A cross-match of 2MASS and SDSS: newly found L and T dwarfs and an estimate of the space density of T dwarfs

Creators: Metchev, Stanimir A.; Kirkpatrick, J. Davy; Berriman, G. Bruce; Looper, Dagny

Abstract

We report new L and T dwarfs found in a cross-match of the SDSS Data Release 1 and 2MASS. Our simultaneous search of the two databases effectively allows us to relax the criteria for object detection in either survey and to explore the combined databases to a greater completeness level. We find two new T dwarfs in addition to the 13 already known in the SDSS DR1 footprint. We also identify 22 new candidate and bona fide L dwarfs, including a new young L2 dwarf and a peculiar potentially metal-poor L2 dwarf with unusually blue near-IR colors. These discoveries underscore the utility of simultaneous database cross-correlation in searching for rare objects. Our cross-match completes the census of T dwarfs within the joint SDSS and 2MASS flux limits to the ≈97% level. Hence, we are able to accurately infer the space density of T dwarfs. We employ Monte Carlo tools to simulate the observed population of SDSS DR1 T dwarfs with 2MASS counterparts and find that the space density of T0 - T8 dwarf systems is 0.0070^(+0.0032)_ (-0.0030) pc^-3 (95% confidence interval), i.e., about one per 140 pc^3. Compared to predictions for the T dwarf space density that depend on various assumptions for the substellar mass function, this result is most consistent with models that assume a flat substellar mass function dN/dM ∝ M^0.0. No >T8 dwarfs were discovered in the present cross-match, although less than one was expected in the limited area (2099 deg^2) of SDSS DR1.

Additional Information

© 2008 American Astronomical Society. Received 2007 February 24; accepted 2007 October 18. The SDSS DR1/2MASS database cross-match was funded as a demonstration project by the NSF National Partnership for Advanced Computational Infrastructure and by the National Virtual Observatory, sponsored by the NSF.We thank Serge Monkewitz for developing the cross-match engine.We thank Gillian Knapp for assistance with SDSS and Katelyn Allers for providing us with her IRTF SpeX spectrum of G196-3B. We acknowledge Tiffany Meshkat for help with the acquisition and reduction of the Lick PFCam data. This research has made use of the NASA/IPAC Infrared Science Archive (IRSA), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research has also benefitted from the M, L, and T dwarf compendium housed at DwarfArchives.org and maintained by Chris Gelino, Davy Kirkpatrick, and Adam Burgasser. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. The Sloan Digital Sky Survey is managed by ARC for the Participating Institutions: the University of Chicago, Fermilab, the Institute for Advanced Study, the Japan Participation Group, Johns Hopkins University, the Korean Scientist Group, Los Alamos National Laboratory, the Max Planck Institute for Astronomy, the Max Planck Institute for Astrophysics, New Mexico State University, the University of Pittsburgh, the University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington. Funding for SDSS has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, NASA, the NSF, the US Department of Energy, the Japanese Monbukagakusho, and the Max Planck Society. Support for S. A. M. was provided by NASA through the Spitzer Fellowship Program, under award 1273192. Facilities: Keck:I, PO:1.5m, UH:2.2m, IRTF, Shane, Spitzer

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