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 starforming 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 Lyα-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 nonionizing to ionizing radiation (FUV /FLyC) that are in tension with current stellar population synthesis models. We measure average values of (FUV /FLyC) for our LBG and LAE samples, correcting for foreground galaxy contamination and HI absorption in the IGM. We find (FUV /FLyC) LBG corr = 82± 45 and (FUV /FLyC) LAE corr = 7.4 ± 3.6. These flux-density ratios correspond respectively to relative LyC escape fractions of f esc, rel = 5 − 8% and f LAE esc, rel = 18 − 49%, absolute LyC escape fractions of f esc = 1 − 2% and f LAE esc = 5 − 15%, and a comoving LyC emissivity from star-forming galaxies of 8.8− 15.0× 10 ergs s Hz Mpc. In order to study the differential properties of galaxies with and without LyC detections, we analyze narrowband Lyα imaging and rest-frame near-infrared imaging, finding that while LAEs with LyC detections have lower Lyα 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. Subject headings: galaxies: high-redshift – intergalactic medium – cosmology: observations – diffuse radiation