A measurement of galaxy halo mass from the surrounding HI Ly{\alpha}
  absorption
  We measure the dark matter halo masses of z~2.36 UV color-selected
star-forming galaxies by matching the observed median HI Ly{\alpha} absorption
around them, as observed in the spectra of background QSOs, to the absorption
around haloes above a given mass in cosmological simulations. Focusing on
transverse separations 0-2 pMpc and line of sight separations 154-616 km/s, we
find a minimum halo mass of log10(Mmin/Msun)=11.6(+0.2)(-0.2), which is in good
agreement with published halo mass estimates from clustering analyses. We
verified that the measured halo mass is insensitive to a change in the
cosmological parameters (WMAP1 vs. WMAP3) and to the inclusion of strong AGN
feedback. One unique strength of this method is that it can be used in narrow
field galaxy-QSO surveys, i.e. ~30 x 30 arcseconds. In addition, we find that
the observed anisotropy in the 2-D HI Ly{\alpha} absorption distribution on
scales of 1.5-2 pMpc is consistent with being a consequence of large-scale gas
infall into the potential wells occupied by galaxies.
