NARROWBAND LYMAN-CONTINUUM IMAGING OF GALAXIES AT z ～ 2.85

摘要

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 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 nonionizing UV, we observe that many NB3420-detected galaxies exhibit spatial offsets between their LyC and nonionizing UV emission and are characterized by extremely blue NB3420–V colors, corresponding to low ratios of nonionizing 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 H I absorption in the intergalactic medium. We find and . These flux density ratios correspond, respectively, to relative LyC escape fractions of % and %, absolute LyC escape fractions of % and %, and a comoving LyC emissivity from star-forming galaxies of 8.8-15.0 × 1024 erg s–1 Hz–1 Mpc–3. 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 interstellar medium.