Gottlieb's Wicked Adventure in Oz (II)

by Steve Gottlieb

In the late 1980's, Cal Tech astronomer Alan Dressler announced that our corner of the universe was being dragged in the direction of Centaurus by an unseen but massive collection of galaxies dubbed the "Great Attractor". I was fascinated by Alan Dressler's captivating story ("Voyage to the Great Attractor") of the discovery by the "Seven Samurai" astronomers of a massive supercluster of galaxies that was pulling the Milky Way, and entire Local Group, the Virgo cluster and the Hydra-Centaurus Supercluster. The "Seven Samurai" found that superimposed on the general Hubble flow, everything in our local universe was streaming in the general direction of Centaurus at 600 km/sec. Pretty exciting stuff, so when Alan spoke at a 1996 ASP conference, I rushed up and had him autograph my copy of the book. Unfortunately, the core of the "Great Attractor" lies mostly hidden in the "Zone of Avoidance" and is largely obscured by dust in the plane of the milky way. By the mid-90's it was discovered that the central galaxy structure was likely a previously catalogue cluster, Abell 3627, that officially resides in the southern constellation of Triangulum Australe (Southern Triangle), although it sometimes referred to as the "Norma Cluster". Because it is highly obscured, this cluster was previously overlooked but it is comparable in mass to the great Coma cluster (Abell 1656) yet slightly closer (~250 million light years). A increased density of galaxies centered on this cluster extends for 40 degrees across the sky.

Probably because there are no NGC or IC galaxies in Abell 3627 and even only a few in the ESO catalogue, it was not on my observing list from three years back when I observed in Australia. This time, though, I came better prepared with a detailed finder chart and had no problems chasing down the brightest three ESO galaxies in the core.

ESO 137-006 = PGC 57612 16 15 03.9 -60 54 26 V = 12.1; Size 0.8x0.8; Surf Br = 11.7; PA = 124d
18" (7/5/05 - Magellan Observatory, Australia): moderately bright, fairly small, round, 0.7' diameter. Moderate concentration with a 20" brighter core. Symmetrically placed 5' WNW of ESO 137-008 on the west side of the triangle of stars which separate these two galaxies in a very rich star field with a mag 9 star 3' E. This galaxy is one of the three brightest in the highly reddened "Great Attractor" (Abell 3627). The Milky Way is quite rich here, nevertheless ESO 137-006 and 137-008 stood out well.
ESO 137-010 = PGC 57652 16 15 50.2 -60 48 11 V = 11.6; Size 2.0x1.1; Surf Br = 12.4; PA = 167d
18" (7/5/05 - Magellan Observatory, Australia): this galaxy is the northernmost of the three brightest galaxies in the core of Abell 3627 ("Great Attractor") and is situated 7' due north of ESO 137-008. At 228x, it appeared fairly faint, moderately large, elongated 5:2 ~N-S, ~1.2'x0.5', weakly concentrated with a slightly brighter core.
ESO 137-008 = LGG 407-001 = PGC 57649 16 15 46.1 -60 55 07 V = 11.8; Size 0.5x0.5; Surf Br = 10.1
18" (7/5/05 - Magellan Observatory, Australia): this galaxy is in the core of the relatively nearby, but highly reddened "Great Attractor" (Abell 3627 = "Norma Galaxy Cluster")! At 228x it appeared fairly faint, moderately large, oval 3:2 ~N-S, 1.2'x0.8'. Contains a bright, 20" core. A distinctive triangle of stars, which includes a mag 9.5 star, lies 2' W. Situated in a very rich star and fairly bright star field along with ESO 137-006 and ESO 137-010. This galaxy is a superluminous giant with an absolute magnitude of -23.6 and is comparable in instristic brightness to N4889 in the core of the Coma Cluster. These three galaxies look oddly out of place in this rich Milky Way field with a grainy background.

For more background on the discovery of this cluster, check out an excerpt from Ken Croswell's "The Universe at Midnight" at http://kencroswell.com/universeatmidnightexcerpt.html. The best image I've seen is at http://antwrp.gsfc.nasa.gov/apod/ap000104.html

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Posted on sf-bay-tac Jul 30, 2005 10:37:38 PT
Converted by report.pm 1.2 Mar 06, 2006 21:24:33 PT