Advancing the Search for Isolated Pure Dark Matter Halos

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

Approximately 85% of the matter in the Universe exists in an invisible form called dark matter that is distinct from atoms and other known particles. Galaxies are born and grow within regions of higher dark matter density, called halos. The Standard Cosmological Model predicts that for every dark matter halo large enough to host a galaxy, there are many smaller dark matter halos containing no stars and little gas that would be effectively invisible. The abundance and density profiles of such low-mass dark matter halos are especially sensitive to the properties of dark matter. This program aims to determine the minimum dark matter halo mass for galaxy formation by using a population study of the least luminous galaxies around the Milky Way. Even smaller dark matter halos could be detected at cosmological distances via gravitational lensing. The investigator will perform a multiwavelength search for gravitational lenses suitable for detailed follow-up study. Astronomical survey datasets used in this work, including images and object catalogs obtained from the Dark Energy Survey, will be publicly released with data access tools, scientific validation, and documentation to enable research, education, and outreach activities. Science results, images, and experiences from the Dark Energy Survey will be shared on several digital media platforms to connect with broader audiences. The program involves two complementary observational, theoretical, and data analysis components. First, the investigator will conduct a census of low-luminosity galaxies orbiting the Milky Way over the entire high-Galactic-latitude sky using an ensemble of optical surveys. Search algorithms incorporating precise multi-band photometry and astrometry will probe the galaxy population in the extremely low surface brightness regime. The objective is to determine the dark matter halo mass threshold below which baryons have negligible impact on the structure and evolution of dark matter halos. Second, the investigator will combine data from wide-area optical and radio surveys to enlarge the sample of high-redshift strongly lensed radio-loud active galactic nuclei. The multiwavelength search is expected to yield several new targets for high-resolution follow-up with very-long-baseline radio interferometry. With such milliarcsecond- scale angular resolution observations, it would be possible to identify dark matter halos below the mass threshold of galaxy formation. 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.