The Infrared Luminosity Functions of Rich Clusters

Abstract

We present Multiband Imaging Photometer observations of the cluster A3266. About 100 spectroscopic cluster members have been detected at 24 μm. The infrared (IR) luminosity function (LF) in A3266 is very similar to that in the Coma cluster down to the detection limit L _IR ~ 10⁴³ erg s^-1, suggesting a universal form of the bright-end IR LF for local rich clusters with M ~ 10¹⁵ M _sun. The shape of the bright end of the A3266-Coma composite IR LF is not significantly different from that of nearby field galaxies, but the fraction of IR-bright galaxies (star formation rate (SFR) >0.2 M _sun yr^-1) in both clusters increases with cluster-centric radius. The decrease of the blue galaxy fraction toward the high-density cores only accounts for part of the trend; the fraction of red galaxies with moderate SFRs (0.2 M _sun yr^-1 < SFR < 1 M _sun yr^-1) also decreases with increasing galaxy density. These results suggest that for the IR-bright galaxies nearby rich clusters are distinguished from the field by a lower star forming galaxy fraction, but not by a change in L*_IR. The composite IR LF of Coma and A3266 shows strong evolution when compared with the composite IR LF of two z ~ 0.8 clusters, MS 1054 and RX J0152, with L^{*}_IR∝ (1+z)^{3.2^{+0.7}_{-0.7}} and Φ ^{*}_IR∝ (1+z)^{1.7^{+1.0}_{-1.0}}. This L*_IR evolution is indistinguishable from that in the field, and the Φ*_IR evolution is stronger, but still consistent with that in the field. The similarity of the evolution of the bright-end IR LF in very different cluster and field environments suggests either this evolution is driven by the mechanism that works in both environments, or clusters continually replenish their star forming galaxies from the field, yielding an evolution in the IR LF that is similar to the field. The mass-normalized integrated SFRs of clusters within 0.5R ₂₀₀ also evolve strongly with redshift as (1 + z)^5.3.