WISDOM Project -- X. The morphology of the molecular ISM in galaxy
  centres and its dependence on galaxy structure
  We use high-resolution maps of the molecular interstellar medium (ISM) in the
centres of eighty-six nearby galaxies from the millimetre-Wave Interferometric
Survey of Dark Object Masses (WISDOM) and Physics at High Angular Resolution in
Nearby GalaxieS (PHANGS) surveys to investigate the physical mechanisms setting
the morphology of the ISM at molecular cloud scales. We show that early-type
galaxies tend to have smooth, regular molecular gas morphologies, while the ISM
in spiral galaxy bulges is much more asymmetric and clumpy when observed at the
same spatial scales. We quantify these differences using non-parametric
morphology measures (Asymmetry, Smoothness and Gini), and compare these
measurements with those extracted from idealised galaxy simulations. We show
that the morphology of the molecular ISM changes systematically as a function
of various large-scale galaxy parameters, including galaxy morphological type,
stellar mass, stellar velocity dispersion, effective stellar mass surface
density, molecular gas surface density, star formation efficiency and the
presence of a bar. We perform a statistical analysis to determine which of
these correlated parameters best predicts the morphology of the ISM. We find
the effective stellar mass surface (or volume) density to be the strongest
predictor of the morphology of the molecular gas, while star formation and bars
maybe be important secondary drivers. We find that gas self-gravity is not the
dominant process shaping the morphology of the molecular gas in galaxy centres.
Instead effects caused by the depth of the potential well such as shear,
suppression of stellar spiral density waves and/or inflow affect the ability of
the gas to fragment.
