M81 and M82 with Galactic Flux

M 81 Group and Integrated Flux Nebula

Deep exposures and a careful processing reveal that this group is surrounded by huge clouds of dust. The truth is that the galaxies are not surrounded by this dust – the dust is much closer to us than the galaxies – it just happens to look that way. It is basically the dust and dirt of our Milky Way. This dust, unlike classic reflection nebulas – that are usually illuminated by neighbouring stars – is actually illuminated by the glow of our own Milky Way [ESA/Hubble]. It is reported that Steve Mandel named this nebulosity Integrated Flux Nebula (IFN) [astrosociety].

The M 81 Group is a galaxy group in the constellations Ursa Major and Camelopardalis that includes the galaxies Messier 81 and Messier 82, as well as several other galaxies with high apparent brightness. It covers an angle of about  40° × 20° and the approximate center of the group is located at a distance of 3.6 Mpc, making it one of the nearest groups to the Local Group. The distance of the three large galaxies of the picture are all quite similar, as it should be for a group: from 11.5 Mly (M 82) over 11.9 Mly (M 81) to 12.8 Mly (NGC 3077) [wikipedia].

You find here my trials of catching wide fields of this area.

Photo of 2025

Set-Up

About 8 years later I used my Esprit 100 ED with the Riccardi again, hence it is still a 100 mm f/4.1 scope. In the meantime the camera is a ZWO ASI 6200MC  which increased the field of view significantly. While in 2017 the FOV was 2.4° x 1.7° with the Micro Four Third Chip in 2025 the full frame chip delivers 5.0° x 3.3°. This pushes the triplett of the Esprit to its limits but with latest deconvolution picture processing this can be covered satisfactorily. The Esprit was mounted at my mobile UMI17  and guided off-axis.  The entire recording session actually ran in the background while other activities were being conducted. I simply set up the system, roughly aligned it using the Kochab method, and let it work until the next morning.

Frame have been taken at  nights of: 2025 March, 05./17./18./19./20./21. I reduced the exposure time of a single frame to 4 min which halves the 8 min I had with the Atik 383, but this compensates the increases of chip sensitivity of the IMX 455 compared to the KAF 8300.

The picture shows a field of 4.9° x 3.3°. The original scale is 1.9 arcsec/pix. In contrast to many other publications north is almost up (PW=186°). The center of the image is RA: 09^h 55^h 40^s DE: +69^° 04′ 13″.

Processing

For the integration I selected 425 frames with 4 min each. This summarises to a total exposure time of 28 hours and 20 min. In contrast to 2017 the picture processing was a much more easier job. This is not only due to the fact, that the camera has now a Bayer sensor, but also probably due to my somehow improved processing skills.

The processing was quite simple: Flattening of the background without destroying the IFN structures, noise reduction, color calibration, deconvolution, generalized hyperbolic stretch, separate processing of both bright galaxies, careful sharpening, some more noise reduction, separate adaption of saturation for object depending on their luminosity.

Lessons learnt 2025

As addition to 2017 I see:

1. If there is enough SNR in the frames, the processing becomes easier.
2. The modern sensors catch significantly more photons. If the exposure time is long enough the IFN becomes reachable even under suburban skies.

Photo of 2017

Set-up

Used my Esprit 100 ED with the Riccardi which results in a 100 mm f/4.1 scope. Atik 383 L+ with Baader LRGB filters. All on the Avalon Linear guided with a 60 mm finder scope. The nights have been: 2017 March, 23./24./26./27. and April, 26./28./29./30. I took only 8 min frames in order to prevent the core of M81 from saturation. This sounds strange, but with f/4.1 the M 81 center really came close to the full CCD range, hence I decided to be on the safe side. At the end of the day – after blinking, FHWM and eccentricity measurements – a few frames had been rejected and I had 99/22/21/21 frames of the LRGB channels which equal almost 22 h exposure time.

The picture shows a field of 2.4° x 1.7°. The original scale is 2.7 arcsec/pix. In contrast to many other publications north is almost up (PW=178°). The center of the image is RA: 09^h 56^h 19^s DE: +69^° 13′ 02″.

Processing

Picture processing was a hard job. Mostly carried out in PI, I tried to focus on two issues:

1. Push the flux background as much as possible. Anyway not to blow up the stars. Find the right way somewhere between fully denoised creamy nebulas and grainy background.
2. Avoid pushing the galaxies to much and keep the level of the galaxies low enough. Compress the dynamics of the galaxies as much as necessary but keep the impression as natural as possible.

The final composition of the pic was done in PS. Also some optimisations (sharpening of parts, partly denoising of the flux) was done here. Last but not least I would say that the picture took about 11 h exposure time and more than 50 h processing time distributed threw two months with intermissions.

The picture shows the integrated luminance (13 h) pushed using a ingenious method described by G. Wechselberger: Enhance Nebula without pushing the Stars. The tutorial can be found at skypixels. The result of the pushing was used for LRGB combination. I inverted a copy of the result and stretched it further in order to reveal more of the flux nebula.

 

Lessons learnt 2017

The flux nebula needs:

1. Dark sky. I spent one night out in the field of Breddorfer Moor, which is significant darker than my suburban garden. During this night much more flux revealed than during all other nights.
2. Really long exposure times. I planned 10 h for luminance only. Which was a good plan, but my impatience forced me to start with the processing this year. Maybe I prolongate the exposure next year.
3. Processing of the flux is difficult. I needed many trys, rejecting most of them. There is still much to learn.