PHAT Stellar Cluster Survey I. Year 1 Catalog and Integrated Photometry

TL;DR

The PHAT survey's first catalog of 601 stellar clusters in M31, derived from high-resolution HST imaging, significantly expands previous data and provides detailed photometry, sizes, and luminosities for understanding star cluster populations.

Contribution

This paper presents the first comprehensive catalog of stellar clusters in M31 from the PHAT survey, including new detections and detailed photometric and size measurements.

Findings

Identified 601 clusters in Year 1, quadrupling previous catalogs.

Provided integrated photometry in six bands for each cluster.

Analyzed cluster luminosity function and size distribution.

Abstract

The Panchromatic Hubble Andromeda Treasury (PHAT) survey is an on-going Hubble Space Telescope (HST) multi-cycle program to obtain high spatial resolution imaging of one-third of the M31 disk at ultraviolet through near-infrared wavelengths. In this paper, we present the first installment of the PHAT stellar cluster catalog. When completed, the PHAT cluster catalog will be among the largest and most comprehensive surveys of resolved star clusters in any galaxy. The exquisite spatial resolution achieved with HST has allowed us to identify hundreds of new clusters that were previously inaccessible with existing ground-based surveys. We identify 601 clusters in the Year 1 sample, representing more than a factor of four increase over previous catalogs within the current survey area (390 arcmin^2). This work presents results derived from the first \sim25% of the survey data; we estimate that the final sample will include \sim2500 clusters. For the Year 1 objects, we present a catalog with positions, radii, and six-band integrated photometry. Along with a general characterization of the cluster luminosities and colors, we discuss the cluster luminosity function, the cluster size distributions, and highlight a number of individually interesting clusters found in the Year 1 search.