%0 Generic %1 bouwens2015using %A Bouwens, R. J. %A Smit, R. %A Labbe, I. %A Franx, M. %A Caruana, J. %A Oesch, P. %A Stefanon, M. %A Rasappu, N. %D 2015 %K escape fraction galaxies halpha uv %T Using the Inferred Halpha Emission from z~4-5 Galaxies to Measure the Lyman-Continuum Photon Production Efficiency xi_ion: Implications for the Escape Fraction %U http://arxiv.org/abs/1511.08504 %X Galaxies represent one of the preferred candidate sources to drive the reionization of the universe. Even as gains are made in mapping the galaxy UV luminosity density to z>6, significant uncertainties remain regarding the Lyman-continuum (LyC) photon production efficiency xi_ion and the escape fraction f_esc. However, dramatic progress can be made in assessing the impact of z>~6 galaxies on the reionization of the universe, using the Halpha fluxes inferred from z=4-5 galaxies based on their IRAC broad-band fluxes. Here, we provide the first-ever direct estimates of the LyC photon production efficiency xi_ion for z>~4 galaxies, by comparing the LyC photons implied by the inferred H$\alpha$ luminosities for a $z=4$-5 sample with the dust-corrected UV-continuum luminosities. We find log_10 xi_ion/Hz / ergs to have a mean value of 25.28_-0.09^+0.10 and 25.34_-0.08^+0.09 for sub-L* z=4-5 galaxies adopting Calzetti and SMC dust laws, respectively. Reassuringly, both derived values are consistent with standardly assumed xi_ion's in reionization models, with a slight preference for higher xi_ion's (by ~0.1 dex) adopting the SMC dust law. A modest ~0.03-dex increase in these estimates would result if the escape fraction for ionizing photons is non-zero and galaxies dominate the ionizing emissivity at z~4.4. High values of xi_ion (~25.5-25.9 dex) are derived for the bluest galaxies (beta<-2.3) in our samples, independent of dust law and consistent with results for a z=7.045 galaxy. Such elevated values of xi_ion would have important consequences, indicating that f_esc cannot be in excess of 13% unless the galaxy UV luminosity function does not extend down to -13 mag or the clumping factor is greater than 3. A low escape fraction would fit well with the low rate of Lyman-continuum leakage observed at z~3.

@misc{bouwens2015using, abstract = {Galaxies represent one of the preferred candidate sources to drive the reionization of the universe. Even as gains are made in mapping the galaxy UV luminosity density to z>6, significant uncertainties remain regarding the Lyman-continuum (LyC) photon production efficiency xi_{ion} and the escape fraction f_{esc}. However, dramatic progress can be made in assessing the impact of z>~6 galaxies on the reionization of the universe, using the Halpha fluxes inferred from z=4-5 galaxies based on their IRAC broad-band fluxes. Here, we provide the first-ever direct estimates of the LyC photon production efficiency xi_{ion} for z>~4 galaxies, by comparing the LyC photons implied by the inferred H$\alpha$ luminosities for a $z=4$-5 sample with the dust-corrected UV-continuum luminosities. We find log_{10} xi_{ion}/[Hz / ergs] to have a mean value of 25.28_{-0.09}^{+0.10} and 25.34_{-0.08}^{+0.09} for sub-L* z=4-5 galaxies adopting Calzetti and SMC dust laws, respectively. Reassuringly, both derived values are consistent with standardly assumed xi_{ion}'s in reionization models, with a slight preference for higher xi_{ion}'s (by ~0.1 dex) adopting the SMC dust law. A modest ~0.03-dex increase in these estimates would result if the escape fraction for ionizing photons is non-zero and galaxies dominate the ionizing emissivity at z~4.4. High values of xi_{ion} (~25.5-25.9 dex) are derived for the bluest galaxies (beta<-2.3) in our samples, independent of dust law and consistent with results for a z=7.045 galaxy. Such elevated values of xi_{ion} would have important consequences, indicating that f_{esc} cannot be in excess of 13% unless the galaxy UV luminosity function does not extend down to -13 mag or the clumping factor is greater than 3. A low escape fraction would fit well with the low rate of Lyman-continuum leakage observed at z~3.}, added-at = {2015-11-30T10:12:26.000+0100}, author = {Bouwens, R. J. and Smit, R. and Labbe, I. and Franx, M. and Caruana, J. and Oesch, P. and Stefanon, M. and Rasappu, N.}, biburl = {https://www.bibsonomy.org/bibtex/211e67aef0471f0a9661d5fcf74b6b583/miki}, description = {[1511.08504] Using the Inferred Halpha Emission from z~4-5 Galaxies to Measure the Lyman-Continuum Photon Production Efficiency xi_{ion}: Implications for the Escape Fraction}, interhash = {e29659c5bc841a5772d557b7d19a7e1d}, intrahash = {11e67aef0471f0a9661d5fcf74b6b583}, keywords = {escape fraction galaxies halpha uv}, note = {cite arxiv:1511.08504Comment: 12 pages, 6 figures, 3 tables, submitted to the Astrophysical Journal}, timestamp = {2015-11-30T10:12:42.000+0100}, title = {Using the Inferred Halpha Emission from z~4-5 Galaxies to Measure the Lyman-Continuum Photon Production Efficiency xi_{ion}: Implications for the Escape Fraction}, url = {http://arxiv.org/abs/1511.08504}, year = 2015 }