University of Connecticut

Events Calendar

Physics Colloquium

Friday, September 28, 2018
3:30pm – 4:30pm

Storrs Campus

Prof. Steve Finkelstein, Department of Astronomy, University of Texas, Austin

Understanding the Reionization of the Universe Now and with JWST

The universe just after the Big Bang was a dark place, while the remnant radiation from the Big Bang cooled, and gas began to pile into dark matter halos. After a few hundred million years, the as-yet unseen first galaxies began to form, and the ionizing radiation produced by their massive stars ionized the intergalactic medium, in a process known as reionization. The search for these first galaxies, and an understanding of the process of reionization, has been a major goal of extragalactic astronomy for decades. While it is commonly assumed that massive stars within star-forming galaxies provide the needed ionizing photons to reionize the intergalactic medium, the commonly assumed ionizing photon escape fractions in the range of 10-50% have thus far exceeded what has been observed (except in a few extreme cases). I will discuss the results of a new semi-empirical model, combining simulated galaxy escape fractions with observed rest-UV galaxy luminosity functions. We find that we can successfully match all observational constraints on reionization by 1) forming stars to physically-motivated halo mass limits; 2) allowing galaxies to be more efficient ionizing photon producers at higher redshift, and 3) allowing a (not strong) contribution from AGNs. This predicts that reionization is a smoother process than previous models, with a predicted volume-averaged ionized fraction of 20% at z=10. JWST will soon dramatically improve our view of the z~10 universe and validate whether significant star-formation is occurring in that epoch, and I will conclude by discussing a recently-approved JWST Early Release Science program which will begin to probe this epoch.


Prof. Kate Whitaker

Physics Department (primary)

Control Panel