Luminous High-Redshift Stars and Dark Matter Substructure Using Galaxy Cluster Lenses

University Of Minnesota-Twin Cities, Minneapolis MN

Investigators

Abstract

More than four fifths of the matter in the universe consists of a form of matter that does not interact with or produce light and is, therefore, dark. Despite decades of searches, the nature of the dark matter is not yet known. As light passes through or close to a galaxy cluster, its path is bent by both the dark and luminous matter, and cluster lenses can create multiple, magnified images of background galaxies. In this project, scientists the University of Minnesota will measure the lensing magnification of mirrored images of ionized gas clouds in these background galaxies to carry out a new test of leading theories of dark matter. A second component of the program will be to seek to identify individual stars that are highly magnified in imaging from the upcoming Large Survey of Space and Time (LSST). These magnified stars are visible across most of the observable universe and studying them will open a new window into the universe when it was much younger. Moreover, changes in these stars’ brightness should provide new evidence about the nature of dark matter. In collaboration with the University of Minnesota’s Bell Museum, the team will also develop a new live-facilitated program for its 120-seat planetarium about past and current questions surrounding the cosmic expansion. The planetarium show, which will be targeted towards middle-school students but able to engage adults, will become a part of the Bell Museum’s regular daily rotation, and reach tens of thousands of students and visitors. The research team will acquire ground-based spectroscopy of pairs of mirrored images of HII regions in magnified arcs. Differences between the brightnesses, and therefore magnifications, of these pairs of images must arise from dark-matter substructure, since the large sizes of HII regions imply that their fluxes are not affected by microlensing from stars in the foreground cluster. These measurements will be compared to predictions from both cold dark matter (CDM) and ultralight boson dark matter. The second goal of this project is to study stars at cosmological distances that are sufficiently magnified to be detected. The team will develop tools to identify these events in LSST data, and obtain follow-up spectroscopy and imaging to study the detailed properties of the luminous stars beyond the local universe. The stars’ light curves should contain rapid fluctuations if axion minihalos are present in the galaxy cluster. 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.