A spectroscopic analysis of the ionizing photon production efficiency in JADES and CEERS: implications for the ionizing photon budget

Abstract

We have used a combined sample of JADES and CEERS objects in order to constrain ionizing photon production efficiency ($\hat{I}{¾}_{\mathrm{ion}}$) from JWST/NIRSpec and JWST/NIRCam data. We examine 163 objects at 1.06 < z < 6.71 with significant (3$\ddot{I}ƒ$) spectroscopic detections of H$\hat{I}\pm$ and H${\hat{I}}^2$ in order to constrain intrinsic H$\hat{I}\pm$ luminosities corrected from nebular dust attenuation via Balmer decrements. We constrain dust-corrected UV luminosities from best-fit spectral-energy distribution modeling. We find a sample median log${}_{10}$($\hat{I}¾\mathrm{ion},0$/erg Hz${}^{-1}$) = $25.29_{-0.37}^{+0.29}$, assuming f${}_{\mathrm{esc}}$=0 for the escape fraction of Lyman continuum emission. We find significant correlation between $\hat{I}{¾}_{\mathrm{ion},0}$ and z, with 17 objects at z > 4.64 having median log${}_{10}$($\hat{I}{¾}_{\mathrm{ion},0}$/erg Hz${}^{-1}$) = $25.38^{+0.38})-0.38$, with those below having log${}_{10}$($\hat{I}{¾}_{\mathrm{ion},0}$/erg Hz${}^{-1}$) = $25.24_{-0.33}^{+0.30}$. We also find significant, positive correlations between $\hat{I}{¾}_{\mathrm{ion},0}$ and LUV; Wλ([O iii]); [O iii]λ5007/[O ii]λλ3726, 3729; and inverse correlations with metallicity. In contrast with some previous results, we find no trends between $\hat{I}{¾}_{\mathrm{ion},0}$ and stellar mass, stellar dust attenuation, or UV slope. Applying a multivariate fit to $\hat{I}{¾}_{\mathrm{ion},0}$, z, and MUV to an empirically-motivated model of reionization, and folding in f${}_{\mathrm{esc}}$ estimates from direct observations of the Lyman continuum at z ~ 3 from the Keck Lyman Continuum Spectroscopic survey, we find that the number of ionizing photons entering the IGM causes reionization to end at z ~ 5 - 7.

17 pages, 8 figures, submitted to ApJ