Daily Image
09-07-2010
Illuminating Hanny's Voorwerp: a closer look at the centre of IC 2497
| Submitter: | Gyula Jozsa, Mike Garrett |
| Description: | The current hypothesis to explain the physics behind the green nebulosity called "Hanny's Voorwerp" is that it is part of a huge gas cloud, illuminated and heated by an active galactic nucleus (AGN) at the centre of its neighbouring galaxy IC 2497 (see our former daily image and former press release). The image shows a composite of newly published high-resolution radio images of the centre of IC 2497, overlaid on an optical image of the galaxy together with Hanny's Voorwerp. Using the European Very Long Baseline Interferometry Network (EVN) we confirm the existence of a central point source in addition to a newly detected one (visible as purple dots in the image). A straightforward interpretation is that we are looking at an AGN (newly detected point source to the North) with a jet directed towards Hanny's Voorwerp that is interacting with the interstellar material around the core of IC 2497 (point source to the South). With the UK's Multi-Element Radio Linked Interferometer Network (MERLIN) we also detect extended emission around the two point sources (red and yellow in the image). Most radio emission comes from the extended source, this morphology together with far infra-red measurements, suggests this nuclear region is the site of massive star formation (producing 70 solar masses in stars per year, 4 times more than the nearby starburst poster-child galaxy M82!). Nuclear star forming regions can contain lots of gas and dust. Hence, the new radio observations offer one obvious explanation why the AGN at the centre has not been detected at other wavelengths - it may well be hidden behind huge amounts of dust and gas. Further information can be found in our press release and the corresponding A&A letter by Rampadarath et al. (arXiv:1006.4096). |
| Copyright: | Image credits: William Keel, Anna Manning, 3.5-m WIYN Telescope (optical image), and ASTRON |
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