Herschel observations of Cen A: stellar heating of two extragalactic dust clouds

TL;DR

This study uses multi-wavelength observations to analyze two cold dust clouds near Centaurus A, revealing their properties and suggesting they are heated by the galaxy's jets, with new detections and detailed characterization.

Contribution

First multi-wavelength survey of Cen A's dust clouds providing detailed measurements of their temperature, mass, and gas-dust ratio, including the first sub-mm detection of the southern cloud.

Findings

Two cold dust clouds with temperatures around 12.6K and 15.1K.

Cloud masses are approximately 10^5.8 and 10^5.6 solar masses.

Gas-dust ratio is about 100, consistent with previous measurements.

Abstract

We present the first results of a multi-wavelength survey, incoporating Herschel-SPIRE, Spitzer, GALEX and ATCA observations, of a 1 deg x 1 deg field centred on Centaurus A. As well as detecting the inner lobes of the active galactic nucleus (AGN) jet and counterjet, we have found two clouds, bright at sub-mm wavelengths, ~15 kpc from the centre of Cen A that are co-aligned with the jets. Flux measurements at Herschel wavelengths have proved vital in constraining fits to the Spectral Energy Distributions (SEDs). The clouds are well fit by a single-temperature, modified blackbody spectrum (beta=2) indicating that we are looking at two cold dust clouds on the outskirts of Cen A. The temperature and masses of the clouds are: T_{north} = 12.6^{+1.1}_{-1.2} K, T_{south} = 15.1^{+1.7}_{-1.6} K; log(M_{north} / M_o) = 5.8^{+0.2}_{-0.2}, log(M_{south} / M_o) = 5.6^{+0.2}_{-0.2} and the gas-dust ratio for both clouds is ~100. The measured values for the northern dust cloud are consistent with previous measurements from ISO while the southern cloud is a new sub-mm detection. The two dust clouds are located at the termini of the partial HI ring that surrounds Cen A which is also where the gas column density peaks... abridged