The Discovery of Remote Globular Clusters in M33

TL;DR

This paper reports the discovery of four remote globular clusters in M33, extending our understanding of its outer halo and suggesting possible tidal interactions with M31.

Contribution

It is the first to identify and characterize remote globular clusters in M33 using survey and HST data, revealing their properties and spatial distribution.

Findings

Four new remote globular clusters discovered in M33

Clusters have properties similar to Milky Way and M31 outer halo GCs

Asymmetrical distribution suggests tidal interactions with M31

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. Indeed, they bear a strong resemblance to the outer halo GC population of the Milky Way and M31 in terms (V-I)o colors. 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 globular cluster distribution at large radii.