Bibcode
Hidalgo, Sebastian L.; Aparicio, Antonio; Martínez-Delgado, David; Gallart, Carme
Bibliographical reference
The Astrophysical Journal, Volume 705, Issue 1, pp. 704-716 (2009).
Advertised on:
11
2009
Journal
Citations
72
Refereed citations
64
Description
We present the star formation history (SFH) and its variations with
galactocentric distance for the Local Group dwarf galaxy of Phoenix.
They have been derived from a (F555W, F814W) color-magnitude diagram
obtained from WFPC2@HST data, which reaches the oldest main-sequence
turnoffs. The IAC-star and IAC-pop codes and the MinnIAC suite have been
used to obtain the star formation rate as a function of time and
metallicity, ψ(t, z). We find that Phoenix has had ongoing but
gradually decreasing star formation over nearly a Hubble time. The
highest level of star formation occurred from the formation of the
galaxy till 10.5 Gyr ago, when 50% of the total star formation had
already taken place. From that moment, star formation continues at a
significant level until 6 Gyr ago (an additional 35% of the stars are
formed in this time interval), and at a very low level till the present
time. The chemical enrichment law shows a trend of slowly increasing
metallicity as a function of time until 6-8 Gyr ago, when metallicity
starts to increase steeply to the current value. We have paid particular
attention to the study of the variations of the SFH as a function of
radius. Young stars are found in the inner region of the galaxy only,
but intermediate-age and old stars can be found at all galactocentric
distances. The distribution of mass density in alive stars and its
evolution with time has been studied. This study shows that star
formation started at all galactocentric distances in Phoenix at an early
epoch. If stars form in situ in Phoenix, the star formation onset took
place all over the galaxy (up to a distance of about 400 pc from the
center), but preferentially out of center regions. After that, our
results are compatible with a scenario in which the star formation
region envelope slowly shrinks as time goes on, possibly as a natural
result of pressure support reduction as gas supply diminishes. As a
consequence, the star formation stopped first (about 7-8 Gyr ago) in
outer regions and the scale length of the stellar mass density
distribution decreased with time. Finally, no traces of a true, old halo
are apparent in Phoenix either in its stellar age distribution or in the
stellar mass density distribution, at least out to 0.5 kpc (about 2.5
scale length) from the center.
Related projects
Milky Way and Nearby Galaxies
The general aim of the project is to research the structure, evolutionary history and formation of galaxies through the study of their resolved stellar populations, both from photometry and spectroscopy. The group research concentrates in the most nearby objects, namely the Local Group galaxies including the Milky Way and M33 under the hypothesis
Martín
López Corredoira