  A key feature of a large population of low-mass, late-type disk galaxies are
star-forming disks with exponential light distributions. They are typically
also associated with thin and flat morphologies, blue colors, and dynamically
cold stars moving along circular orbits within co-planar thin gas disks.
However, the latter features do not necessarily always imply the former, in
fact, a variety of different kinematic configurations do exist. In this work,
we use the cosmological hydrodynamical IllustrisTNG Simulation to study the
nature and origin of dynamically hot, sometimes even counter-rotating,
star-forming disk galaxies in the lower stellar mass range (between $5\times
10^9\,\mathrm{M_{\odot}}$ and $2\times 10^{10}\,\mathrm{M_{\odot}}$). We find
that being dynamically hot arises in most cases as an induced transient state,
for example due to galaxy interactions and merger activities, rather than as an
age-dependent evolutionary phase of star-forming disk galaxies. The dynamically
hot but still actively star-forming disks show a common feature of hosting
kinematically misaligned gas and stellar disks, and centrally concentrated
on-going star formation. The former is often accompanied by disturbed gas
morphologies, while the latter is reflected in low gas and stellar spins in
comparison to their dynamically cold, normal disk counterparts. Interestingly,
observed galaxies from MaNGA with kinematic misalignment between gas and stars
show remarkably similar general properties as the IllustrisTNG galaxies, and
therefore are plausible real-world counterparts. In turn, this allows us to
make predictions for the stellar orbits and gas properties of these misaligned
galaxies.
