The Nature of Starbursts : II. The Duration of Starbursts in Dwarf
  Galaxies
  The starburst phenomenon can shape the evolution of the host galaxy and the
surrounding intergalactic medium. The extent of the evolutionary impact is
partly determined by the duration of the starburst, which has a direct
correlation with both the amount of stellar feedback and the development of
galactic winds, particularly for smaller mass dwarf systems. We measure the
duration of starbursts in twenty nearby, ongoing, and "fossil" starbursts in
dwarf galaxies based on the recent star formation histories derived from
resolved stellar population data obtained with the Hubble Space Telescope.
Contrary to the shorter times of 3-10 Myr often cited, the starburst durations
we measure range from 450 - 650 Myr in fifteen of the dwarf galaxies and up to
1.3 Gyr in four galaxies; these longer durations are comparable to or longer
than the dynamical timescales for each system. The same feedback from massive
stars that may quench the flickering SF does not disrupt the overall burst
event in our sample of galaxies. While five galaxies present fossil bursts,
fifteen galaxies show ongoing bursts and thus the final durations may be longer
than we report here for these systems. One galaxy shows a burst that has been
ongoing for only 20 Myr; we are likely seeing the beginning of a burst event in
this system. Using the duration of the starbursts, we calculate that the bursts
deposited 10^(53.9)-10^(57.2) ergs of energy into the interstellar medium
through stellar winds and supernovae and produced 3%-26% of the host galaxy's
mass.
