L. Carigi, S. Meneses-Goytia, J. Garcia-Rojas
We have computed the Galactic Habitable Zones (GHZs) of the Andromeda galaxy (M31) based mainly, but not exclusively, on the probability of terrestrial planet formation, which depends on the metallicity (Z) of the interstellar medium. 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, the most probable GHZ with basic life is located between 6 and 17 kpc on planets with ages between 4.5 and 1 Gy, and the most probable GHZ with complex life that survived supernova explosions is located between 3 and 13 kpc on planets with ages between 6.5 and 4.5 Gy. Since the star formation history of M31 has been more efficient and its GHZ is wider and older compared to those of the Milky Way, the number of planets harboring life in M31 may be higher than that of our galaxy.
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http://arxiv.org/abs/1208.4198
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