Photometric Survey for Stellar Clusters in the Outer Part of M33

TL;DR

This paper provides a comprehensive catalog of 4780 extended sources in M33's outer region, including new stellar cluster candidates, background galaxies, and known objects, based on deep ground-based imaging.

Contribution

It introduces a new catalog of stellar clusters and background objects in M33's outskirts, with photometry and profile estimates, expanding the known globular cluster population.

Findings

Identification of 3554 new candidate stellar clusters

Detection of 122 bright, likely globular clusters

Potential to extend the globular cluster luminosity function by up to 3 magnitudes

Abstract

We present a catalog of 4780 extended sources from the outer field of M33. The catalog includes 73 previously identified clusters or planetary nebulae, 1153 likely background galaxies, and 3554 new candidate stellar clusters. The survey is based on deep ground-based images obtained with the MegaCam instrument on the CFHT telescope. We provide g'r'i' photometry for detected objects as well as estimates of the FWHM and ellipticity of their profiles. The sample includes 122 new, relatively bright, likely globular clusters. Follow-up observations of fainter candidates from our list may extend the faint-end of the observed luminosity function of globular clusters in M33 by up to 3 magnitudes. The catalog includes several cluster candidates located in the outskirts of the galaxy. These objects are promising targets for deep photometry with the HST. We present a color-magnitude diagram for one detected object, showing that it is an extended and low-surface-brightness old cluster located at an angular distance of 27' from the center of M33.