2025ApJ...986..145P

We present the variations in far-ultraviolet (FUV) and Hα star formation rates (SFR), SFR_UV and SFR_Hα, respectively, at subkiloparsec scales in 11 galaxies as part of the Deciphering the Interplay between the Interstellar Medium, Stars, and the Circumgalactic medium survey. Using archival GALEX FUV imagery and Hα+[N II] narrowband images obtained with the Vatican Advanced Technology Telescope, we detect a total of 1335 (FUV-selected) and 1474 (Hα-selected) regions of recent high-mass star formation, respectively. We find the Hα-to-FUV SFR ratios tend to be lower primarily for FUV-selected regions, where SFR_Hα generally underestimates the SFR by an average factor of 2-3, for SFR < 10^–4M_⊙ yr^–1. In contrast, the SFRs are generally observed to be consistent for Hα-selected regions. This discrepancy arises from morphological differences between the two indicators. Extended FUV morphologies and larger areas covered by FUV-only regions, along with decreasing overlap between FUV clumps and compact H II regions with R/R₂₅ suggest that stochastic sampling of the initial mass function may be more pronounced in the outer regions of galaxies. Our observed Hα-to-FUV SFR ratios are also consistent with stochastic star formation model predictions. However, using larger apertures that include diffuse FUV emission results in an offset of 1 dex between SFR_Hα and SFR_UV, suggesting that the observed low Hα-to-FUV SFR ratios in galaxies are likely caused by diffuse FUV emission, which can contribute ∼60%-90% to the total FUV flux.