Searching for dark matter substructure: a deeper wide-area community survey for Roman

Understand

We recommend a deeper extension to the High-Latitute Wide Area Survey planned to be conducted by the Nancy Grace Roman Space Telescope (\emph{Roman}).

• While this deeper-tier survey extension can support a range of astrophysical investigations, it is particularly well suited to characterize the dark matter substructure in galactic halos and reveal the microphysics of dark matter through gravitational lensing.
• We quantify the expected yield of \emph{Roman} for finding galaxy-galaxy-type gravitational lenses and motivate observational choices to optimize the \emph{Roman} core community surveys for studying dark matter substructure.
• In the proposed survey, we expect to find, on average, one strong lens with a characterizable substructure per \emph{Roman} tile (0.28 squared degrees), yielding approximately 500 such high-quality lenses.