Hickson Compact Group 23 (HCG 23)

HCG 23 contains 5 galaxies and is located in northwestern Eridanus. Unfortunately it is quite low in my sky. In the fall warm water and cold air above results in both poor seeing and a lot of rising water vapor. Both make imaging this low virtually impossible. This image is obscured by over 2 magnitudes because of these issues.

HCG (Hickson Compact Groups) are a visual group. They need not be related. Usually most are but often one or more galaxies is just a line of sight member. This group consists of 5 galaxies, A through E. E is the odd man out with a redshift twice that of the other 4 showing it a distant interloper. The other 4 are about 200 to 210 million light-years from us. The fifth being 450 million light-years distant. Also a compact group is just that -- compact. Other related galaxies are usually in the area, just too distant to meet the compact requirement. Hickson set several requirements for his groups. They must contain 4 or more galaxies that vary no more than 3 magnitudes in brightness. They must be compact enough that the average surface brightness is brighter than 26th magnitude per second of arc. Also they must be isolated so not the core of a galaxy cluster. For more on this subject see: http://ned.ipac.caltech.edu/level5/S..._contents.html .

There are many other members of the same group that four of the 5 members belong to. This larger not compact group is centered about NGC 1208 on the far right of my image.

Galaxies in compact groups are often interacting, hence the desire to located such groups. Two of the 5 galaxies in this group certainly look like they've interacted. NGC 1215 is a peculiar spiral with and inner ring around the nearly invisible bar that spawns two wide arms that form an outer ring. MCG -02-08-050 has an off center core surrounded by a blue ring. The other two true members, NGC 1214 and NGC 1216 appear rather normal.

I measure NGC 1214 at 90,000 light-years, NGC 1215 at 110,000 light-years, NGC 1216 at 70,000 light-years and MCG -02-08-050 at 34,000 light-years in size. The interloper, MCG -02-08-54 is 70,000 light-years across. But the big galaxy in the image is NGC 1208 at 140,000 light-years, a giant spiral indeed. But the real giant is IC 1880 at over 260,000 light-years in diameter.

Normally I'd have moved the field east but I wanted to pick up the obvious flat galaxy in the upper left corner. There's no distance info available at NED for it however.

Conditions for this image were lousy so it is a candidate to be retaken. I doubt that will happen however.

14" LX200R @ f/10, L=4x10 RGB=2x10, STL-11000XM, Paramount ME

Rick