# High-Latitude Wide-Area Survey (HLWAS)

Roman’s broadest survey sweeps thousands of square degrees of sky away from the Milky Way’s dusty plane, imaging and taking spectra of galaxies across most of cosmic history.

By measuring the shapes of distant galaxies, astronomers can detect the faint distortion caused by dark matter along the line of sight — weak gravitational lensing. Mapping where galaxies sit in three dimensions also traces the imprint of sound waves from the early universe. Together these tell us how fast the universe has expanded and how structure has grown, the two strongest clues to what dark energy is.

The survey is split into tiers of different depth. Current plans cover roughly 2,400 square degrees in several filters plus about 2,700 more in a single filter, using the Y, J, H and F184 filters and the grism for spectroscopy, over about two years of observing time.

Its footprint is designed to overlap with Rubin Observatory’s ground-based survey and ESA’s Euclid, so the three datasets can calibrate one another.

- **Area:** ≈ 2,400 deg² multi-filter + ≈ 2,700 deg² single-filter
- **Filters:** F106, F129, F158, F184 + grism
- **Observing time:** ≈ 2 years
- **Science:** Dark energy, dark matter, galaxy evolution