  JWST/MIRI imaging of the nearby galaxies IC 5332, NGC 628, NGC 1365 and NGC
7496 from PHANGS reveals a richness of gas structures that in each case form a
quasi-regular network of interconnected filaments, shells and voids. We examine
whether this multi-scale network of structure is consistent with the
fragmentation of the gas disk through gravitational instability. We use
FilFinder to detect the web of filamentary features in each galaxy and
determine their characteristic radial and azimuthal spacings. These spacings
are then compared to estimates of the most Toomre-unstable length (a few kpc),
the turbulent Jeans length (a few hundred pc) and the disk scale height (tens
of pc) reconstructed using PHANGS-ALMA observations of the molecular gas as a
dynamical tracer. Our analysis of the four galaxies targeted in this work
indicates that Jeans-scale structure is pervasive. Future work will be
essential for determining how the structure observed in gas disks impacts not
only the rate and location of star formation but also how stellar feedback
interacts positively or negatively with the surrounding multi-phase gas
reservoir.
