Directly imaging damped Lyman-alpha galaxies at z>2. I: Methodology and
  First Results
  We present the methodology for, and the first results from, a new imaging
program aimed at identifying and characterizing the host galaxies of damped
Lyman-alpha absorbers (DLAs) at z>2. We target quasar sightlines with multiple
optically-thick HI absorbers and use the higher-redshift system as a "blocking
filter" (via its Lyman-limit absorption) to eliminate all far-ultraviolet (FUV)
emission from the quasar. This allows us to directly image the rest-frame FUV
continuum emission of the lower-redshift DLA, without any quasar contamination
and with no bias towards large impact parameters. We introduce a formalism
based on galaxy number counts and Bayesian statistics with which we quantify
the probability that a candidate is the DLA host galaxy. This method will allow
the identification of a bona fide sample of DLAs that are too faint to be
spectroscopically confirmed. The same formalism can be adopted to the study of
other quasar absorption line systems (e.g. MgII absorbers). We have applied
this imaging technique to two QSO sightlines. For the z~2.69 DLA towards
J073149+285449, a galaxy with impact parameter b=1.54"=11.89 kpc and implied
star formation rate (SFR) of ~5 M/yr is identified as the most reliable
candidate. In the case of the z~2.92 DLA towards J211444-005533, no likely host
is found down to a 3-sigma SFR limit of 1.4 M/yr. Studying the HI column
density as a function of the impact parameter, including 6 DLAs with known
hosts from the literature, we find evidence that the observed HI distribution
is more extended than what is generally predicted from numerical simulation.
