3.3 {\mu}m PAH observations of the central kiloparsecs of Centaurus A

TL;DR

This study uses high-resolution 3.3 μm imaging to investigate PAH emission in Centaurus A's central region, revealing that PAHs survive near the AGN and generally trace star formation, with some spatial offsets and potential nuclear dust structures.

Contribution

First high-resolution 3.3 μm PAH imaging of Centaurus A's nucleus, analyzing PAH survival, distribution, and relation to star formation and nuclear activity.

Findings

PAH emission is present in the nucleus, indicating survival in harsh environments.

PAH feature-to-continuum ratio decreases towards the AGN.

Spatial offsets between PAH emission and star formation sites are observed.

Abstract

Aims. The aim of this work is to further investigate the nature of PAH excitation and emission especially in the context of tracing star formation in a variety of extragalactic environments. Here we turn our attention to the energetic environment of the closest AGN in our sample, Centaurus A. Methods. Using ISAAC on the ESO VLT UT1 (Antu) we have made high spatial resolution 3.3 {\mu}m imaging observations of the central kiloparsec of CenA. These observations have been compared with star formation tracers in the near- and mid-infrared, as well as with mid-infrared tracers of nuclear activity. Results. The nucleus is not devoid of PAH emission, implying that the PAH particles are not destroyed in the nucleus as might be expected for such a harsh environment. However, we see the feature to continuum ratio decrease towards the AGN. As well, the 3.3 {\mu}m PAH feature emission generally traces the sites of star formation in Cen A, but in detail there are spatial offsets, consistent with an earlier study of the starburst galaxies NGC 253 and NGC 1808. However, the feature-to-continuum ratio does not drop at the positions of star formation as was previously seen in that earlier study. The cause for this difference remains uncertain. Finally, our data reveal possible evidence for a nearly face-on, circular or spiral, dust structure surrounding the nucleus.