ON THE DETECTION OF IONIZING RADIATION ARISING FROM STAR-FORMING GALAXIES AT REDSHIFT z ∼ 3-4: LOOKING FOR ANALOGS OF "STELLAR RE-IONIZERS"

We use the spatially resolved, multi-band photometry in the GOODS South field acquired by the CANDELS project to constrain the nature of candidate Lyman continuum (LyC) emitters at redshift z similar to 3.7 identified using ultradeep imaging below the Lyman limit (1 sigma limit of approximate to 30 AB in a 2 '' diameter aperture). In 19 candidates out of a sample of 20 with flux detected at >3 sigma level, the light centroid of the candidate LyC emission is offset from that of the Lyman break galaxy (LBG) by up to 1 ''.5. We fit the spectral energy distribution of the LyC candidates to spectral population synthesis models to measure photometric redshifts and the stellar population parameters. We also discuss the differences in the UV colors between the LBG and the LyC candidates, and how to estimate the escape fraction of ionizing radiation (f(esc)) in cases, like in most of our galaxies, where the LyC emission is spatially offset from the host galaxy. In all but one case we conclude that the candidate LyC emission is most likely due to lower redshift interlopers. Based on these findings, we argue that the majority of similar measurements reported in the literature need further investigation before it can be firmly concluded that LyC emission is detected. Our only surviving LyC candidate is an LBG at z = 3.795, which shows the bluest (B - V) color among LBGs at similar redshift, a stellar mass of M similar to 2x10(9) M-circle dot, weak interstellar absorption lines, and a flat UV spectral slope with no Ly alpha in emission. We estimate its fesc to be in the range 25%-100%, depending on the dust and intergalactic attenuation.