Unveiling the Kinematics and Dynamics of Ionized Gas in the Nearby Irregular Galaxy NGC 4449

A detailed kinematic analysis of ionized gas in the nearby irregular galaxy NGC 4449 is presented. Observations were conducted in the spectral lines of Hα and [S II]. Our scanning Fabry-Perot interferometric observations are presented from both a global and a local perspective. We have analyzed the global velocity field, the spatially extended diffuse gaseous component, and the H II region populations and, furthermore, have determined the rotation curve based on the heliocentric radial velocities of the global Hα spatial distribution. Our results for NGC 4449 show that the optical velocity field decreases in radial velocity along the optical bar from northeast to southwest, presenting an anticorrelation relative to the outer velocity field of the H I component. This is in agreement with previous studies. The diffuse gaseous component that permeates the entire galaxy is analyzed (up to a limiting surface brightness of ∼3.165 × 10-5 ergs cm-2 s-1 sr-1) in terms of its radial velocity field, as well as its velocity dispersions. We find that the diffuse gas component presents peculiar kinematic features, such as abrupt velocity gradients and highly supersonic velocity dispersions (σ ∼ 4 times the values of the nearest H II regions), but that its kinematic and dynamical influence is important on both global and local scales. The optical rotation curve of this nearby irregular galaxy shows that the northeast sector rotates like a solid body (vrot ∼ 40 km s-1 at R = 2 kpc). In contrast, for the southwest side our results are not conclusive; the behavior of the gas at those locations is chaotic. We conclude that the origin of such complex kinematics and dynamics is undoubtedly related to the aftermath of an interaction experienced by this galaxy in the past.