Probing Direct Contributions of Galaxies and AGN to Cosmic Reionization in a Quasar Field J0226+0302 with JWST NIRCam and NIRSpec

Abstract

We present JWST Cycle 2 NIRCam and NIRSpec observations in a quasar field J0226+0302 at z=6.5412 to probe the direct connections between the intergalactic medium (IGM), galaxies, and AGN during reionization. This field was previously observed by the JWST ASPIRE program and eight [OIII]-emitting galaxies were detected at 5.3<z<6.4 with a single NIRCam pointing. Using new NIRCam and NIRSpec observations, we identify 65 additional line-emitting galaxies at 5.3<z<6.4. The IGM-galaxy cross-correlation function shows a ~2 sigma excess IGM transmission at ~10-40 cMpc from galaxies when compared with the average IGM transmission, suggesting a significant contribution from regions traced by star-forming galaxies to the local ionizing background during reionization. The IGM-galaxy cross-correlation function is consistent with THESAN simulations with an IGM neutral fraction of 5%-7% and an average ionizing photon escape fraction f_esc of 6% from galaxies. Among 49 line-emitting galaxies observed by NIRSpec, we identify four AGN through detection of broad H-alpha emission lines with an AGN fraction of (8+/-4)%. By measuring the IGM effective optical depth around the AGN and the IGM-AGN cross-correlation function, we find that the IGM transmission is higher within 5 cMpc/h of the AGN than around the majority of [OIII] emitters. We interpret the excess IGM transmission as resulting from the local radiation enhancement by the AGN, and estimate f_esc of 50%-100% of the AGN from the IGM-AGN cross-correlation function. Future JWST NIRSpec observations in quasar fields will yield a more constraining IGM-AGN cross-correlation function, providing further insights into the roles of galaxies and AGN in reionization.