[16.03] The Space Density of Field Methane (``T") Dwarfs

AAS 201st Meeting, January, 2003
Session 16. Stars in SDSS
Poster, Monday, January 6, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[16.03] The Space Density of Field Methane (``T") Dwarfs

M. J. Collinge, G. R. Knapp (Princeton), X. Fan (IAS, Univ. Arizona), R. H. Lupton, V. Narayanan, M. A. Strauss, J. E. Gunn, D. J. Schlegel, Z. Ivezic (Princeton), C. M. Rockosi (Univ. Washington), T. R. Geballe (Gemini Obs.), S. K. Leggett (UKIRT), D. Golimowski (JHU), S. L. Hawley (Univ. Washington)

We describe a complete magnitude-limited sample of 11 field methane (T) dwarfs brighter than z \approx 20.2 selected from the imaging data of the Sloan Digital Sky Survey (SDSS). We discuss the optical and near-infrared colors of these and other extremely red objects and show that T dwarfs occupy a unique region in optical color-color space. The area density of methane dwarfs in this sample is one per 140 square degrees, and the space density is about one per 160 pc³. We use simulations to show that this is consistent with an IMF that is slowly rising toward lower mass through the substellar regime (dn/dm \propto m^-\alpha, where \alpha < 1), in reasonable agreement with the results of many open cluster studies. The inferred mass density in substellar objects is about 10% of that in stars.

Funding for the SDSS is provided by the Alfred P. Sloan Foundation, NASA, NSF, DoE, Monbukagakusho, the Max Planck Society and the member institutions. The SDSS web site is http://www.sdss.org/.

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