Due to enduring bad weather, I have currently the "opportunity"  to dig in my backlog of historical data, and here we are, with this one. The quality of initial data was questionable, and it was fun to correct funny gradients, vignetting, et cetera, as a Pixinsight training session.

NGC 4631
Other designation: Whale Galaxy, UGC 7865, PGC 42637, Arp 281, Caldwell 32
Distance: 30Mly

NGC 4631 is a barred spiral galaxy in the constellation Canes Venatici. This galaxy's slightly distorted wedge shape gives it the appearance of a herring or a whale, hence its nickname. Because this nearby galaxy is seen edge-on from earth, professional astronomers observe this galaxy to better understand the gas and stars located outside the plane of the galaxy.

NGC 4631 contains a central starburst, which is a region of intense star formation. The strong star formation is evident in the emission from ionized hydrogen and interstellar dust heated by the stars formed in the starburst. The most massive stars born in star formation regions only burn hydrogen gas through fusion for a short period of time, after which they explode as supernovae. So many supernovae have exploded in the center of NGC 4631 that they are blowing gas out of the plane of the galaxy. This superwind can be seen in X-rays and in spectral line emission. The gas from this superwind has produced a giant, diffuse corona of hot, X-ray emitting gas around the whole galaxy.

NGC 4631 has a nearby companion dwarf elliptical galaxy, NGC 4627, included in the closeup here. NGC 4627 and NGC 4631 together were listed in the Atlas of Peculiar Galaxies as an example of a "double galaxy" or a galaxy pair.

NGC 4631 and NGC 4627 are part of the NGC 4631 Group, a group of galaxies that also includes the interacting galaxies NGC 4656 and NGC 4657, visible in the large field enclosed here. However, exact group identification is problematic because this galaxy and others lie in a part of the sky that is relatively crowded. Estimates of the number of galaxies in this group range from 5 to 27, and different studies identify very different galaxy sets for this group.