Charles E. Kaufman Foundation

2019 New Investigator Grant

Rachel Bezanson, Ph.D. Assistant Professor, Department of Physics and Astronomy, University of Pittsburgh

Dancing of the Stars: Testing the Formation of the Largest Elliptical Galaxies


Galaxies are the largest cosmic building blocks that can directly impact human or extraterrestrial life; they house the vast majority of the gas, stars, and planets in the Universe. There are two primary types of galaxies: spiral galaxies - like our Milky Way - and larger, rounder elliptical galaxies. This project focuses on the formation and evolution of the latter, elliptical galaxies. Growing evidence over the last decade suggests that ellipticals are built gradually; not by a dramatic crash between two large Milky Ways, but by slowly cannibalizing many neighboring galaxies. This research project aims to test this formation mechanism by studying the detailed properties of galaxies in the distant - and therefore early - Universe, focusing on those which will eventually grow into today’s elliptical galaxies. This project is made possible by the Large Early Galaxy Astrophysics Census (LEGA-C) survey of thousands of galaxies so distant that we observe their light as it was emitted half the age of the Universe in the past. The LEGA-C survey required _130 nights using the Very Large Telescope (VLT) in Chile, one of the largest telescopes in the world, to obtain unprecedented spectroscopic information about the compositions and motions of stars and gas in these early galaxies. For this project we will leverage the extraordinary dataset to study the motions of stars inside of galaxies, determining where they lie on the spectrum between orderly paths, like stars in our Milky Way or planets in our Solar System, or disordered paths, like stars in round elliptical galaxies or bees in a swarm. We will quantify the relative importance of these orbits and determine how they depend on the age or stellar histories in galaxies. We will also assess if orbits depend on whether galaxies live in a region of the Universe that is densely packed with other galaxies with which to interact. This investigation will test and deepen our understanding of the slow formation of the largest galaxies in the Universe.

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