Is this 3 or 4 merging?

http://www.legacysurvey.org/viewer?ra=29.0926&dec=26.7586&zoom=14&layer=decals-dr7&spectra

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I’d say only two spiral galaxies interacting (may be merging, but may also be a “fly-by”; one needs perhaps another 200 million years or so to be able to tell which).

It looks to me as if there are at least three galaxies interacting here. the one at the centre of your image looks to me as if it has already merged with another galaxy, and there are tidal trails suggesting interaction with two others.

Nice one!