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Abstract We present the variations in far-ultraviolet (FUV) and Hαstar formation rates (SFR), SFR_UVand 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+[Nii] 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_Hαgenerally 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 Hiiregions withR/R₂₅suggest 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_Hαand 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. 

Abstract We explore the growth of the stellar disks in 14 nearby spiral galaxies as part of the Deciphering the Interplay between the Interstellar medium, Stars, and the Circumgalactic medium (DIISC) survey. We study the radial distribution of specific star formation rates (sSFRs) and investigate the ratio of the difference in the outer and inner sSFRs (Δ_sSFR= sSFR_out– sSFR_in) of the disk and the total sSFR, Δ_sSFR/sSFR, to quantify disk growth. We find Δ_sSFR/sSFR and the Higas fraction to show a mild correlation of Spearman’sρ= 0.30, indicating that star formation and disk growth are likely to proceed outward in galactic disks with high Higas fractions. The Higas fractions and Δ_sSFR/sSFR of the galaxies also increase with the distance to the nearestL_⋆neighbor, suggesting that galaxies are likely to sustain the cold gas in their interstellar medium and exhibit inside-out growth in isolated environments. However, the Hicontent in their circumgalactic medium (CGM), probed by the Lyαequivalent width (W_Lyα) excess, is observed to be suppressed in isolated environments, as is apparent from the strong anticorrelation between theW_Lyαexcess and the distance to the fifth nearestL_⋆neighbor (Spearman’sρ= −0.62). As expected,W_Lyαis also found to be suppressed in cluster galaxies. We find no relation between theW_Lyαexcess of the detected CGM absorber and Δ_sSFR/sSFR, implying that the enhancement and suppression of the circumgalactic Higas does not affect the direction in which star formation proceeds in a galactic disk or vice versa.