Galaxies Of The Centaur

Centaurus has fascinated observers, both amateur and professional alike, since antiquity. Its random flourish of bright stars, gathered into different patterns to meet the whims and dreams of humankind, are a delightful and inviting distraction on a winter's evening. Scattered amongst these stellar beacons lie some of the most dynamic and appealing deep sky objects in the heavens. Old friends like omega Centauri and Centaurus A (NGC 5128) and the ever popular alpha Centauri are lovingly ogled, easy targets for the small telescope and even the humble binocular.

However, once one has completed the routine check list of 'gems', perhaps something a little harder and yet just as worthwhile may be contemplated to stimulate the observer's eye. Scattered throughout our 'Centaur' and away from the blanketing dust and gas of the Centaurus Arm lie the galaxies, many in clusters and pairs, most needing a dark sky and preferably a large telescope to spot.

Our first target, the barred spiral NGC 4945 is easy to locate. Look for the magnificent globular cluster omega Centauri and draw a line connecting it to 3rd magnitude gamma Centauri. Around halfway along and south of this line lie xi1 and xi2 Centauri of spectral types B and A and magnitudes 4.3 and 4.8. NGC 4945 lies 30' to the northeast of xi1, spanning a whopping 15' or so in length and 2' in width. Lying NE-SW (43°) in orientation, this superb galaxy appears as a large and fairly bright glow in a low power eyepiece field. Much of the galaxy is mottled with a brighter extended central region and further detail can be 'pulled' from the galaxy with high power. NGC 4945 belongs to the Centaurus Group of galaxies including members M83 in Hydra, NGC 5128 (Centaurus A) as well as NGC 5102 and NGC 5068.

J. Dunlop described it as:

"...a beautiful long nebula, about 10' long and 2' broad forming an angle with the meridian, about 30 south preceding and north following: the brightest and broadest part is rather nearer the south preceding extremity than the centre, and it gradually diminishes in breadth and brightness towards the extremeties, but the breadth is much better defined than the length. A small star near the north, and a smaller star near the south extremity, but neither of them is involved in the nebula. I have strong suspicions that the nebula is resolvable into stars. with very slight compression towards the centre. I have no doubt but it is resolvable. I can see the stars, they are merely points."

NGC 4945A is a barred spiral lying 17' to the southeast of NGC 4945. Look for a smallish and difficult slightly extended glow (PA 55°) close to a magnitude 8.3 star. Easier to spot is NGC 4976, located around 30' to the northeast of xi1 and lying 5' west of a magnitude 7.8 yellow star. This galaxy appears slightly extended with an obvious central region and a stellar core.

There are a number of bright though small galaxies domiciled around the great omega Centauri. NGC 5064 lies west of a group of 3 stars of magnitude 6 and 7 that appear southwest of omega. NGC 5064 appears as a small, round glow northeast of a 9th magnitude star and large mirrors should show some elongation to this 11.9 magnitude galaxy. Discovered by Sir John Herschel in 1837, he recorded it as:

"pretty bright, small, round, pretty suddenly little brighter in the middle."

NGC 5156 lies east of a slightly skewed line of 3 bright stars south of omega Centauri. Look for a bright star northeast of the central star of this trio, NGC 5156 lies in the same eyepiece field. Here we have a bright though small face on spiral showing a slightly brighter central region. Another of Sir John Herschel's discoveries, he recorded it as:

"pretty bright, slightly elongated, gradually a little brighter in the middle; has an 8th mag. star 5' distant, pos. S.p."

NGC 5206 is a faint, large and round glow a little under 2° southeast of omega Centauri and around 7' northwest of a bright star which interferes. Keep the star out of the eyepiece field for best results.

NGC 5266 lies around 2.5° east of NGC 5206, appearing as a large and bright oval with a slightly brighter central region. Three faint stars lie close. Sir John Herschel recorded it as:

"bright, pretty large, slightly elongated, gradually a little brighter in the middle, resolvable, three very small stars nearby."

The standout galaxy in this region, in my humble opinion, and one of the best in the heavens is NGC 5128 or Centaurus A. Lying just over 4° to the north of omegaCentauri, binoculars under a dark sky will show a small round glow bisected by an obvious dust lane. James Dunlop discovered this enigmatic galaxy from Parramatta, Australia and included it in his catalogue of 1827. He wrote:

"a very singular double nebula, about 2.5' long and 1' broad, a little unequal: there is a pretty bright small star in the south extremity of the southernmost of the two, resembling a bright nucleus: the northern and rather smaller nebula is faint in the middle, and has the appearance of a condensation of the nebulous matter near each extremity. These two nebulae are completely distinct from each other, and no connection of the nebulous matters between them. There is a very minute star in the dark space between the preceding extremities of the nebula.: they are extended in the parallel of the equator nearly."Sir John Herschel was equally taken with this 'nebula' . describing it as: "A most wonderful object; a nebula very bright; very large; little elongated, very gradually much brighter in the middle; of an elliptic figure, cut away in the middle by a perfectly definite straight cut 40 arcsec broad; pos = 120.3; dimensions of the nebula 5'x4'. The internal edges have a gleaming light like the moonlight touching the outline in a transparency."

This is a magnificent galaxy, the dark band cutting right across the disc with much structure seen within this dark lane in larger mirrors. I first observed NGC 5128 with a 20cm f6.7 dobsonian telescope under the light polluted sky of Mt Eden, Auckland, New Zealand. Once the field was identified, it took a minute or so for the faint ghostly glow of the galaxy to appear. In fact, the dark dust band was easier to see because of its contrast with the surrounding gas. Patience from a suburban site is a must but these type of objects can be reached and will reward well. Of course, a dark sky makes it easy and careful observation and high power will astound the observer.

To the west of NGC 5128 lies a rough v-shaped accumulation of 5 stars, what I call the 'Golden Triangle'. These stars are what I use to direct me to NGC 5128. Within this asterism of orange stars lie 4 faint galaxies available to larger mirrors. NGC 5026 is a face on barred spiral appearing small and round with a central brightening. A 7th magnitude star lies near to the northeast.

NGC 5011 is a long and extended lenticular galaxy and lies among a number of foreground field stars. Lenticular galaxies show no disk structure and appear rather like elliptical galaxies with whom they have sometimes been mistakingly identified. NGC 5011A lies to the southwest and is quite faint. NGC 4988 is also a lenticular galaxy and appears as a faint extended streak just under 3' south of a pair of 9th and 10th magnitude stars.

A small group of faint galaxies huddle around a 7th magnitude star to the southwest of NGC 5128. The brightest of this group is NGC 5090, discovered by Sir John Herschel at the Cape Of Good Hope. He recorded it as:

"pretty faint, round, 30 arcseconds. The third of four."

The 7th magnitude star to the northeast must be kept clear of the eyepiece field to take full advantage of this elliptical system. Next to NGC 5090 lies the spiral NGC 5091, appearing as a small and faint streak of light. These two galaxies are interacting. Other galaxies in the immediate area are NGC 5082, NGC 5086 and the very faint NGC 5090A and NGC 5090B.

NGC 5237 lies around 3° to the east of NGC 5128, just south of a pair of 7th magnitude stars. This is a large and faint oval shaped possible elliptical though the type is uncertain.

Finally, NGC 5483 is a face on spiral residing a couple of degrees off the Lupus border. Look for a faint and round glow northeast of a 6th magnitude star. This would be a nice target for astrophotographers with its beautiful and prominent spiral arms.

Many other galaxies lie throughout this region including a large cluster northwest of NGC 5128, a tantalising treat for those under a dark sky with large mirrors.

Clear skies and good hunting ~CosMos