Old stellar populations of the small magellanic cloud

Andrew E. Dolphin, Alistair R. Walker, Paul W. Hodge, Mario Mateo, Edward W Olszewski, Robert A. Schommer, Nicholas B. Suntzeff

Research output: Contribution to journalArticle

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Abstract

We present WFPC2 and ground-based VI photometry of NGC 121 and a nearby field in the outer SMC. For NGC 121, we measure a true distance modulus of μ0 = 18.96 ± 0.04 (distance of 61.9 ± 1.1 kpc), age of 10.6 ± 0.5 Gyr, metallicity of [Fe/H] = -1.03 ± 0.06, and initial mass of 4.1 ± 0.4 × 105 M, assuming a Salpeter IMF with lower cutoff at 0.1 M. In the outer SMC field, we find evidence of stars covering a wide range of ages - from 2 Gyr to at least 9-12 Gyr old. We have measured the distance, extinction, and star formation history (past star formation rates and enrichment history) using a CMD-fitting algorithm. The distance modulus of the SMC is measured to be μ0 = 18.88 ± 0.08, corresponding to a distance of 59.7 ± 2.2 kpc. The overall star formation rate appears to have been relatively constant over this period, although there may be small gaps in the star-forming activity too small to be resolved. The lack of current star-forming activity is a selection effect, as the field was intentionally chosen to avoid recent activity. The mean metallicity of this field has increased from an average of [Fe/ H] = -1.3 ± 0.3 for stars older than 8 Gyr to [Fe/H] = -0.7 ± 0.2 in the past 3 Gyr.

Original languageEnglish (US)
Pages (from-to)303-313
Number of pages11
JournalAstrophysical Journal
Volume562
Issue number1 PART I
DOIs
StatePublished - 2001

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Magellanic clouds
IMF
history
stars
star formation rate
extinction
metallicity
histories
photometry
star formation
coverings
cut-off
rate
effect

Keywords

  • Galaxies: evolution
  • Galaxies: stellar content
  • Magellanic Clouds

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Dolphin, A. E., Walker, A. R., Hodge, P. W., Mateo, M., Olszewski, E. W., Schommer, R. A., & Suntzeff, N. B. (2001). Old stellar populations of the small magellanic cloud. Astrophysical Journal, 562(1 PART I), 303-313. https://doi.org/10.1086/323873

Old stellar populations of the small magellanic cloud. / Dolphin, Andrew E.; Walker, Alistair R.; Hodge, Paul W.; Mateo, Mario; Olszewski, Edward W; Schommer, Robert A.; Suntzeff, Nicholas B.

In: Astrophysical Journal, Vol. 562, No. 1 PART I, 2001, p. 303-313.

Research output: Contribution to journalArticle

Dolphin, AE, Walker, AR, Hodge, PW, Mateo, M, Olszewski, EW, Schommer, RA & Suntzeff, NB 2001, 'Old stellar populations of the small magellanic cloud', Astrophysical Journal, vol. 562, no. 1 PART I, pp. 303-313. https://doi.org/10.1086/323873
Dolphin AE, Walker AR, Hodge PW, Mateo M, Olszewski EW, Schommer RA et al. Old stellar populations of the small magellanic cloud. Astrophysical Journal. 2001;562(1 PART I):303-313. https://doi.org/10.1086/323873
Dolphin, Andrew E. ; Walker, Alistair R. ; Hodge, Paul W. ; Mateo, Mario ; Olszewski, Edward W ; Schommer, Robert A. ; Suntzeff, Nicholas B. / Old stellar populations of the small magellanic cloud. In: Astrophysical Journal. 2001 ; Vol. 562, No. 1 PART I. pp. 303-313.
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AB - We present WFPC2 and ground-based VI photometry of NGC 121 and a nearby field in the outer SMC. For NGC 121, we measure a true distance modulus of μ0 = 18.96 ± 0.04 (distance of 61.9 ± 1.1 kpc), age of 10.6 ± 0.5 Gyr, metallicity of [Fe/H] = -1.03 ± 0.06, and initial mass of 4.1 ± 0.4 × 105 M⊙, assuming a Salpeter IMF with lower cutoff at 0.1 M⊙. In the outer SMC field, we find evidence of stars covering a wide range of ages - from 2 Gyr to at least 9-12 Gyr old. We have measured the distance, extinction, and star formation history (past star formation rates and enrichment history) using a CMD-fitting algorithm. The distance modulus of the SMC is measured to be μ0 = 18.88 ± 0.08, corresponding to a distance of 59.7 ± 2.2 kpc. The overall star formation rate appears to have been relatively constant over this period, although there may be small gaps in the star-forming activity too small to be resolved. The lack of current star-forming activity is a selection effect, as the field was intentionally chosen to avoid recent activity. The mean metallicity of this field has increased from an average of [Fe/ H] = -1.3 ± 0.3 for stars older than 8 Gyr to [Fe/H] = -0.7 ± 0.2 in the past 3 Gyr.

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