Simulating the interstellar medium of galaxies with radiative transfer,
  non-equilibrium thermochemistry, and dust
  We present a novel framework to self-consistently model the effects of
radiation fields, dust physics and molecular chemistry (H$_2$) in the
interstellar medium (ISM) of galaxies. The model combines a state-of-the-art
radiation hydrodynamics module with a non-equilibrium thermochemistry module
that accounts for H$_2$ coupled to a realistic dust formation and destruction
model, all integrated into the new stellar feedback framework SMUGGLE. We test
this model on high-resolution isolated Milky-Way (MW) simulations. We show that
photoheating from young stars makes stellar feedback more efficient, but this
effect is quite modest in low gas surface density galaxies like the MW. The
multi-phase structure of the ISM, however, is highly dependent on the strength
of the interstellar radiation field. We are also able to predict the
distribution of H$_2$, that allow us to match the molecular Kennicutt-Schmidt
(KS) relation, without calibrating for it. We show that the dust distribution
is a complex function of density, temperature and ionization state of the gas
which cannot be reproduced by simple scaling relations often used in the
literature. Our model is only able to match the observed dust temperature
distribution if radiation from the old stellar population is considered,
implying that these stars have a non-negligible contribution to dust heating in
the ISM. Our state-of-the-art model is well-suited for performing next
generation cosmological galaxy formation simulations, which will be able to
predict a wide range of resolved ($\sim 10$ pc) properties of galaxies.
