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

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.

To appear in The Astrophysical Journal Letters

References in corpus (5)

• The Haunted Halos of Andromeda and Triangulum: A panorama of galaxy formation in action
• Investigating the Andromeda Stream: III. A Young Shell System in M31
• An almost head-on collision as the origin of two off-centre rings in the Andromeda galaxy
• Unveiling the Boxy Bulge and Bar of the Andromeda Spiral Galaxy
• SDSS surface photometry of M 31 with absorption corrections

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• The Recent Stellar Archeology of M31 - The Nearest Red Disk Galaxy
• Formation of the Andromeda Giant Stream: Asymmetric Structure and Disc Progenitor
• Hunting A Wandering Supermassive Black Hole in M31 Halo -- Hermitage of Black Hole
• Seeing Red in M32: Constraints on the Stellar Content from Near- and Mid-Infrared Observations and Applications for Studies of More Distant Galaxies
• Kinematics and Metallicity of Red Giant Branch Stars in the Northeast Shelf of M31