Nanayakkara, ThemiyaBrinchmann, JarleGlazebrook, KarlBouwens, Rychard JohnKewley, LisaTran, Kim-VyCowley, MichaelFisher, Deanne BKacprzak, GlennLabbe, IvoStraatman, Caroline2022-06-292022-06-290004-637Xhttp://hdl.handle.net/1885/268559The ionizing photon production efficiency, ξion, is a critical parameter that provides a number of physical constraints to the nature of the early Universe, including the contribution of galaxies to the timely completion of the reionization of the Universe. Here we use KECK/MOSFIRE and ZFOURGE multi-band photometric data to explore the ξion of a population of galaxies at z∼2 with log10(M∗/M⊙)∼9.0−11.5. Our 130 \Halpha\ detections show a median log10(ξion[Hz/erg]) of 24.8±0.5 when dust corrected using a Calzetti et al. (2000) dust prescription. Our values are typical of mass/magnitude selected ξion values observed in the z∼2 Universe. Using BPASSv2.2.1 and Starburst99 stellar population models with simple parametric star-formation-histories (SFH), we find that even with models that account for effects of stellar evolution with binaries/stellar rotation, model galaxies at log10(ξion[Hz/erg])≲25.0 have low Hα equivalent widths (EW) and redder colors compared to our z∼2 observed sample. We find that introducing star-bursts to the SFHs resolve the tension with the models, however, due to the rapid time evolution of ξion, Hα EWs, and rest-frame optical colors, our Monte Carlo simulations of star-bursts show that random distribution of star-bursts in evolutionary time of galaxies are unlikely to explain the observed distribution. Thus, either our observed sample is specially selected based on their past SFH or stellar models require additional mechanisms to reproduce the observed high UV luminosity of galaxies for a given production rate of hydrogen ionizing photonsT.N., J.B., and R.B. acknowledge the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) top grant TOP1.16.057. J.B. acknowledges support by Fundação para a Ciência e a Tecnologia (FCT) through national funds (UID/FIS/04434/2013) and Investigador FCT contract IF/01654/2014/CP1215/CT0003, and by FEDER through COMPETE2020 (POCI-01-0145-FEDER-007672). G.G.K. acknowledges the support of the Australian Research Council through the Discovery Project DP170103470. Parts of this research were supported by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013.application/pdfen-AU© 2020. The American Astronomical SocietyReconstructing the Observed Ionizing Photon Production Efficiency at Z ~2 Using Stellar Population Models202010.3847/1538-4357/ab65eb2021-08-01