2005AJ....130.1049S

We present sensitive and high-resolution 21 cm observations of the dwarf irregular (Im) galaxy DDO 43, in conjunction with optical broadband and narrowband images in U, B, V, and Hα. The observations are used to examine the relationship of its H I morphology and kinematics to past and present star formation. Optically, it is a small (R₂₅=990 pc), faint (M_Bof -14.0) dwarf Im with a slightly boxy shape. In H I, DDO 43 has an extended (R_HI_/RH_=2.8) gas envelope. There is a high-density ridge associated with the optical body of the galaxy containing several higher density knots and lower density holes. The largest hole is ∼850x530 pc. No expansion is detected, so it must be relatively old. The largest and potentially oldest (7-70 Myr) of the six identified star clusters is located at the western edge of the hole. Four of the other clusters are located near high-density peaks. There are several H II regions, most (but not all) of which are associated with peaks in the H I surface density. The overall star formation rate is average for its type. In many ways, DDO 43 is a very typical dwarf Im galaxy. Its H I morphology is consistent with a history of episodes of localized star formation that create holes and shells in the interstellar medium, some of which can overlap. These features are located within the area of solid-body rotation in the galaxy; the lack of shear in these small systems allows such structures to persist for long periods of time.