NGC/IC Project Restoration Effort

===== NGC 6166 has been a thorn in the side for cataloguers since Holmberg included it in his multiple galaxy list in 1937. There is no problem with the identification of N6166 itself. It is the brightest in Abell 2199 (and a prototypical "cD" galaxy), but is also composed of several interacting galaxies. That is part of the problem. Briefly, the companion's in Holmberg's list are not part of the galaxy itself, but are separate galaxies in the cluster surrounding N6166; all are 2-3 arcmin away, and all have magnitudes around B = 15.5 to 16. None of them are in RC3. On the other hand, Minkowski found in the late 50's that N6166 is itself made up of several components (see his classic paper on the system in AJ 66, 558, 1961). The three brightest are easily visible on the POSS1 prints, while the fourth is almost lost in the overexposed blur of the second. These are all within 5 or 10 arcsec of the "center" of N6166. The first three had separate entries in RC1, and the fourth is mentioned in the notes (the RC1 notes are wrong when they say that these are the Holmberg companions), but since they are clearly parts of the main galaxy itself, we dropped them from RC2 and RC3. Their positions are (measured by me with respect to 2 nearby GSC objects, one a galaxy, the other a star): Component RA (1950) Dec A 16 26 55.3 +39 39 37 B 16 26 56.2 +39 39 42 C 16 26 56.0 +39 39 35 D 16 26 56.4 +39 39 39 (Also see the position table where I've entered other, better, more recent positions for the knots.) For the entire N6166 complex, GSC has: A - D 16 26 55.57 +39 39 37.9 which is just about what a magnitude weighted mean of my individual measures would give. Unfortunately, for the companions, RNGC followed RC1, but (of course!) managed to confuse the identifications and did not give the Holmberg letters for the individual objects. I've found in my copy of MCG the identifications that we had adopted before we sorted out the mess then. I've put them in square brackets below because they were never published -- by us, at least! -- and perhaps shouldn't be. But if one were going to assign suffixes based on the Holmberg list, and wanted to make these suffixes similar to the others in use (starting with capital A rather than little b), then these are the suffixes that would be assigned. I think that this is what RNGC was trying to do. Anyhow, here are the correct identifications for the five Holmberg galaxies: Ho 751 BO MCG +7-34- RNGC CGCG [RC2 1st cut] a 1 60 6166 224-039 [N6166] b 24 50 6166D --- [N6166A] c 53 76 6166B 224-045 [N6166B] d 15 48 6166C --- [N6166C] e 12 56 6166A --- [N6166D] The "BO" numbers are from a paper by Harvey Butcher and Gus Oemler in which they give positions, magnitudes, and colors for nearly 200 galaxies in the cluster (ApJS 57, 665, 1985). In addition, there are two Zwicky compact galaxies nearby: I Zw 153 No. 1 = BO 61, and I Zw 153 No. 2 = BO 95. Finally, NED has the Holmberg, Butcher-Oemler, MCG, CGCG, and many other names explicitly linked for the companions. It has also (as of December 2007; I'm still thinking about this ...) adopted the "RC2 1st cut" identifications for the companions, and has added -- except for the brightest -- its "NED0n" designation to the condensations in NGC 6166 itself. Not ideal, in my opinion, but at least the names and positions for the condensations and the five companions are clear and unambiguous.

===== NGC 6166 18" (7/13/07): moderately bright, moderately large, oval 4:3 SW-NE, clumpy with a brighter core. The major axis is collinear with mag 14 star 2.7' NE. This cD galaxy is surrounded by a swarm of very small, faint galaxies and 10 companions were viewed from Lassen within a 9' circle! 17.5" (8/1/92): fairly faint, fairly small, elongated 4:3 SW-NE, broad concentration. Brightest and largest of seven galaxies in AGC 2199 within a 5' circle! The following close companions were viewed: NGC 6166A = MCG +07-34-050 2.3' SW, NGC 6166B = MCG +07-34-076 2.9' E, NGC 6166C = MCG +07-34-048 3.1' NW, NGC 6166D = MCG +07-34-056 2.0' S, MCG +07-34-064 4.8' SSE and an anonymous galaxy just off the south edge of NGC 6166. 13.1" (5/26/84): fairly faint, fairly small, slightly elongated. Brightest and largest in A2199. Several faint companions are near.