Dark Matter Annihilation Feedback in Cosmological Simulations II: The
  Influence on Gas and Halo Structure
  We present new cosmological hydrodynamic simulations that incorporate Dark
Matter Annihilation Feedback (DMAF), whereby energy released from the
annihilation of dark matter particles through decay channels such as photon or
positron-electron pairs provide additional heating sources for local baryonic
material. For annihilation rates comparable to WIMP-like particles, we find
that the key influence of DMAF is to inhibit gas accretion onto halos. Such
diminished gas accretion early in the lifetimes of halos results in reduced gas
fractions in smaller halos, and the delayed halo formation times of larger
structures, suggesting that DMAF could impact the stellar age distribution in
galaxies, and morphology of dwarfs. For a dark matter particle mass of
$m_\chi\sim10$~MeV, there is a `critical halo mass' of $\sim10^{13}$
M$_{\odot}$ at $z=0$, below which there are large differences when compared to
$\Lambda$CDM, such as a reduction in the abundance of halo structures as large
as 25 percent, reduced gas content by 50 percent and central gas densities
reduced down to 10 percent within halos of mass $\sim10^{12}$ M$_{\odot}$ but
with increasing effects in smaller halos. Higher dark matter particle mass
models have a smaller `critical halo mass'. For a $m_\chi\sim100$~MeV model, we
find differences start appearing below halo masses of $\sim10^{12}$ M$_\odot$
and a $m_\chi\gtrsim 1$~GeV model, this mass scale lies below the resolution of
our simulations, though we still observe changes in the morphology of dwarf
galaxies.
