The Star Formation History of M32

Abstract

We use deep HST ACS/HRC observations of a field within M32 (F1) and an M31 background field (F2) to determine the star formation history (SFH) of M32 from its resolved stellar population. We find that 2-5Gyr old stars contribute \som40%+/- 17% of M32's mass, while 55%+/-21% of M32's mass comes from stars older than 5 Gyr. The mass-weighted mean age and metallicity of M32 at F1 are <Age>=6.8+/-1.5 Gyr and <[M/H]>=-0.01+/-0.08 dex. The SFH additionally indicates the presence of young (<2 Gyr old), metal-poor ([M/H]\sim-0.7) stars, suggesting that blue straggler stars contribute ~2% of the mass at F1; the remaining \sim3% of the mass is in young metal-rich stars. Line-strength indices computed from the SFH imply a light-weighted mean age and metallicity of 4.9 Gyr and [M/H] = -0.12 dex, and single-stellar-population-equivalent parameters of 2.9+/-0.2 Gyr and [M/H]=0.02+/-0.01 dex at F1 (~2.7 re). This contradicts spectroscopic studies that show a steep age gradient from M32's center to 1re. The inferred SFH of the M31 background field F2 reveals that the majority of its stars are old, with \sim95% of its mass already acquired 5-14 Gyr ago. It is composed of two dominant populations; \sim30%+/-7.5% of its mass is in a 5-8 Gyr old population, and \sim65%+/-9% of the mass is in a 8-14 Gyr old population. The mass-weighted mean age and metallicity of F2 are <Age>=9.2+/-1.2 Gyr and <[M/H]>=-0.10+/-0.10 dex, respectively. Our results suggest that the inner disk and spheroid populations of M31 are indistinguishable from those of the outer disk and spheroid. Assuming the mean age of M31's disk at F2 (\sim1 disk scale length) to be 5-9 Gyr, our results agree with an inside-out disk formation scenario for M31's disk.

Accepted to ApJ. 24 pages, 18 figures. A high-resolution version can be downloaded from http://www.astro.rug.nl/~monachesi/monachesi-sfh.pdf

References in corpus (9)

• Radial migration in galactic disks caused by resonance overlap of multiple patterns: Self-consistent simulations
• The ACS LCID project. V. The Star Formation History of the Dwarf Galaxy \objectname[]{LGS-3}: Clues for Cosmic Reionization and Feedback
• The ACS LCID project. VI. The SFH of the Tucana dSph and the relative ages of the isolated dSph galaxies
• The radial distribution of blue straggler stars and the nature of their progenitors
• The stellar population histories of early-type galaxies. III. The Coma Cluster
• The Star Formation Histories of the Bulge and Disk of M31 from Gemini North+NIRI/Altair and HST/NICMOS
• Search and analysis of blue straggler stars in open clusters
• The Deepest HST Color-Magnitude Diagram of M32: Evidence for Intermediate-Age Populations
• The Brightest Stars in M32: Comparing Predictions from Spectra with the Resolved Stellar Content

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