Stellar Population Studies with the SDSS. I. The Vertical Distribution of Stars in the Milky Way

Details Stellar Population Studies with the SDSS. I. The Vertical Distribution of Stars in the Milky Way Stellar Population Studies with the SDSS. I. The Vertical Distribution of Stars in the Milky Way

May 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001apj...553..184c&link_type=abstract

The Astrophysical Journal, Volume 553, Issue 1, pp. 184-197.

Astronomy and Astrophysics

Astronomy

173

Galaxy: Stellar Content, Galaxy: Structure

Scientific paper

We present star count data from the Sloan Digital Sky Survey for 5.8×105 stars brighter than g'=21 mag over 279 deg2 in two samples north and south of the Galactic plane. Using these high-latitude (49°<|b|<64°) star counts we determine the Sun's distance from the Galactic midplane to be 27+/-4 pc and the scale height of the old thin disk to be 330+/-3 pc. Because of the photometric accuracy and large area sky coverage of these data, the color-magnitude diagram clearly reveals a significant thick-disk population distinct in color from a Galactic halo population. The position of the thick-disk turnoff is at g'-r'~0.33. Several questions about the existence of the thick disk and its origin are addressed through a set of model fits to the star count data. Our best-fit model gives a thick-disk scale height between 580 and 750 pc, below the original proposal of Gilmore and Reid, and the corresponding space number density normalization is 13%-6.5% of the thin disk. The conclusions reached in this paper favor a scenario in which the thick disk formed through the heating of a preexisting thin disk, with the heating mechanism being the merging of a satellite galaxy. The density law for the Galactic halo population is also investigated. We find that the data support a flattened halo with c/a~0.55+/-0.06 and a relatively flat power-law index (2.5+/-0.3). The axis ratio of the visible halo found in this paper is compatible with that of dark halo, suggesting that they have the same shape and dynamical origin. Based on observations obtained with the Sloan Digital Sky Survey.

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