THE RELATION BETWEEN COOL CLUSTER CORES ANDHERSCHEL-DETECTED STAR FORMATION IN BRIGHTEST CLUSTER GALAXIES

Abstract

We present far-infrared (FIR) analysis of 68 brightest cluster galaxies (BCGs) at 0.08 < z < 1.0. Deriving total infrared luminosities directly from Spitzer and Herschel photometry spanning the peak of the dust component (24-500 μm), we calculate the obscured star formation rate (SFR). 22 +6.2 −5.3 % of the BCGs are detected in the farinfrared, with SFR = 1-150 M yr −1 . The infrared luminosity is highly correlated with cluster X-ray gas cooling times for cool-core clusters (gas cooling time <1 Gyr), strongly suggesting that the star formation in these BCGs is influenced by the cluster-scale cooling process. The occurrence of the molecular gas tracing Hα emission is also correlated with obscured star formation. For all but the most luminous BCGs (L TIR > 2 × 10 11 L ), only a small ( 0.4 mag) reddening correction is required for SFR(Hα) to agree with SFR FIR . The relatively low Hα extinction (dust obscuration), compared to values reported for the general star-forming population, lends further weight to an alternate (external) origin for the cold gas. Finally, we use a stacking analysis of non-cool-core clusters to show that the majority of the fuel for star formation in the FIR-bright BCGs is unlikely to originate from normal stellar mass loss.

STAR-FORMING BRIGHTEST CLUSTER GALAXIES AT 0.25 < z < 1.25: A TRANSITIONING FUEL SUPPLY

“…These surveys include both optically selected (McDonald 2011;M. McDonald et al, in preparation) and X-ray-selected (Donahue et al 1992Hoffer et al 2012;Rawle et al 2012;Fraser-McKelvie et al 2014;Donahue et al 2015) clusters, and are being compared here to an SZ-selected sample. For the ACCEPT (Cavagnolo et al 2009) and CLASH ) samples, we apply a small correction because both of these cluster samples are biased toward cool core clusters.…”

“…Figure 5 demonstrates that, at 0.5z1, BCGs are evolving similarly to the cluster member galaxies, suggesting a common fueling mechanism. At low-z (z0.5), the evolution of BCGs is less rapid than in the cluster environment, suggesting that the quenching processes acting on member Donahue et al 1992Donahue et al , 2010Donahue et al , 2015McDonald 2011;Hoffer et al 2012;Rawle et al 2012;Fraser-McKelvie et al 2014). Samples marked with an asterisk in the legend have had a bias correction applied, assuming that non-cool cores have passively evolving BCGs and that the true underlying fraction of cool cores is 30% (see Section 3.2).…”

“…Early work focused on searching for multiphase gas and star formation in brightest cluster galaxies (BCGs). Numerous studies have found evidence for ultraviolet (UV) and infrared (IR) continuum (e.g., McNamara & O'Connell 1989;Hicks & Mushotzky 2005;O'Dea et al 2008;McDonald et al 2011b;Hoffer et al 2012;Rawle et al 2012;Fraser-McKelvie et al 2014;Donahue et al 2015), warm, ionized gas (e.g., Hu et al 1985;Johnstone et al 1987;Heckman et al 1989;Crawford et al 1999;Edwards et al 2007;Hatch et al 2007;McDonald et al 2010McDonald et al , 2011a, and both warm and cold molecular gas (e.g., Jaffe & Bremer 1997;Donahue et al 2000;Edge 2001;Edge et al 2002;Edge & Frayer 2003;Salomé & Combes 2003;Hatch et al 2005;Jaffe et al 2005;Johnstone et al 2007;Oonk et al 2010;McDonald et al 2012c)-all of which are indicative of ongoing or recent star formation. Star-forming BCGs were found preferentially in galaxy clusters with "cool cores," as identified by a central density enhancement in the ICM (e.g., Vikhlinin et al 2007;Santos et al 2008;Hudson et al 2010) or low central entropy/cooling time (e.g., Cavagnolo et al 2008Cavagnolo et al , 2009Hudson et al 2010).…”

Far-ultraviolet morphology of star-forming filaments in cool core brightest cluster galaxies

“…Eleven of these targets constitute the Herschel CC clusters Open Time Key Project sample of A. Edge and collaborators (Edge et al 2010a,b;Mittal et al 2011Mittal et al , 2012Rawle et al 2012;Tremblay et al 2012a,b;Hamer et al 2014), selected to span a wide range of both cooling flow and BCG physical properties. The remaining five targets are from the non-overlapping sample of O'Dea et al (2010), selected from the Quillen et al (2008) sample on the basis of elevated infrared-estimated SFRs.…”

The regulation of star formation in cool-core clusters: imprints on the stellar populations of brightest cluster galaxies

“…BCGs, particularly those residing at the centres of cool-core clusters (Hu, Cowie & Wang 1985;McCarthy et al 2004McCarthy et al , 2008Cavagnolo et al 2008) exhibit "blue cores" (Bildfell et al 2008) corresponding to the presence of a small fraction (∼ 1 per cent) of very young stars (Sarazin & O'Connell 1983;Cardiel, Gorgas & Aragon-Salamanca 1995, 1998Pipino et al 2009). These BCGs also reveal activity in their radio emission (Burns 1990;Best et al 2007), or have optical emission-line nebulae (Crawford et al 1999;Edwards et al 2007;Loubser & Soechting 2013), excess UV light (McNamara & O'Connell 1989;Rafferty, McNamara & Nulsen 2008;Donahue et al 2010), far-infrared emission from warm dust (Quillen et al 2008), and molecular gas (Edge et al 2002;Rawle et al 2012). Nevertheless, this forms far from a complete picture as BCGs in the nearby Universe exhibit diverse morphologies, differences in their stellar populations, and therefore star formation histories (Loubser et al 2009;Donahue et al 2015), despite the fact that most are located in a similar, privileged environment in the very centres of Xray luminous clusters.…”