2012ApJ...745...97M

Query : 2012ApJ...745...97M

2012ApJ...745...97M - Astrophys. J., 745, 97 (2012/January-3)

The star formation history of M32.

MONACHESI A., TRAGER S.C., LAUER T.R., HIDALGO S.L., FREEDMAN W., DRESSLER A., GRILLMAIR C. and MIGHELL K.J.

Abstract (from CDS):

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 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 re). 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 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.

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Journal keyword(s): galaxies: elliptical and lenticular, cD - galaxies: evolution - galaxies: individual (M32, M31) - galaxies: stellar content - Local Group

Simbad objects: 8

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Number of rows : 8
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2026 		#notes
1 M 32 GiG 00 42 41.82480 +40 51 54.6120 9.51 9.03 8.08     ~ 2236 2
2 M 31 AGN 00 42 44.330 +41 16 07.50 4.86 4.36 3.44     ~ 13622 1
3 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 12317 1
4 M 33 GiG 01 33 50.8965749232 +30 39 36.630403128 6.17 6.27 5.72     ~ 6226 1
5 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 19090 0
6 NAME Virgo Cluster ClG 12 30 47.8 +12 23 07           ~ 7107 0
7 Z 318-18 G 15 09 08.0 +67 13 21   13.60 10.6     ~ 1459 0
8 NAME Local Group GrG ~ ~           ~ 9325 0

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