Institute of Astronomy

The Star Formation & Chemical Evolution Timescales of Two Nearby Dwarf Spheroidal Galaxies

SpeakerTalk DateTalk Series
Thomas de Boer (Kapteyn Astronomical Institute)20 January 2012Institute of Astronomy Galaxies Discussion Group

Abstract

We present the detailed Star Formation History of the nearby Sculptor
and Fornax dwarf spheroidal galaxies, from wide-field photometry of
resolved stars, going down to the oldest Main Sequence Turn-Off. The
accurately flux calibrated, wide-field Colour-Magnitude Diagrams are
used directly in combination with spectroscopic metallicities of
individual RGB stars to constrain the ages of different stellar
populations, and derive the Star Formation History with particular
accuracy.
The detailed Star Formation History shows the star formation at
different ages and metallicities, at different positions in the galaxy,
and shows that the known metallicity gradients are well matched to an
age gradient. The obtained SFH is used to determine accurate age
estimates for individual RGB stars, for which spectroscopic abundances
(alpha-elements, r- and s-process elements) are known. In this way, we
obtain the accurate age-metallicity relation of each galaxy, as well as
the temporal evolution of alpha-element abundances.
This allows us to study, for the first time, the timescale of chemical
evolution in these two dwarf galaxies, and determine an accurate age of
the "knee" in the alpha-element distribution. Finally, we compare the
timescale of chemical evolution in both dwarf galaxies, and determine
whether the chemical abundance patterns seen in galaxies with recent
episodes of star formation are a direct continuation of those with only
old populations.

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