We conduct a deep mid-infrared census of nine massive galaxy clusters at (0 < z < 1.3) with a total of ~ 1500 spectroscopically confirmed member galaxies using Spitzer /IRAC photometry and established mid-infrared color selection techniques. Of the 949 cluster galaxies that are detected in at least three of the four IRAC channels at the >= 3 sigma level, we identify 12 that host mid-infrared selected active galactic nuclei (IR-AGN). To compare the IR-AGN across our redshift range, we define two complete samples of cluster galaxies: (1) optically-selected members with rest-frame VAB magnitude < -21.5 and (2) mid-IR selected members brighter than (M*_3.6 +0.5), i.e. essentially a stellar mass cut. In both samples, we measure f_IR-AGN ~ 1% with a strong upper limit of ~3% at z < 1. This uniformly low IR-AGN fraction at z < 1 is surprising given the fraction of 24 micrometer sources in the same galaxy clusters is observed to increase by about a factor of four from z ~ 0 to z ~ 1; this indicates that most of the detected 24 micrometer flux is due to star formation. Only in our single galaxy cluster at z = 1.24 is the IR-AGN fraction measurably higher at ~15% (all members; ~70% for late-types only). In agreement with recent studies, we find the cluster IR-AGN are predominantly hosted by late-type galaxies with blue optical colors, i.e. members with recent/ongoing star formation. The four brightest IR-AGN are also X-ray sources; these IR+X-ray AGN all lie outside the cluster core (R_proj > 0.5 Mpc) and are hosted by highly morphologically disturbed members. Although our sample is limited, our results suggest that f_IR-AGN in massive galaxy clusters is not strongly correlated with star formation at z < 1, and that IR-AGN have a more prominent role at z > 1.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/148357 |
| Date | 14 March 2013 |
| Creators | Tomczak, Adam 1987- |
| Contributors | Tran, Kim-Vy |
| Source Sets | Texas A and M University |
| Detected Language | English |
| Type | Thesis, text |
| Format | application/pdf |
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