The Keck Lyman Continuum Spectroscopic Survey (KLCS)-. The Emergent Ionizing Spectrum of Galaxies at z similar to 3

We present results of a deep spectroscopic survey quantifying the statistics of the escape of ionizing radiation from star -forming galaxies at z similar to 3. We measure the ratio of ionizing to non-ionizing UV flux density f(900)/f(1500)obs, where f(900) is the mean flux density evaluated over the range [880, 910] angstrom. We quantify the emergent ratio of ionizing to non-ionizing UV flux density by analyzing high signal-to-noise ratio composite spectra formed from subsamples with common observed properties and numbers sufficient to reduce the statistical uncertainty in the modeled IGM+CGM correction to obtain precise values of < f(900)/f(1500)>(out), including a full-sample average < f(900)/f(1500)>(out) 0.057 +/- 0.006. We show that < f(900)/f(1500)>(out) increases., monotonically with W lambda(Ly alpha), inducing an inverse correlation with UV luminosity as a by-product. We fit the composite spectra using stellar spectral synthesis together with models of the ISM in which a fraction f(c) of the stellar continuum is covered by gas with column density NH (I). We show that the composite spectra simultaneously constrain the intrinsic properties of the stars (L90041500)int along with f(c), N-H (I), E (B - V), and f(esc,abs), the absolute escape fraction of ionizing photons. We find a sample-averaged f(esc,abs) 0.09 +/- 0.01, with subsamples falling along a linear relation < f(esc),(abs)> similar or equal to 0.75[W-lambda(Ly alpha)/110 angstrom]. Using the far-UV luminosity function, the distribution function n(W(Lya)), and the relationship between WA(Ly alpha) and < f(900)/f(1500)>(out), we estimate the total ionizing emissivity of z similar to 3 star forming galaxies with M-uv <= -19.5, which exceeds the contribution of quasi-stellar objects by a factor of similar to 3, and accounts for similar to 50% of the total is an element of(Lyc) at z similar to 3 estimated using indirect methods.