Markarian's Chain is a stretch of galaxies that forms part of the Virgo Cluster. When viewed from Earth, the galaxies lie along a smoothly curved line. Charles Messier first discovered two of the galaxies, M84 and M86, in 1781. The other galaxies seen in the chain were discovered by William Herschel and are now known primarily by their catalog numbers in John Louis Emil Dreyer's New General Catalogue, published in 1888. It was ultimately named after the Armenian astrophysicist, Benjamin Markarian, who discovered their common motion in the early 1960s. Member galaxies include M84 (NGC 4374), M86 (NGC 4406), NGC 4477, NGC 4473, NGC 4461, NGC 4458, NGC 4438 and NGC 4435 (source: Wikipedia).
Near the center there appear the pair of interacting galaxies NGC 4438 and NGC 4435, about 50 million light-years away, known to some as Markarian's Eyes. At least seven galaxies in the chain appear to move coherently, although others appear to be superposed by chance. Six of the points on the chain can be marked by galaxies. The other two points are pairs of galaxies (Wikipedia).

The initial project was to integrate my data set in large collaboration aiming at capturing the entire chain, however my setting being inadapted with respect to the focal length, it was unsuitable for the project. So, I decided to progress alone with the hope to capture as much as possible signal on the HaLRGB channels, but more specifically in Ha. As a matter of fact, an hydrogen bridge has been described between M86 and NGC4438. This bridge has been already captured and illustrated with fantastic images by several brillant astrophotographers in Astrobin, therefore I tried to achieve my own result with my setting. As I have a remote scope in Spain, achieving 100 hours accumulated exposures was finally not so much of an issue, whereas capturing the extremely weak Ha emissions using my F/7 scope was another story...

The result:

For the processing, I used the now classical approach to process the RGB layers (Channel combination, BXT, SPCC,...), whereas for the Ha channel very frustratingly I failed to see a clear, dinstinguishable signal from and between the galaxies. I therefore applied Continuum Subtraction to separate the general Ha emission of the galaxies, from the bridge and the streams. Using this process, I obtained a much cleaner signal, that however required further processing. As a matter of fact, I observed very bright regions around M86 and the eyes, for which I had to apply masks to avoid burning the image, whereas the bridge was close to the background, thus needing particular attention to separate signal from noise. While I tried to generate a coherent image, I cannot exclude some artefacts on the Ha channel (and possibly on some very weak signals on L).

As usual don't hesitate to provide input and constructive feedback.

CS!

Nicola