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C.M Mendelowitz, L.D Matthews, J.E Hibbard (National Radio Astronomy Observatory), E.M Wilcots (University of Wisconsin- Madison)
Superthin galaxies are examples of low surface brightness (LSB) spiral galaxies seen edge-on. These galaxies are gas-rich and exhibit diffuse, highly flattened stellar disks with little or no bulge component and extremely small stellar scale heights. One interesting property of many superthin galaxies is that they exhibit rotation curves that appear to rise slowly throughout their stellar disks. However, some recent work has suggested that observational effects (including projection, internal extinction, and beam smearing) may account for some or all of these slowly rising rotation curves. To explore this question, we utilize new HI 21-cm line data from the Very Large Array (VLA) and optical R- and B- band data from the WIYN telescope for the nearby superthin galaxy UGC~711. We derive an HI rotation curve, as well as global optical and HI properties for this galaxy, and show that it is consistent with an LSB galaxy seen edge-on. We also compare and contrast its properties with the superthin UGC~7321, as recently studied by Matthews et al. (1999, AJ, 118, 2751). Even after taking into account beam smearing and projection effects, we find the rotation curve of UGC~711 continues to rise slowly to the last measured point. Using the observed light and HI profiles, we decompose the rotation curve into the contributions from stars, gas, and dark matter. We find that the slowly rising velocity curve requires a significant dark matter contribution at all radii.