Optical Properties of Cooling Flow Central Cluster Ellipticals

Abstract

Central cluster galaxies in cooling flows show the signatures of gaseous accretion and ongoing star formation at rates ranging between 1-100 solar masses per year. Their blue morphologies usually reflect the low net angular momentum content of the less than 10,000 K gas from which the accretion population formed, and the effects of interactions between the cool gas and their FR I radio sources. For example, there is strong evidence that star formation is being triggered, in part, by interactions between the 10,000 K gas and the radio sources in some objects. Disk star formation on kiloparsec scales is rare in cooling flows. The optically determined star formation rates, assuming the Local initial mass function (IMF), are typically factors of 10-100 smaller than the cooling rates determined from X-ray observations, and signatures of the remaining material have not been identified outside of the X-ray band. The IMF is poorly understood in cooling flows; most of the cooling material may be deposited in low-mass stars or some other form of dark matter. Continued study of the interactions between radio sources and the intercluster medium will further our understanding of how elliptical galaxies, particularly radio ellipticals in the early universe, evolve.