Winds and radiation in unison: a new semi-analytic feedback model for
  cloud dissolution
  Star clusters interact with the interstellar medium (ISM) in various ways,
most importantly in the destruction of molecular star-forming clouds, resulting
in inefficient star formation on galactic scales. On cloud scales, ionizing
radiation creates \hii regions, while stellar winds and supernovae drive the
ISM into thin shells. These shells are accelerated by the combined effect of
winds, radiation pressure and supernova explosions, and slowed down by gravity.
Since radiative and mechanical feedback is highly interconnected, they must be
taken into account in a self-consistent and combined manner, including the
coupling of radiation and matter. We present a new semi-analytic
one-dimensional feedback model for isolated massive clouds ($\geq
10^5\,M_{\odot}$) to calculate shell dynamics and shell structure
simultaneously. It allows us to scan a large range of physical parameters (gas
density, star formation efficiency, metallicity) and to estimate escape
fractions of ionizing radiation $f_{\rm{esc,i}}$, the minimum star formation
efficiency $\epsilon_{\rm{min}}$ required to drive an outflow, and recollapse
time scales for clouds that are not destroyed by feedback. Our results show
that there is no simple answer to the question of what dominates cloud
dynamics, and that each feedback process significantly influences the
efficiency of the others. We find that variations in natal cloud density can
very easily explain differences between dense-bound and diffuse-open star
clusters. We also predict, as a consequence of feedback, a $4-6$ Myr age
difference for massive clusters with multiple generations.
