SEAMLESS Survey: A Closer Look at Seven Local Volume Dwarf Galaxies in Diverse Environments
We present Hubble Space Telescope (HST) imaging of six Local Volume dwarf galaxies identified by the SEAMLESS survey - Cetus B, Hydrus A, Ursa Major C, Hydra B, Grapes, and M83-dw14 - along with Centaurus C (Cen C), discovered serendipitously in the M83-dw14 field. We report the discovery of M83-dw14 and Cen C for the first time. Our HST imaging resolves each system into individual stars, enabling measurements of tip of the red giant branch (TRGB) distances (3.6-6.5 Mpc), structural parameters, and star formation histories (SFHs). We complement these data with new HI observations from the Very Large Array for Ursa Major C, Hydra B, and M83-dw14 (also covering Cen C), and from the Green Bank Telescope for Grapes, together with existing HI limits for Cetus B and Hydrus A. With accurate TRGB distances, we place each target in its environmental context, ranging from a confirmed satellite (M83-dw14) to isolated systems (Hydrus A, Hydra B, Grapes, Cen C). Cen C ($M_V=-7.96$) is among the faintest isolated dwarfs known. It matches the size and luminosity of Leo T, the lowest mass gas-rich galaxy currently known, yet unlike Leo T it shows neither detected HI ($\log(M_{\rm HI}/M_{\odot})<5.3$) nor recent star formation. Ursa Major C shows strongly asymmetric, spatially offset HI, suggesting that feedback may efficiently displace gas in such low-mass systems. Overall, our sample exhibits a broad range of SFHs and quenching states that does not track simply with present-day environment. This diversity is consistent with recent evidence that similarly varied SFHs occur even among isolated low-mass dwarfs, pointing to the important roles of inhomogeneous reionization, stochastic mass assembly, and internal feedback alongside environmental effects.