The Ionizing Photon Production Efficiency (ξ_(ion)) of Lensed Dwarf Galaxies at z ∼ 2
Abstract
We measure the ionizing photon production efficiency (ξ_(ion)) of low-mass galaxies (10^(7.8)–10^(9.8) M⊙) at 1.4 < z < 2.7 to better understand the contribution of dwarf galaxies to the ionizing background and reionization. We target galaxies that are magnified by strong-lensing galaxy clusters and use Keck/MOSFIRE to measure nebular emission-line fluxes and Hubble Space Telescope to measure the rest-UV and rest-optical photometry. We present two methods of stacking. First, we take the average of the log of Hα-to-UV luminosity ratios (L_(Hα) /L_(UV)) of galaxies to determine the standard log(ξ_(ion)). Second, we take the logarithm of the total L_(Hα) over the total L_(UV). We prefer the latter, as it provides the total ionizing UV luminosity density of galaxies when multiplied by the nonionizing UV luminosity density. Log(ξ_(ion)) calculated from the second method is ~0.2 dex higher than the first method. We do not find any strong dependence between log(ξ_(ion)) and stellar mass, far-UV magnitude (M_(UV)), or UV spectral slope (β). We report a value of log(ξ_(ion)) ~ 25.47 ± 0.09 for our UV-complete sample (−22 < M_(UV) < −17.3) and ~25.37 ± 0.11 for our mass-complete sample (7.8 < log(M*) < 9.8). These values are consistent with measurements of more massive, more luminous galaxies in other high-redshift studies that use the same stacking technique. Our log(ξ 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(ξ_(ion)) and the equivalent widths of Hα and [O III] λ5007 fluxes, confirming that these equivalent widths can be used to estimate ξ_(ion).
Additional Information
© 2020 The American Astronomical Society. Received 2019 December 11; revised 2020 April 29; accepted 2020 May 1; published 2020 June 3. 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. We thank the anonymous referee for providing useful comments that helped improve the quality of this paper. This material is based on work supported by the National Science Foundation under grant No. 1617013. Support for programs No. 12201, 12931, 13389, and 14209 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. D.R.W. acknowledges fellowship support from the Alfred P. Sloan Foundation and the Alexander von Humboldt Foundation. Facilities: Keck:I (MOSFIRE) - , HST (WFC3 - , ACS) - .Attached Files
Published - Emami_2020_ApJ_895_116.pdf
Accepted Version - 1912.06152.pdf
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Additional details
- Eprint ID
- 103677
- Resolver ID
- CaltechAUTHORS:20200603-135415853
- NSF
- AST-1617013
- NASA
- NAS5-26555
- Alfred P. Sloan Foundation
- Alexander von Humboldt Foundation
- Created
-
2020-06-03Created from EPrint's datestamp field
- Updated
-
2021-11-16Created from EPrint's last_modified field
- Caltech groups
- Infrared Processing and Analysis Center (IPAC)