Bibcode
Battaglia, G.; Tolstoy, E.; Helmi, A.; Irwin, M. J.; Letarte, B.; Jablonka, P.; Hill, V.; Venn, K. A.; Shetrone, M. D.; Arimoto, N.; Primas, F.; Kaufer, A.; Francois, P.; Szeifert, T.; Abel, T.; Sadakane, K.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 459, Issue 2, November IV 2006, pp.423-440
Fecha de publicación:
11
2006
Revista
Número de citas
288
Número de citas referidas
254
Descripción
Aims.As part of the DART project we have used the ESO/2.2m Wide Field
Imager in conjunction with the VLT/FLAMES GIRAFFE spectrograph to study
the detailed properties of the resolved stellar population of the Fornax
dwarf spheroidal galaxy out to and beyond its tidal radius. Fornax dwarf
spheroidal galaxy has had a complicated evolution and contains
significant numbers of young, intermediate age and old stars. We
investigate the relation between these different components by studying
their photometric, kinematic and abundance distributions.
Methods: . We re-derived the structural parameters of the Fornax dwarf
spheroidal using our wide field imaging covering the galaxy out to its
tidal radius, and analysed the spatial distribution of the Fornax stars
of different ages as selected from colour-magnitude diagram analysis. We
have obtained accurate velocities and metallicities from spectra in the
Ca II triplet wavelength region for 562 Red Giant Branch stars which
have velocities consistent with membership of the Fornax dwarf
spheroidal. Results: .We have found evidence for the presence of
at least three distinct stellar components: a young population (few 100
Myr old) concentrated in the centre of the galaxy, visible as a Main
Sequence in the colour-magnitude diagram; an intermediate age population
(2-8 Gyr old); and an ancient population (>10 Gyr), which are
distinguishable from each other kinematically, from the metallicity
distribution and in the spatial distribution of stars found in the
colour-magnitude diagram. Conclusions: . From our spectroscopic
analysis we find that the "metal rich" stars ([Fe/H]> -1.3) show a
less extended and more concentrated spatial distribution, and display
colder kinematics than the "metal poor" stars ([Fe/H]<-1.3). There is
tentative evidence that the ancient stellar population in the centre of
Fornax does not exhibit equilibrium kinematics. This could be a sign of
a relatively recent accretion of external material, such as the merger
of another galaxy or other means of gas accretion at some point in the
fairly recent past, consistent with other recent evidence of
substructure (Coleman et al. 2004, AJ, 127, 832; 2005, AJ, 129, 1443).