Z-FIRE: ISM PROPERTIES OF THE z = 2.095 COSMOS CLUSTER

ABSTRACT We investigate the ISM properties of 13 star-forming galaxies within the COSMOS cluster. We show that the cluster members have [N ii]/H and [O iii]/Hβ emission-line ratios similar to field galaxies, yet systematically different emission-line ratios (by ∼0.17 dex) from the majority of local star-forming galaxies. We find no statistically significant difference in the [N ii]/H and [O iii]/Hβ line ratios or ISM pressures among the cluster galaxies and field galaxies at the same redshift. We show that our cluster galaxies have significantly larger ionization parameters (by up to an order of magnitude) than local star-forming galaxies. We hypothesize that these high ionization parameters may be associated with large specific star formation rates (SFRs; i.e., a large SFR per unit stellar mass). If this hypothesis is correct, then this relationship would have important implications for the geometry and/or the mass of stars contained within individual star clusters as a function of redshift.