A Pioneering Test of Stellar Population Complexity Outside the Milky Way

University Of Utah, Salt Lake City UT

Investigators

Abstract

The investigator will test the uniqueness of the Milky Way Galaxy's chemical composition. Their goal is understanding how other galaxies change with time, based on observations of stars in the Milky Way (MW). Observations of individual stars in the MW show that the chemistry and the motions of stars are related. These relationships have guided our understanding of how other galaxies change over time and chemically enrich the Universe. Studying the changes in other galaxies over time is extremely difficult. The project team will pioneer new techniques for testing if these patterns occur in the Andromeda Galaxy, the nearest galaxy that is similar to the MW. These measurements will provide insight into that galaxy's history, the uniqueness of the MW, and the usefulness of these systems for tracing how galaxies have grown since the Big Bang. To analyze existing high-resolution, near-infrared (NIR) spectra spanning a large fraction of Andromeda's bulge and disk, the project team will first construct a library of Simple Stellar Population (SSP) models based on theoretical isochrones and nearly 400,000 stellar spectra observations. The public release of this NIR library will fill a gap in the suite of SSP libraries available to the community. The project team will apply this library in two approaches to modeling the Andromeda integrated spectra, one using multi-component spectral fitting and one using machine learning with the SSP models as a training set. The comparison of the two approaches will be used to evaluate the consistency and robustness of the results in different parts of the galaxy. This program will constrain the presence of overlapping stellar populations in the inner regions of Andromeda with distinct dynamical and chemical properties that reflect their diverse histories, information that previously has been measured only in the MW. By revealing how similar Andromeda is to the MW in this important regard, this project will clarify to what extent our high-resolution picture of the MW can be applied to interpreting the unresolved starlight in other galaxies. More generally, these results will test theories of bulge and inner disk evolution and how that evolution is reflected in the constituent stellar populations. This program also supports efforts to promote scientific literacy to two important groups local to the project team: Utah's refugee community and visitors to Utah's national parks. The team will develop astronomy-themed workshops as part of an after-school program that helps middle- and high-school students from refugee families integrate into American classrooms and find social support. These workshops will promote positive perceptions of science and teach critical thinking, communication, and computational skills to students who face unique challenges to their education because of their family histories. The project also includes an extension of a high-impact outreach internship program to bring astronomy education to about 18,000 visitors at Bryce Canyon National Park. These two efforts will be linked by a visit of students from the refugee community to Bryce Canyon for an immersive outdoor experience under some of the US's darkest skies. 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.