Indications of M-dwarf Deficits in the Halo and Thick Disk of the Galaxy
  We compared the number of faint stars detected in deep survey fields with the
current stellar distribution model of the Galaxy and found that the detected
number in the H band is significantly smaller than the predicted number. This
indicates that M-dwarfs, the major component, are fewer in the halo and the
thick disk. We used archived data of several surveys in both the north and
south field of GOODS (Great Observatories Origins Deep Survey), MODS in
GOODS-N, and ERS and CANDELS in GOODS-S. The number density of M-dwarfs in the
halo has to be 20+/-13% relative to that in the solar vicinity, in order for
the detected number of stars fainter than 20.5 mag in the H band to match with
the predicted value from the model. In the thick disk, the number density of
M-dwarfs must be reduced (52+/-13%) or the scale height must be decreased (~600
pc). Alternatively, overall fractions of the halo and thick disks can be
significantly reduced to achieve the same effect, because our sample mainly
consists of faint M-dwarfs. Our results imply that the M-dwarf population in
regions distant from the Galactic plane is significantly smaller than
previously thought. We then discussed the implications this has on the
suitability of the model predictions for the prediction of non-companion faint
stars in direct imaging extrasolar planet surveys by using the best-fit number
densities.
