Nancy Grace Roman Space Telescope Program 2002 (Cycle 1)

Principal Investigator: Karoline Gilbert (Space Telescope Science Institute)

Abstract: Our knowledge of the astrophysical processes underpinning the growth and evolution of galaxies is anchored by observations of the Local Group. As the nearest spirals outside our Milky Way, Andromeda (M31) and Triangulum (M33) provide the richest possible targets for expanding our detailed understanding of stars, stellar evolution, the dusty ISM, feedback, dark matter physics, and small-scale cosmology, at spatial resolutions and sensitivities that are unavailable for any massive galaxies outside the Milky Way. This proposal leverages Roman's survey speed, high spatial resolution, and NIR coverage to deliver multi-epoch photometry for more than half a billion stars across the M31 and M33 system through: (1) wide-area two-filter, two-epoch imaging, covering the entirety of the stellar disks and inner halo regions; (2) panchromatic SEDs over the entirety of their HI disks; (3) deep fields anchoring the ancient star formation in both galaxies, and (4) ground-breaking studies of variability in M31's star-forming disk. When integrated into M31+M33's rich archival imaging and spectroscopy (spanning the X-ray to the radio), Roman data products will transform our understanding of their interconnected dynamical history, evolving disk structure, and stellar and ISM constituents. The maximum impact for first-epoch M31+M33 observations is Cycle 1, to yield the longest possible time baseline for proper motions and variability studies. These enable (1) full modeling of the dynamical accretion history of M31+M33 by bringing Gaia-like phase-space data to the other dominant galaxies in the Local Group, and (2) mapping the 3D disk structure, using pioneering individual distance measurements to RGB stars. This early, rich dataset will fundamentally shift the level at which we understand stars in the NIR and the galaxies most sensitive to departures from CDM, fueling subsequent generations of rigorous and transformative studies with Roman and JWST, from parsec to megaparsec scales.

Summary of Observations: This survey comprises 4 observational components, each of which employs separate dithering, cadence, depth, and exposure strategies. (1) Contiguous wide-area imaging observations covering 50.5 (5.6) sq. deg. in M31's (M33's) inner halo regions, with a 2-filter (F062, F129) first epoch and a 1-filter (F129) 2nd epoch at the end of the primary mission, with at least a 4 year (preferably 4.5 year) baseline between the two epochs (charged time 172.22 hours). (2) Additional imaging observations covering the HI disks of M31 and M33 (7.5 and 0.94 sq. deg.), with the 5 normal-width filters not included in the wide-area imaging, as well as additional sub-pixel dithers in F062 (charged time 60.11 hours). (3) A time-domain imaging component in F087 and F213, with low-cadence observations (4 epochs per year in each filter) covering the full star-forming disk (1.7 sq. deg.) of M31 over the full five years of the prime mission, as well as 1 high-cadence pointing (24 epochs per year in F087, 4 in F213) observed over 2 years (charged time 38.93 hours). (4) Two deep fields, one each in M31 and M33, reaching the oMSTO in F062 and F158 with epochs cadenced for RRLy characterization (charged time 39.43 hours).

For more details about the program, please see https://roman.ipac.caltech.edu/cycle1-approved-programs/2002.

For the status of the program's observations, visit https://www.stsci.edu/roman-program-info/program/?program=2002.