Disentangling the circumnuclear environs of centaurus A: Gaseous spiral arms in a giant elliptical galaxy

Abstract

We report the existence of spiral arms in the recently formed gaseous and dusty disk of the closest giant elliptical, NGC5128 (Centaurus A), using high-resolution 12CO(2-1) observations of the central 3′ (3 kpc) obtained with the Submillimeter Array. 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 44 × 19 (80pc × 40pc). The spiral arms extend from the circumnuclear gas at a radius of 200pc to at least 1 kpc. The general properties of the arms are similar to those in spiral galaxies: they are trailing, the width is ∼500± 200pc, and the pitch angle is 20°. From independent estimates of the time when the H I-rich galaxy merger occurred, we infer that the formation of spiral arms happened on a timescale of less than 108 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. © © 2012. The American Astronomical Society. All rights reserved.