Starbursting Brightest Cluster Galaxy: a Herschel view of the massive cluster MACS J1931.8-2634

TL;DR

This study uses Herschel FIR imaging to analyze dust-obscured star formation in the galaxy cluster MACS J1931.8-2634, revealing a luminous BCG with significant star formation and no evidence of cooling flows, indicating complex galaxy evolution processes.

Contribution

First detailed FIR analysis of the star formation and AGN activity in the BCG of MACS J1931.8-2634 using Herschel data, including SED decomposition and X-ray cooling flow assessment.

Findings

The BCG is an Ultra Luminous Infrared Galaxy with SFR=150 M_sun/yr.

FIR SED shows equal contributions from AGN and starburst.

No evidence of gas cooling below 1.8 keV in the core.

Abstract

We investigate the dust-obscured star formation properties of the massive, X-ray selected galaxy cluster MACS J1931.8-2634 at $z$=0.352. Using far-infrared (FIR) imaging in the range 100-500$\mu$m obtained with the \textit{Herschel} telescope, we extract 31 sources (2$\sigma$) within $r\sim$1 Mpc from the brightest cluster galaxy (BCG). Among these sources we identify six cluster members for which we perform an analysis of their spectral energy distributions (SEDs). We measure total infrared luminosity (L$_{IR}$), star formation rate (SFR) and dust temperature. The BCG, with L$_{IR}$=1.4$\times$10$^{12}$L$_\odot$ is an Ultra Luminous Infrared Galaxy and hosts a type II AGN. We decompose its FIR SED into AGN and starburst components and find equal contributions from AGN and starburst. We also recompute the SFR of the BCG finding SFR=150$\pm$15 M$_\odot$yr$^{-1}$. We search for an isobaric cooling flow in the cool core using {\sl Chandra} X-ray data, and find no evidence for gas colder than 1.8 keV in the inner 30 kpc, for an upper limit to the istantaneous mass-deposition rate of 58 M$_\odot$yr$^{-1}$ at 95 % c.l. This value is $3\times$ lower than the SFR in the BCG, suggesting that the on-going SF episode lasts longer than the ICM cooling events.