Abstract
The Nancy Grace Roman Space Telescope is capable of delivering an
unprecedented all-sky, high-spatial resolution, multi-epoch infrared map to the
astronomical community. This opportunity arises in the midst of numerous
ground- and space-based surveys that will provide extensive spectroscopy and
imaging together covering the entire sky (such as Rubin/LSST, Euclid, UNIONS,
SPHEREx, DESI, SDSS-V, GALAH, 4MOST, WEAVE, MOONS, PFS, UVEX, NEO Surveyor,
etc.). Roman can uniquely provide uniform high-spatial-resolution (~0.1 arcsec)
imaging over the entire sky, vastly expanding the science reach and precision
of all of these near-term and future surveys. This imaging will not only
enhance other surveys, but also facilitate completely new science. By imaging
the full sky over two epochs, Roman can measure the proper motions for stars
across the entire Milky Way, probing 100 times fainter than Gaia out to the
very edge of the Galaxy. Here, we propose NANCY: a completely public, all-sky
survey that will create a high-value legacy dataset benefiting innumerable
ongoing and forthcoming studies of the universe. NANCY is a pure expression of
Roman's potential: it images the entire sky, at high spatial resolution, in a
broad infrared bandpass that collects as many photons as possible. The majority
of all ongoing astronomical surveys would benefit from incorporating
observations of NANCY into their analyses, whether these surveys focus on
nearby stars, the Milky Way, near-field cosmology, or the broader universe.