The effects of metallicity on the Galactic disk population of white
  dwarfs
  It has been known for a long time that stellar metallicity plays a
significant role in the determination of the ages of the different Galactic
stellar populations, when main sequence evolutionary tracks are employed. Here
we analyze the role that metallicity plays on the white dwarf luminosity
function of the Galactic disk, which is often used to determine its age. We
employ a Monte Carlo population synthesis code that accounts for the properties
of the population of Galactic disk white dwarfs. Our code incorporates the most
up-to-date evolutionary cooling sequences for white dwarfs with hydrogen-rich
and hydrogen-deficient atmospheres for both carbon-oxygen and oxygen-neon
cores. We use two different models to assess the evolution of the metallicity,
one in which the adopted metallicity is constant with time, but with a moderate
dispersion, and a second one in which the metallicity increases with time. We
found that our theoretical results are in a very satisfactory agreement with
the observational luminosity functions obtained from the Sloan Digital Sky
Survey (SDSS) and from the SuperCOSMOS Sky Survey (SSS), independently of the
adopted age-metallicity law. In particular, we found that the age-metallicity
law has no noticeable impact in shaping the bright branch of the white dwarf
luminosity function, and that the position of its cut-off is almost insensitive
to the adopoted age-metallicity relationship. Because the shape of the bright
branch of the white dwarf luminosity function is insensitive to the
age-metallicity law, it can be safely employed to test the theoretical
evolutionary sequences, while due to the limited sensitivity of the position of
the drop-off to the distribution of metallicities, its location provides a
robust indicator of the age of the Galactic disk.
