A new study of stellar substructures in the Fornax dwarf spheroidal galaxy

T. J.L. De Boer, E. Tolstoy, A. Saha, E. W. Olszewski

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Abstract

Using deep V,B - V wide-field photometry, we have conducted a new study of stellar over-densities in the Fornax dwarf spheroidal galaxy by determining detailed star formation histories from colour-magnitude diagram analysis. We have concentrated on the relatively young stellar component (<4 Gyr old), and compared this to the underlying Fornax field population. We have studied in more detail the previously known inner shell-like structure and shown that it has a well-defined age-metallicity relation with a peak at ≈1.5 Gyr, [Fe/H] = -0.6 dex. Comparison to the Fornax centre shows that the over-dense feature is consistent with the age-metallicity relation of young field stars, and likely formed from Fornax gas. This is consistent with a scenario in which the over-density was formed by the re-accretion of previously expelled gas. We have also discovered a new stellar over-density, located 0.3 degrees (0.7 kpc) from the centre, which is only 100 Myr old, with solar metallicity. This feature constitutes some of the youngest, most metal-rich stars stars observed in Fornax to date. It is unclear how the young over-density was formed, although the age and metallicity of stars suggest this feature may represent the last star formation activity of the Fornax dSph.

Original languageEnglish (US)
Article numberA103
JournalAstronomy and astrophysics
Volume551
DOIs
StatePublished - Mar 11 2013

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Keywords

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

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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