The gas-to-dust mass ratio of Centaurus A as seen by Herschel

TL;DR

This study measures the gas-to-dust mass ratio in Centaurus A using Herschel observations, revealing a central increase potentially caused by dust sputtering or jet activity, and provides detailed dust and gas mass estimates.

Contribution

First detailed Herschel-based analysis of Centaurus A's dust and gas distribution, highlighting a central increase in the gas-to-dust ratio and exploring possible physical causes.

Findings

Total dust mass of approximately 1.59 x 10^7 solar masses

Average gas-to-dust ratio of 103, rising to 275 near the center

Dust temperatures decreasing from 30 K to 20 K with radius

Abstract

We present photometry of the nearby galaxy NGC 5128 (Centaurus A) observed with the PACS and SPIRE instruments on board the Herschel Space Observatory, at 70, 160, 250, 350 and 500 {\mu}m, as well as new CO J = 3-2 observations taken with the HARP-B instrument on the JCMT. Using a single component modified blackbody, we model the dust spectral energy distribution within the disk of the galaxy using all five Herschel wavebands, and find dust temperatures of ~30 K towards the centre of the disk and a smoothly decreasing trend to ~20 K with increasing radius. We find a total dust mass of (1.59 \pm 0.05) \times 10^7 M\odot, and a total gas mass of (2.7 \pm 0.2) \times 10^9 M\odot. The average gas-to-dust mass ratio is 103 \pm 8 but we find an interesting increase in this ratio to approximately 275 toward the centre of Cen A. We discuss several possible physical processes that may be causing this effect, including dust sputtering, jet entrainment and systematic variables such as the XCO factor. Dust sputtering by X-rays originating in the AGN or the removal of dust by the jets are our most favoured explanations.