The universal rotation curve of low surface brightness galaxies IV: the
  interrelation between dark and luminous matter
  We investigate the properties of the baryonic and the dark matter components
in low surface brightness (LSB) disc galaxies, with central surface brightness
in the B band $\mu_0 \geq 23 \, mag \, arcsec^{-2}$. The sample is composed by
72 objects, whose rotation curves show an orderly trend reflecting the idea of
a universal rotation curve (URC) similar to that found in the local high
surface brightness (HSB) spirals in previous works. This curve relies on the
mass modelling of the coadded rotation curves, involving the contribution from
an exponential stellar disc and a Burkert cored dark matter halo. We find that
the dark matter is dominant especially within the smallest and less luminous
LSB galaxies. Dark matter halos have a central surface density $\Sigma _0 \sim
100 \, M_{\odot} pc^{-2}$, similar to galaxies of different Hubble types and
luminosities. We find various scaling relations among the LSBs structural
properties which turn out to be similar but not identical to what has been
found in HSB spirals. In addition, the investigation of these objects calls for
the introduction of a new luminous parameter, the stellar compactness $C_*$
(analogously to a recent work by Karukes \& Salucci), alongside with the
optical radius and the optical velocity in order to reproduce the URC.
Furthermore, a mysterious entanglement between the properties of the luminous
and the dark matter emerges.
