Hubble Space Telescope observations of the local group dwarf galaxy Leo I

Carme Gallart, Wendy L. Freedman, Mario Mateo, Cesare Chiosi, Ian B. Thompson, Antonio Aparicio, Gianpaolo Bertelli, Paul W. Hodge, Myung G. Lee, Edward W Olszewski, Abhijit Saha, Peter B. Stetson, Nicholas B. Suntzeff

Research output: Contribution to journalArticle

37 Citations (Scopus)

Abstract

We present deep HST F555W (V) and F814W (I) observations of a central field in the Local Group dwarf spheroidal (dSph) galaxy Leo I. The resulting color-magnitude diagram (CMD) reaches I ≃ 26 and reveals the oldest ≃ 10-15 Gyr old turnoffs. Nevertheless, a horizontal branch is not obvious in the CMD. Given the low metallicity of the galaxy, this likely indicates that the first substantial star formation in the galaxy may have been somehow delayed in Leo I in comparison with the other dSph satellites of the Milky Way. The subgiant region is well and uniformly populated from the oldest turnoffs up to the 1 Gyr old turnoff, indicating that star formation has proceeded in a continuous way, with possible variations in intensity but no big gaps between successive bursts, over the galaxy's lifetime. The structure of the red clump of core He-burning stars is consistent with the large amount of intermediate-age population inferred from the main sequence and the subgiant region. In spite of the lack of gas in Leo I, the CMD clearly shows star formation continuing until 1 Gyr ago and possibly until a few hundred Myr ago in the central part of the galaxy.

Original languageEnglish (US)
Pages (from-to)665-674
Number of pages10
JournalAstrophysical Journal
Volume514
Issue number2 PART 1
StatePublished - Apr 1 1999

Fingerprint

dwarf galaxies
Hubble Space Telescope
color-magnitude diagram
diagram
galaxies
star formation
clumps
metallicity
bursts
gas
stars
life (durability)
gases

Keywords

  • Galaxies: evolution
  • Galaxies: individual (Leo I)
  • Galaxies: photometry
  • Galaxies: stellar content

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Gallart, C., Freedman, W. L., Mateo, M., Chiosi, C., Thompson, I. B., Aparicio, A., ... Suntzeff, N. B. (1999). Hubble Space Telescope observations of the local group dwarf galaxy Leo I. Astrophysical Journal, 514(2 PART 1), 665-674.

Hubble Space Telescope observations of the local group dwarf galaxy Leo I. / Gallart, Carme; Freedman, Wendy L.; Mateo, Mario; Chiosi, Cesare; Thompson, Ian B.; Aparicio, Antonio; Bertelli, Gianpaolo; Hodge, Paul W.; Lee, Myung G.; Olszewski, Edward W; Saha, Abhijit; Stetson, Peter B.; Suntzeff, Nicholas B.

In: Astrophysical Journal, Vol. 514, No. 2 PART 1, 01.04.1999, p. 665-674.

Research output: Contribution to journalArticle

Gallart, C, Freedman, WL, Mateo, M, Chiosi, C, Thompson, IB, Aparicio, A, Bertelli, G, Hodge, PW, Lee, MG, Olszewski, EW, Saha, A, Stetson, PB & Suntzeff, NB 1999, 'Hubble Space Telescope observations of the local group dwarf galaxy Leo I', Astrophysical Journal, vol. 514, no. 2 PART 1, pp. 665-674.
Gallart C, Freedman WL, Mateo M, Chiosi C, Thompson IB, Aparicio A et al. Hubble Space Telescope observations of the local group dwarf galaxy Leo I. Astrophysical Journal. 1999 Apr 1;514(2 PART 1):665-674.
Gallart, Carme ; Freedman, Wendy L. ; Mateo, Mario ; Chiosi, Cesare ; Thompson, Ian B. ; Aparicio, Antonio ; Bertelli, Gianpaolo ; Hodge, Paul W. ; Lee, Myung G. ; Olszewski, Edward W ; Saha, Abhijit ; Stetson, Peter B. ; Suntzeff, Nicholas B. / Hubble Space Telescope observations of the local group dwarf galaxy Leo I. In: Astrophysical Journal. 1999 ; Vol. 514, No. 2 PART 1. pp. 665-674.
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abstract = "We present deep HST F555W (V) and F814W (I) observations of a central field in the Local Group dwarf spheroidal (dSph) galaxy Leo I. The resulting color-magnitude diagram (CMD) reaches I ≃ 26 and reveals the oldest ≃ 10-15 Gyr old turnoffs. Nevertheless, a horizontal branch is not obvious in the CMD. Given the low metallicity of the galaxy, this likely indicates that the first substantial star formation in the galaxy may have been somehow delayed in Leo I in comparison with the other dSph satellites of the Milky Way. The subgiant region is well and uniformly populated from the oldest turnoffs up to the 1 Gyr old turnoff, indicating that star formation has proceeded in a continuous way, with possible variations in intensity but no big gaps between successive bursts, over the galaxy's lifetime. The structure of the red clump of core He-burning stars is consistent with the large amount of intermediate-age population inferred from the main sequence and the subgiant region. In spite of the lack of gas in Leo I, the CMD clearly shows star formation continuing until 1 Gyr ago and possibly until a few hundred Myr ago in the central part of the galaxy.",
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