Ultra-diffuse Galaxies as Extreme Star-forming Environments. II. Star Formation and Pressure Balance in H i-rich UDGs

In addition to occupying the extreme, diffuse tail of dwarf galaxy population, Ultra-Diffuse Galaxies (UDGs) are themselves a key laboratory in which study star formation extreme low-density environments. second paper this series, we compare spatially resolved activity 22 HI-selected UDGs and 21 "normal" galaxies within 120 Mpc predictions pressure-regulated, feedback-modulated (PRFM) theory formation. To do so, employ joint SED fitting method that allows us estimate rate stellar mass surface density from UV-optical imaging. We find PRFM framework extends successfully UDG regime - although our sample show unusually low densities given their HI content, efficiency can be naturally explained by structure UDGs. fact, when cast framework, relationship between midplane pressure is good agreement not only with reference sample, but also measurements more massive galaxies. Our results suggest despite efficiencies, HI-rich need forming stars an exotic manner. likely H$_2$-poor compared even overall population.