Bibcode
Battaglia, G.; Rejkuba, M.; Tolstoy, E.; Irwin, M. J.; Beccari, G.
Referencia bibliográfica
Monthly Notices of the Royal Astronomical Society, Volume 424, Issue 2, pp. 1113-1131.
Advertised on:
8
2012
Número de citas
17
Número de citas referidas
16
Descripción
We present results from a wide-area photometric survey of the Phoenix
dwarf galaxy, one of the rare dwarf irregular/dwarf spheroidal
transition-type galaxies (dTs) of the Local Group (LG). These objects
offer the opportunity to study the existence of possible evolutionary
links between the late- and early-type LG dwarf galaxies, since the
properties of dTs suggest that they may be dwarf irregulars in the
process of transforming into dwarf spheroidals.
Using FORS at the Very Large Telescope (VLT), we have acquired VI
photometry of Phoenix. The data reach a signal-to-noise ratio (S/N)
˜ 10 just below the horizontal branch of the system and consist of
a mosaic of images that covers an area of 26 × 26
arcmin2 centred on the coordinates of the optical centre of
the galaxy.
Examination of the colour-magnitude diagram and luminosity function
revealed the presence of a bump above the red clump, consistent with
being a red giant branch bump.
The deep photometry combined with the large area covered allows us to
put on a secure ground the determination of the overall structural
properties of the galaxy and to derive the spatial distribution of stars
in different evolutionary phases and age ranges, from 0.1 Gyr to the
oldest stars. The best-fitting profile to the overall stellar population
is a Sérsic profile of Sérsic radius RS= 1.82
± 0.06 arcmin and m= 0.83 ± 0.03.
We confirm that the spatial distribution of stars is found to become
more and more centrally concentrated the younger the stellar population,
as reported in previous studies. This is similar to the stellar
population gradients found for close-by Milky Way dwarf spheroidal
galaxies. We quantify such spatial variations by analysing the surface
number density profiles of stellar populations in different age ranges;
the parameters of the best-fitting profiles are derived, and these can
provide useful constraints to models exploring the evolution of dwarf
galaxies in terms of their star formation.
The disc-like distribution previously found in the central regions in
Phoenix appears to be present mainly among stars younger than 1 Gyr, and
absent for the stars >rsim5 Gyr old, which on the other hand show a
regular distribution also in the centre of the galaxy. This argues
against a disc-halo structure of the type found in large spirals such as
the Milky Way. Based on FORS observations collected at the European
Southern Observatory (ESO), proposal 083.B-0252.