May: Diversity of Galaxy Shapes

Abstract

Galaxy M109 is a stunning example of a “barred spiral galaxy.” This category of spiral galaxies is defined by a distinct bar of densely packed stars elongating the nucleus of the galaxy. The spiral arms originate from the ends of this bar. M109 is the brightest of 50 galaxies in the M109 Group, a large group of galaxies located in the constellation Ursa Major at a distance of 55 million light-years. Imaging. Although relatively small among the galaxies chosen for this book, M109 concentrates its photons of magnitude 9.8 into a bright core and crisp spiral arms. The best detail is extracted with long exposures and luminance layering, but nice results can be obtained from the suburbs with as little as 2 h of exposures. Use a long focal length to obtain high resolution and a frame of around 20 arcmin or less. As with other small objects, you will gather the sharpest details under steady skies, with accurate tracking and careful focus. Processing. If you have rich data in your luminance, apply deconvolution after aligning and combining your luminance images. Then, after either digital development or curves/levels, sharpen the core and brighten the spiral arms with your favorite tools. When sharpening in Photoshop, deselect the center of the core and feather the selection a few pixels, or you may get an unnatural round bright circle at the core. Also, deselect the 13th magnitude foreground star in the north side of M109 when sharpening. Consider sharpening in two phases, each gently. The first, with a radius of 5–8 pixels, is to enrich the small scale contrast within the spiral arms. The second, with a radius of 15–20 pixels, is to enhance the borders of the bar and spiral arms by dimming the dark lanes. Finally, shrink any excessive bloating in the ninth magnitude star just to the southwest of M109 (Fig. 5.1).