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B. F. Williams (Penn State), P. R. Durrell (YSU), R. Ciardullo (Penn State), J. J. Feldmeier (NOAO), G. H. Jacoby (WIYN), S. Sigurdsson (Penn State), T. von Hippel (U. Texas), H. Ferguson (STScI), N. Tanvir (U. Hertfordshire), M. Arnaboldi (Torino Obs./ESO), O. Gerhard (MPE Garching), A. Aguerri (IAC), K. C. Freeman (Mt. Stromlo), M. Vinciguerra (Penn State)
Deep HST ACS\/ images of Virgo from the VICS project (Ciardullo et al.) contain 4 resolved objects that appear to be intergalactic globular clusters (IGCs). Evidence for this interpretation comes from the objects' integrated colors and magnitudes, which are consistent with those of Virgo globulars, their radial surface brightness profiles, which are well-fit by King models, and from the overdensity of resolved stars that surround each object. These stars, which have the colors and magnitudes expected from objects on the red giant branch, show that at least 2 of the clusters are metal-poor, with [Fe/H] \lesssim -1. Taking the effects of the ACS\/ PSF into account, the best-fit core radii are \gtrsim 2~pc, possibly larger than those of typical Galactic clusters, hinting that the objects could be less dynamically evolved than their Galactic counterparts. The tidal radii of the brightest 2 clusters are ~100~pc; when used in conjunction with models, these radii place constraints on the objects' origins. The properties of these globular clusters provide additional information for numerical simulations of the production of intracluster stars.
Support for this work was provided by NASA through grant number GO-10131 from the Space Telescope Science Institute.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.