High Resolution HI VLA Observations of the Barred Spiral Galaxies NGC 1398 and NGC 1784

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Session 6 -- Normal Galaxies: Structure and Dynamics
Display presentation, Monday, 9:20-6:30, Pauley Room

[6.16] High Resolution HI VLA Observations of the Barred Spiral Galaxies NGC 1398 and NGC 1784

E.M. Moore (Boston University), S.T. Gottesman (University of Florida)

Observations of the atomic hydrogen of the barred spiral galaxies NGC 1398 and NGC 1784 have been made at the C/D and B/C array configurations of the Very Large Array. After calibration, the datasets from the two configurations were combined to give a spatial resolution of 20-25\char'175. The velocity resolution is 21 km s$^{-1}$. Moment maps of the HI surface density and radial velocity will be presented along with rotation curves and HI radial density profiles. The radio data is compared with available surface photometry.

NGC 1398 is a SBab(r)I galaxy. It is a large (6.6\char'23), strikingly symmetric galaxy with a bright optical bar and an inner ring. In addition, thin, well defined, nearly circular spiral arms start tangent to the ring and extend out close to a full revolution, accented by bright, discrete regions. Radio observations reveal a large central depletion in the HI gas, elongated perpendicular to the optical bar. The inner ring structure found in the optical photometry is absent at this level of resolution in the radio. By convolving down the data, an upper limit on the central low density region was set at 6.4 $\times$ 10$^{19}$ cm$^2$. The HI integrated flux is 51 Jy km s$^{-1}$, corresponding to a total atomic hydrogen mass of 3.15 $\times$ 10$^9$M$_\odot$. The velocity field of NGC 1398 indicates that the motion of the galaxy appears to be regular with little noncircular motion.

NGC 1784 is a SBc(rs)I-II system with a bright, narrow bar and an inner ring. Further out there are several faint, knotty arms. The arms are not clean with low level spurs and feathers seem throughout the outer disk. Radio observations show that the HI gas peaks in a narrow, high density annulus. More interesting is the evidence of a severe warp in the gas disk and noncircular motion which appears in several velocity channels. The integrated flux is 60.1 Jy km s$^{-1}$, corresponding to a mass of 1.17 $\times 10^{10}M_\odot$.

This work was supported in part by NSF grants AST-9022827 and AST-9116525.

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