A new optical and H I study of the nearby galaxy NGC 1313

We describe the results of a λ21 cm study of the morphology and dynamics of the nearby, southern, barred spiral galaxy NGC 1313 made with the Australia Telescope Compact Array (ATCA). The galaxy has a high H I surface density (the azimuthal average peaking at ∼13 script M sign_⊙ pc^-2) and a very extensive (24 kpc) disk, containing outer H I arms with no stellar counterparts even on very deep UK Schmidt and Anglo-Australian Telescope (AAT) images. Kinematically, NGC 1313 is a well-behaved rotating disk system inclined at 48°, and we discount the suggestions of previous authors that it is a multiple system. Significant kinematic distortions are brought about by the presence of a number of H I "supershells," the largest of which spans 20% of the total H I diameter of the galaxy. The presence of these supershells is responsible for previous erroneous suggestions that NGC 1313 is an asymmetric rotator. For the largest supershell, the required power is ∼3×10³⁹ erg s^-1 over its dynamical age of 10⁷ yr. This is one of the largest supershells so far discovered. Its existence implies that the neutral gas disk of NGC 1313 has a scale height of order 1 kpc to prevent the bubble blowing out of the disk. The kinematic signature of an expanding bubble and a rotating disk can be used to show that the spiral arms of NGC 1313 are trailing.