University of Connecticut

Events Calendar

Physics Colloquium

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

Storrs Campus
PB-38

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.

Contact:

Prof. Kate Whitaker

Physics Department (primary)

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