Constraints on the distribution and energetics of fast radio bursts
  using cosmological hydrodynamic simulations
  We present constraints on the origins of fast radio bursts (FRBs) using large
cosmological simulations. We calculate contributions to FRB dispersion measures
(DMs) from the Milky Way, from the local Universe, from cosmological
large-scale structure, and from potential FRB host galaxies, and then compare
these simulations to the DMs of observed FRBs. We find that the Milky Way
contribution has previously been underestimated by a factor of ~2, and that the
foreground-subtracted DMs are consistent with a cosmological origin,
corresponding to a source population observable to a maximum redshift
z~0.6-0.9. We consider models for the spatial distribution of FRBs in which
they are randomly distributed in the Universe, track the star-formation rate of
their host galaxies, track total stellar mass, or require a central
supermassive black hole. Current data do not discriminate between these
possibilities, but the predicted DM distributions for different models will
differ considerably once we begin detecting FRBs at higher DMs and higher
redshifts. We additionally consider the distribution of FRB fluences, and show
that the observations are consistent with FRBs being standard candles, each
burst producing the same radiated isotropic energy. The data imply a constant
isotropic burst energy of ~7e40 erg if FRBs are embedded in host galaxies, or
~9e40 erg if FRBs are randomly distributed. These energies are 10-100 times
larger than had previously been inferred. Within the constraints of the
available small sample of data, our analysis favours FRB mechanisms for which
the isotropic radiated energy has a narrow distribution in excess of 1e40 erg.
