The True Durations of Starbursts: HST Observations of Three Nearby Dwarf
  Starburst Galaxies
  The duration of a starburst is a fundamental parameter affecting the
evolution of galaxies yet, to date, observational constraints on the durations
of starbursts are not well established. Here we study the recent star formation
histories (SFHs) of three nearby dwarf galaxies to rigorously quantify the
duration of their starburst events using a uniform and consistent approach. We
find that the bursts range from ~200 - ~400 Myr in duration resolving the
tension between the shorter timescales often derived observationally with the
longer timescales derived from dynamical arguments. If these three starbursts
are typical of starbursts in dwarf galaxies, then the short timescales (3 - 10
Myr) associated with starbursts in previous studies are best understood as
"flickering" events which are simply small components of the larger starburst.
In this sample of three nearby dwarfs, the bursts are not localized events. All
three systems show bursting levels of star formation in regions of both high
and low stellar density. The enhanced star formation moves around the galaxy
during the bursts and covers a large fraction of the area of the galaxy. These
massive, long duration bursts can significantly affect the structure, dynamics,
and chemical evolution of the host galaxy and can be the progenitors of
"superwinds" that drive much of the recently chemically enriched material from
the galaxy into the intergalactic medium.
