2016MNRAS.458..425V

We have identified 274 M-type brown dwarfs in the Hubble Space Telescope's Wide Field Camera 3 pure parallel fields from the Brightest of Reionizing Galaxies (BoRG) survey for high-redshift galaxies. These are near-infrared observations with multiple lines of sight out of our Milky Way. Using these observed M-type brown dwarfs, we fitted a Galactic disc and halo model with a Markov chain Monte Carlo analysis. This model worked best with the scalelength of the disc fixed at h=2.6 kpc. For the scaleheight of the disc, we found kpc and for the central number density, # pc^–3. For the halo, we derived a flattening parameter κ=0.45±0.04 and a power-law index p=2.4±0.07. We found the fraction of M-type brown dwarfs in the local density that belong to the halo to be f_h=0.0075. We found no correlation between subtype of M-dwarf and any model parameters. The total number of M-type brown dwarfs in the disc and halo was determined to be . We found an upper limit for the fraction of M-type brown dwarfs in the halo of 7 per cent. The upper limit for the total Galactic disc mass in M-dwarfs is M_☉, assuming all M-type brown dwarfs have a mass of 80 M_J.