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| Title: |
| A Glimpse into the Past: The Recent Evolution of Globular Clusters |
| Authors: |
| Kalirai, Jasonjot S.; Strader, Jay; Anderson, Jay; Richer, Harvey B. |
| Affiliation: |
| AA(University of California Observatories, University of California at Santa Cruz, Santa Cruz, CA 95060; .; Hubble Fellow.), AB(Hubble Fellow.; Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138; .), AC(Space Telescope Science Institute, Baltimore, MD 21218; .), AD(Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada; .) |
| Publication: |
| The Astrophysical Journal, Volume 682, Issue 1, pp. L37-L40. (ApJ Homepage) |
| Publication Date: |
| 07/2008 |
| Origin: |
| UCP |
| ApJ Keywords: |
| Galaxies: Elliptical and Lenticular, cD, Galaxies: Star Clusters, Galaxy: Globular Clusters: General, Stars: Evolution |
| Abstract Copyright: |
| (c) 2008: The American Astronomical Society |
| DOI: |
| 10.1086/590660 |
| Bibliographic Code: |
| 2008ApJ...682L..37K |
Abstract
We present the serendipitous discovery of 195 extragalactic globular
clusters (GCs) in one of the deepest optical images ever obtained, a 126
orbit Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS)
imaging study of the nearby Galactic GC NGC 6397. The distant GCs are
all found surrounding a bright elliptical galaxy in the field and are
among the faintest objects detected in the image, with magnitudes 26
<~ F814W <~ 30. We measure the redshift of the parent elliptical
galaxy, using the Gemini Multi-Object Spectrograph (GMOS) on Gemini
South, to be z = 0.089 (375 Mpc). This galaxy, and its associated
clusters, therefore ranks as one of the most distant such systems
discovered to date. The measured light from these clusters was emitted
1.2 Gyr ago (the look-back time) and therefore the optical properties
hold clues for understanding the evolution of GCs over the past Gyr. We
measure the color function of the bright GCs and find that both a blue
and red population exist, and that the colors of each subpopulation are
redder than GCs in local elliptical galaxies of comparable luminosity.
For the blue clusters, the observed color difference from z=0.089 to
today is only slightly larger than predictions from stellar evolution
(e.g., changes in the luminosity and color of the main-sequence turnoff
and the morphology of the horizontal branch). A larger color difference
is found in the red clusters, possibly suggesting that they are very
metal-rich and/or significantly younger than 12 Gyr.
Based on observations with the NASA/ESA Hubble Space Telescope, obtained
at the Space Telescope Science Institute, which is operated by the
Association of Universities for Research in Astronomy, Inc., under NASA
contract NAS5-26555. These observations are associated with proposal
GO-10424.
Based on observations obtained at the Gemini Observatory, which is
operated by the Association of Universities for Research in Astronomy,
Inc., under a cooperative agreement with the NSF on behalf of the Gemini
partnership: the National Science Foundation (United States), the
Particle Physics and Astronomy Research Council (United Kingdom), the
National Research Council (Canada), CONICYT (Chile), the Australian
Research Council (Australia), CNPq (Brazil), and CONICET (Argentina).
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