Stellar and Nebular Emission from Forming Galaxies: Connecting the High Redshift Universe to the Fossil Record

Cecilia Payne-Gaposhkin Lecture
December 6, 2018
Phillips Auditorium

Massive stars provide the most easily observed tracers of the galaxy formation process over the first several billion years of the universe’s history. In addition to being the most likely sources of EUV radiation that reionized the universe at z ~ 7-8, they are responsible for for producing most of the metals that enrich the interstellar, circumgalactic, and intergalactic medium that fuels subsequent generations of stars. Simultaneously, their high luminosities and violent deaths inject large amounts of energy and momentum into their environment, rivaled only by supermassive black holes in the degree to which they affect the galaxy formation process. However, by the present-day, most massive galaxies are long past their historical growth phase, with the bulk of their star formation having occurred in the distant past. Only the integrated population of low-mass stars that formed during a galaxy's peak growth phase remain, comprising a fossil record of the chemical patterns that prevailed during the course of their formation. It is now possible to observe directly the massive star populations in galaxies as they are forming at high redshift (i.e., the ``birth record'') for comparison with the fossil record encoded in the integrated spectra of their present-day descendants. I will argue that massive stars in high redshift galaxies are distinct from those found in any star-forming galaxy at z = 0, and that the differences have important implications for cosmic reionization, the physical interpretation high-z galaxy observations, and understanding the connection to the present-day universe.

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