Nancy Grace Roman Space Telescope Program 2003 (Cycle 1)

Principal Investigator: Sangeeta Malhotra (NASA Goddard Space Flight Center)

Abstract: GRACE is an ultradeep grism survey of 1.5 deg^2 at 40 hours depth and 2.4 deg^2 at >10 hours depth, designed as a maximally efficient survey of LyA emitters(LAE) at z=7-10 to obtain definitive measurements of the epoch and pace of reionization. End-to-end simulations of the Roman grism show that 40 hour depth detects a line flux of 1e-17 ergs/cm^2/s at 5-sigma, reaching the characteristic luminosity L* of LAEs at z=7-9. The area yields excellent statistics for testing a range of models allowed by JWST constraints, and will increase the known sample of z > 7 LAEs by at least 10x. The same data set will yield a large, densely sampled volume at cosmic noon that contains many robust protoclusters placed in the cosmic web. The high resolution of Roman’s grism and proposed sensitivity optimizes detection and characterization of emission and absorption features to determine the star formation history (SFH), star formation rate (SFR), metallicity, and precise cartography in the cosmic web at z=1.5-3 - connecting >10 Mpc scales to 1 Kpc scales. GRACE answers questions like “how did galaxies influence their environment?” and “how did the environment shape galaxies?” in the first 3/4 of the universe’s history. We will deliver 290,000 emission-line redshifts to train photo-z’s for faint galaxies in the redshift desert. GRACE will also determine the faint end of the AGN luminosity function independent of color selection, fill gaps in the redshift evolution of little red dots, find and characterize Galactic M/L/T/Y dwarfs, and enable a kinematic lensing pilot. These transformative goals all REQUIRE a survey that is at least 6 times deeper than HLWAS-deep with higher spectral resolution than HLTDS-deep. GRACE bridges a large gap in depth and area between JWST and Roman/Euclid surveys, and therefore leaves a legacy above and beyond the proposed science. A deep, early survey with repeated observations of a single field will characterize systematics undetectable in shallower data.

Summary of Observations: GRACE is an ultradeep WFI grism spectroscopic survey to construct a sensitive 3D map of galaxies covering 1.5 deg^2. Located in the CDFS, the survey utilizes a circular six-pointing tiling pattern to ensure uniform field coverage regardless of the position angle (PA). The strategy employs 48 PAs (SP_500_16, BOXGAP9_1). Fully accounting for dithering and roll angle variation, GRACE will achieve an on-source integration time of t_exp > 40 hours over 1.5 deg^2 (and t_exp > 10 hours over a total area of 2.4 deg^2). This depth reaches a 5sigma emission-line sensitivity of 10^-17 erg/cm^2/s over the 1.5 deg^2 full-depth survey area. The grism observations are paired with imaging in the Y106, J129, H158, and F184 filters. Using 3 ks exposures per filter, we achieve 5sigma depths ranging from 27.9 to 27.1 mag. We have designed the 6-pointing grism observations to always be accompanied by the same 6-pointing imaging configuration, assuring matching PA distributions. Overall, we request 360 hrs for GRISM observations and 20 hrs for YJHF imaging, with APT overheads this totals to a 421 hr survey. We have specified a wide range of V3 position angles in our experimental design, to yield high quality grism spectra for all objects in the field while retaining considerable scheduling flexibility, and also to ensure a range of scheduling epochs that will support spectroscopic time-domain investigations. Additionally, our field (CDFS) does not conflict with Galactic bulge scheduling seasons. We can work with the science operations center to make further adjustments to our roll angle constraints if needed for increased scheduling flexibility.

For more details about the program, please see https://roman.ipac.caltech.edu/cycle1-approved-programs/2003.

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=2003.