2MASS photometry and age estimate of globular clusters in the outer halo of M31

TL;DR

This study uses 2MASS and previous data to determine ages and masses of 10 outer halo globular clusters in M31, revealing most are older than 3 billion years and suggesting some were accreted from satellite galaxies.

Contribution

First photometric analysis of outer halo M31 globular clusters combining 2MASS and literature data to estimate their ages, metallicities, and masses, providing insights into their origins.

Findings

All clusters are older than 3 Gyr.

Four clusters are older than 10 Gyr.

Masses range from 7.0×10^4 to 1.02×10^6 solar masses.

Abstract

We present the first photometric results in J, H, and K_s from 2MASS imaging of 10 classical globular clusters in the far outer regions of M31. Combined with the V and I photometric data from previous literature, we constructed the color-color diagram between J-K_s and V-I. By comparing the integrated photometric measurements with evolutionary models, we estimate the ages of these clusters. The results showed that, all of these clusters are older than $3\times 10^9$ yrs, of which 4 are older than 10 Gyrs and the other 6 are in intermediate ages between 3-8 Gyrs. The masses for these outer halo GCs are from $7.0\times 10^4 M_sun$ to $1.02\times 10^6 M_sun$. We argued that, GC2 and GC3, the ages, metallicities and the distance moduli of which are nearly the same, were accreted from the same satellite galaxy, if they did not form {\it in situ}. The statistical results show that, ages and metallicities for these 10 M31 outer halo GCs do not vary with projected radial position, and the relationship between age and metallicity doest not exit.