  We investigated the kinematics and dynamics of gas structures on galaxy-cloud
scales in two spiral galaxies NGC5236 (M83) and NGC4321 (M100) using CO (2$-$1)
line. We utilized the FILFINDER algorithm on integrated intensity maps for the
identification of filaments in two galaxies. Clear fluctuations in velocity and
density were observed along these filaments, enabling the fitting of velocity
gradients around intensity peaks. The variations in velocity gradient across
different scales suggest a gradual and consistent increase in velocity gradient
from large to small scales, indicative of gravitational collapse, something
also revealed by the correlation between velocity dispersion and column density
of gas structures. Gas structures at different scales in the galaxy may be
organized into hierarchical systems through gravitational coupling. All the
features of gas kinematics on galaxy-cloud scale are very similar to that on
cloud-clump and clump-core scales studied in previous works. Thus, the
interstellar medium from galaxy to dense core scales presents
multi-scale/hierarchical hub-filament structures. Like dense core as the hub in
clump, clump as the hub in molecular cloud, now we verify that cloud or cloud
complex can be the hub in spiral galaxies. Although the scaling relations and
the measured velocity gradients support the gravitational collapse of gas
structures on galaxy-cloud scales, the collapse is much slower than a pure
free-fall gravitational collapse.
