Extended dust emission in NGC 7465

Abstract

We present SCUBA 850-μm, JCMT CO(J=2→1), B-band imaging and VLA H i observations of the NGC 7465/4/3 group of galaxies. The 850-μm emission associated with NGC 7465 extends to at least ∼2R25 and is well correlated with the H i. We investigate a range of possible mechanisms by which dust beyond R25 may be heated to give the observed extended submillimetre emission. By modelling the dust heating by stars in two extreme geometries, we fail to find any reasonable star formation scenario that is consistent with both the 850-μm and optical data. Furthermore, we do not detect any CO(J=2→1) emission coincident with the extended dust and atomic gas as would be expected if significant star formation were occurring. We show that shock-heating of dust via cloud-cloud collisions in the stripped interstellar medium of NGC 7465 could be sufficient to explain the extended 850-μm emission and lack of optical emission in the stripped gas, and suggest that cloud-cloud collisions may be an important dust heating mechanism in gas-rich systems.