The Nuclear Ring in the Barred Spiral Galaxy IC 4933

TL;DR

This study uses infrared imaging and spectroscopy to analyze the structure and star formation activity of the nuclear ring in galaxy IC 4933, revealing complex age gradients and geometric considerations.

Contribution

It provides detailed imaging and spectroscopic analysis of the nuclear ring in IC 4933, highlighting its structure, star formation patterns, and potential geometric shape.

Findings

Detection of a star-forming nuclear ring 1.5 kpc in diameter.

Identification of a bipolar azimuthal age gradient in the ring.

Observation that youngest star-forming regions do not align with expected contact points.

Abstract

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 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 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.