DIISC-III. Signatures of Stellar Disk Growth in Nearby Galaxies

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 H i gas fraction to show a mild correlation of Spearman’s ρ = 0.30, indicating that star formation and disk growth are likely to proceed outward in galactic disks with high H i gas fractions. The H i gas fractions and Δ_sSFR/sSFR of the galaxies also increase with the distance to the nearest L _⋆ 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 H i content in their circumgalactic medium (CGM), probed by the Lyα equivalent width (W _Lyα) excess, is observed to be suppressed in isolated environments, as is apparent from the strong anticorrelation between the W _Lyα excess and the distance to the fifth nearest L _⋆ neighbor (Spearman’s ρ = −0.62). As expected, W _Lyα is also found to be suppressed in cluster galaxies. We find no relation between the W _Lyα excess of the detected CGM absorber and Δ_sSFR/sSFR, implying that the enhancement and suppression of the circumgalactic H i gas does not affect the direction in which star formation proceeds in a galactic disk or vice versa.