SCYON Abstract

Received on October 10 2009

The Nuclear Ring in the Barred Spiral Galaxy IC 4933

AuthorsStuart D. Ryder (1), Samuel Illingworth (2), Robert Sharp (1), and Catherine Farage (3)
Affiliation(1) Anglo-Australian Observatory, Australia
(2) University of Leicester, UK
(3) Australian National University, Australia
Accepted byPublications of the Astronomical Society of Australia


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 uprime band with GMOS on Gemini South confirms that this ring is not purely an artifact 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 unraveled. Integral field spectroscopy with the GNIRS spectrograph on Gemini South shows the equivalent width of the Paβ 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 90o.