2017/08/08 by Williams, Benjamin F., Dolphin, Andrew E., Dalcanton, Julianne J. +7
#Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences
paper · doi:10.48550/arxiv.1708.02617
We map the star formation history across M31 by fitting stellar evolution models to color-magnitude diagrams of each 83''×83'' (0.3×1.4 kpc, deprojected) region of the PHAT survey outside of the innermost 6'×12' portion. We find that most of the star formation occurred prior to ∼8 Gyr ago, followed by a relatively quiescent period until ∼4 Gyr ago, a subsequent star formation episode about 2 Gyr ago and a return to relative quiescence. There appears to be little, if any, structure visible for populations with ages older than 2 Gyr, suggesting significant mixing since that epoch. Finally, assuming a Kroupa IMF from 0.1-100 M\odot, we find that the total amount of star formation over the past 14 Gyr in the area over which we have fit models is 5×1010 M\odot. Fitting the radial distribution of this star formation and assuming azimuthal symmetry, (1.5±0.2)×1011 M\odot of stars have formed in the M31 disk as a whole, (9±2)×1010 M\odot of which has likely survived to the present after accounting for evolutionary effects. This mass is about one fifth of the total dynamical mass of M31.