Collaborative Research: The Final Frontier: Spectroscopic Probes of Galaxies at the Epoch of Reionization

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

The cosmic Dark Ages (before the first stars formed) are thought to have ended around 500 million years after the Big Bang when early light sources produced enough energetic photons to ionize the neutral hydrogen. This era is referred to as reionization. It is when the first galaxies formed. But when exactly did reionization occur and how long did it last? What were the sources responsible for ionizing the neutral gas? Was it the first galaxies or accretion onto black holes? This project will answer these questions by using the best telescopes in the world. The observations will include images and spectra of the first galaxies, which enable a first glimpse of the chemical composition of this important population. The project also includes a strong educational/public outreach component. To help train tomorrow's scientists, the PI will develop an observing course intended for K-12 students. The PI and co-PI are also developing courses for non-science majors. The epoch of reionization, which signified the transformation of the universe from opaque to transparent, is poorly understood. When did it start/end? Was it patchy or smooth? How did galaxies reionize the universe (if they did)? What are the properties of the earliest galaxies? To answer these questions, over the last decades, several surveys have explored the high redshift universe at progressively increasing depth. However, they still either lack the sample size or depth (or both). What emerges from these surveys is that the answers to these questions are likely tied to the properties of even fainter galaxies. This project will address the problem by conducting a spectroscopic study of a large sample of previously unexplored faint galaxy populations at redshifts z > 6. This will be achieved by using galaxy clusters that serve as cosmic telescopes and by pre-selecting sources from deep ancillary imaging and low-resolution spectroscopy data. This project will (1) provide the timeline of reionization, (2) identify the exact role first galaxies played in this process, and (3) give insight on the stellar properties of the earliest galaxies. The educational/public outreach component of this project will include developing an observing course for California State Summer School for Mathematics and Science (COSMOS), intended for K-12 students. In addition, the investigators are also developing new university courses entitled the "Physics of California'' and "The physics of sustainable energy'' for non- science majors. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.