Powderday: Dust Radiative Transfer for Galaxy Simulations
  We present Powderday, a flexible, fast, open-source dust radiative transfer
package designed to interface with galaxy formation simulations. Powderday
builds on FSPS population synthesis models, Hyperion dust radiative transfer,
and employs yt to interface between different software packages. We include our
stellar population synthesis modeling on the fly, which allows for significant
run-time flexibility in the assumed stellar physics. We include a model for
nebular line emission that can employ either precomputed Cloudy lookup tables
(for efficiency), or direct photoionization calculations for all young stars
(for flexibility). The dust content follows either observationally-motivated
prescriptions, direct modeling from galaxy formation simulations, or a novel
approach that includes the dust content via learning-based algorithms from the
SIMBA cosmological galaxy formation simulation. AGN can additionally be
included via a range of prescriptions. The output of these models are broadband
SEDs, as well as filter-convolved images. Powderday is designed to eliminate
last-mile efforts by researchers that employ different hydrodynamic galaxy
formation models, and seamlessly interfaces with GIZMO, AREPO, GASOLINE,
CHANGA, and ENZO. We demonstrate the capabilities of the code via three
applications: a model for the star formation rate (SFR) - infrared luminosity
relation in galaxies (including the impact of AGN); the impact of circumstellar
dust around AGB stars on the mid-infrared emission from galaxy SEDs; and the
impact of galaxy inclination angle on dust attenuation laws.
