The viscous evolution of circumstellar discs in young star clusters
  Stars with circumstellar disks may form in environments with high stellar and
gas densities which affects the disks through processes like truncation from
dynamical encounters, ram pressure stripping, and external photoevaporation.
Circumstellar disks also undergo viscous evolution which leads to disk
expansion. Previous work indicates that dynamical truncation and viscous
evolution play a major role in determining circumstellar disk size and mass
distributions. However, it remains unclear under what circumstances each of
these two processes dominates. Here we present results of simulations of young
stellar clusters taking viscous evolution and dynamical truncations into
account. We model the embedded phase of the clusters by adding leftover gas as
a background potential which can be present through the whole evolution of the
cluster, or expelled after 1 Myr. We compare our simulation results to actual
observations of disk sizes, disk masses, and accretion rates in star forming
regions. We argue that the relative importance of dynamical truncations and the
viscous evolution of the disks changes with time and cluster density. Viscous
evolution causes the importance of dynamical encounters to increase in time,
but the encounters cease soon after the expulsion of the leftover gas. For the
clusters simulated in this work, viscous growth dominates the evolution of the
disks.
