The relationship between brightest cluster galaxy star formation and the intracluster medium in CLASH.
FOGARTY K., POSTMAN M., LARSON R., DONAHUE M. and MOUSTAKAS J.
Abstract (from CDS):
We study the nature of feedback mechanisms in the 11 CLASH brightest cluster galaxies (BCGs) that exhibit extended ultraviolet and nebular line emission features. We estimate star formation rates (SFRs), dust masses, and starburst durations using a Bayesian photometry-fitting technique that accounts for both stellar and dust emission from the UV through far-IR. By comparing these quantities to intracluster medium (ICM) cooling times and freefall times derived from X-ray observations and lensing estimates of the cluster mass distribution, we discover a tight relationship between the BCG SFR and the ICM cooling time to freefall time ratio, tcool/tff, with an upper limit on the intrinsic scatter of 0.15 dex. Furthermore, starburst durations may correlate with ICM cooling times at a radius of 0.025 R500, and the two quantities converge upon reaching the gigayear regime. Our results provide a direct observational link between the thermodynamical state of the ICM and the intensity and duration of BCG star formation activity, and appear consistent with a scenario where active galactic nuclei induce condensation of thermally unstable ICM overdensities that fuel long-duration (>1 Gyr) BCG starbursts. This scenario can explain (a) how gas with a low cooling time is depleted without causing a cooling flow and (b) the scaling relationship between SFR and tcool/tff. We also find that the scaling relation between SFR and dust mass in BCGs with SFRs 100 M☉ yr–1 is similar to that in star-forming field galaxies; BCGs with large ( 100 M☉ yr–1) SFRs have dust masses comparable to extreme starbursts.