Witnessing Galaxies Reionizing the Intergalactic Medium with JWST
Speaker: Daichi Kashino
Abstract:
Cosmic reionization is the last major phase transition of the universe, occurring in the first billion years after the Big Bang. Understanding this process is one of the pivotal goals in modern astrophysics. The commissioning of JWST heralded a new era in investigating the roles of galaxies in reionizing the intergalactic medium, thanks to its unprecedented high sensitivity and dispersing power in near infrared.
In the presentation, I will present early results from our ongoing EIGER (Emission-line galaxies and Intergalactic Gas in the Epoch of Reionization) survey, a JWST/NIRCam WFSS campaign in the fields of luminous z>6 quasars. The existence of these background quasars enables us to determine the ionization condition along their lines of sight from analysis of the high signal-to-noise quasar spectra. The primary objective of the project is to characterize the cross correlation between galaxies (as pinpointed by JWST) and the IGM conditions during the tail end of the epoch of reionization. In the first quasar field, we confirmed roughly 150 [OIII]5008-emitting galaxies over the redshift range of z=5.3–6.9. Through analyzing the distribution of these galaxies and the transmission spectrum of this corresponding quasar, we identified individual spatial coincidence between the groups of galaxies and highly ionized regions, as well as a mean excess IGM transmission in both Lyman-alpha and Lyman-beta around ~6 cMpc away from the galaxies at z~6. This is interpreted as direct evidence of local reionization by galaxies — indicating that we are witnessing galaxies reionizing the surrounding IGM. I may also showcase further preliminary results from other quasar fields currently being analyzed.