Disentangling the circumnuclear environs of Centaurus A: Gaseous Spiral
  Arms in a Giant Elliptical Galaxy
  We report the existence of spiral arms in the recently formed gaseous and
dusty disk of the closest giant elliptical, NGC 5128 (Centaurus A), using high
resolution 12CO(2-1) observations of the central 3 arcmin (3 kpc) obtained with
the Submillimeter Array (SMA). This provides evidence that spiral-like features
can develop within ellipticals if enough cold gas exists. We elucidate the
distribution and kinematics of the molecular gas in this region with a
resolution of 4.4 x 1.9 (80 pc x 40 pc). The spiral arms extend from the
circumnuclear gas at a radius of 200 pc to at least 1 kiloparsec. The general
properties of the arms are similar to those in spiral galaxies: they are
trailing, the width is \sim 500 \pm 200 pc, and the pitch angle is 20 degrees.
From independent estimates of the time when the HI-rich galaxy merger occurred,
we infer that the formation of spiral arms happened on a time scale of less
than \sim10^8 yr. The formation of spiral arms increases the gas density and
thus the star formation efficiency in the early stages of the formation of a
disk.
