Nancy Grace Roman Space Telescope Program 2001 (Cycle 1)

Principal Investigator: Haojing Yan (University of Missouri - Columbia)

Abstract: We propose the Roman eXtreme Deep Field (RXDF), an imaging survey to AB=30 (5sigma) over >140x larger area than the Hubble XDF full-depth area (ACS+WFC3/IR). The RXDF will cover the full Roman wavelength range with 7 bands, reaching AB=30 in RZYJH, AB=29 in F, and AB=28 in K, over a full-depth area of ~700 arcmin^2 embedded in a total area >1200 arcmin^2, and farexceeding the depths of the Core Community Surveys (CCS). The RXDF is within the Euclid Ultra Deep Field near the NEP, a strategic long-term field for generational space facilities, with a wealth of multi-wavelength data including extensive JWST coverage. The observations cover 3 epochs at a 1-year cadence, each epoch divided into 3 sub-epochs ~10 days apart, enabling time domain studies on time baselines over ~10 days to over ~2 years. Only the RXDF can address critical questions in reionization, large scale structure, SMBH growth, little red dots (LRDs), and high-z SNe; the volumes probed by HST+JWST are ~100x too small at these extreme depths, and even the deepest CCS tiers are too shallow. Specifically: (1) How does the full galaxy LF, from the bright to the faint end, evolve over z~6-14, crucial for constraining reionization models? (2) How does the UVLF scale with halo mass, what are the timescales for star formation burstiness, and what is the angular correlation function across the full LF, crucial in differentiating models for the excess of bright galaxies? (3) When do the first LSS overdensities appear, and how do they evolve over z~6-14? (4) How do the lowest luminosity AGN evolve from z>6 and build up their SMBHs, and how do they evolve with their hosts? (5) What is the nature of LRDs, and what mechanisms power their UV excess? (6) What are the progenitors of SLSNe, and what is their primary production mechanism? Furthermore, a wealth of additional science will be enabled by engaging the community with our rapidly released datasets, revolutionizing a wide range of science for a lasting legacy.

Summary of Observations: The RXDF program aims to reach the deepest imaging sensitivities at Roman's limit, across all seven broad bands sampling its full wavelength coverage. It will observe one WFI pointing using a bespoke 8-point mosaic dithering pattern to cover the detector gaps with minimal dilution of the exposure map, and with additional sub-pixel dithering to best reconstruct the Roman PSF that is undersampled. Our target field covers the premier JWST time-domain imaging field of the NEXUS program. The large Roman FOV is well matched to completely encompass the NEXUS field within a single pointing and to extend to a 2x larger flanking area, and we will reach 2.5 mag deeper over 0.8-1.7 um in the overlapping region and extend bluer to 0.5 um. While it is primarily for deep extragalactic science, RXDF will also be a multiwavelength, extremely deep time-domain imaging program by itself. The intention is for RXDF to span three epochs, each separated by ~1 year (APT Pass Plans 1, 2, and 3), with each epoch split into three sub-epochs separated by the maximal amount consistent with PA_V3 hold-time: ~10 days apart (APT Survey Steps 1-3, 4-6, and 7-9). The PA will be adjusted (allowed by +/- 15 deg) to ensure that all observations will be within the same footprint. The very low zodiacal background in the RXDF makes the program flexible to the Roman scheduling. If our starting time cannot be scheduled at the beginning of the mission, the last epoch will be pushed to the 3rd year, which is allowed by the Roman policy (confirmed by the Helpdesk). To minimize the impact of readout noise in the individual exposures, RXDF uses long-duration MA Table settings ranging from IM_600_16 up to IM_1000_16. The resulting 376 hours of science time are highly efficiently obtained in just 386 hours of total charged time, and reach 5-sigma limits unprecedented for such a wide area: 30 mag in RZYJH, 29 mag in F and 28 mag in K (all in AB system).

For more details about the program, please see https://roman.ipac.caltech.edu/cycle1-approved-programs/2001.

See also this presentation of the program made at the 2026 Roman Science Conference.

For the status of the program's observations, visit https://www.stsci.edu/roman-program-info/program/?program=2001.