We have identified a major global enhancement of star formation in the inner M31 disk that occurred between 2-4 Gyr ago, producing ∼60% of the stellar mass formed in the past 5 Gyr. The presence of this episode in the inner disk was discovered by modeling the optical resolved star color-magnitude diagrams of low extinction regions in the main disk of M31 (3<R<20 kpc) as part of the Panchromatic Hubble Andromeda Treasury. This measurement confirms and extends recent measurements of a widespread star formation enhancement of similar age in the outer disk, suggesting that this burst was both massive and global. Following the galaxy-wide burst, the star formation rate of M31 has significantly declined. We briefly discuss possible causes for these features of the M31 evolutionary history, including interactions with M32, M33 and/or a merger.
@article{arxiv.1504.02120,
title = {A Global Star Forming Episode in M31 2-4 Gyr Ago},
author = {Benjamin F. Williams and Julianne J. Dalcanton and Andrew E. Dolphin and Daniel R. Weisz and Alexia R. Lewis and Dustin Lang and Eric F. Bell and Martha Boyer and Morgan Fouesneau and Karoline M. Gilbert and Antonela Monachesi and Evan Skillman},
journal= {arXiv preprint arXiv:1504.02120},
year = {2015}
}
Comments
12 pages, 2 tables, 6 figures, accepted for publication in ApJ