Spatially Resolved Imaging at 350um of Cold Dust in Nearby Elliptical Galaxies

TL;DR

This study presents the first resolved submillimeter imaging of cold dust in nearby elliptical galaxies, revealing star-formation as the primary heating source and survival of dust in cluster environments despite hot X-ray gas.

Contribution

It provides the first resolved FIR to submm continuum images of cold dust in elliptical galaxies and links dust heating to star formation triggered by accretion or mergers.

Findings

Cold dust temperatures range from 22K to 32K.

Star formation is the dominant heating source of dust.

Cold dust and CO can survive in hot X-ray environments.

Abstract

Continuum observations at 350um are presented of seven nearby elliptical galaxies, for which CO-gas disks have recently been resolved with interferometry mapping. These SHARCII mapping results provide the first clearly resolved far-infrared(FIR) to submillimeter(submm) continuum emission from cold dust (with temperatures 32K > T > 22K) of any elliptical galaxy at a distance >40Mpc. The measured FIR excess shows that the most likely and dominant heating source of this dust is not dilute stellar radiation or cooling flows, but rather star-formation, that could have been triggered by an accretion or merger event and fueled by dust-rich material that has settled in a dense region co-spatial with the central CO-gas disks. The dust is detected even in two cluster ellipticals that are deficient in HI, showing that, unlike the HI, cold dust and CO in ellipticals can survive in the presence of hot X-ray gas, even in galaxy clusters. No dust cooler than 20K, either distributed outside the CO disks, or co-spatial with and heated by the entire dilute stellar optical galaxy (or very extended HI), is currently evident.