Chemical evolution and the galactic habitable zone of M31 (the Andromeda
  Galaxy)
  We have computed the Galactic Habitable Zones (GHZs) of the Andromeda galaxy
(M31) based on the probability of terrestrial planet formation, which depends
on the metallicity (Z) of the interstellar medium, and the number of formed
stars per surface unit. The GHZ was therefore obtained from a chemical
evolution model built to reproduce a precise metallicity gradient in the
galactic disk, [O/H](r) $ = -0.015 \pm 0.003 dex kpc^{-1} x r(kpc) + 0.44 \pm
0.04 dex $. This gradient is the most probable when intrinsic scatter is
present in the observational data. The chemical evolution model predicted a
higher star formation history in both the halo and disk components of M31 and a
less efficient inside-out galactic formation, compared to those of the Milky
Way. If we assumed that Earth-like planets form with a probability law that
follows the Z distribution shown by stars with detected planets and the SFH
predicted by the CEM, the most probable GHZ per pc$^2$ is located between 3 and
7 kpc for planets with ages between 6 and 7 Gy, approximately. But the highest
number of stars with habitable planets is in a ring located between 12 and 14
kpc with mean age of $\sim$7 Gy. 11 % and 6.5 % of the all formed stars in M31
may have planets with basic and complex life, respectively.
