Mid-infrared imaging of active galaxies

Active nuclei and embedded star clusters

¹ European Southern Observatory, Casilla 19001, Santiago 19, Chile e-mail: egallian@eso.org
² UMR7158 CEA-CNRS-U.Paris7, DSM/DAPNIA/Service d'Astrophysique, CEA/Saclay, 91191 Gif-sur-Yvette, France

Received: 11 March 2005
Accepted: 5 April 2005

Abstract

High resolution, mid-infrared (MIR) images of nine nearby active galaxies are presented. The data were obtained with the TIMMI 2 instrument mounted at the ESO 3.6 m telescope using a set of N-band narrow filters. The resulting images have an angular resolution of 0.6´´-1´´. The MIR emission has been resolved in four galaxies: NGC 253, NGC 1365, NGC 1808 and NGC 7469. The images show a circumnuclear population of unknown MIR sources in NGC 1365 and NGC 1808, coincident with radio sources. These MIR/radio sources are interpreted in terms of embedded young star clusters. A high-resolution MIR map of NGC 253 is also presented, and enables the identification of a previously unknown MIR counterpart to the radio nucleus. Extended MIR emission is detected in NGC 7469, and concurs with previous observations in the NIR and radio. For this source, an interesting morphological difference between the 10.4  and the 11.9  emission is observed, suggesting the presence of a dust-rich micro-bar. Our MIR images of Circinus do not show resolved emission from the nucleus down to an angular scale of 0.5´´. In the case of NGC 2992, an upper limit to the extended MIR emission can be set. We provide new MIR flux measurements for the unresolved AGN in NGC 5995, IZw1 and IIZw136.