Early Results from GLASS-JWST. XIII. A Faint, Distant, and Cold Brown Dwarf

January 2023 • 2023ApJ...942L..29N

Authors • Nonino, Mario • Glazebrook, Karl • Burgasser, Adam J. • Polenta, Gianluca • Morishita, Takahiro • Lepinzan, Marius • Castellano, Marco • Fontana, Adriano • Merlin, Emiliano • Bonchi, Andrea • Paris, Diego • Treu, Tommaso • Vulcani, Benedetta • Wang, Xin • Santini, Paola • Vanzella, Eros • Nanayakkara, Themiya • Mercurio, Amata • Rosati, Piero • Grillo, Claudio • Bradac, Marusa

Abstract • We present the serendipitous discovery of a late T-type brown dwarf candidate in JWST NIRCam observations of the Early Release Science Abell 2744 parallel field. The discovery was enabled by the sensitivity of JWST at 4 μm wavelengths and the panchromatic 0.9-4.5 μm coverage of the spectral energy distribution. The unresolved point source has magnitudes F115W = 27.95 ± 0.15 and F444W = 25.84 ± 0.01 (AB), and its F115W-F444W and F356W-F444W colors match those expected for other known T dwarfs. We can exclude it as a reddened background star, high redshift quasar, or a very high redshift galaxy. Comparison with stellar atmospheric models indicates a temperature of T _eff ≈ 650 K and surface gravity $\mathrm{log}g\approx 5.25$ , implying a mass of 0.03 M _⊙ and age of 5 Gyr. We estimate the distance of this candidate to be 570-720 pc in a direction perpendicular to the Galactic plane, making it a likely thick disk or halo brown dwarf. These observations underscore the power of JWST to probe the very low-mass end of the substellar mass function in the Galactic thick disk and halo. *Based on data collected with JWST.

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Takahiro Morishita

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