Measuring the Milky Way in M-dwarfs

We report 274 M-dwarfs found in the Brightest of Reionizing Galaxies (BoRG) survey for high redshift galaxies. Using these, we fitted a model for the disk and halo with a fixed scale length at h = 2.6 kpc. We found a scale height z0 of 0.60±0.03 kpc, flattening parameter κ of 0.45±0.04 and a powerlaw-index p of 2.4±0.07. For the total number of M-dwarfs in the disk and halo we found 26.7_(-6.2)^(+9.3)×10^9. The upper limit for the halo fraction of M-dwarfs in the halo is 7_(-4)^(+5) %. The total mass upper limit was determined to be 1.99_(-0.5)^(+0.73)×10^9 Solar masses

The size and shape of the Milky Way disc and halo from M-type brown dwarfs in the BoRG survey.

We have identified 274 M-type brown dwarfs in the Hubble Space Telescope\u27s 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 z0=0.29+0.02−0.019 z0=0.29−0.019+0.02 kpc and for the central number density, ρ0=0.29+0.20−0.13 ρ0=0.29−0.13+0.20 # 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 fh = 0.0075 +0.0025−0.0019 −0.0019+0.0025 . 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 58.2+9.81−6.70×109 58.2−6.70+9.81×109 . We found an upper limit for the fraction of M-type brown dwarfs in the halo of 7 +5−4 −4+5  per cent. The upper limit for the total Galactic disc mass in M-dwarfs is 4.34+0.73−0.5×109 4.34−0.5+0.73×109 M⊙, assuming all M-type brown dwarfs have a mass of 80 MJ