Section 4.4.3 Starburst Galaxy: NGC 5236/Messier 83:
An SBc(s)II galaxy, NGC 5236 or Messier 83, at an inclination of 24° that displays a grand design two-armed structure. At a distance of 4.7 Mpc it is one of the finest spirals in the sky and is sometimes referred to as the 'Southern Pinwheel'. It's starburst nature may have been triggered by an earlier interaction with its companion galaxy, NGC 5253.
A secondary classification of I? is adopted.
Dong et al. (2008) present Spitzer imaging at 3.6, 4.5, 5.8 and 8.0 µm for two fields 19.5 kpc from the center of the galaxy. Combined with GALEX and HI data, star clusters in the outskirts of the galaxy are age dated between 1 Myr and 1 Gyr, with a mean age of 180 Myr. The low density stars (and gas) still seem to have formed following the laws favored in more high density regions.
Muraoka et al. (2009) present CO (J=32) emission maps using the Atacama Submillimeter Telescope Experiment. An effective resolution of 25" over an 8' x 8' region allows detection of fifty-four Giant Molecular-cloud Associations (GMAs) in arm and inter-arm areas. The inter-arm GMAs could be affected by shear motion - in which unvirialised GMAs with large velocity dispersions have star formation suppressed.
Tilanus and Allen (1993) compare VLA HI and optical H observations and do not detect large (60-90 km s-1) streaming velocities, suggesting that the galaxy possesses a small density wave. Tilanus and Allen (1993) also suggest that the HI ring and large extent of HI may be caused by a previous interaction.