Disentangling the circumnuclear environs of Centaurus A: Gaseous Spiral Arms in a Giant Elliptical Galaxy

TL;DR

This study reveals the presence of gaseous spiral arms in the elliptical galaxy Centaurus A, showing that spiral structures can form in ellipticals with sufficient cold gas, influencing star formation processes.

Contribution

First high-resolution observation of spiral arms in a giant elliptical galaxy, demonstrating their development in cold gas-rich environments.

Findings

Spiral arms extend from 200 pc to at least 1 kpc.

Arms are trailing with a pitch angle of 20 degrees.

Formation occurred within less than 10^8 years.

Abstract

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.