  We study the formation and evolution of dark galaxies using the IllustrisTNG
cosmological hydrodynamical simulation. We first identify dark galaxies with
stellar-to-total mass ratios, $M_* / M_{\text{tot}}$, smaller than $10^{-4}$,
which differ from luminous galaxies with $M_* / M_{\text{tot}} \geq 10^{-4}$.
We then select the galaxies with dark matter halo mass of $\sim 10^9 \,
h^{-1}$$\rm M_{\odot}$ for mass completeness, and compare their physical
properties with those of luminous galaxies. We find that at the present epoch
($z=0$), dark galaxies are predominantly located in void regions without
star-forming gas. We also find that dark galaxies tend to have larger sizes and
higher spin parameters than luminous galaxies. In the early universe, dark and
luminous galaxies show small differences in the distributions of spin and local
environment estimates, and the difference between the two samples becomes more
significant as they evolve. Our results suggest that dark galaxies tend to be
initially formed in less dense regions, and could not form stars because of
heating from cosmic reionization and of few interactions and mergers with other
systems containing stars unlike luminous galaxies. This study based on
numerical simulations can provide important hints for validating dark galaxy
candidates in observations and for constraining galaxy formation models.
