  We combine new high sensitivity ultraviolet (UV) imaging from the Wide Field
Camera 3 (WFC3) on the Hubble Space Telescope (HST) with existing deep
HST/Advanced Camera for Surveys (ACS) optical images from the Great
Observatories Origins Deep Survey (GOODS) program to identify UV-dropouts,
which are Lyman break galaxy (LBG) candidates at z~1-3. These new HST/WFC3
observations were taken over 50 sq.arcmin in the GOODS-South field as a part of
the Early Release Science program. The uniqueness of these new UV data is that
they are observed in 3 UV/optical (WFC3 UVIS) channel filters (F225W, F275W and
F336W), which allows us to identify three different sets of UV-dropout samples.
We apply Lyman break dropout selection criteria to identify F225W-, F275W- and
F336W-dropouts, which are z~1.7, 2.1 and 2.7 LBG candidates, respectively. Our
results are as follows: (1) these WFC3 UVIS filters are very reliable in
selecting LBGs with z~2.0, which helps to reduce the gap between the well
studied z~>3 and z~0 regimes, (2) the combined number counts agrees very well
with the observed change in the surface densities as a function of redshift
when compared with the higher redshift LBG samples; and (3) the best-fit
Schechter function parameters from the rest-frame UV luminosity functions at
three different redshifts fit very well with the evolutionary trend of the
characteristic absolute magnitude, and the faint-end slope, as a function of
redshift. This is the first study to illustrate the usefulness of the WFC3 UVIS
channel observations to select z<3 LBGs. The addition of the new WFC3 on the
HST has made it possible to uniformly select LBGs from z~1 to z~9, and
significantly enhance our understanding of these galaxies using HST sensitivity
and resolution.
