In 1982, astronomer Paul Hickson, professor of astronomy at the University of British Columbia , published a study of 100 compact galaxy groups scattered throughout the sky.  In his paper "Systematic Properties of Compact Groups of Galaxies", Hickson defined a compact galaxy group as a small, relatively isolated collection of four or five individual systems that are set in close proximity to one another, and that differ in brightness by no more than 3 magnitudes.  Further, so as to avoid including the central regions of dense galaxy clusters, Hickson stipulated an "isolation factor" requiring that there not be a non-member galaxy of similar magnitude within three radii of the group's center.

Surveying the Palomar Observatory Sky Survey, Hickson created an inventory of 100 such groupings.  The entries in the Hickson Compact Group, or HCG, catalog are ordered numerically according to increasing right ascension.  The classic example of a compact galaxy group, and the first of the genre to be discovered, is Stephan's Quintet in Pegasus (October 2017 Cosmic Challenge), which Hickson cross-referenced as HCG 92.

Stephan's Quintet is probably the best-known example of a compact galaxy group, but it is by no means the brightest.  That honor falls to HCG 44, nicknamed the Leo Quartet.  HCG 44, itemized in the table below, is easily pinpointed a little less than halfway between the stars Adhafera [Zeta (ζ) Leonis] and Algieba [Gamma (γ) Leonis] along the sickle of Leo the Lion.  If you center your finderscope on Adhafera (Zeta), you will see 6th-magnitude 39 Leonis just 20' to its south-southeast.  Without moving the aim, look for two 7.6-magnitude stars closer to the southern edge of the finder field.  See them? Good.

Members of Hickson Compact Group 44

Recenter your telescope on the western star in that pair, listed as SAO 81276 (aka HD 89224), insert a medium-power eyepiece, and take a look just to its south.  Two faint blurs should be immediately visible.  The smaller and easternmost of the two blurs is NGC 3193, found just 1' to the south of 9th-magnitude SAO 81279.  My 10-inch scope at 106x reveals this E2 elliptical as a bright, round glow highlighted by a brighter core.

NGC 3193 plays second fiddle to the group's brightest member, the edge-on spiral NGC 3190.  Its cigar-shaped disk appears elongated northwest-to-southeast and surrounds a faint stellar nucleus.  Photographs reveal that, like many edge-on spirals, NGC 3190 is bisected by a lane of opaque dust that runs along its galactic plane south of the central core.  I have failed to see the lane through my 10-inch under suburban skies, but others report success under darker conditions with the same aperture.  Larger instruments show that the dark lane's western tip appears to curl northward slightly due to the tug of an external gravitation source.

That source of gravity is most likely NGC 3187, a dim barred spiral just 5' to the northwest.  Shining at magnitude 13.4 and spanning some 4'x2', NGC 3187 is the faintest of the group.  Its inherent low surface brightness is easily overwhelmed by the light of nearby HD 89224, our finder star 6' to the northeast.  Move the star out of the field and the galaxy's faint glow should pop into view with averted vision.  Look for a dim, featureless smudge of grayish light that is oriented parallel to NGC 3190 and just 1' north of two 14th-magnitude field stars. Large instruments will also show two faint extensions of NGC 3187's spiral disk. The western end curls northward, while the eastern tip curls southward, forming a unique S-shape.

The final member of the four, NGC 3185. To find it, hop south from NGC 3190 to a pair of 10th-magnitude stars. Together with three similarly bright stars to their east, they form a distended "M". Look 5' due west of the southernmost star in the pair for NGC 3185.Its diffuse glow draws to a slightly brighter core and appears extended slightly northwest-southeast.  With averted vision, the southwestern edge of the galaxy appears to just kiss a 14th-magnitude field star.  That star is well within the Milky Way, however, so don’t mistake it for an extragalactic supernova.

Larger apertures may also spot PGC 86788, is a dwarf spiral galaxy about 100 million light-years away. It appears isolated but might still be gravitationally linked to HCG 44.

Another galactic photobomber, PGC 2806871 is a faint dwarf spiral galaxy at around 250 million light years from the Milky Way. It has no physical association with the galaxy group.

Have a favorite challenge object of your own?  I'd love to hear about it, as well as how you did with this month's challenge.  Contact me through my website or post to this month's discussion forum.

Remember that half of the fun is the thrill of the chase.  Game on!