We present a new analysis of the ionizing emissivity ( \dot { N } _ { ion } , s ^ { -1 } Mpc ^ { -3 } ) for galaxies during the epoch of reionization and their potential for completing and maintaining reionization .
We use extensive SED modelling – incorporating two plausible mechanisms for the escape of Lyman continuum photon – to explore the range and evolution of ionizing efficiencies consistent with new results on galaxy colours ( \beta ) during this epoch .
We estimate \dot { N } _ { ion } for the latest observations of the luminosity and star-formation rate density at z < 10 , outlining the range of emissivity histories consistent with our new model .
Given the growing observational evidence for a UV colour-magnitude relation in high-redshift galaxies , we find that for any plausible evolution in galaxy properties , red ( brighter ) galaxies are less efficient at producing ionizing photons than their blue ( fainter ) counterparts .
The assumption of a redshift and luminosity evolution in \beta leads to two important conclusions .
Firstly , the ionizing efficiency of galaxies naturally increases with redshift .
Secondly , for a luminosity dependent ionizing efficiency , we find that galaxies down to a rest-frame magnitude of M _ { UV } \approx - 15 alone can potentially produce sufficient numbers of ionizing photons to maintain reionization as early as z \sim 8 for a clumping factor of C _ { \textsc { Hii } } \leq 3 .