Messier 83 Southern Pinwheel Galaxy

Messier 83 is a face-on galaxy in the constellation Hydra and a showcase object of the southern sky. Due to its similarity to M101, it is also called the „Southern Pinwheel Galaxy.“ In my imaging, my goal was to capture the tidal stream that appears like an additional spiral arm north of the galaxy. This structure was first mentioned in a paper by Malin and Hadley in 1997. David Malin was a pioneer in astrophotography, and together with Hadley, he successfully detected this tidal tail on photographic plates. They used special techniques that later became known as the „Malin Technique.“ Among other methods, they combined positive and negative exposures in a way that significantly enhanced contrast.

Despite the very dark Namibian skies, the relatively fast optics, and the long exposure time, I was surprised by how faint this arc actually is. It only becomes truly distinct in the inverted version. (I’m not entirely sure, but this method of presenting the inverted arc alongside a positive-color galaxy might originate from Malin and Hadley’s work.)

Another striking feature of the galaxy is its pronounced halo, which extends far into space. Around this halo, a darker region can be observed. At first, I thought this was an artifact of gradient removal, but I found this effect on other deep images as well, such as the APOD from July 3, 2024.

To reveal as much detail as possible in the galaxy while preserving depth, I applied various techniques: the drizzle method and a blending of a short stack (only frames with good FWHM) and the full stack.