%0 Generic %1 shivaei2017mosdef %A Shivaei, Irene %A Reddy, Naveen A. %A Siana, Brian %A Shapley, Alice E. %A Kriek, Mariska %A Mobasher, Bahram %A Freeman, William R. %A Sanders, Ryan L. %A Coil, Alison L. %A Price, Sedona H. %A Fetherolf, Tara %A Azadi, Mojegan %A Leung, Gene %A Zick, Tom %D 2017 %K high-z ionization photon production %T The MOSDEF Survey: Direct Observational Constraints on the Ionizing Photon Production Efficiency, $\xi_ion$, at z~2 %U http://arxiv.org/abs/1711.00013 %X We combine spectroscopic measurements of H$\alpha$ and H$\beta$ and UV continuum photometry for a sample of 676 galaxies from the MOSFIRE Deep Evolution Field survey to constrain hydrogen ionizing photon production efficiencies ($\xi_ion$, xi_ion) at z=1.4-2.6. We find average log(xi_ion/Hz erg$^-1$)=25.06 (25.34), assuming the Calzetti (SMC) curve when correcting the UV emission for dust attenuation. We conclude that the large scatter of 0.28 dex in xi_ion cannot be solely explained by measurement uncertainties or variations in the assumed dust attenuation curve from object to object. Rather, our analysis suggests that the scatter in xi_ion is also affected by galaxy-to-galaxy variations in stellar population properties, including the slope and upper mass cutoff of the IMF, stellar metallicity, bursty star formation, and binary/single star evolution. Moreover, we find that xi_ion is elevated in galaxies with high ionization states (i.e., high OIII/OII) and low oxygen abundances (low NII/H$\alpha$ and high OIII/H$\beta$). However, xi_ion does not correlate with the offset from the z~0 star-forming locus in the BPT diagram, suggesting no change in the hardness of ionizing radiation accompanying the offset from the z~0 sequence. We also find that the xi_ion of galaxies with blue UV spectral slopes ($\beta$~-2.1) is elevated by a factor of ~2 relative to the average xi_ion of the sample. If these blue galaxies are similar to those at z>6, our results suggest that a lower LyC escape fraction is required for galaxies to maintain reionization, compared to that previously assumed based on the canonical xi_ion predictions from stellar population models. We also demonstrate that even with robust, dust-corrected H$\alpha$ measurements, the UV dust attenuation curve is an important source of uncertainty that on average causes ~0.3 dex systematic uncertainty in xi_ion measurements.

@misc{shivaei2017mosdef, abstract = {We combine spectroscopic measurements of H$\alpha$ and H$\beta$ and UV continuum photometry for a sample of 676 galaxies from the MOSFIRE Deep Evolution Field survey to constrain hydrogen ionizing photon production efficiencies ($\xi_{\rm ion}$, xi_ion) at z=1.4-2.6. We find average log(xi_ion/[Hz erg$^{-1}$])=25.06 (25.34), assuming the Calzetti (SMC) curve when correcting the UV emission for dust attenuation. We conclude that the large scatter of 0.28 dex in xi_ion cannot be solely explained by measurement uncertainties or variations in the assumed dust attenuation curve from object to object. Rather, our analysis suggests that the scatter in xi_ion is also affected by galaxy-to-galaxy variations in stellar population properties, including the slope and upper mass cutoff of the IMF, stellar metallicity, bursty star formation, and binary/single star evolution. Moreover, we find that xi_ion is elevated in galaxies with high ionization states (i.e., high [OIII]/[OII]) and low oxygen abundances (low [NII]/H$\alpha$ and high [OIII]/H$\beta$). However, xi_ion does not correlate with the offset from the z~0 star-forming locus in the BPT diagram, suggesting no change in the hardness of ionizing radiation accompanying the offset from the z~0 sequence. We also find that the xi_ion of galaxies with blue UV spectral slopes ($\beta$~-2.1) is elevated by a factor of ~2 relative to the average xi_ion of the sample. If these blue galaxies are similar to those at z>6, our results suggest that a lower LyC escape fraction is required for galaxies to maintain reionization, compared to that previously assumed based on the canonical xi_ion predictions from stellar population models. We also demonstrate that even with robust, dust-corrected H$\alpha$ measurements, the UV dust attenuation curve is an important source of uncertainty that on average causes ~0.3 dex systematic uncertainty in xi_ion measurements.}, added-at = {2017-11-02T10:32:17.000+0100}, author = {Shivaei, Irene and Reddy, Naveen A. and Siana, Brian and Shapley, Alice E. and Kriek, Mariska and Mobasher, Bahram and Freeman, William R. and Sanders, Ryan L. and Coil, Alison L. and Price, Sedona H. and Fetherolf, Tara and Azadi, Mojegan and Leung, Gene and Zick, Tom}, biburl = {https://www.bibsonomy.org/bibtex/210052eca8e1722d3eac18b83dc8bbc4d/miki}, description = {[1711.00013] The MOSDEF Survey: Direct Observational Constraints on the Ionizing Photon Production Efficiency, $\xi_{\rm ion}$, at z~2}, interhash = {f0a18f03c654cd625fdade7e09d861cc}, intrahash = {10052eca8e1722d3eac18b83dc8bbc4d}, keywords = {high-z ionization photon production}, note = {cite arxiv:1711.00013Comment: 14 pages, 8 figures, 1 table, submitted to ApJ}, timestamp = {2017-11-02T10:32:17.000+0100}, title = {The MOSDEF Survey: Direct Observational Constraints on the Ionizing Photon Production Efficiency, $\xi_{\rm ion}$, at z~2}, url = {http://arxiv.org/abs/1711.00013}, year = 2017 }