma$ difference between the total SFR normalised by cluster mass for non-radio-halo/relic hosting clusters ($21.5\pm1.9$ M$_{\odot}$yr$^{-1}$/$10^{14}$M$_{\odot}$) and for clusters with radio haloes and relics ($26.1\pm1.4$ M$_{\odot}$yr$^{-1}$/$10^{14}$M$_{\odot}$). There is a $\approx4\times$ decline in the mass normalised total SFR of clusters for galaxies with SFR above the luminous infrared galaxies (LIRGs) SFR limit at our redshift slice, corresponding to 2 Gyr in look-back time. This is consistent with the rapid decline in SF activity with decreasing redshift amongst cluster LIRGs seen by previous studies using infrared-derived SFR.