Deep ACS slitless grism observations and identification of stellar sources are presented within the Great Observatories Origins Deep Survey ( GOODS ) North and South fields which were obtained in the Probing Evolution And Reionization Spectroscopically ( PEARS ) program .
It is demonstrated that even low resolution spectra can be a very powerful means to identify stars in the field , especially low mass stars with stellar types M0 and later .
The PEARS fields lay within the larger GOODS fields , and we used new , deeper images to further refine the selection of stars in the PEARS field , down to a magnitude of { { z _ { 850 } } } = 25 using a newly developed stellarity parameter .
The total number of stars with reliable spectroscopic and morphological identification was 95 and 108 in the north and south fields respectively .
The sample of spectroscopically identified stars allows constraints to be set on the thickness of the Galactic thin disk as well as contributions from a thick disk and a halo component .
We derive a thin disk scale height , as traced by the population of M4 to M9 dwarfs along two independent lines of sight , of { h _ { thin } = 370 ^ { +60 } _ { -65 } pc } .
When including the more massive M0 to M4 dwarf population , we derive { h _ { thin } = 300 \pm 70 pc } .
In both cases , we observe that we must include a combination of thick and halo components in our models in order to account for the observed numbers of faint dwarfs .
The required thick disk scale height is typically { h _ { thick } = 1000 pc } and the acceptable relative stellar densities of the thin disk to thick disk and the thin disk to halo components are in the range of { 0.00025 < f _ { halo } < 0.0005 } and { 0.05 < f _ { thick } < 0.08 } and are somewhat dependent on whether the more massive M0 to M4 dwarfs are included in our sample .