The IC4329 Cluster

by Steve Gottlieb

In the southern constellations of Centaurus, Hydra and Antlia is a relatively nearby supercluster, dubbed the Hydra - Centaurus Supercluster. Because of its modest distance, several of its constituent cluster members provide spectacular galaxy fields even to observers at our latitude. In the constellation of Hydra at 27 degrees south declination is the Abell 1060 or Hydra I Cluster. Using my 13-incher at Digger Pines I found seven NGC galaxies in one field. The NGC 3257/81 Cluster is located further south in Antlia at 35 south declination. I've explored this region with my 17.5-incher from the dark skies at Fiddletown and picked up ten galaxies within a one degree circle.

A few years ago, Jim Shields and I examined a third Centaurus Supercluster member, the IC4329 Cluster in Centaurus. The cluster lies a little more than two degrees east of the beautiful galaxy M83. A stunning ESO photograph and finder chart can be found in Exploring the Southern Sky.

I first became aware of the cluster several years ago from a short description I read of two very interesting interacting members--NGC 5291 and its neighbor MCG-05-33-005, better known as the Seashell Galaxy due to its whelk-like appearance on photographs. Due to the strong gravitational attraction of this close encounter a huge double tail consisting of massive HII knots has been pulled out of this pair, producing a total linear diameter for the system of 600,000 light years! The Seashell has been highly disturbed by the interaction with its massive neighbor and I was looking forward to just glimpsing this unusual mag 15-16 galaxy.

At 220X NGC 5291 appeared fairly faint, small and round with a small, bright core. Nearly attached at its southern end was the Seashell, extremely faint, very small and round. John Herschel discovered NGC 5291 in his explorations of the southern sky at the Cape of Good Hope with his 18 1/4-inch reflector of 20-foot focal length, but missed its companion.

Several other NGC galaxies including NGC 5292, 5298, 5302 and 5304 were located by Jim and I, but strangely Herschel bypassed the brightest and largest galaxy member, IC 4329. With a total blue magnitude of 12.6, I found this object a moderately bright, large oval extended WSW-ENE, with a bright stellar core.

Another highly unusual cluster member is located just three arcminutes east. This spiral, called IC 4329A or MCG-05-33-021, contains an unusually bright nucleus with exceptional energy output. This makes it one of the most energetic galaxies in a class called Seyfert galaxies. With my 17.5-incher it appeared fairly faint, very small and slightly elongated. A sharp stellar nucleus is prominent visually.

With a finder chart I was able to located 13 galaxies in a 40 arcminute field, including several anonymous galaxies not catalogued in the NGC or IC. Detailed data on the cluster can be found in the Spring, 1986 issue of Deep Sky, along with a sketch of the cluster by Jeff Corder. Be adventurous and give this unusual galaxy cluster a try at the next star party.