  We study two dimensional Fabry-Perot interferometric observations of the
nearby face-on late-type spiral galaxy, NGC 628, in order to analyse the
ionized gas component of the interstellar medium. Covering the galaxy out to a
radius larger than 12 kpc, and with a spatial sampling of 1.6 arcsec, we
investigate the large-scale dynamics as well as feedback from individual HII
regions into their surrounding medium. We study the role of gravitational
perturbations along with that of external triggers which can disturb the
kinematics and morphology of NGC 628. We verify the presence of an inner
rapidly rotating disc-like component in NGC 628, which we interpret as caused
by slow secular evolution of the large-scale spiral arms and oval structure. In
combination with auxiliary data, we find indication for that gas is falling in
from the outer parts towards the central regions, where a nuclear ring has
formed at the location of the inner Lindblad resonance radius of an m=2
perturbation which could help build a pseudo-bulge in NGC 628. Moreover, we
calculate radial profiles of the emission-line velocity dispersion which we use
to study the role of feedback from individual HII regions. The mean velocity
dispersion for the ionized gas (even when excluding pixels belonging to
individual HII regions) is almost constant out to 12 kpc, although it varies
from 14 to 20 km/s, with a steady decline in the outer parts. The current paper
demonstrates a number of tools that we have developed for building a solid
frame work for studying the evolution of structure in spiral galaxies using two
dimensional kinematic observations.

Astrophysics