  We explore the nature of low surface brightness galaxies (LSBGs) in the
hydrodynamic cosmological simulation TNG100 of the IllustrisTNG project,
selecting a sample of LSBGs ($r$-band effective surface brightness $\mu_r >
22.0$ mag arcsec$^{-2}$) at $z=0$ over a wide range of stellar masses
($M_{\ast} = 10^{9}$-$10^{12}$ M$_\odot$). We find LSBGs of all stellar masses,
although they are particularly prevalent at $M_{\ast} < 10^{10}$ M$_\odot$. We
show that the specific star formation rates of LSBGs are not significantly
different from those of high surface brightness galaxies (HSBGs) but, as a
population, LSBGs are systematically less massive and more extended than HSBGs,
and tend to display late-type morphologies according to a kinematic criterion.
At fixed stellar mass, we find that haloes hosting LSBGs are systematically
more massive and have a higher baryonic fraction than those hosting HSBGs. We
find that LSBGs have higher stellar specific angular momentum and halo spin
parameter values compared to HSBGs, as suggested by previous works. We track
the evolution of these quantities back in time, finding that the spin
parameters of the haloes hosting LSBGs and HSBGs exhibit a clear bifurcation at
$z \sim 2$, which causes a similar separation in the evolutionary tracks of
other properties such as galactic angular momentum and effective radius,
ultimately resulting in the values observed at $z =$ 0. The higher values of
specific stellar angular momentum and halo spin in LSBGs seem to be responsible
for their extended nature, preventing material from collapsing into the central
regions of the galaxies, also causing LSBGs to host less massive black holes at
their centres.
