Dwarf Star-Forming Galaxies in the Local Universe: the HST Perspective
Alessandra Aloisi, JHU/CAS
In hierarchical clustering scenarios, dwarf galaxies are the first
systems to collapse and start forming stars. The very low metal
content, high gas fraction and ongoing star-formation make some of
them (IZw18 or SBS 0335-052) very similar to primordial galaxies in
the early Universe. Dwarf star-forming systems have also been
suggested to be the local counterparts of the faint blue galaxies seen
in excess at intermediate redshift (z~0.5-1). Understanding the
star-formation history of dwarf irregular and blue compact galaxies is
thus fundamental not only for the comprehension of the astrophysical
mechanisms involved, but also for its cosmological implications. We
present the state of the art of a project to infer the evolutionary
history of some benchmark nearby (d = 2-10 Mpc) dwarf star-forming
galaxies: IZw18, NGC 1569 and NGC 1705. The project is carried out
with HST data in different spectral ranges. Imaging in the optical/NIR
bands (WFPC2/NICMOS) will allow to resolve the stellar populations of
these galaxies. Their star formation history over a Hubble time will
be inferred by comparing the observed color-magnitude diagrams with
synthetic ones. Spectroscopy in the UV/optical band (FOS, GHRS, STIS)
of HII regions/SSCs and a few individual stars will allow to deduce
chemical abundances in both the gas and the stars, gas kinematics, and
its interaction with the stellar population. The results of this
project will be finally inserted into the more general picture that is
emerging for the evolutionary history of dwarf irregular/blue compact
galaxies.