Gottlieb's Wicked Adventures in Oz (IV)

by Steve Gottlieb

In the last adventure, I mentioned how the Spiral Planetary, NGC 5189, was misclassified as an emission nebula until a few years back. As another example of the poor professional coverage of the southern sky consider the Circinus Galaxy -- a large, nearby neighbor to the Milky Way (only 4 megaparsecs or 13 million light years distant) completely unknown until 1977. It was finally discovered at Mt Stromlo, in the hills above Canberra, Australia on a Schmidt survey of southern Milky Way nebulae and is located at 14 13.2 -65 20 (2000). The discovery report can be read at http://adsabs.harvard.edu/cgi-bin/bib_query?1977A%26A....55..445F. Of course, extremely faint or low surface brightness are still uncovered today, but surprisingly this galaxy is bright enough to be easily visible in an 8-inch amateur scope, though I'm sure few have heard, let alone observed this still little-known galaxy.

So, why the late discovery date of 1977? Besides the obvious answer of poor southern sky survey, this highly obscured spiral is located just 4 degrees from the galaxy plane where visual extinction is several magnitudes and not a region you usually go searching for galaxies. Photographically, the Circinus galaxy measures some 7'x3', though radio observations extend to the size out to 80'. Visually, though, it's mainly the core that is bright enough to poke through the dust in the milky way. If this galaxy was located in a different part of the sky, it would probably rank as one of the top showpieces in the southern sky.

The Circinus Galaxy is the focus of a great deal of current astronomical research (see the APOD image and some of the links at http://antwrp.gsfc.nasa.gov/apod/ap001204.html) as it's a great example of a nearby starburst (active nucleus) galaxy that is powered by a massive black hole. Chandra also showed it was a powerful X-ray source, supporting the black hole model (http://antwrp.gsfc.nasa.gov/apod/ap010516.html).

I wasn't sure what to expect when I peered into the 16 Nagler on the 18-inch at Magellan Observatory on July 5th. At 128x, I was surprised the Circinus Galaxy was immediately seen as a moderately bright, 30" roundish glow with a fairly even, high surface brightness surrounded by a dense mat of stars. As this galaxy is situated in a very rich star field, the core of the galaxy mimics a planetary in terms of size and surface brightness and appears strangely out of place in this setting. At 228x, there was a strong impression of a much fainter outer halo oriented SW-NE, ~2'x1' in size, particularly using averted vision. Just off the SW side (1' from center) is a mag 12 star, comparable in brightness to the galaxy and a number of additional mag 11-12 stars are within a few arc minutes of the galaxy.

Posted on sf-bay-tac Jul 30, 2005 18:07:31 PT
Converted by report.pm 1.2 Mar 06, 2006 21:30:21 PT