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An infrared survey of brightest cluster galaxies. II : why are some brightest cluster galaxies forming stars?

O'Dea, C.P. and Baum, S.A. and Privon, G. and Noel-Storr, J. and Quillen, A.C. and Zufelt, N. and Park, J. and Edge, A. and Russell, H. and Fabian, A.C. and Donahue, M. and Sarazin, C.L. and McNamara, B. and Bregman, J.N. and Egami, E. (2008) 'An infrared survey of brightest cluster galaxies. II : why are some brightest cluster galaxies forming stars?', Astrophysical journal., 681 (2). pp. 1035-1045.


Quillen et al. presented an imaging survey with the Spitzer Space Telescope of 62 brightest cluster galaxies with optical line emission located in the cores of X-ray-luminous clusters. They found that at least half of these sources have signs of excess IR emission. Here we discuss the nature of the IR emission and its implications for cool core clusters. The strength of the mid-IR excess emission correlates with the luminosity of the optical emission lines. Excluding the four systems dominated by an AGN, the excess mid-IR emission in the remaining brightest cluster galaxies is likely related to star formation. The mass of molecular gas (estimated from CO observations) is correlated with the IR luminosity as found for normal star-forming galaxies. The gas depletion timescale is about 1 Gyr. The physical extent of the IR excess is consistent with that of the optical emission-line nebulae. This supports the hypothesis that star formation occurs in molecular gas associated with the emission-line nebulae and with evidence that the emission-line nebulae are mainly powered by ongoing star formation. We find a correlation between mass deposition rates () estimated from the X-ray emission and the star formation rates estimated from the IR luminosity. The star formation rates are 1/10 to 1/100 of the mass deposition rates, suggesting that the reheating of the intracluster medium is generally very effective in reducing the amount of mass cooling from the hot phase but not eliminating it completely.

Item Type:Article
Keywords:Cooling flow, Galaxies, Clusters, Elliptical and lenticular, cD, Star formation, Infrared.
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Publisher statement:© 2008. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
Date accepted:No date available
Date deposited:04 September 2013
Date of first online publication:July 2008
Date first made open access:No date available

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