Arp 229 (Gary Imm)

Arp 229

This object consists of a pair of elliptical galaxies at the top left of the image. The large elliptical is the magnitude 12 NGC 507 and the smaller one above is the magnitude 14 NGC 508. They are located 210 million light years away in the constellation of Pisces at a declination of +33 degrees. I did not center them in the image because of the bright 9th magnitude star HD 8347, just off the top right of the image, which created quite a distraction. Its glow is still seen at top right.

NGC 507 spans 5 arc-minutes in our apparent view, which corresponds to a huge actual diameter of 280,000 light years. Dr. Arp categorized this object in the category of Galaxies with Concentric Rings. Looking closely, you can see the “ring” which Arp identified. These tend to be called shells now and not rings. I was careful to try not to overprocess this object and create artifacts that would affect the shell.

Roughly 10 percent of ellipticals have these shells, which were first discovered fairly recently in 1980. I don't fully understand the "shell" mechanism - my thought would be that the stars should have a constant light/density gradient away from the galaxy core, but they don't. The shells remind me a bit of mid-region galaxy rings, so perhaps it is a similar mechanism - gravitational interaction with another galaxy causes waves of material to compress and spread outward, initiating star formation.

This object is part of a galaxy group, naturally known as the NGC 507 group. All of the galaxies in this image are members of this group. It is an interesting assortment of galaxies! The highlights include the polar ring galaxy IC 1689 at bottom left, the warped edge-on spiral galaxy NGC 504 just above image center, the odd IC 1685 to the right of center, and the beautiful grand spiral ring galaxy NGC 494 near the right edge.

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Rarely Imaged Small DSOs
ZWO ASI1600MM/QHY163M
Texas Astronomy
Arp's Peculiar Galaxies
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Status	Advanced success
Started	...
Astrometry.net job	4110488
PixInsight job	I90NGNY1O509NMJ7RP1TT9VW8RJW5PE6
PixInsight queue size	n/a
PixInsight stage	n/a

RA (center)	01h23m30s.733
RA (top/left)	01h24m11s.539
RA (top/right)	01h22m44s.122
RA (bottom/right)	01h22m50s.570
RA (bottom/left)	01h24m17s.223

Dec (center)	+33°09′35″.48
Dec (top/left)	+33°17′57″.20
Dec (top/right)	+33°16′29″.85
Dec (bottom/right)	+33°01′12″.97
Dec (bottom/left)	+33°02′39″.92

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Arp 229

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