Structural evolution in elliptical galaxies: the age–shape relation |
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Authors: | Barbara S Ryden Duncan A Forbes AI Terlevich |
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Institution: | 1Department of Astronomy, Ohio State University, Columbus, OH 43210, USA;2Centre for Astrophysics and Supercomputing, Swinburne University, Hawthorn, VIC 3122, Australia;3School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT |
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Abstract: | We test the hypothesis that the apparent axial ratio of an elliptical galaxy is correlated with the age of its stellar population. We find that old ellipticals (with estimated ages t >7.5 Gyr) are rounder on average than younger ellipticals. The statistical significance of this shape difference is greatest at small radii; a Kolmogorov–Smirnov test comparing the axial ratios of the two populations at R = R e/16 yields a statistical significance greater than 99.96 per cent. The relation between age and apparent shape is linked to the core/power-law surface brightness profile dichotomy. Core ellipticals have older stellar populations, on average, than power-law ellipticals and are rounder in their inner regions. Our findings are consistent with a scenario in which power-law ellipticals are formed in gas-rich mergers, while core ellipticals form in dissipationless mergers, with cores formed and maintained by the influence of a binary black hole. |
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Keywords: | galaxies: elliptical and lenticular cD galaxies: evolution galaxies: photometry galaxies: structure |
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