Astronomy and Astrophysics – Astrophysics
Scientific paper
2005-08-08
Astrophys.J.636:90-94,2005
Astronomy and Astrophysics
Astrophysics
48 pages, 24 Figures, PDF, Submitted to Astrophys.J. and refereed. For complete pdf file with better figures, see: http://ph
Scientific paper
10.1086/498058
We present new (B,I) photometry for the globular cluster systems in eight Brightest Cluster Galaxies (BCGs), obtained with the ACS/WFC camera on the Hubble Space Telescope. In the very rich cluster systems that reside within these giant galaxies, we find that all have strongly bimodal color distributions All the BCGs show population gradients, with much higher relative numbers of red clusters within 5 kpc of their centers, consistent with their having formed at later times than the blue, metal-poor population. A striking new feature of the color distributions emerging from our data is that for the brightest clusters (M_I < -10.5) the color distribution becomes broad and less obviously bimodal. we suggest that it may be a characteristic of many BCGs. Furthermore, the blue (metal-poor) clusters become progressively redder with increasing luminosity, following a mass/metallicity scaling relation Z ~ M^0.55. We argue that these GCS characteristics are consistent with a hierarchical-merging formation picture in which the metal-poor clusters formed in protogalactic clouds or dense starburst complexes with gas masses in the range 10^7 - 10^10 M_Sun, but where the more massive clusters on average formed in bigger clouds with deeper potential wells where more pre-enrichment could occur.
Baum William A.
Hanes David A.
Harris William E.
Karakla D.
Kavelaars John J.
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