The mean H$\alpha$ EW and Lyman-continuum photon production efficiency for faint $z\approx4-5$ galaxies

Understand

We present the first measurements of the Lyman-continuum photon production efficiency $\xi_{\textrm{ion,0}}$ at $z\sim4$-5 for galaxies fainter than 0.2 $L^*$ ($-$19 mag).

• $\xi_{\textrm{ion,0}}$ quantifies the production rate of ionizing photons with respect to the UV luminosity density assuming a fiducial escape fraction of zero.
• Extending previous measurements of $\xi_{\textrm{ion,0}}$ to the faint population is important, as ultra-faint galaxies are expected to contribute the bulk of the ionizing emissivity.
• We probe $\xi_{\textrm{ion,0}}$ to such faint magnitudes by taking advantage of 200-hour depth Spitzer/IRAC observations from the GREATS program and $\approx$300 3<$z$<6 galaxies with spectroscopic redshifts from the MUSE GTO Deep + Wide programs.