NGC 6166

History and Accurate Positions for the NGC/IC Objects (Corwin 2004)

NGC 6166 has been a thorn in the side for cataloguers since Holmberg included it in his multiple galaxy list in 1937. While there is no problem with the identification of N6166 itself, it is the brightest in Abell 2199, and is also composed of several interacting galaxies.

Briefly, Holmberg's companions 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

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, RNGC followed RC1, but (of course!) managed to confuse the identifications and did not give the Holmberg letters for the individual objects. I've also 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 because they were never published -- by us, at least! -- and 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.

Historical observations

William Herschel (c.1784)

Synonyms: H II-875

Discovered in 1791 by William Herschel with an 18.7-inch f/13 speculum telescope. He called it "pB, S, lE, vgmbM."

Published comments

Photo index

by Jim Lucyk: Sky&Tel. 11/84 p398.

Sulentic & Tifft (1973)

(Sulentic and Tifft 1973) notes that this is a 14.0 mag galaxy. Their coded description reads E,R,BM,BRIGHTEST OF4.

Minkowski (1961)

, Astronomical Journal, Vol 66, p558-561) reports that NGC 6166 has a B25 magnitude of 13.30 and a B-V colour of 0.85.

Modern observations

Brian Skiff

UGC: pa35:.

POSS: pa45. brtst in Abell 2199.

25cm - mod f, nrly circ, 0'.75 diam, poss elong NE-SW. smooth mod concen w/o

distinct core or nuc. BS, 23May1982, Anderson Mesa.