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Published Online January 19, 2006
Science DOI: 10.1126/science.1122294

Reports

Submitted on November 7, 2005
Accepted on December 22, 2005

Explaining the Color Distributions of Globular Cluster Systems in Elliptical Galaxies

Suk-Jin Yoon 1*, Sukyoung Ken Yi 1, Young-Wook Lee 2

1 Department of Astronomy & Center for Space Astrophysics, Yonsei University, Seoul 120-749, Korea; Astrophysics, University of Oxford, Keble Road, Oxford OX1 3RH, UK.
2 Department of Astronomy & Center for Space Astrophysics, Yonsei University, Seoul 120-749, Korea.

* To whom correspondence should be addressed.
Suk-Jin Yoon , E-mail: sjyoon{at}galaxy.yonsei.ac.kr

The colors of globular clusters in most of large elliptical galaxies are bimodal. This is generally taken as evidence for the presence of two cluster subpopulations that have different geneses. Here we find however that, due to the non-linear nature of the metallicity-to-color transformation, a coeval group of old clusters with a unimodal metallicity spread can exhibit color bimodality. The models of cluster colors indicate that the horizontal-branch stars are the main drivers behind the empirical non-linearity. We show that the scenario gives remarkably simple and cohesive explanations for all the key observations, and could simplify theories of elliptical galaxy formation.




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Science. ISSN 0036-8075 (print), 1095-9203 (online)