The production and escape of Lyman-Continuum radiation from star-forming galaxies at z~2 and their redshift evolution

Understand

We study the production rate of ionizing photons of a sample of 588 H$\alpha$ emitters (HAEs) and 160 Lyman-$\alpha$ emitters (LAEs) at $z=2.2$ in the COSMOS field in order to assess the implied emissivity from galaxies, based on their UV luminosity.

• By exploring the rest-frame Lyman Continuum (LyC) with GALEX/$NUV$ data, we find f$_{\rm esc} < 2.8\, (6.4)$% through median (mean) stacking.
• By combining the H$\alpha$ luminosity density with IGM emissivity measurements from absorption studies, we find a globally averaged $\langle$f$_{\rm esc}\rangle$ of $5.9^{+14.5}_{-4.2}$ % at $z=2.2$ if we assume HAEs are the only source of ionizing photons.
• We find similarly low values of the global $\langle$f$_{\rm esc}\rangle$ at $z\approx3-5$, also ruling out a high $\langle$f$_{\rm esc}\rangle$ at $z<5$.