LoCuSS: The mid-infrared Butcher-Oemler effect

Details LoCuSS: The mid-infrared Butcher-Oemler effect LoCuSS: The mid-infrared Butcher-Oemler effect

2009-08-20

arxiv.org/abs/0908.3003v1

Astronomy and Astrophysics

Astrophysics

Cosmology and Extragalactic Astrophysics

11 pages, 7 figures, accepted for publication in ApJ

Scientific paper

We study the mid-infrared (MIR) properties of galaxies in 30 massive galaxy clusters at 0.025x10^10L_sun) within r_200, finding a steady increase in the fraction with redshift from ~3% at z=0.02 to ~10% by z=0.30, and an rms cluster-to-cluster scatter about this trend of 0.03. The best-fit redshift evolution model is of the form f_SF ~ (1+z)^5.7, which is stronger redshift evolution than that of L*_IR in both clusters and the field. We find that, statistically, this excess is associated with galaxies found at large cluster-centric radii, implying that the MIR Butcher-Oemler effect can be explained by a combination of both the global decline in star-formation in the universe since z~1 and enhanced star formation in the infall regions of clusters at intermediate redshifts. This picture is supported by a simple infall model based on the Millennium Simulation semi-analytic galaxy catalogs, whereby star-formation in infalling galaxies is instantaneously quenched upon their first passage through the cluster, in that the observed radial trends of f_SF trace those inferred from the simulations. We also find that f_SF does not depend on simple indicators of the dynamical state of clusters, including the offset between the brightest cluster galaxy and the peak of the X-ray emission. This is consistent with the picture described above in that most new star-formation in clusters occurs in the infall regions, and is thus not sensitive to the details of cluster-cluster mergers in the core regions.

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