A near-infrared polarized bipolar cone in the Circinus galaxy |
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| Authors: | M Ruiz D M Alexander S Young J Hough S L Lumsden C A Heisler † |
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| Institution: | Department of Physical Sciences, University of Hertfordshire, Hatfield, Herts AL10 9AB;International School for Advanced Studies, SISSA, Via Beirut 2–4, 34014 Trieste, Italy;Department of Physics and Astronomy, University of Leeds, Leeds LS2 9JT;Mount Stromlo and Siding Spring Observatories, Private Bag, Weston Creek PO, Weston, ACT 2611, Australia |
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| Abstract: | We present near-infrared broad-band polarization images of the nuclear regions of the Circinus galaxy in the J , H and K bands. For the first time the south-eastern reflection cone is detected in polarized light, which is obscured at optical wavelengths behind the galactic disc. This biconical structure is clearly observed in J - and H -band polarized flux, whilst in the K band a more compact structure is detected. Total flux J − K and H − K colour maps reveal a complex colour gradient toward the south-east direction (where the Circinus galactic disc is nearer to us). We find enhanced extinction in an arc-shaped structure, at about 200 pc from the nucleus, probably part of the star formation ring.
We model the polarized flux images with the scattering and torus model of Young et al., with the same basic input parameters as used by Alexander et al. in the spectropolarimetry modelling of Circinus. The best fit to the polarized flux is achieved with a torus radius of ∼16 pc, and a visual extinction A V , through the torus, to the near-infrared emission regions of >66 mag. |
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| Keywords: | galaxies: active galaxies: individual: Circinus galaxies: nuclei galaxies: starburst infrared: galaxies |
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