The evolution of normal galaxies is predominantly driven by
stars. Young, massive stars with masses above ~ 5
M
forming in
starbursts provide the thermal and non-thermal luminosity responsible
for the observed global galactic parameters
(Heckman 1998).
The tight
connection of stellar and galactic properties permits the use of stars
as tracers of starbursts as a whole. Therefore, understanding and
reading the clock set by stellar evolution is a necessary prerequisite
for age-dating starbursts. It is not a sufficient condition, however, as
the complex morphology of stars, gas, and dust in a starburst make it
difficult to interpret such an idealized clock.