We use deep imaging from the JWST Advanced Deep Extragalactic Survey (JADES) to study the evolution of the ionizing photon production efficiency, ξion. We estimate ξion for a sample of 677 galaxies at z ∼ 4–9 using NIRCam (Near-Infrared Camera) photometry. Specifically, combinations of the medium and wide bands F335M–F356W and F410M–F444W to constrain emission lines that trace ξion: Hα and [O iii]. Additionally, we use the spectral energy distribution fitting code prospector to fit all available photometry and infer galaxy properties. The flux measurements obtained via photometry are consistent with FRESCO (First Reionisation Epoch Spectroscopic Complete Survey) and NIRSpec-derived fluxes. Moreover, the emission-line-inferred measurements are consistent with the prospector estimates. We also confirm the observed ξion trend with redshift and MUV, and find: log ξion(z, MUV) = (0.05 ± 0.02)z + (0.11 ± 0.02)MUV + (27.33 ± 0.37). We use prospector to investigate correlations of ξion with other galaxy properties. We see a clear correlation between ξion and burstiness in the star formation history of galaxies, given by the ratio of recent to older star formation, where burstiness is more prevalent at lower stellar masses. We also convolve our ξion relations with luminosity functions from the literature, and constant escape fractions of 10 per cent and 20 per cent, to place constraints on the cosmic ionizing photon budget. By combining our results, we find that if our sample is representative of the faint low-mass galaxy population, galaxies with bursty star formation are efficient enough in producing ionizing photons and could be responsible for the reionization of the Universe.
As the James Webb Space Telescope approaches scientific operation, there is much interest in exploring the redshift range beyond that accessible with Hubble Space Telescope imaging. Currently, the only means to gauge the presence of such early galaxies is to age-date the stellar population of systems in the reionisation era. As a significant fraction of z ≃ 7−8 galaxies are inferred from Spitzer photometry to have extremely intense [O iii] emission lines, it is commonly believed these are genuinely young systems that formed at redshifts z < 10, consistent with a claimed rapid rise in the star formation density at that time. Here, we study a spectroscopically confirmed sample of extreme [O iii] emitters at z = 1.3−3.7, using both dynamical masses estimated from [O iii] line widths and rest-frame UV to near-infrared photometry to illustrate the dangers of assuming such systems are genuinely young. For the most extreme of our intermediate redshift line emitters, we find dynamical masses 10−100 times that associated with a young stellar population mass, which are difficult to explain solely by the presence of additional dark matter or gaseous reservoirs. Adopting non-parametric star formation histories, we show how the near-infrared photometry of a subset of our sample reveals an underlying old (>100 Myr) population whose stellar mass is ≃ 40 times that associated with the starburst responsible for the extreme line emission. Without adequate rest-frame near-infrared photometry, we argue it may be premature to conclude that extreme line emitters in the reionisation era are low-mass systems that formed at redshifts below z ≃ 10.
more » « less- NSF-PAR ID:
- 10367704
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 513
- Issue:
- 4
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- p. 5211-5223
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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