Hubble Space Telescope Observations of Field Ultracool Dwarfs at High
  Galactic Latitude
  We present a sample of 17 newly discovered ultracool dwarf candidates later
than ~M8, drawn from 231.90 arcmin2 of {\it Hubble Space Telescope} Wide Field
Camera 3 infrared imaging. By comparing the observed number counts for
17.5<J_125<25.5 AB mag to an exponential disk model, we estimate a vertical
scale height of z_scl=290 +- 25 (random) +- 30 (systematic) pc for a binarity
fraction of f_b=0. While our estimate is roughly consistent with published
results, we suggest that the differences can be attributed to sample
properties, with the present sample containing far more substellar objects than
previous work. We predict the object counts should peak at J_{125}~24 AB mag
due to the exponentially-declining number density at the edge of the disc. We
conclude by arguing that trend in scale height with spectral type may breakdown
for brown dwarfs since they do not settle onto the main sequence.
