Flaring stellar disk in the low surface brightness galaxy UGC 7321
  We theoretically study the vertical structure of the edge-on low surface
brightness (LSB) galaxy UGC 7321. This is one of the few well-observed LSBs. We
modeled it as a gravitationally coupled disk system of stars and atomic
hydrogen gas in the potential of the dark matter halo and treated the realistic
case where the rotation velocity varies with radius. We used a dense and
compact halo as implied by the observed rotation curve in this model. We
calculated the thickness of stellar and HI disks in terms of the half-width at
half-maximum of the vertical density distribution in a region of R=0 to 12 kpc
using input parameters constrained by observations. We obtain a mildly
increasing disk thickness up to R=6 kpc, in a good agreement with the observed
trend, and predict a strong flaring beyond this. To obtain this trend, the
stellar velocity dispersion has to fall exponentially at a rate of 3.2R_D ,
while the standard value of 2R_D gives a decreasing thickness with radius.
Interestingly, both stellar and HI disks show flaring in the outer disk region
although they are dynamically dominated by the dark matter halo from the very
inner radii. The resulting vertical stellar density distribution cannot be fit
by a single sech^2/n function, in agreement with observations, which show wings
at larger distances above the mid-plane. Invoking a double-disk model to
explain the vertical structure of LSBs as done in the literature may therefore
not be necessary.
