Abstract

Using an improved model of reionization to craft a legacy JWST galaxy evolution survey

Steven Finkelstein (The University of Texas at Austin)

I will present the results of our new analysis of the contribution of both galaxies and AGNs to the reionization of the intergalactic medium (IGM). The time evolution of reionization, and the ionizing sources, are poorly constrained primarily due to the lack of knowledge about the escape fraction of ionizing photons from star-forming galaxies. Using the results of detailed zoom-in hydrodynamical simulations, we parameterize the escape fraction as a function of halo mass and combine this with observations of the evolution of the galaxy luminosity function at high redshift. This fiducial model does not complete reionization by z=6. We then run a MCMC analysis, using the observations of quasars and the electron scattering optical depth to the CMB to constrain a number of free parameters, including a scale factor applied to the simulation escape fraction results, a contribution from AGN, minimum halo mass for star formation, and the Lyman continuum photon production efficiency, finding that star-forming galaxies alone can fully reionize the universe by z~6 with an escape fraction of only ~5% (~4% if AGNs contribute significantly). This model makes a number of important predictions for the number density and ionizing efficiency of galaxies at z > 8, and I will discuss these in the context of the design for a JWST extragalactic legacy survey.

Talk