Watching our Galaxy Grow Up: The Mass and Color Evolution of the Milky Way
Research by Gail Zasowski1, Julie Imig2, and Hayley Coluccio1
1University of Utah, 2Space Telescope Science Institute
Using our rich observations within the Milky Way to better understand galaxy evolution requires understanding what the Milky Way looks like "as a galaxy"—that is, its "true" shape and abundance profiles (unskewed by observational biases), signatures of past mergers and significant accretion events, and even its total stellar mass and integrated spectrum, which have historically been difficult to constrain. We explored a new approach to determining the Milky Way's integrated mass and colors, using recent measurements of the intrinsic density profiles of stellar populations spanning nearly 13 billion years in time and a factor of 30 in heavy element abundance (representing nearly all of the Galaxy's stars). We traced the evolution of the Milky Way in various diagnostic spaces, explored the impact of specific galactic interactions on the present-day Milky Way's integrated properties, and use high-resolution simulations to identify "young" Galactic twins and their eventual fates, compared to the real Milky Way's path. From the simulation comparisons, we found strong evidence for an earlier-than-average stellar mass assembly of the Milky Way, and that present-day Milky Way twins follow a similar growth history, albeit at slightly later times; we also found that twins of the early Milky Way are in no way guaranteed to follow the Milky Way subsequent path. This empirical study offers new constraints on our "Galaxy as a galaxy"—today and across cosmic time—and on its place in the general galactic population. The paper describing this project has been accepted for publication in the Astrophysical Journal; a preprint is available on arXiv. Many of the calculations for this project were performed on CHPC machines.