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A census of mid-infrared selected active galactic nuclei in massive galaxy clusters at 0 ≲z≲ 1.3


Tomczak, A R; Tran, K V H; Saintonge, A (2011). A census of mid-infrared selected active galactic nuclei in massive galaxy clusters at 0 ≲z≲ 1.3. Astrophysical Journal, 738(1):65.

Abstract

We conduct a deep mid-infrared (mid-IR) 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-IR color selection techniques. Of the 949 cluster galaxies that are detected in at least three of the four IRAC channels at the >=3σ level, we identify 12 that host mid-IR-selected active galactic nuclei (IR-AGNs). To compare the IR-AGNs across our redshift range, we define two complete samples of cluster galaxies: (1) optically selected members with rest-frame V AB 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 that the fraction of 24 μm 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 μm 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 that the cluster IR-AGNs are predominantly hosted by late-type galaxies with blue optical colors, i.e., members with recent/ongoing star formation. The four brightest IR-AGNs are also X-ray sources; these IR+X-ray AGNs 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-AGNs have a more prominent role at z >~ 1.

We conduct a deep mid-infrared (mid-IR) 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-IR color selection techniques. Of the 949 cluster galaxies that are detected in at least three of the four IRAC channels at the >=3σ level, we identify 12 that host mid-IR-selected active galactic nuclei (IR-AGNs). To compare the IR-AGNs across our redshift range, we define two complete samples of cluster galaxies: (1) optically selected members with rest-frame V AB 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 that the fraction of 24 μm 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 μm 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 that the cluster IR-AGNs are predominantly hosted by late-type galaxies with blue optical colors, i.e., members with recent/ongoing star formation. The four brightest IR-AGNs are also X-ray sources; these IR+X-ray AGNs 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-AGNs have a more prominent role at z >~ 1.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Institute for Computational Science
Dewey Decimal Classification:530 Physics
Language:English
Date:2011
Deposited On:23 Feb 2012 22:04
Last Modified:05 Apr 2016 15:40
Publisher:Institute of Physics Publishing
ISSN:0004-637X
Publisher DOI:https://doi.org/10.1088/0004-637X/738/1/65
Related URLs:http://arxiv.org/abs/1105.0602
Permanent URL: https://doi.org/10.5167/uzh-60040

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