A Large Group of Asymptotic Giant Branch Stars in the Disk of M31: A Missing Piece of the Puzzle?

TL;DR

This study investigates a stellar grouping near M31, revealing it as a potential dwarf galaxy or a fossil star-forming region, with properties suggesting a complex origin and star formation history.

Contribution

The paper identifies and characterizes a large stellar structure in M31's disk, proposing its possible origins as a satellite galaxy or a star-forming remnant.

Findings

The structure has a lower surface brightness than the surrounding disk.

It contains stars older than 100 Myr with bluer colors.

Its properties resemble those of dwarf galaxies with similar brightness.

Abstract

The properties of a stellar grouping that is ~ 3.5 kpc to the north east of the center of M31 is examined. This structure has (1) a surface brightness that is lower than the surrounding disk, (2) a more-or-less round appearance, (3) a size of ~ 300 arcsec (~ 1 kpc), and (4) an integrated brightness M_K = 6.5. It is populated by stars with ages > 100 Myr and J-K colors that tend to be bluer than those of stars in the surrounding disk. Comparisons with model luminosity functions suggest that the star formation rate in this object has changed twice in the past few hundred Myr. Fitting a Sersic function to the light profile reveals a power-law index and effective surface brightness that are similar to those of dwarf galaxies with the same integrated brightness. Two possible origins for this object are considered: (1) it is a heretofore undiscovered satellite of M31 that is seen against/in/through the M31 disk, or (2) it is a fossil star-forming region in the M31 disk.