Relationships between the Stellar, Gaseous, and Star Formation Disks in
  LITTLE THINGS Dwarf Irregular Galaxies: Indirect Evidence for Substantial
  Fractions of Dark Molecular Gas
  The stellar, gaseous and young stellar disks in the LITTLE THINGS sample of
nearby dIrrs are fitted with functions to search for correlations between the
parameters. We find that the HI radial profiles are generally flatter in the
center and fall faster in the outer regions than the V-band profiles, while
young stars are more centrally concentrated, especially if the HI is more
centrally flat. This pattern suggests that the HI is turning into molecules in
the center and the molecular clouds are forming stars and FUV. A model that
assumes the molecular surface density is proportional to the total gas surface
density to a power of 1.5 or 2, in analogy with the Kennicutt-Schmidt relation,
reproduces the relationship between the ratio of the visible to the HI scale
length and the HI Sersic index. The molecular fraction is estimated as a
function of radius for each galaxy by converting the FUV to a molecular surface
density using conventional calibrations. The average molecular fraction inside
3R_D is 23+/-17%. However, the break in the stellar surface brightness profile
has no unified tracer related to star formation.
