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Physics and Astronomy


We present a tally of Milky Way late-type dwarf stars in 68 Wide Field Camera 3 (WFC3) pure-parallel fields (227 arcmin2) from the Brightest of Reionizing Galaxies survey for high-redshift galaxies. Using spectroscopically identified M-dwarfs in two public surveys, the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey and the Early Release Science mosaics, we identify a morphological selection criterion using the half-light radius (r50), a near-infrared J − H, G − J color region where M-dwarfs are found, and a V − J relation with M-dwarf subtype. We apply this morphological selection of stellar objects, color–color selection of M-dwarfs, and optical–near-infrared color subtyping to compile a catalog of 274 M-dwarfs belonging to the disk of the Milky Way with a limiting magnitude of mF125W < 24(AB). Based on the M-dwarf statistics, we conclude that (1) the previously identified north–south discrepancy in M-dwarf numbers persists in our sample; there are more M-dwarfs in the northern fields on average than in southern ones, (2) the Milky Way’s single disk scale-height for M-dwarfs is 0.3–4 kpc, depending on subtype, (3) the scale-height depends on M-dwarf subtype with early types (M0–4) high scale-height (z0 = 3–4 kpc) and later types M5 and above in the thin disk (z0 = 0.3–0.5 kpc), (4) a second component is visible in the vertical distribution, with a different, much higher scale-height in the southern fields compared to the northern ones. We report the M-dwarf component of the Sagittarius stream in one of our fields with 11 confirmed M-dwarfs, seven of which are at the stream’s distance. In addition to the M-dwarf catalog, we report the discovery of 1 T-dwarfs and 30 L-dwarfs from their near-infrared colors. The dwarf scale-height and the relative low incidence in our fields of L- and T-dwarfs in these fields makes it unlikely that these stars will be interlopers in great numbers in color-selected samples of high-redshift galaxies. The relative ubiquity of M-dwarfs however will make them ideal tracers of Galactic halo substructure with EUCLID and reference stars for James Webb Space Telescope observations


Copyright 2014. The American Astronomical Society. All rights reserved.

Original Publication Information

Holwerda, B. W., et al. "Milky Way Red Dwarfs in the BoRG Survey: Galactic Scale-Height and the Distribution of Dwarf Stars in WFC3 Imaging." 2014. The Astrophysical Journal 788(1): 18 pp.