THE NEUTRAL INTERSTELLAR-MEDIUM IN NEARBY DWARF GALAXIES .3. SAGITTARIUS DIG, LGS-3, AND PHOENIX

We present new VLA observations of the H I medium of the Local Group d warf galaxies Sag DIG, LGS 3, and Phoenix. Sag DIG is a gas-rich, blue dwarf irregular with some known recent star formation, whereas LGS 3 and Phoenix are gas-poor, red galaxies of intermediate irregular/spher oidal type with little recent star formation. These galaxies complete a small sample of Local Group and near-local Group irregular and ellip tical galaxies that have been mapped in H I and, where possible, in CO . We compare the properties and kinematics of the ISM in these differe nt galaxy types in order to gain some insights into the relationship b etween galaxy properties, star formation, and the ISM. Both Sag DIG an d LGS 3 have larger H I extents and higher H I fluxes than previously known, and in both cases the H I extends significantly farther than th e stellar component. Neither one shows convincing signs of rotation; b oth seem to derive a significant amount of their support against gravi ty from random motions in the gas. The dwarf galaxies of the sample su pport the idea that there are large variations in the dark/luminous ma ss ratio at a given luminosity. The high sensitivity and high spectral and spatial resolution of these observations also make it possible to study the physical properties of the H I medium. The H I in Sag DIG i s decomposed into broad (sigma = 10 km s(-1)) and narrow (sigma = 5 km s(-1)) components, with the broad component distributed throughout th e galaxy and the narrow component concentrated into a small number of prominent clumps of about 8 x 10(5) M.. It is argued that these H I co mponents are in fact cold and warm phases of the H I medium, as in Gal actic H I and in the dwarf irregular Leo A. LGS 3, on the other hand, shows little sign of such a two-phase H I structure. This new informat ion on the phase structure of the ISM in dwarf galaxies is consistent with theoretical models of the H I medium if the H I line width is gre ater than purely thermal widths. The lack of a cold H I phase may be a reason for the lack of recent star formation in LGS 3; we suggest tha t the presence of a cold H I phase serves as a better indicator of con ditions appropriate for star formation than measures of total H I cont ent.The Phoenix dwarf and LGS 3 have between interpreted as two dwarf spheroidal galaxies which are unusual in that they contain H I. The pr esence of H I in LGS 3 is interesting, then, in the context of models that remove the gas from dwarf spheroidals by a burst of star formatio n. Either LGS 3 has not had a burst of star formation sufficient to re move its gas, or gas removal was not complete. It is not clear whether the Phoenix dwarf has H I. The current observations show emission in the vicinity of the galaxy at + 55 km s(-1) and -23 km s(-1) (heliocen tric). However, none of this emission is coincident with the optical g alaxy. Until the stellar velocities in Phoenix are known, we cannot di stinguish whether any of the detected H I is actually associated with the galaxy or is perhaps associated with the Magellanic Stream.