Globular cluster systems in fossil groups: NGC 6482, NGC 1132, and ESO 306-017^⋆

¹ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile
² Centro de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, 58090 Morelia, México
e-mail: k.alamo@crya.unam.mx
³ Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council of Canada, Victoria, BC V9E 2E7, Canada
⁴ Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, 7820436 Macul, Santiago, Chile
⁵ Department of Physics, University of California, Davis, CA 956160, USA
⁶ Institute for Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, L-413, Livermore, CA 94550, USA
⁷ School of Mathematics and Physics, The University of Queensland, Brisbane, QLD 4072, Australia
⁸ Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany

Received: 26 March 2012
Accepted: 14 August 2012

Abstract

We study the globular cluster (GC) systems in three representative fossil group galaxies: the nearest (NGC 6482), the prototype (NGC 1132) and the most massive known to date (ESO 306-017). This is the first systematic study of GC systems in fossil groups. Using data obtained with the Hubble Space Telescope Advanced Camera for Surveys in the F475W and F850LP filters, we determine the GC color and magnitude distributions, surface number density profiles, and specific frequencies. In all three systems, the GC color distribution is bimodal, the GCs are spatially more extended than the starlight, and the red population is more concentrated than the blue. The specific frequencies seem to scale with the optical luminosities of the central galaxy and span a range similar to that of the normal bright elliptical galaxies in rich environments. We also analyze the galaxy surface brightness distributions to look for deviations from the best-fit Sérsic profiles; we find evidence of recent dynamical interaction in all three fossil group galaxies. Using X-ray data from the literature, we find that luminosity and metallicity appear to correlate with the number of GCs and their mean color, respectively. Interestingly, although NGC 6482 has the lowest mass and luminosity in our sample, its GC system has the reddest mean color, and the surrounding X-ray gas has the highest metallicity.