Stellar Clusters in M31 from PHAT: Survey Overview and First Results

TL;DR

The PHAT survey uses HST to image a large part of M31, leading to the discovery of hundreds of new stellar clusters and significantly expanding existing catalogs.

Contribution

This paper provides an overview of the PHAT survey and reports the first results, including the identification of numerous new stellar clusters in M31.

Findings

Hundreds of new stellar clusters identified.

Cluster catalog size tripled within the survey footprint.

High-resolution imaging enabled detection of low-mass clusters.

Abstract

The Panchromatic Hubble Andromeda Treasury (PHAT) is an on-going Hubble Space Telescope (HST) multi-cycle program that will image one-third of the M31 disk at high resolution, with wavelength coverage from the ultraviolet through the near-infrared. This dataset will allow for the construction of the most complete catalog of stellar clusters obtained for a spiral galaxy. Here, we provide an overview of the PHAT survey, a progress report on the status of observations and analysis, and preliminary results from the PHAT cluster program. Although only ~20% of the survey is complete, the superior resolution of HST has allowed us to identify hundreds of new intermediate and low mass clusters. As a result, the size of the cluster sample within the Year 1 survey footprint has grown by a factor of three relative to previous catalogs.