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The role of rest-frame UV data in studies of stellar populations : the legacy of GALEX and HST in the Milky Way and the local universe

Luciana Bianchi

Massive stars drive the dynamical and chemical evolution of their host
galaxy. Mapped across large portions of galaxies, they provide a precise
time- and spatial- tomography of the young stellar populations, because
they evolve on fast time-scales. Massive stars are very luminous,
and dominate the light of distant star-burst galaxies.
Studies of stellar populations in local galaxies, spanning a variety of
environments and conditions, allow us to understand the star-formation process,
and the co-evolution of massive stars and dust. Results from such
studies inform stellar and galaxy evolution models, which underpin our
interpretation of the integrated light from galaxies in the distant, younger
The identification and characterisation of hot (young) massive stars, and
of the evolved descendants of intermediate-mass stars, the hot white dwarfs,
requires UV data.
GALEX has performed the first comprehensive sky surveys in far-UV and
near-UV broad bands, providing unprecedented wide-field, sensitive views of
young stellar populations in nearby extended galaxies, as well as a census
of Milky Way hot stars, and of star-forming galaxies and QSOs at redshifts
up to about 2. Hubble’s resolution has enabled multi-band
measurements of the resolved stellar constituents of nearby star-forming
regions : the spatial structuring of resolved young populations reveals how
gas and dust condense to form stars, and how local starbursts evolve and
dissolve with time. I will describe our contribution to this topic, and
show results from the GALEX surveys, and from HST’s PHAT and TrImS surveys.