  We model the shape and density profile of the dark matter halo of the low
surface brightness, superthin galaxy UGC 7321, using the observed rotation
curve and the HI scale height data as simultaneous constraints. We treat the
galaxy as a gravitationally coupled system of stars and gas, responding to the
gravitational potential of the dark matter halo. An isothermal halo of
spherical shape with a core density in the range of 0.039 - 0.057 M_sun/pc^3
and a core radius between 2.5 - 2.9 kpc, gives the best fit to the observations
for a range of realistic gas parameters assumed. We find that the best-fit core
radius is only slightly higher than the stellar disc scale length (2.1 kpc),
unlike the case of the high surface brightness galaxies where the halo core
radius is typically 3-4 times the disc scale length of the stars. Thus our
model shows that the dark matter halo dominates the dynamics of the low surface
brightness, superthin galaxy UGC 7321 at all radii, including the inner parts
of the galaxy.
