AstroSat/UVIT Cluster Photometry in the Northern Disk of M31

TL;DR

This study uses UVIT on AstroSat to perform photometry of 239 clusters in M31, deriving their ages, metallicities, and other properties, revealing recent star formation activity around 4 million years ago.

Contribution

It provides new UV photometry data for M31 clusters and applies stellar models to derive their physical properties, highlighting recent star formation in the galaxy's disk.

Findings

Most clusters are in spiral arms with metallicities between -0.3 and +0.3.

A narrow peak at ~4 Myr indicates recent star formation.

Young clusters are high metallicity and concentrated in bright spiral regions.

Abstract

The Andromeda Galaxy (M31) is an object of ongoing study with the Ultraviolet Imaging Telescope (UVIT) on AstroSat. UVIT FUV and NUV photometry is carried out here for a set of 239 clusters in the NE disk and bulge of M31 which overlap with the HST/PHAT survey. Padova stellar models were applied to derive ages, masses, metallicities and extinctions for 170 clusters. The ages show a narrow peak at $\sim$4 Myr and a broad peak around 100 Myr. log(Z/Z$_{\odot}$) values are mostly between $-0.3$ and $+0.3$. The 7 clusters in the bulge are low metallicity and high mass. Most clusters are in the spiral arms and have metallicities in the range noted above. The youngest clusters are mostly high metallicity and are concentrated along the brightest parts of the spiral arms. The UVIT FUV and NUV data are sensitive to young stars and detect a new metal rich peak in star formation in the disk at age $\sim4$ Myr.