Probing the Nuclear and Circumnuclear Activity of NGC1365 in the Infrared

TL;DR

This study uses multi-wavelength infrared observations to analyze the nuclear and circumnuclear activity of NGC1365, revealing the dominance of star formation in the ring and the minor contribution of the AGN to the infrared emission.

Contribution

It provides a detailed infrared analysis of NGC1365's ILR region, combining new Herschel and Gemini data with archival Spitzer data, and models the AGN's contribution using CLUMPY torus models.

Findings

Star formation is concentrated in the ring resolved by Herschel and Spitzer data.

The AGN contributes only about 5% to the infrared emission within 5kpc.

Dust temperatures and masses are similar to other nuclear starburst regions.

Abstract

We present new far-infrared (70-500micron) Herschel PACS and SPIRE imaging observations as well as new mid-IR Gemini/T-ReCS imaging (8.7 and 18.3micron) and spectroscopy of the inner Lindblad resonance (ILR) region (R<2.5kpc) of the spiral galaxy NGC1365. We complemented these observations with archival Spitzer imaging and spectral mapping observations. The ILR region of NGC1365 contains a Seyfert 1.5 nucleus and a ring of star formation with an approximate diameter of 2kpc. The strong star formation activity in the ring is resolved by the Herschel/PACS imaging data, as well as by the Spitzer 24micron continuum emission, [NeII]12.81micron line emission, and 6.2 and 11.3micron PAH emission. The AGN is the brightest source in the central regions up to lambda~24micron, but it becomes increasingly fainter in the far-infrared when compared to the emission originating in the infrared clusters (or groups of them) located in the ring. We modeled the AGN unresolved infrared emission with the CLUMPY torus models and estimated that the AGN contributes only to a small fraction (~5%) of the infrared emission produced in the inner ~5kpc. We fitted the non-AGN 24-500micron spectral energy distribution of the ILR region and found that the dust temperatures and mass are similar to those of other nuclear and circumnuclear starburst regions. Finally we showed that within the ILR region of NGC1365 most of the on-going star formation activity is taking place in dusty regions as probed by the 24micron emission.