Mass modelling of superthin galaxies: IC5249, UGC7321 and IC2233
  Superthin galaxies are low surface brightness disc galaxies, characterised by
optical discs with strikingly high values of planar-to-vertical axes ratios
($>$ 10), the physical origin and evolution of which continue to be a puzzle.
We present mass models for three superthin galaxies: IC5249, UGC7321 and
IC2233. We use high resolution rotation curves and gas surface density
distributions obtained from HI 21 cm radio-synthesis observations, in
combination with their two-dimensional structural surface brightness
decompositions at Spitzer 3.6 $\mu$m band, all of which were available in the
literature. We find that while models with the pseudo-isothermal (PIS) and the
Navarro-Frenk-White (NFW) dark matter density profiles fit the observed
rotation curves of IC5249 and UGC7321 equally well, those with the NFW profile
does not comply with the slowly-rising rotation curve of IC2233. Interestingly,
for all of our sample galaxies, the best-fitting mass models with a PIS dark
matter density profile indicate a {\it compact} dark matter halo i.e.,
$R_c/R_D$ $<$ 2 where $R_c$ is the core radius of the PIS dark matter halo, and
$R_D$ is the radial scale-length of the exponential stellar disc. The compact
dark matter halo may be fundamentally responsible for the superthin nature of
the stellar disc, and therefore our results may have important implications for
the formation and evolution models of superthin galaxies in the universe.
