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The Star Formation History of M32

Monachesi, Antonela and Trager, Scott C. and Lauer, Tod R. and Hidalgo, Sebastián L. and Freedman, Wendy and Dressler, Alan and Grillmair, Carl and Mighell, Kenneth J. (2012) The Star Formation History of M32. Astrophysical Journal, 745 (1). p. 97. ISSN 0004-637X.

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We use deep Hubble Space Telescope Advanced Camera for Surveys/High Resolution Channel 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 2-5 Gyr old stars contribute ~40% ± 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] ~ –0.7) stars, suggesting that blue straggler stars contribute ~2% of the mass at F1; the remaining ~3% 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 r_e ). This contradicts spectroscopic studies that show a steep age gradient from M32's center to 1 re . The inferred SFH of the M31 background field F2 reveals that the majority of its stars are old, with ~95% of its mass already acquired 5-14 Gyr ago. It is composed of two dominant populations; ~30% ± 7.5% of its mass is in a 5-8 Gyr old population, and ~65% ± 9% of the mass is in an 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 (~1 disk scale length) to be ~5-9 Gyr, our results agree with an inside-out disk formation scenario for M31's disk.

Item Type:Article
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Freedman, Wendy0000-0003-3431-9135
Grillmair, Carl0000-0003-4072-169X
Additional Information:© 2012 American Astronomical Society. Received 2011 July 15; accepted 2011 November 15; published 2012 January 4. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with GO proposal 10572. We thank Reynier Peletier, Eline Tolstoy, and Antonio Aparicio for their valuable comments on an early version of this paper. A.M. wishes to thank the hospitality of the Instituto de Astrofísica de Canarias and the Department of Physics and Astronomy of Michigan State University, where part of this work was carried out. We thank the anonymous referee for the very careful reading of the manuscript and comments which helped to improve this paper. This work has made use of the IAC-STAR synthetic CMD computation code. IAC-STAR is supported and maintained by the computer division of the Instituto de Astrofísica de Canarias. NOVA is acknowledged for financial support. Support for program GO-10572 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. T.R.L. and K.J.M. acknowledge the support from The National Optical Astronomy Observatory, which is operated by AURA, Inc., under cooperative agreement with the National Science Foundation. Facility: HST (ACS)
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Nederlandse Onderzoekschool voor de Astronomie (NOVA)UNSPECIFIED
Space Telescope Science InstituteUNSPECIFIED
National Optical Astronomy Observatory (NOAO)UNSPECIFIED
NASANAS 5-26555
Subject Keywords:galaxies: elliptical and lenticular, cD; galaxies: evolution; galaxies: individual (M32, M31); galaxies: stellar content; Local Group
Issue or Number:1
Record Number:CaltechAUTHORS:20120405-154510903
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Official Citation:The Star Formation History of M32 Antonela Monachesi et al. 2012 ApJ 745 97
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:29996
Deposited By: Jason Perez
Deposited On:12 Apr 2012 19:53
Last Modified:17 Nov 2019 06:02

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