The Efficiency of Stellar Reionization: Effects of Rotation, Metallicity, and Initial Mass Function

We compute the production rate of photons in the ionizing Lyman continua (LyC) of H I (lambda < 912 A), He I (lambda < 504 A), and He II (lambda < 228 A) using recent stellar evolutionary tracks coupled to a grid of non-LTE, line-blanketed (WM-basic) model atmospheres. The median LyC production efficiency is QLyC = (6+/-2) x10⁶0 LyC photons per Msun of star formation (range 3. 1-9. 4x10⁶0) corresponding to a revised calibration of 10^53. 3+/-0. 2 photons/s per Msun/yr. Efficiencies in the helium continua are QHeI ~ 10⁶0 photons/Msun and QHeII ~ 10⁵6 photons/Msun at solar metallicity and larger at low metallicity. The critical star formation rate needed to maintain reionization against recombinations at z = 7 is rhoSFR = (0. 012 Msun/yr/Mpc³) (1+z) /8³ [ (CH /3) (0. 2/ fₑsc) for fiducial values of IGM clumping factor CH = 3 and LyC escape fraction fₑsc = 0. 2. The boost in LyC production efficiency is an important ingredient, together with metallicity, CH, and fₑsc, in assessing whether IGM reionization was complete by z ~ 7. Monte-Carlo sampled spectra of coeval starbursts during the first 5 Myr have intrinsic flux ratios of F (1500) /F (900) = 0. 4-0. 5 and F (912^-) /F (912^+) = 0. 4-0. 7 in the far-UV (1500A), the LyC (900A), and at the Lyman edge (912A). These ratios can be used to calibrate the LyC escape fractions in starbursts.