This
Astrobin Debut Object is a galaxy group of 4 galaxies, called Hickson 47, located 450 million light years away in the constellation of Leo at a declination of +14 degrees.
This is a true cluster – all 4 galaxies are approximately the same distance away.
The largest and brightest galaxy, Hickson 47a, is also known as UGC 5644. It is a magnitude 15 galaxy which spans 1 arc-minute in our apparent view. This corresponds to a Milky Way size diameter of 120,000 light years. From our view perspective, the disk is inclined about 25 degrees from edge-on.
47a has a wonderfully odd structure – a bright yellow core surrounded by a faint oval lens, a mid-region ring, 2 very different arms (one diffuse and one sharp), and a fantastic long arc of blue star-forming clouds. I see a faint star stream bridge between 47a and 47b. Perhaps that interaction has initiated the star formation in 47a.
Above the 47a/b pair of galaxies is another pair, 47c and 47d. Like the bridge between 47a and 47b, I also see a faint star stream bridge between 47c and 47d. It is very unusual to see 2 star stream bridges in one small galaxy cluster.
This is another of those backgrounds where the galaxies outnumber the stars.
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.
Comments