M81 and M82 are two bright galaxies that lie about 12 million light-years away from us. My previous image of this galaxy pair dates back to January 2017 and I considered it one of my best images for a long time. It was nice to revisit this classic with my new camera and with more post-processing experience.

If you have some time, take a look at the full resolution image. Most of my processing was dedicated to the details inside the two main galaxies.

During processing, I noticed a faint glow on the right side of the auto-stretched luminance master and I would normally attribute such an uneven background due to passing clouds or insufficient flat-field calibration. However, this part of the sky contains galactic cirrus: very fine interstellar dust particles that exist above the plain of our own Milky way galaxy. It is often called Integrated Flux Nebula (IFN) by amateur astronomers, because the dust reflects the combined light flux from millions of stars inside our own galaxy. This IFN is extremely faint and notoriously difficult to capture, so I was quite surprised to see it in my stack. I always thought that you needed very dark skies (SQM >21) to capture the IFN! The background is stretched a bit further than my usual comfort level to enhance the IFN's visibility.

You can also see a couple slightly darker lines to the right of M81’s core, perpendicular to the galaxy’s dust bands (recommended to watch the full resolution image). These abnormal dark lines were originally thought to be a tidal tail of M81, but recent research suggest that these bands are likely galactic cirrus from our own Milky way and part of "Arp's Loop". So we're basically seeing the shadow(!) of galactic cirrus here. For clarfication, see this image by R Jay GaBany: https://www.cosmotography.com/images/small_ngc3031.html

The H-alpha jets around M82 are pretty weak, and I unfortunately could not reveal much structure in these jets despite the fair amount of Ha integration time (2h). Integration time of the color channels is still pretty low, only 20 minutes, so the background is basically grey instead of brown (the color of galactic cirrus). I would like to revisit this target next year to obtain deeper RGB stacks.