The Ionizing Photon Production Efficiency (ξ<SUB>ion</SUB>) of Lensed Dwarf Galaxies at z ∼ 2

International audienceWe measure the ionizing photon production efficiency (ξion) of low-mass galaxies (107.8-109.8 M⊙) at 1.4 Hα/LUV) of galaxies to determine the standard log(ξion). Second, we take the logarithm of the total LHα over the total LUV. We prefer the latter, as it provides the total ionizing UV luminosity density of galaxies when multiplied by the nonionizing UV luminosity density. log(ξion) calculated from the second method is ∼0.2 dex higher than the first method. We do not find any strong dependence between log(ξion) and stellar mass, far-UV magnitude (MUV), or UV spectral slope (β). We report a value of log(ξion) ∼ 25.47 ± 0.09 for our UV-complete sample ( $-22 {M}_{\mathrm{UV}} -17.3$ ) and ∼25.37 ± 0.11 for our mass-complete sample (7.8 *) ion) is 0.2-0.3 dex higher than low-redshift galaxies of similar mass, indicating an evolution in the stellar properties, possibly due to metallicity or age. We also find a correlation between log(ξion) and the equivalent widths of Hα and [O III] λ5007 fluxes, confirming that these equivalent widths can be used to estimate ξion. * Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. This research is based on observations made with the NASA/ESA Hubble Space Telescope obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs 12201, 12931, 13389, and 14209