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

Abstract

A detailed kinematic analysis of ionized gas in the nearby irregular galaxy NGC 4449 is presented. Observations are conducted in the spectral lines of Hα and [S II]. Our scanning Fabry-Perot interferometric observations are presented from both a global as well as a local perspective. We have analysed the global velocity field, the spatially extended diffuse gaseous component (DIG), 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 has a decreasing value in radial velocity along the optical bar from NE to SW, presenting an anticorrelation relative to the outer velocity field of the H I component. This is in agreement with previous studies. The DIG component that permeates the entire galaxy was analysed (up to a limiting surface brightness of ∼ 3.165×10 −5 ergs cm −2 s −1 steradian −1 ) in terms of its radial velocity field as well as its velocity dispersions. We find that the diffuse gas component presents peculiar kinematical 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 kinematical and dynamical influence is important on both global and local scales. The optical rotation curve of this nearby irregular shows that the NE sector rotates like a solid body (V rot ∼40 km s −1 at R =2 kpc). In contrast, for the SW 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.

Magnetic fields in Local Group dwarf irregulars

“…As some galaxies show evidence of gravitational interactions, these esimates are only approximate. For example, for strongly interacting NGC 4449 Valdez-Gutiérrez et al (2002) estimate that the systematic rotation on the receding side of the galaxy is about velocity for dwarfs is about 30 km s −1 at a radius r = 2 kpc. For differential rotation and flat rotation curve, this corresponds to a shear of 15 km s −1 kpc −1 .…”

GHASP: an Hα kinematic survey of spiral and irregular galaxies – III. 15 new velocity fields and study of 46 rotation curves

“…16 the radial position–velocity diagram. Nevertheless, we checked the consistency of our data with those of Valdez‐Gutierrez et al (2002), by tracing the rotation curve with their kinematical parameters applied on our GHASP data. The agreement is good but we go further out because of the larger extension of our velocity field, and find a strong decrease of the curve on the redshifted side beyond 100 arcsec, together with a strong increase on the blueshifted side.…”

STARBURSTS IN THE LOCAL UNIVERSE: NEWHUBBLE SPACE TELESCOPEADVANCED CAMERA FOR SURVEYS OBSERVATIONS OF THE IRREGULAR GALAXY NGC 4449

“…The ionized gas shows a very turbulent morphology with filaments, shells, and bubbles which extend for several kpc (Hunter & Gallaghger 1990). The kinematics of the H ii regions within the galaxy is chaotic, again suggesting the possibility of a collision or merger (e.g., Valdez-Gutiérrez et al 2002). Some 40% of the X-ray emission in NGC 4449 comes from hot gas with a complex morphology similar to that observed in Hα, implying an expanding super-bubble with a velocity of ∼220 km s −1 (Summers et al 2003).…”