Stellar population studies with SDSS. I. The vertical distribution of stars in the milky way

Bing Chen, Chris Stoughton, J. Allyn Smith, Alan Uomoto, Jeffrey R. Pier, Brian Yanny, Željko Ivezić, Donald G. York, John E. Anderson, James Annis, Jon Brinkmann, István Csabai, Masataka Fukugita, Robert Hindsley, Robert Lupton, Jeffrey A. Munn

Research output: Contribution to journalArticlepeer-review

303 Scopus citations


We present star count data from the Sloan Digital Sky Survey for 5.8 × 10 5 stars brighter than g′ = 21 mag over 279 deg 2 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.

Original languageEnglish (US)
Pages (from-to)184-197
Number of pages14
JournalAstrophysical Journal
Issue number1 PART 1
StatePublished - May 20 2001

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Galaxy: Stellar content
  • Galaxy: Structure


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