Compact galaxy cluster (AWM 4) surrounding NGC 6051

Last week (July 22-26) a group of Northern California observers (Marko Johnston, Carter Scholz, Peter Natscher, Mark Wagner, Dave Cooper and myself) and a couple of West Texans (Jimi and Connie Lowrey) met at Lassen National Park for 4 nights of camping at Summit Lake (image below) and observing at two prime spots in the park.

Attachment 1306

One target Jimi suggested we observe with my 24-inch f/3.7 Starstructure is a galaxy group surrounding NGC 6051. This little known group was highlighted in a 1977 paper by Albert, White and Morgan "cD Galaxies in Poor Clusters. II". The paper lists 7 "poor clusters" which include a single dominant cD galaxy -- in this case, NGC 6051 in Serpens, with the cluster listed as AWM 4. In fact, all these clusters are fairly compact and make great targets!

We tackled this cluster on the last night from the Bumpass Hell parking lot (elevation 8200 ft). During the day this lot is filled with cars heading off on a hike to the dramatic Bumpass Hell hydrothermal area, a field of boiling mudpots, and steaming fumaroles.

Here's the view from the Bumpass Hell lot as well as a roadside view within the park (both from a previous trip in July)

Attachment 1307

Attachment 1308

As far as the cluster, NGC 6051 has 5 companions (that we observed) within a distance of 3 arcminutes! Visually, this is quite comparable to a challenging Hickson, except for the single bright member. Because of the AWM paper, 4 of these objects carry PGC numbers and one has a high LEDA number. We used Megastar to identify the members, though I discovered an error after I got home. IC 4588 is labeled PGC 57025 in Megastar and NGC 6051 is incorrectly equated with IC 4588. The objects are correctly labeled in this image.

Attachment 1310

The faintest of the group was PGC 140564 (missing from Megastar, even as a MAC) just 1.2' WNW of NGC 6051. This is a close pair, but we only saw a single extremely faint glow, which appeared elongated. The others appeared as a very faint, 12" knots, except for PGC 57014, a 3:1 edge-on spiral.

A note by U.C. Berkeley astronomer Stauffer and Spinrad, "Redshifts for galaxies in the poor cluster AWM-4" (PASP, 90, 20) proposes that AWM 4 consists of two superimposed clusters, as two of the galaxies (AWM 4-3 and 4-5) have significantly higher redshifts.

If you have a chance, check out this group!