The episodic star formation history of the Carina dwarf spheroidal galaxy

T. J L De Boer, E. Tolstoy, B. Lemasle, A. Saha, Edward W Olszewski, M. Mateo, M. J. Irwin, G. Battaglia

Research output: Contribution to journalArticle

26 Citations (Scopus)

Abstract

We present deep photometry of the Carina dwarf spheroidal galaxy in the B and V filters from CTIO/MOSAIC out to and beyond the tidal radius of rell ≈ 0.48 degrees. The accurately calibrated photometry is combined with spectroscopic metallicity distributions of red giant branch (RGB) stars to determine the detailed star formation and chemical evolution history of Carina. The star formation history (SFH) confirms the episodic formation history of Carina and quantifies the duration and strength of each episode in great detail as a function of radius from the centre. Twomain episodes of star formation occurred at old (>8 Gyr) and intermediate (2-8 Gyr) ages, both enriching stars starting from low metallicities ([Fe/H] < -2 dex). By dividing the SFH into two components, we determine that 60 ± 9 percent of the total number of stars formed within the intermediate-age episode. Furthermore, within the tidal radius (0.48 degrees or 888 pc) a total mass in stars of 1.07 ± 0.08 × 106 M was formed, giving Carina a stellar mass-to-light ratio of 1.8 ± 0.8. By combining the detailed SFH with spectroscopic observations of RGB stars, we determined the detailed age-metallicity relation of each episode and the timescale of α-element evolution of Carina from individual stars. The oldest episode displays a tight age-metallicity relation during ≈6 Gyr with steadily declining α-element abundances and a possible α-element "knee" visible at [Fe/H] ≈ -2.5 dex. The intermediate-age sequence displays a more complex age-metallicity relation starting from low metallicity and a sequence in α-element abundances with a slope much steeper than observed in the old episode, starting from [Fe/H] = -1.8 dex and [Mg/Fe] ≈ 0.4 dex and declining to Mg-poor values ([Mg/Fe] ≈ -0.5 dex). This clearly indicates that the two episodes of star formation formed from gas with different abundance patterns, which is inconsistent with simple evolution in an isolated system.

Original languageEnglish (US)
Article numberA10
JournalAstronomy and Astrophysics
Volume572
DOIs
StatePublished - Dec 1 2014

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dwarf galaxies
metallicity
star formation
histories
stars
history
radii
photometry
mass to light ratios
chemical evolution
stellar mass
slopes
filter
timescale
filters
gases
gas

Keywords

  • Galaxies: dwarf
  • Galaxies: evolution
  • Galaxies: stellar content
  • Hertzsprung-Russell and C-M diagrams
  • Local Group

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

De Boer, T. J. L., Tolstoy, E., Lemasle, B., Saha, A., Olszewski, E. W., Mateo, M., ... Battaglia, G. (2014). The episodic star formation history of the Carina dwarf spheroidal galaxy. Astronomy and Astrophysics, 572, [A10]. https://doi.org/10.1051/0004-6361/201424119

The episodic star formation history of the Carina dwarf spheroidal galaxy. / De Boer, T. J L; Tolstoy, E.; Lemasle, B.; Saha, A.; Olszewski, Edward W; Mateo, M.; Irwin, M. J.; Battaglia, G.

In: Astronomy and Astrophysics, Vol. 572, A10, 01.12.2014.

Research output: Contribution to journalArticle

De Boer, TJL, Tolstoy, E, Lemasle, B, Saha, A, Olszewski, EW, Mateo, M, Irwin, MJ & Battaglia, G 2014, 'The episodic star formation history of the Carina dwarf spheroidal galaxy', Astronomy and Astrophysics, vol. 572, A10. https://doi.org/10.1051/0004-6361/201424119
De Boer, T. J L ; Tolstoy, E. ; Lemasle, B. ; Saha, A. ; Olszewski, Edward W ; Mateo, M. ; Irwin, M. J. ; Battaglia, G. / The episodic star formation history of the Carina dwarf spheroidal galaxy. In: Astronomy and Astrophysics. 2014 ; Vol. 572.
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abstract = "We present deep photometry of the Carina dwarf spheroidal galaxy in the B and V filters from CTIO/MOSAIC out to and beyond the tidal radius of rell ≈ 0.48 degrees. The accurately calibrated photometry is combined with spectroscopic metallicity distributions of red giant branch (RGB) stars to determine the detailed star formation and chemical evolution history of Carina. The star formation history (SFH) confirms the episodic formation history of Carina and quantifies the duration and strength of each episode in great detail as a function of radius from the centre. Twomain episodes of star formation occurred at old (>8 Gyr) and intermediate (2-8 Gyr) ages, both enriching stars starting from low metallicities ([Fe/H] < -2 dex). By dividing the SFH into two components, we determine that 60 ± 9 percent of the total number of stars formed within the intermediate-age episode. Furthermore, within the tidal radius (0.48 degrees or 888 pc) a total mass in stars of 1.07 ± 0.08 × 106 M⊙ was formed, giving Carina a stellar mass-to-light ratio of 1.8 ± 0.8. By combining the detailed SFH with spectroscopic observations of RGB stars, we determined the detailed age-metallicity relation of each episode and the timescale of α-element evolution of Carina from individual stars. The oldest episode displays a tight age-metallicity relation during ≈6 Gyr with steadily declining α-element abundances and a possible α-element {"}knee{"} visible at [Fe/H] ≈ -2.5 dex. The intermediate-age sequence displays a more complex age-metallicity relation starting from low metallicity and a sequence in α-element abundances with a slope much steeper than observed in the old episode, starting from [Fe/H] = -1.8 dex and [Mg/Fe] ≈ 0.4 dex and declining to Mg-poor values ([Mg/Fe] ≈ -0.5 dex). This clearly indicates that the two episodes of star formation formed from gas with different abundance patterns, which is inconsistent with simple evolution in an isolated system.",
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