The growth of H II regions around massive stars: the role of metallicity
  and dust
  Gas metallicity $Z$ and the related dust-to-gas ratio $f_\textrm{d}$ can
influence the growth of HII regions via metal line cooling and UV absorption.
We model these effects in star-forming regions containing massive stars. We
compute stellar feedback from photoionization and radiation pressure (RP) using
Monte Carlo radiative transfer coupled with hydrodynamics, including stellar
and diffuse radiation fields. We follow a $10^5$ M$_\odot$ turbulent cloud with
$Z/$Z$_\odot$ = 2, 1, 0.5, 0.1 and $f_\textrm{d} = 0.01 Z/$Z$_\odot$ with a
cluster-sink particle method for star formation. The models evolve for at least
1.5 Myr under feedback. Lower $Z$ results in higher temperatures and therefore
larger HII regions. For $Z \ge$Z$_\odot$, radiation pressure $P_\textrm{rad}$
can dominate locally over the gas pressure $P_\textrm{gas}$ in the inner
half-parsec around sink particles. Globally, the ratio of
$P_\textrm{rad}/P_\textrm{gas}$ is around 1 (2 Z$_\odot$), 0.3 (Z$_\odot$), 0.1
(0.5 Z$_\odot$), and 0.03 (0.1 Z$_\odot$). In the solar model, excluding RP
results in an ionized volume several times smaller than the fiducial model with
both mechanisms. Excluding RP and UV attenuation by dust results in a larger
ionized volume than the fiducial case. That is, UV absorption hinders growth
more than RP helps it. The radial expansion velocity of ionized gas reaches
$+$15 km/s outwards, while neutral gas has inward velocities for most of the
runtime, except for 0.1 Z$_\odot$ which exceeds $+$4 km/s. $Z$ and
$f_\textrm{d}$ do not significantly alter the star formation efficiency, rate,
or cluster half-mass radius, with the exception of 0.1 Z$_\odot$ due to the
earlier expulsion of neutral gas.
