Evaluating Galactic Habitability Using High Resolution Cosmological
  Simulations of Galaxy Formation
  We present the first model that couples high-resolution simulations of the
formation of Local Group galaxies with calculations of the galactic habitable
zone (GHZ), a region of space which has sufficient metallicity to form
terrestrial planets without being subject to hazardous radiation. These
simulations allow us to make substantial progress in mapping out the asymmetric
three-dimensional GHZ and its time evolution for the Milky Way (MW) and
Triangulum (M33) galaxies, as opposed to works that generally assume an
azimuthally symmetric GHZ.
  Applying typical habitability metrics to MW and M33, we find that while a
large number of habitable planets exist as close as a few kiloparsecs from the
galactic centre, the probability of individual planetary systems being
habitable rises as one approaches the edge of the stellar disc. Tidal streams
and satellite galaxies also appear to be fertile grounds for habitable planet
formation.
  In short, we find that both galaxies arrive at similar GHZs by different
evolutionary paths, as measured by the first and third quartiles of surviving
biospheres. For the Milky Way, this interquartile range begins as a narrow band
at large radii, expanding to encompass much of the galaxy at intermediate times
before settling at a range of 2-13kpc. In the case of M33, the opposite
behaviour occurs - the initial and final interquartile ranges are quite
similar, showing gradual evolution. This suggests that galaxy assembly history
strongly influences the time evolution of the GHZ, which will affect the
relative time lag between biospheres in different galactic locations. We end by
noting the caveats involved in such studies and demonstrate that high
resolution cosmological simulations will play a vital role in understanding
habitability on galactic scales, provided that these simulations accurately
resolve chemical evolution.
