2003AJ....125.2455U

We have used the Very Large Array to image the isolated ``superthin'' galaxy UGC 7321 in the H I line with a spatial resolution of 16" and a spectral resolution of 24 kHz (5.2 km.s<sup>–1</sup>). We have reached a sensitivity of (0.36-0.40) mJy beam<sup>–1</sup> channel<sup>–1</sup>, which correspond to a column density of (8-9)x10<sup>18</sup> atoms cm<sup>–2</sup> (1 σ). UGC 7321 has a gas-rich disk, with M<sub>HI</sub>=(1.06±0.01)x10<sup>9</sup> d<sup>2</sup><sub>10</sub>M<sub>☉</sub> and M<sub>HI</sub>/L<sub>B</sub>=1.0 (d<sub>10</sub> is the distance to UGC 7321 in units of 10 Mpc, the value adopted in this paper), and no detectable radio continuum emission (F<sub>CONT</sub>=0.41±0.25 mJy). The global H I distribution of UGC 7321 is rather symmetric and extends to ∼1.5 times the optical radius (D<sub>HI</sub>=8'.65±0'.15 at n<sub>HI</sub>=3x10<sup>19</sup> atoms cm<sup>–2</sup>). An ``integral sign'' warp is observed in the H I disk, commencing near the edge of the stellar distribution and twisting back toward the equatorial plane in the outermost regions. In addition, the position-velocity diagram suggests the presence of a bar or inner arm within ∼40" from the center. The rotation curve of UGC 7321 is slowly rising; it reaches its asymptotic velocity of ∼110 km.s^–1 at ∼2'.5 from the center (about 0.9 optical radii) and declines near the edge of the H I disk. The ratio of the inferred dynamical mass to the mass in gas and stars is ∼12d^–1₁₀, implying that UGC 7321 is a highly dark-matter-dominated galaxy.