STAR FORMATION AND AGN ACTIVITY IN GALAXY CLUSTERS FROM z = 1–2: A MULTI-WAVELENGTH ANALYSIS FEATURING HERSCHEL/PACS

Abstract

We present a detailed, multi-wavelength study of star formation (SF) and active galactic nucleus (AGN) activity in 11 near-infrared (IR) selected, spectroscopically confirmed massive (10 14 M e ) galaxy clusters at 1 < z < 1.75. Using new deep Herschel/PACS imaging, we characterize the optical to far-IR spectral energy distributions (SEDs) for IR-luminous cluster galaxies, finding that they can, on average, be well described by field galaxy templates. Identification and decomposition of AGNs through SED fittings allows us to include the contribution to cluster SF from AGN host galaxies. We quantify the star-forming fraction, dust-obscured SF rates (SFRs) and specific SFRs for cluster galaxies as a function of cluster-centric radius and redshift. In good agreement with previous studies, we find that SF in cluster galaxies at z  1.4 is largely consistent with field galaxies at similar epochs, indicating an era before significant quenching in the cluster cores (r < 0.5 Mpc). This is followed by a transition to lower SF activity as environmental quenching dominates by z ∼ 1. Enhanced SFRs are found in lower mass (   < < M M 10.1 log 10.8) cluster galaxies. We find significant variation in SF from cluster to cluster within our uniformly selected sample, indicating that caution should be taken when evaluating individual clusters. We examine AGNs in clusters from z = 0.5-2, finding an excess AGN fraction at z  1, suggesting environmental triggering of AGNs during this epoch. We argue that our results-a transition from field-like to quenched SF, enhanced SF in lower mass galaxies in the cluster cores, and excess AGNs-are consistent with a co-evolution between SF and AGNs in clusters and an increased merger rate in massive halos at high redshift.

Merger driven star-formation activity in Cl J1449+0856 at z=1.99 as seen by ALMA and JVLA

“…Delaye et al 2014;Strazzullo et al 2015). A recent study by Alberts et al (2016) focussed on galaxy clusters in the range 1<z<2, and concluded that environmental interactions and an increased galaxy merger rate were triggering the heightened AGN fraction in the cores of some 11 massive clusters. (2014), normalised to the green data points.…”

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

“…While the addition of the far-infrared SED modelling analysis to the IRAC colour diagnostic does not help to uncover the exact fraction of low-or moderate-luminosity AGN which may be residing in completely host-dominated SpARCS BCGs, it should 'pick up' the mid-infrared emission of those AGN which are not classified as continuumdominated in IRAC colour space, longward of the IRAC bands in the infrared SED (as also noted in, e.g., Alberts et al 2016). Where potentially many AGN/star-forming BCGs could reside all over the IRAC colour space, they should not be able to 'hide' as easily in the SED between 8 and 40 µm (after which point AGN emission begins to steeply drop off), where we do not observe a combined AGN/starforming signature, not even at the 1% AGN level.…”

“…Therefore, the source of the star formation in optically and/or non-X-ray-detected BCGs, such as those from SpARCS, is less obvious. While cluster galaxies exhibit similar gas depletion timescales and star formation rates to field counterparts when including recycled gas from internal stellar mass losses over the lifetime of the galaxy (Boselli et al 2014), the threat of ram-pressure stripping on shorter timescales increases with time as galaxy clusters grow more massive, leading to relatively suppressed star formation in cluster cores at z <∼ 1 (Muzzin et al 2012(Muzzin et al , 2014Alberts et al 2014Alberts et al , 2016. Nevertheless, the quantities of cold molecular gas observed to remain in gas-deficient (with respect to the field) galaxies in cluster cores at z = 0 (Boselli et al 2014) are non-negligible in the context of this study: the BCG acts as a reservoir for the residual gas carried by satellite galaxies that merge with it throughout its lifetime.…”

“…Based on Alberts et al (2014Alberts et al ( , 2016, we can assume that a typical satellite galaxy in the core of a 10 14 M cluster at z ∼ 2 embodies a similar molecular gas fraction to a field galaxy counterpart with the same mass and initial star formation rate. Carilli & Walter (2013) show that the molecular gas fractions of a large sample of field galaxies evolve as fgas ∼ 0.1 × (1 + z) 2 (fgas ≡ Mgas/Mstars), which yields Mgas = 9 × 10 9 M for a 10 10 M satellite galaxy at this redshift, and Mgas = 9 × 10 10 M for a high-mass 10 11 M major-merger companion.…”

The VIMOS Public Extragalactic Redshift Survey (VIPERS)

“…On the other hand, the debate is still open on the possible link between the peak of the SFRD at z ∼ 1.5-2 and the absence, or even inversion, of the correlation between star formation activity and local density at such redshift (e.g. Mortlock et al 2015;Alberts et al 2016;Cucciati et al 2006;Elbaz et al 2007;Cooper et al 2008;Grützbauch et al 2011a). …”