PHAT. XIX. The Ancient Star Formation History of the M31 Disk

Journal Article · Sun Sep 10 00:00:00 EDT 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/AA862A· OSTI ID:22875813

Williams, Benjamin F.; Dalcanton, Julianne J.; Weisz, Daniel R.; Lewis, Alexia R.; Choi, Yumi ^[1]; Dolphin, Andrew E. ^[2]; Bell, Eric F. ^[3]; Rosenfield, Philip ^[4]; Skillman, Evan ^[5]; Monachesi, Antonela ^[6]

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1. Department of Astronomy, Box 351580, University of Washington, Seattle, WA 98195 (United States)
2. Raytheon, 1151 E. Hermans Road, Tucson, AZ 85706 (United States)
3. Department of Astronomy, University of Michigan, 1085 South University Ave., Ann Arbor, MI 48109 (United States)
4. Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA (United States)
5. Department of Astronomy, University of Minnesota, 116 Church St. SE, Minneapolis, MN 55455 (United States)
6. Departamento de Física y Astronomía, Universidad de La Serena, Av. Juan Cisternas 1200 N, La Serena (Chile)

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 Panchromatic Hubble Andromeda Treasury (PHAT) survey outside of the innermost 6{sup ′}×12{sup ′} 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 initial mass function from 0.1 to 100 M {sub ⊙}, 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 × 10{sup 10} M {sub ⊙}. Fitting the radial distribution of this star formation and assuming azimuthal symmetry, (1.5 ± 0.2) × 10{sup 11} M {sub ⊙} of stars has formed in the M31 disk as a whole, (9 ± 2) × 10{sup 10} M {sub ⊙} 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.

• OSTI ID: 22875813
• Journal Information: Astrophysical Journal, Vol. 846, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
GALAXIES
MASS
SPATIAL DISTRIBUTION
STAR EVOLUTION
STARS
SYMMETRY