ULTRACOOL FIELD BROWN DWARF CANDIDATES SELECTED AT 4.5 μm

Abstract

We have identified a sample of cool field brown dwarf candidates using IRAC\ndata from the Spitzer Deep, Wide-Field Survey (SDWFS). The candidates were\nselected from 400,000 SDWFS sources with [4.5] <= 18.5 mag and required to have\n[3.6]-[4.5] >= 1.5 and [4.5] - [8.0] <= 2.0 on the Vega system. The first color\nrequirement selects objects redder than all but a handful of presently known\nbrown dwarfs with spectral classes later than T7, while the second eliminates\n14 probable reddened AGN. Optical detection of 4 of the remaining 18 sources\nimplies they are likely also AGN, leaving 14 brown dwarf candidates. For two of\nthe brightest candidates (SDWFS J143524.44+335334.6 and SDWFS\nJ143222.82+323746.5), the spectral energy distributions including near-infrared\ndetections suggest a spectral class of ~ T8. The proper motion is < 0.25 "/yr,\nconsistent with expectations for a luminosity inferred distance of >70 pc. The\nreddest brown dwarf candidate (SDWFS J143356.62+351849.2) has [3.6] -\n[4.5]=2.24 and H - [4.5] > 5.7, redder than any published brown dwarf in these\ncolors, and may be the first example of the elusive Y-dwarf spectral class.\nModels from Burrows et al. (2003) predict larger numbers of cool brown dwarfs\nshould be found for a Chabrier (2003) mass function. Suppressing the model\n[4.5] flux by a factor of two, as indicated by previous work, brings the\nBurrows models and observations into reasonable agreement. The recently\nlaunched Wide-field Infrared Survey Explorer (WISE) will probe a volume ~40x\nlarger and should find hundreds of brown dwarfs cooler than T7.\n

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Affiliated Institutions

• University of Florida US
• University of California, Berkeley US
• Center for Astrophysics Harvard & Smithsonian US
• University of Arizona US
• Jet Propulsion Laboratory US
• University of California, Los Angeles US
• Infrared Processing and Analysis Center US
• California Institute of Technology US
• Monash University AU
• Kitt Peak National Observatory US

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