by Tobias Westmeier (UWA/ICRAR)

This colourful picture of NGC 300, a medium-sized spiral galaxy in the nearby Sculptor Group, combines two separate data sets: an optical image (from the Digitized Sky Survey) showing mainly young, blue stars along the galaxy’s spiral arms, and a radio image from the Australia Telescope Compact Array (ATCA) that shows the galaxy’s extended neutral hydrogen disc (shown in red) . The gas disc is significantly more extended than the stellar disk and – surprisingly – appears to have a different orientation. Such conspicuous warping of the gas disc is thought to be the result of a recent encounter with a companion galaxy whose gravitational forces would have distorted the outer parts of the disc. A closer inspection of the deep radio image also reveals an asymmetry in the morphology of the outer gas disc itself, suggesting that the gas is affected by ram-pressure forces as NGC 300 moves through the intergalactic medium of the Sculptor Group in an approximately south-easterly direction (lower-left in the image). — The results of the analysis of the radio data have been published by Westmeier, Braun & Koribalski .