The discovery of remote globular clusters in M33

Abstract

We present the discovery of four remote star clusters in M33, one of which is of an extended nature. Three of the clusters were discovered using survey data from the Isaac Newton Telescope Wide-Field Camera while one was discovered serendipitously in a deep image taken with the Hubble Space Telescope's Advanced Camera for Surveys. With projected radii of 38-113 arcmin (9.6-28.5 kpc for an assumed M33 distance of 870 kpc), these clusters lie significantly beyond all but one of the currently confirmed clusters in M33. The clusters have magnitudes and colors consistent with their being old to intermediate-age globular clusters (GCs). Indeed, they bear a strong resemblance to the outer halo GC population of the Milky Way and M31 in terms (V - I)0 color. The three outermost clusters are projected on the far side of M33 with respect to M31, an asymmetry that could suggest tidal interactions have affected M33's GC distribution at large radii. © 2009. The American Astronomical Society. All rights reserved.