STAR FORMATION ACTIVITY IN CLASH BRIGHTEST CLUSTER GALAXIES

The CLASH X-ray selected sample of 20 galaxy clusters contains 10 brightest cluster galaxies (BCGs) that exhibit significant (>5 sigma) extinction-corrected star formation rates (SFRs). Star formation activity is inferred from photometric estimates of UV and H alpha+[N II] emission in knots and filaments detected in CLASH Hubble Space Telescope ACS and WFC3 observations. UV-derived SFRs in these BCGs span two orders of magnitude, including two with a SFR greater than or similar to 100 M-circle dot yr(-1). These measurements are supplemented with [O II], [O III], and H beta fluxes measured from spectra obtained with the SOAR telescope. We confirm that photoionization from ongoing star formation powers the line emission nebulae in these BCGs, although in many BCGs there is also evidence of a LINER-like contribution to the line emission. Coupling these data with Chandra X-ray measurements, we infer that the star formation occurs exclusively in low-entropy cluster cores and exhibits a correlation with gas properties related to cooling. We also perform an in-depth study of the starburst history of the BCG in the cluster RXJ1532.9 +3021, and create 2D maps of stellar properties on scales down to similar to 350 pc. These maps reveal evidence for an ongoing burst occurring in elongated filaments, generally on similar to 0.5-1.0 Gyr timescales, although some filaments are consistent with much younger (less than or similar to 100 Myr) burst timescales and may be correlated with recent activity from the active galactic nucleus. The relationship between BCG SFRs and the surrounding intracluster medium gas properties provide new support for the process of feedback-regulated cooling in galaxy clusters and is consistent with recent theoretical predictions.