This image contains an intriguing quartet of interacting galaxies in Pegasus (NGC 7769, 7770, 7771, and 7771A) that is partially obscured by an extensive cloud of galactic cirrus. This galaxy group has rarely been imaged, with less than 40 Astrobin posts in total to date. The image spans about 29'x21', with a plate scale of about 0.62"/pixel, and a position angle close to zero, with north up and west to the right. It is the result of nearly 23 hours of exposures (just over 13 hours in luminance and just over 9 hours in RGB filters combined) taken over the course of nine nights in October and November.

The group is at a distance of about 200 million light-years, and is dominated by two large spiral galaxies: the nearly edge-on NGC 7771, near the image centre, and the face-on grand-design spiral NGC 7769 to the north-west. NGC 7771 forms a close triplet with the disk-like S0 galaxy NGC 7770 to the south, and edge-on NGC 7771A to the west. The small elliptical galaxy left of the face-on spiral, catalogued as LEDA 214992, does not appear to be associated with the galaxy group. 

Velocity measurements of HI regions surrounding the group and the morphologies of the spiral galaxies suggest that they are circling each other, and have already passed through their first closest approach, causing the evident tidal disruptions. Estimates of the ages of starburst regions in the different galaxies indicate that the encounter occurred on the order of a hundred million years ago. The HI maps also show an enormous tidal tail that extends from NGC 7771 to the south-east for about 100 kpc (i.e., about 6’), with a clump near the end that has an optical counterpart known as NGC 7771B (classified by NED as "part of a galaxy") that in my image looks like a tiny blue spade pointed almost straight-up! The estimated mass of NGC 7771B is large enough to suggest that it might eventually condense to form a new tidal dwarf galaxy.

I was curious to know if the galactic cirrus in this image is part of a catalogued object, so I used SIMBAD to search for objects under the category of "interstellar medium", within a few degrees of the galaxy group. The nearest hit is an HI region whose centre is only 50’ north-west of the image centre, and covers a few square degrees, overlapping with this field-of-view, so it seems plausible if not likely that the galactic cirrus in the image is an optical counterpart of a portion of the larger cloud [†]. That cloud turns out to be quite remarkable! It is classified as a compact high-velocity cloud (CHVC). The general category of high-velocity clouds (HVCs) are HI regions that move at high speeds (up to hundreds of km/sec) relative to the mean motion of material in the galaxy, and can be enormous (up to millions of solar masses). Compact HVCs (CHVCs) are isolated regions of small angular size (less than a few degrees). A comprehensive study of a group of CHVCs (including the cloud overlapping my FOV) supports a conjecture that these objects lie outside our galaxy, and are scattered throughout the Local Group, with a net in-fall towards the Milky Way or the barycentre of the Local Group! 

[†] In fact, careful inspection of DESI Legacy Survey optical/infrared image mosaics, which span a much wider region, reveals counterparts that include my FOV and that appear to cover almost the entire cloud, in close correspondence with an HI map of the cloud (the HI map can be found on-line in Fig.7 of a paper that I discuss at the end of the paragraph above).