Star Formation Activity in a Young Galaxy Cluster at Z = 0.866

Abstract

The galaxy cluster RXJ1257+4738 at z = 0.866 is one of the highest redshift clusters with a richness of multiwavelength data, and thus a good target to study the star formation-density relation at early epochs. Using a sample of spectroscopically-confirmed cluster members, we derive the star formation rates of our galaxies using two methods, (I) the relation between SFR and total infrared luminosity extrapolated from the observed Spitzer MIPS 24µm imaging data, and (II) spectral energy distribution (SED) fitting using the MAGPHYS code, including eight different bands.We show that, for this cluster, the SFR-density relation is very weak and seems to be dominated by the two central galaxies and the SFR presents a mild dependence on stellar mass, with more massive galaxies having higher SFR. However, the specific SFR (SSFR) decreases with stellar mass, meaning that more massive galaxies are forming less stars per unit of mass, and thus suggesting that the increase in star-forming members is driven by cluster assembly and infall.If the environment is somehow driving the SF, one would expect a relation between the SSFR and the cluster centric distance, but that is not the case. A possible scenario to explain this lack of correlation is the contamination by infalling galaxies in the 18 inner part of the cluster which may be on their initial pass through the cluster center. As these galaxies have higher SFRs for their stellar mass, they enhance the mean SSFR in the center of the cluster.

Star-formation rates of cluster galaxies: nature versus nurture

“…Therefore only in the past few years have such data sets become available. For cluster galaxies, the dependence of the SFR on M star seems to still persist but the SFR-density for a single cluster was found to be very weak (e.g., Pintos-Castro et al 2013;Laganá et al 2016). Although to determine if these results, for a relatively young cluster, is representative of high-redshift systems, more investigation is needed.…”

ALMA Lensing Cluster Survey: average dust, gas, and star-formation properties of cluster and field galaxies from stacking analysis

“…We divided their equation by factor 1.7 (e.g. Genzel et al 2010 ;Lagan á et al 2016 ;Man et al 2016 ) in order to base our SFR (equation 4 ) on a Chabrier ( 2003 ) IMF.…”