Narrowband Lyman-Continuum Imaging of Galaxies at z ~ 2.85
  We present results from a survey for z~2.85 Lyman-Continuum (LyC) emission in
the HS1549+1933 field and place constraints on the amount of ionizing radiation
escaping from star-forming galaxies. Using a custom narrowband filter (NB3420)
tuned to wavelengths just below the Lyman limit at z>=2.82, we probe the LyC
spectral region of 49 Lyman break galaxies (LBGs) and 91 Lya-emitters (LAEs)
spectroscopically confirmed at z>=2.82. Four LBGs and seven LAEs are detected
in NB3420. Using V-band data probing the rest-frame non-ionizing UV, we observe
that many NB3420-detected galaxies exhibit spatial offsets between their LyC
and non-ionizing UV emission and are characterized by extremely blue NB3420-V
colors, corresponding to low ratios of non-ionizing to ionizing radiation
(F_UV/F_LyC) that are in tension with current stellar population synthesis
models. We measure average values of F_UV/F_LyC for our LBG and LAE samples,
correcting for foreground galaxy contamination and HI absorption in the IGM. We
find (F_UV/F_LyC)_corr^LBG=82 +/- 45 and (F_UV/F_LyC)_corr^LAE=7.4 +/- 3.6.
These flux-density ratios correspond respectively to relative LyC escape
fractions of f_esc,rel^LBG=5-8% and f_esc,rel^LAE=18-49%, absolute LyC escape
fractions of f_esc^LBG=1-2% and f_esc^LAE=5-15%, and a comoving LyC emissivity
from star-forming galaxies of 8.8-15.0 x 10^24 ergs/s/Hz/Mpc^3. In order to
study the differential properties of galaxies with and without LyC detections,
we analyze narrowband Lya imaging and rest-frame near-infrared imaging, finding
that while LAEs with LyC detections have lower Lya equivalent widths on
average, there is no substantial difference in the rest-frame near-infrared
colors of LBGs or LAEs with and without LyC detections. These preliminary
results are consistent with an orientation-dependent model where LyC emission
escapes through cleared paths in a patchy ISM.
