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From Environment to Assembly: Roman Spatially Resolved Stellar Mass and SFH Maps
Program ID 19049
Science Category Galaxies
Program Type Analysis
Category Medium
Principal Investigator Yongda Zhu
PI Institution University of Arizona, Steward Observatory
Co-Investigators
  • Jiani Ding (University of Arizona, Steward Observatory)
  • Minghao Yue (University of Arizona, Steward Observatory)
  • Zhiyuan Ji (University of Arizona, Steward Observatory)
  • Christopher Willmer (University of Arizona, Steward Observatory)
  • Yang Sun (University of Arizona, Steward Observatory)
  • Pierluigi Rinaldi (Space Telescope Science Institute / STScI)
  • Xiaohui Fan (University of Arizona, Steward Observatory)
  • Zheng Ma (University of Arizona, Steward Observatory)
  • Tristen Shields (University of Arizona, Steward Observatory)
  • Junyu Zhang (University of Arizona, Steward Observatory)
  • George Rieke (University of Arizona, Steward Observatory)
  • Marcia Rieke (University of Arizona, Steward Observatory)
  • Eiichi Egami (University of Arizona, Steward Observatory)
Abstract Galaxy environment trends are usually interpreted as halo-mass effects, but they may also encode halo assembly history through internal structure. We propose a Roman HLWAS-Deep analysis program to deliver spatially resolved stellar mass and star-formation history (SFH) maps for galaxies at z~1-3, spanning the rise, peak, and decline of cosmic star formation. Roman is uniquely required because it is the first mission that combines uniform near-IR imaging for resolved mapping with grism and photometric redshifts over a 19.2 deg^2 footprint (COSMOS+XMM-LSS), suppressing field-to-field variance and sampling rare overdense environments. Our flagship test is binary and quantitative: at fixed stellar mass and redshift, do outer assembly gradients (and their intrinsic scatter) vary with overdensity beyond mass-matched expectations? We will measure mass concentration, t50/t90 profiles and gradients, radial recent-growth indicators, and clumpiness of recent growth, and relate them to overdensity (and filament proximity where feasible). Survey-scale resolved nonparametric SFH fitting is made feasible by an ANN-accelerated emulator calibrated with JWST overlap regions via forward modeling. We will release public resolved map products, calibrated uncertainties, and environment-structure scaling relations that enable broad Roman-era legacy science.