Probing the Nature and Origin of Ultra Diffuse Galaxies (UDGs) with Deep and Wide-Field Imaging

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Ultra-diffuse galaxies (UDGs) are a newly discovered population of galaxies. They are extremely faint, but spatially very extended, and are almost blended in the brightness of the night sky. Such diffuse galaxies are fragile, and cannot survive in gravitational encounters with other galaxies. However, astronomers are finding a great number of UDGs in clusters of galaxies, where such encounters would occur. This research program will investigate the nature and origin of these UDGs. It will study (1) whether UDGs are distinct from other types of galaxies such as the Milky Way and dwarf galaxies; (2) how they are protected from the gravitational disruptions; and (3) whether they have even fainter outskirts. The effects of gravitational encounters should appear clearly in the outskirts. This project will engage a variety of students in the research.This program will use deep and wide-field imaging of eight local clusters of galaxies. The data are taken with the Hyper Suprime-Cam (HSC) on the Subaru telescope. These unique data will show the very faint outskirts of UDGs, as well as their large-scale environments. The program will perform the most reliable census and resolved analysis of the UDG population within, outside, and among the clusters. The main goals are (1) to confirm whether UDGs are distinct from dwarf and normal galaxies in their properties parameter spaces; (2) to constrain how they formed and how they their properties depend on their environments; and (3) to image their fainter outskirts and to discover even fainter, more extended UDGs. The project focuses primarily on UDGs, but aims to yield a broader, coherent picture that connects UDGs, dwarfs, and normal galaxies. UDGs are faint and extended, and are difficult to be detected and analyzed. The observations and data reduction will be optimized to achieve these goals.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.