| The ACS Virgo Cluster Survey X. Half-light radii of globular clusters in early-type galaxies: environmental dependencies and a standard ruler for distance estimation (2005) | |||||||||||||||
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| Also archived in: arXiv :astro-ph/0508219 v1 9 Aug 2005. We have measured half-light radii, rh, for thousands of globular clusters (GCs) belonging to the one hundred early-type galaxies observed in the ACS Virgo Cluster Survey and the elliptical galaxy NGC 4697. An analysis of the dependencies of the measured half-light radii on both the properties of the GCs themselves and their host galaxies reveals that, in analogy with GCs in the Galaxy but in a milder fashion, the average half-light radius increases with increasing galactocentric distance or, alternatively, with decreasing galaxy surface brightness. For the first time, we find that the average half-light radius decreases with the host galaxy color. We also show that there is no evidence for a variation of rh with the luminosity of the GCs. Finally, we find in agreement with previous observations that the average rh depends on the color of GCs, with red GCs being ~ 17% smaller than their blue counterparts. We show that this difference is probably a consequence of an intrinsic mechanism, rather than projection effects, and that it is in good agreement with the mechanism proposed in Jordan (2004). We discuss these findings in light of two simple pictures for the origin of the rh of GCs and show that both lead to a behavior in rough agreement with the observations. After accounting for the dependencies on galaxy color, galactocentric radius and underlying surface brightness, we show that the average GC half-light radii (rh) can be successfully used as a standard ruler for distance estimation. We outline the methodology, provide a calibration for its use, and discuss the prospects for this distance estimator with future observing facilities. We find (rh) = 2.7± 0.35 pc for GCs with (g − z) = 1.2 mag in a galaxy with color (g − z)gal = 1.5 mag and at an underlying surface z-band brightness of µz = 21 mag arcsec−2. Using this technique, we place an upper limit of 3.4 Mpc on the 1- line-of-sight depth of the Virgo Cluster. Finally, we examine the form of the rh distribution for our sample galaxies and provide an analytic expression which successfully describes this distribution [for exact rh and line-of-sight depth forms, see attached document].. P.C. would like to thank the European Southern Observatory and especially Bruno Leibundgut for their hospitality during the preparation of this paper. Support for programs GO-9401 and GO-10003 was provided through grants from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. P.C. acknowledges additional support provided by NASA LTSA grant NAG5-11714. M.M. acknowledges additional financial support provided by the Sherman M. Fairchild foundation. D.M. is supported by NSF grant AST-020631, NASA grant NAG5-9046, and grant HSTAR-09519.01-A from STScI. M.J.W. acknowledges support through NSF grant AST-0205960. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology. | |||||||||||||||
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