Description
The Habitable Worlds Observatory (HWO) will deliver transformational insights into dark sector science. Theoretical and empirical studies show that satellite counts of ultra-faint dwarfs (i.e., those with stellar masses < 10^5 M_sun) can be valuable probes of potential deviations from a cold dark matter cosmology and subsequently place constraints on the warm dark matter particle mass. With HWO, we aim to survey ultra-faint satellites—down to stellar masses M* ~10^3.5 M_sun—around Milky-Way-mass hosts within a ~10 Mpc volume. We discuss the additional predictions of our novel forecasting, which suggests that we can put breakthrough constraints on warm dark matter models (up to ~13 keV) with ultra-faint satellite censuses of just a few Milky-Way-like hosts. Based on this forecasting and coupled with the proposed >6m aperture of HWO, we present our observing plan that will not only survey the diffuse light of ultra-faint satellites but also resolve their individual stars at extragalactic scales. The addition of extragalactic ultra-faints will improve upon current cutting-edge surveys such as ELVES and SAGA within our proposed survey volume, positioning HWO as a major contributor towards breakthrough advancement of dark sector science.
