* Astronomy

Title: The Nuclear Ring in the Barred Spiral Galaxy IC 4933
Authors: Stuart D. Ryder (1), Samuel Illingworth (2), Robert Sharp (1), Catherine Farage (3) ((1) AAO, (2) University of Leicester, (3) Australian National University)

We present infrared imaging from IRIS2 on the Anglo-Australian Telescope that shows the barred spiral galaxy IC 4933 has not just an inner ring encircling the bar, but also a star-forming nuclear ring 1.5 kpc in diameter. Imaging in the u' band with GMOS on Gemini South confirms that this ring is not purely an artefact due to dust. Optical and near-infrared colours alone however cannot break the degeneracy between age, extinction, and burst duration that would allow the star formation history of the ring to be unravelled. Integral field spectroscopy with the GNIRS spectrograph on Gemini South shows the equivalent width of the Pa-beta line to peak in the north and south quadrants of the ring, indicative of a bipolar azimuthal age gradient around the ring. The youngest star-forming regions do not appear to correspond to where we expect to find the contact points between the offset dust lanes and the nuclear ring unless the nuclear ring is oval in shape, causing the contact points to lead the bar by more than 90 degrees.

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