Star Formation Activity in CLASH Brightest Cluster Galaxies

TL;DR

This study investigates star formation in brightest cluster galaxies within the CLASH sample, revealing correlations with cluster core properties, evidence of ongoing starbursts, and supporting feedback-regulated cooling models.

Contribution

It provides detailed multi-wavelength analysis of star formation activity and history in BCGs, linking it to cluster gas properties and AGN activity, with high-resolution stellar property maps.

Findings

Star formation occurs mainly in low-entropy cluster cores.

Star formation rates range from moderate to very high (>100 M_sun/yr).

Evidence of recent and ongoing starburst activity in filaments.

Abstract

The CLASH X-ray selected sample of 20 galaxy clusters contains ten 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$\alpha$+[\ion{N}{2}] emission in knots and filaments detected in CLASH HST ACS and WFC3 observations. UV-derived SFRs in these BCGs span two orders of magnitude, including two with a SFR $\gtrsim$ 100 M$_{\odot}$ yr$^{-1}$. These measurements are supplemented with [\ion{O}{2}], [\ion{O}{3}], 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 $\sim$350 pc. These maps reveal evidence for an ongoing burst occurring in elongated filaments, generally on $\sim$ 0.5-1.0 Gyr timescales, although some filaments are consistent with much younger ($\lesssim$ 100 Myr) burst timescales and may be correlated with recent activity from the AGN. The relationship between BCG SFRs and the surrounding ICM gas properties provide new support for the process of feedback-regulated cooling in galaxy clusters and is consistent with recent theoretical predictions.