The Colors of Dwarf Elliptical Galaxy Globular Cluster Systems, Nuclei and Stellar Halos

Jennifer M. Lotz; Bryan W. Miller; Henry C. Ferguson

doi:10.1086/422871

paper

The Colors of Dwarf Elliptical Galaxy Globular Cluster Systems, Nuclei and Stellar Halos

arXiv:astro-ph/0406002 · doi:10.1086/422871

Abstract

We present the results of a Hubble Space Telescope WFPC2 F555W and F814W survey of 69 dwarf elliptical galaxies (dEs) in the Virgo and Fornax Clusters and Leo Group. The $V - I$ colors of the dE globular clusters, nuclei, and underlying field star populations are used to trace the dE star-formation histories. We find that the dE globular cluster candidates are as blue as the metal-poor globular clusters of the Milky Way. The observed correlation of the dE globular cluster systems' $V - I$ color with the luminosity of the host dE is strong evidence that the globular clusters were formed within the the halos of dEs and do not have a pre-galactic origin. Assuming the majority of dE clusters are old, the mean globular cluster color- host galaxy luminosity correlation implies a cluster metallicity $-$ galaxy luminosity relation of $Z_{GC} \propto L_{B}^{0.22 \pm 0.05}$ , which is significantly shallower than the field star metallicity - host galaxy luminosity relationship observed in Local Group dwarfs ( $Z_{F S} \propto L^{0.4}$ ). The dE stellar envelopes are $0.1 - 0.2$ magnitudes redder in $V - I$ than their globular clusters and nuclei. This color offset implies separate star-formation episodes within the dEs for the clusters and field stars, while the very blue colors of two dE nuclei trace a third star-formation event in those dEs less than a Gyr ago.

arXiv comment39 pages, including 5 tables and 10 figures; accepted by the Astrophysical Journal

The Colors of Dwarf Elliptical Galaxy Globular Cluster Systems, Nuclei and Stellar Halos

Abstract

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