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L. J. Hainline (Indiana University), J. Eder (Arecibo Observatory)
Previous 21-cm surveys of gas-rich dwarf galaxies such as Schneider et al. (1992) and Schneider et al. (1990) have revealed that many have single-peaked/Gaussian emission line profiles. However, it is controversial whether this profile shape is caused by truly random, turbulent motion of the gas within the galaxy as it suggests. One alternative explanation for the single-peaked shape is that the binning in the low resolution of the surveys masks any rotating component that may be present in the dwarf galaxies. To test this possibility, we present high-resolution (0.65 km/s) 21-cm line spectra of 15 gas-rich dwarf galaxies as an extension of Eder & Schombert (2000). All 15 galaxies showed single-peaked profiles in Eder & Schombert (2000) (at a velocity resolution of 8 km/s), but we find that 9 of the 15 galaxies have double-horned profiles when viewed at 0.65 km/s resolution. From 611-11, a galaxy which we have strong reason to believe has a face-on orientation, and which retained a single-peaked profile at the 0.65 km/s resolution, we estimate a typical velocity dispersion of 12.8 km/s. Upon calculation of HI and dynamical masses for the known rotators, we also see that the gas-rich dwarf galaxies have high mass-light ratios, as is typical for dwarf irregular galaxies. We conclude that most dwarf irregulars are dominated by ordered rotation and contain proportionally large quantities of dark matter as compared with other morphological types. In addition, based on our results, we believe that reliable estimates of dwarf irregular properties can be obtained by combining data from optical CCD images of the galaxies with single-dish 21-cm data.