This
Astrobin Debut Object is a galaxy group of 5 galaxies, called Hickson 12, located 0.7 billion light years away in the constellation of Cetus at a declination of -5 degrees.
This is a true cluster -the 5 galaxies are all at approximately the same distance. I see a bit of disturbance in a couple of galaxy halos, so they might be close enough to each other to be interacting. It is hard to tell at this distance, but none of these 5 galaxies appear to be elliptical, which would be unusual.
Compared to the typical Hickson group, Hickson 12 is further away (at 0.7 bly), slightly smaller in overall size (at 2.6 arc-minutes overall diameter), and slightly dimmer in brightness (at 12.9 group magnitude) than most.
The brightest galaxy of the group, Hickson 12a, is also known as LEDA 5437. It is a magnitude 13.4 galaxy which spans 40 arc-seconds. This corresponds to a large actual diameter of 130,000 light years.
Other galaxies are seen in the image. These may be part of the cluster, but do not qualify for the Hickson 12 group designation because they are not bright enough.
The Hickson catalog is a collection of 100 galaxy groups, established by Paul Hickson in 1982. Hickson compact galaxy groups are strictly defined by 3 criteria: number of galaxies, total magnitude, and isolation from other galaxies. A typical Hickson group has 4 galaxies, but some have up to 8. You can see more about Hickson galaxy groups in my
Astrobin Hickson Collection.
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