Why are some galaxy disks extremely thin?
  Some low surface brightness galaxies are known to have extremely thin stellar
disks with the vertical to planar axes ratio 0.1 or less, often referred to as
superthin disks. Although their existence is known for over three decades, the
physical origin for the thin distribution is not understood. We model the
stellar thickness for a two-component (gravitationally coupled stars and gas)
disk embedded in a dark matter halo, for a superthin galaxy UGC 7321 which has
a dense, compact halo, and compare with a typical dwarf galaxy HoII which has a
non-compact halo. We show that while the presence of gas does constrain the
disk thickness, it is the compact dark matter halo which plays the decisive
role in determining the superthin disk distribution in low-mass disks. Thus the
compact dark matter halo significantly affects the disk structure and this
could be important for the early evolution of galaxies.
