Red but not dead: unveiling the star-forming far-infrared spectral energy distribution of SpARCS brightest cluster galaxies at 0 < z < 1.8

• DOI: 10.1093/mnras/stx722
• Publication Date: 2017-03-24T00:03:48Z
• Authors: N. R. Bonaventura; T. M. A. Webb; A. Muzzin; A. Noble; C. Lidman; G. Wilson; H. K. C. Yee; J. Geach; Y. Hezaveh; D. Shupe; J. Surace
• Keywords: Astrophysics of Galaxies (astro-ph.GA); 0103 physical sciences; FOS: Physical sciences; galaxies: clusters: general – galaxies: evolution – galaxies: formation – galaxies: photometry – galaxies: star formation – infrared: galaxies; 530; Astrophysics - Astrophysics of Galaxies; 01 natural sciences; 520

We present the results of a Spitzer/Herschel infrared photometric analysis of the largest (716) and highest-redshift (z=1.8) sample of Brightest Cluster Galaxies (BCGs), those from the Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS). Given the tension that exists between model predictions and recent observations of BCGs at z<2, we aim to uncover the dominant physical mechanism(s) guiding the stellar-mass buildup of this special class of galaxies, the most massive in the Universe uniquely residing at the centres of galaxy clusters. Through a comparison of their stacked, broadband, infrared spectral energy distributions (SEDs) to a variety of SED model templates in the literature, we identify the major sources of their infrared energy output, in multiple redshift bins between 0 < z < 1.8. We derive estimates of various BCG physical parameters from the stacked ��L�� SEDs, from which we infer a star-forming, as opposed to a 'red and dead' population of galaxies, producing tens to hundreds of solar masses per year down to z=0.5. This discovery challenges the accepted belief that BCGs should only passively evolve through a series of gas-poor, minor mergers since z~4 (De Lucia & Blaizot 2007), but agrees with the improved semi-analytic model of hierarchical structure formation of Tonini et al. (2012), which predicts star-forming BCGs throughout the epoch considered. We attribute the star formation inferred from the stacked infrared SEDs to both major and minor 'wet' (gas-rich) mergers, based on a lack of key signatures (to date) of the cluster cooling flows to which BCG star formation is typically attributed, as well as a number of observational and simulation-based studies that support this scenario.<br/>26 pages, 7 tables, 7 figures<br/>