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A panoramic mid-infrared survey of two distant clusters

Geach, J.E.; Smail, I.; Ellis, R.S.; Moran, S.M.; Smith, G.P.; Treu, T.; Kneib, J.P.; Edge, A.C.; Kodama, T.

A panoramic mid-infrared survey of two distant clusters Thumbnail


J.E. Geach

R.S. Ellis

S.M. Moran

G.P. Smith

T. Treu

J.P. Kneib

T. Kodama


We present panoramic Spitzer MIPS 24 μm observations, covering ~9 × 9 Mpc2 (25' × 25') fields around two massive clusters, Cl 0024+16 and MS 0451-03, at z = 0.39 and z = 0.55, respectively, reaching a 5 σ flux limit of ~200 μJy. Our observations cover a very wide range of environments within these clusters, from high-density regions around the cores out to the turnaround radius. Cross-correlating the mid-infrared catalogs with deep optical and near-infrared imaging of these fields, we investigate the optical/near-infrared colors of the mid-infrared sources. We find excesses of mid-infrared sources with the optical/near-infrared colors expected of cluster members in the two clusters and test this selection using spectroscopically confirmed 24 μm members. The much more significant excess is associated with Cl 0024+16, whereas MS 0451-03 has comparatively few mid-infrared sources. The mid-infrared galaxy population in Cl 0024+16 appears to be associated with dusty star-forming galaxies (typically redder than the general cluster population by up to AV ~ 1-2 mag) rather than emission from dusty tori around active galactic nuclei in early-type hosts. We compare the star formation rates derived from the total infrared (8-1000 μm) luminosities for the mid-infrared sources in Cl 0024+16 with those estimated from a published Hα survey, finding rates 5 times those found from Hα, indicating significant obscured activity in the cluster population. Compared to previous mid-infrared surveys of clusters from z ~ 0-0.5, we find evidence for strong evolution of the level of dust-obscured star formation in dense environments to z = 0.5, analogous to the rise in the fraction of optically selected star-forming galaxies seen in clusters and the field out to similar redshifts. However, there are clearly significant cluster-to-cluster variations in the populations of mid-infrared sources, probably reflecting differences in the intracluster media and recent dynamical evolution of these systems.


Geach, J., Smail, I., Ellis, R., Moran, S., Smith, G., Treu, T., …Kodama, T. (2006). A panoramic mid-infrared survey of two distant clusters. Astrophysical Journal, 649(2), 661-672.

Journal Article Type Article
Publication Date Oct 1, 2006
Deposit Date Sep 12, 2013
Publicly Available Date Jan 3, 2014
Journal Astrophysical Journal
Print ISSN 0004-637X
Electronic ISSN 1538-4357
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 649
Issue 2
Pages 661-672


Published Journal Article (1.5 Mb)

Copyright Statement
© 2006. The American Astronomical Society. All rights reserved. Printed in the U.S.A.

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