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Clues to Globular Cluster Evolution from Multiwavelength Observations of Extragalactic Systems

Published online by Cambridge University Press:  01 September 2007

Arunav Kundu
Affiliation:
Department of Physics & Astronomy, Michigan State University, East Lansing, MI 48824, USA email: [email protected], [email protected]
Thomas J. Maccarone
Affiliation:
School of Physics & Astronomy, University of Southampton, Southampton, UKSO17 1BJ email: [email protected]
Stephen E. Zepf
Affiliation:
Department of Physics & Astronomy, Michigan State University, East Lansing, MI 48824, USA email: [email protected], [email protected]
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Abstract

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We present a study of the globular cluster (GC) systems of nearby elliptical and S0 galaxies at a variety of wavelengths from the X-ray to the infrared. Our analysis shows that roughly half of the low mass X-ray binaries (LMXBs), that are the luminous tracers of accreting neutron star or black hole systems, are in clusters. There is a surprisingly strong correlation between the LMXB frequency and the metallicity of the GCs, with metal-rich GCs hosting three times as many LMXBs as metal-poor ones, and no convincing evidence of a correlation with GC age so far. In some of the galaxies the LMXB formation rate varies with GC color even within the red peak of the typical bimodal cluster color distribution, providing some of the strongest evidence to date that there are metallicity variations within the metal-rich GC peak as is expected in a hierarchical galaxy formation scenario. We also note that any analysis of subtler variations in GC color distributions must carefully account for both statistical and systematic errors. We caution that some published GC correlations, such as the apparent ‘blue-tilt’ or mass-metallicity effect might not have a physical origin and may be caused by systematic observational biases.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2008

References

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