The Fourcade-Figueroa galaxy: a clearly disrupted superthin edge-on
  galaxy
  Studies of the stellar and the HI gas kinematics in dwarf and Low Surface
Brightness (LSB) galaxies are essential for deriving constraints on their dark
matter distribution. Moreover, a key component to unveil in the evolution of
LSBs is why some of them can be classified as superthin. We aim to investigate
the nature of the proto-typical superthin galaxy Fourcade-Figueroa (FF), to
understand the role played by the dark matter halo in forming its superthin
shape and to investigate the mechanism that explains the observed disruption in
the approaching side of the galaxy. Combining new HI 21-cm observations
obtained with the Giant Metrewave Radio Telescope with archival data from the
Australia Telescope Compact Array we were able to obtain sensitive HI
observations of the FF galaxy. These data were modeled with a 3D tilted ring
model in order to derive the rotation curve and surface brightness density of
the neutral hydrogen. We subsequently used this model, combined with a stellar
profile from the literature, to derive the radial distribution of the dark
matter in the FF galaxy. For the FF galaxy the Navarro-Frenk-White dark matter
distribution provides the best fit to the observed rotation curve. However, the
differences with a pseudo-isothermal halo are small. Both models indicate that
the core of the dark matter halo is compact. Even though the FF galaxy
classifies as superthin, the gas thickness about the galactic centre exhibits a
steep flaring of the gas which is in agreement with the edge of the stellar
disk. As suggested previously in the literature, the compact dark matter halo
might be the main responsible for the superthin structure of the stellar disk
in FF. This idea is strengthened through the detection of the mentioned
disruption; the fact that the galaxy is disturbed also seems to support the
idea that it is not isolation that cause its superthin structure.
