Ultra-diffuse Galaxies as Extreme Star-forming Environments. I. Mapping Star Formation in H i-rich UDGs

Abstract Ultra-diffuse galaxies (UDGs) are both extreme products of galaxy evolution and environments in which to test our understanding star formation. In this work, we contrast the spatially resolved formation activity a sample 22 H i -selected UDGs 35 low-mass from NASA Sloan Atlas (NSA) catalog within 120 Mpc. We employ new joint spectral energy distribution fitting method compute rate stellar mass surface density maps that leverage high spatial resolution optical imaging data Hyper Suprime-Cam Subaru Strategic Program UV coverage Galaxy Evolution Explorer, along with radial profiles estimated subset have maps. find low efficiencies as function their atomic gas down scales 500 pc. additionally mass-weighted sizes UDG unremarkable when considered mass—their comparable NSA dwarfs at fixed mass. This is natural result picture where forming stars normally, but efficiencies. compare results predictions contemporary models formation, particular observations difficult reproduce undergo expansion due vigorous feedback should bursty be required z = 0.