GRUMPY: a simple framework for realistic forward-modelling of dwarf
  galaxies
  We present a simple regulator-type framework designed specifically for
modelling formation of dwarf galaxies. We explore sensitivity of model
predictions for the stellar mass--halo mass and stellar mass--metallicity
relations to different modelling choices and parameter values. Despite its
simplicity, when coupled with realistic mass accretion histories of haloes from
simulations and reasonable choices for model parameter values, the framework
can reproduce a remarkably broad range of observed properties of dwarf galaxies
over seven orders of magnitude in stellar mass. In particular, we show that the
model can simultaneously match observational constraints on the stellar
mass-halo mass relation, as well as observed relations between stellar mass and
gas phase and stellar metallicities, gas mass, size, and star formation rate,
as well as general form and diversity of star formation histories (SFHs) of
observed dwarf galaxies. The model can thus be used to predict photometric
properties of dwarf galaxies hosted by dark matter haloes in $N$-body
simulations, such as colors, surface brightnesses, and mass-to-light ratios and
to forward model observations of dwarf galaxies. We present examples of such
modelling and show that colors and surface brightness distributions of model
galaxies are in good agreement with observed distributions for dwarfs in recent
observational surveys. We also show that in contrast with the common
assumption, the absolute magnitude-halo mass relation is generally predicted to
have a non-power law form in the dwarf regime, and that the fraction of haloes
that host detectable ultrafaint galaxies is sensitive to reionization redshift
(zrei) and is predicted to be consistent with observations for zrei<~9.
