This
Astrobin Debut Object is a galaxy group of 7 galaxies called Hickson 70 located in the constellation of Canes Venatici at a declination of +33 degrees. This is not a true cluster - the 7 galaxies of Hickson 70 are comprised of 2 groups at different distances from us and are only aligned through superposition from our apparent view. Dr. Hickson did not consider distance as a criterion when determining his Hickson groups.
The field of view of this image is narrow at 0.2 degrees. This is the only Hickson group comprised of 7 spiral galaxies, which makes for one of the more interesting Hickson groups.
The largest and brightest galaxy, Hickson 70a, is also known as UGC 8990. This magnitude 15 edge-on spiraI galaxy is 400 million light years away. It spans 1 arc-minute, which corresponds to a Milky Way size diameter of 120,000 light years.
Hickson 70b and 70c are the same distance away as 70a. The dramatic inner ring structure of 70b makes it my second favorite galaxy of this group.
Hickson 70d, 70e, 70f, and 70g are all much further away, at about 0.9 billion light years. Hickson 70d is my favorite galaxy of this group with its 3 arm structure. Dr. Arp included a 3 arm structure collection in his
Arp Catalog but none of those galaxies have 3 arms as clearly defined as this one.
Other galaxies are seen in the background, some at the same distance as the Hickson galaxies, but they are too faint to be included in the Hickson group per Dr. Hickson’s magnitude criteria.
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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