Structural Parameters for Globular Clusters in the Outer Halo of M31

TL;DR

This study analyzes the structural properties of ten globular clusters in M31's outer halo using Hubble data, revealing similarities with Milky Way clusters and highlighting their ellipticities and a fundamental energy-mass relation.

Contribution

It provides detailed surface brightness profiles and structural parameters for M31's outer halo globular clusters, demonstrating the existence of a fundamental plane across different environments.

Findings

Clusters in M31 and the Milky Way occupy similar parameter spaces.

Outer halo GCs of M31 exhibit larger ellipticities.

A tight correlation between binding energy and mass supports a universal fundamental plane.

Abstract

In this paper, we present internal surface brightness profiles, using images in the F606W and F814W filter bands observed with the Advanced Camera for Surveys on the {\it Hubble Space Telescope}, for ten globular clusters (GCs) in the outer halo of M31. Standard King models are fitted to the profiles to derive their structural and dynamical parameters. The results show that, in general, the properties of clusters in M31 and the Milky Way fall in the same regions of parameter spaces. The outer halo GCs of M31 have larger ellipticities than most of GCs in M31 and the Milky Way. Their large ellipticities may be due to galaxy tides coming from satellite dwarf galaxies of M31 or may be related to the apparently more vigorous accretion or merger history that M31 has experienced. The tight correlation of cluster binding energy $E_b$ with mass $M_{\rm mod}$ indicates that, the "fundamental plane" does exist for clusters, regardless of their host environments, which is consistent with previous studies.