3.3μm PAH observations of the central kiloparsecs of Centaurus A

Abstract

Aims. The aim of this work is to further investigate the nature of polycyclic aromatic hydrocarbon (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 active galactic nucleus (AGN) in our sample, Centaurus A. Methods. Using ISAAC on the ESO VLT UT1 (Antu) we have made high spatial resolution 3.3 µm 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 µm 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.

Nuclear Star Formation Activity and Black Hole Accretion in Nearby Seyfert Galaxies

“…As we have shown in the previous sections and as presented by others (e.g., Miles et al 1994;Marco & Brooks 2003;Díaz-Santos et al 2010;Hönig et al 2010;González-Martín et al 2013;Sales et al 2013;Tacconi-Garman & Sturm 2013) PAH emission is detected in the vicinity (from tens to a few hundreds parsecs) of the harsh environments of some AGN. Therefore, at least in some galaxies, the PAH molecules are not destroyed (or at least not completely) near the AGN.…”

“…The majority of the nuclear 11.3 µm PAH detections in our sample are galaxies with well-documented nuclear starbursts and/or recent SF activity based on UV and optical observations (González Delgado et al 1998, NGC 5135, NGC 7130), modelling of the optical spectra (Storchi-Bergmann et al 2000, NGC 5135, NGC 5643, NGC 7130, NGC 7582), and near-IR integral field spectroscopy (Davies et al 2007;Tacconi-Garman & Sturm 2013, Circinus, NGC 1068.…”