2018/05/31 by C. C. Steidel, M. Bogosavljevic, A. E. Shapley +5
Physics and Astronomy · #astro-ph.GA #astro-ph.CO
paper · pdf · doi:10.3847/1538-4357/aaed28
45 pages, 31 figures, ApJ, in press
arxiv created 2018/11/19 · arxiv updated 2018/12/26
We present results of a deep spectroscopic survey designed to quantify the statistics of the escape of ionizing photons from star-forming galaxies at z~3. We measure the ratio of ionizing to non-ionizing UV flux density <f900/f1500>obs, where f900 is the mean flux density evaluated over the range [880,910] A. We quantify the emergent ratio of ionizing to non-ionizing UV flux density by analyzing high-S/N composite spectra formed from sub-samples with common observed properties and numbers sufficient to reduce the statistical uncertainty in the modeled IGM+CGM correction to obtain precise values of <f900/f1500>out, including a full-sample average <f900/f1500>out=0.057±0.006. We further show that <f900/f1500>out increases monotonically with Lyα rest equivalent width, 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 fc of the stellar continuum is covered by gas with column density N(HI). We show that the composite spectra simultaneously constrain the intrinsic properties of the stars (L900/L1500)int along with fc, N(HI), E(B-V), and fesc,abs, the absolute escape fraction of ionizing photons. We find a sample-averaged fesc,abs =0.09±0.01, and that subsamples fall along a linear relation ⟨ fesc,abs⟩ ∼ 0.75[W(Lyα)/110 A]. We use the FUV luminosity function, the distribution function n[W(Lyα)], and the relationship between W(Lyα) and <f900/f1500>out to estimate the total ionizing emissivity of z∼3 star-forming galaxies with Muv < -19.5: εLyC∼ 6×1024 ergs/s/Hz/Mpc3, exceeding the contribution of QSOs by a factor of ∼ 3, and accounting for ∼50% of the total εLyC at z∼3 estimated using indirect methods.