M83 = NGC 5236 = MCG-05-32-050 = Southern Pinwheel Galaxy
Barred Spiral Galaxy in Hydra
RA: 13:37:01
Dec: -29:51:57
Mag (V): 7.52
Size: 13.8'×12.9'
I know you're asking yourself, how has this not been featured as the Object of the Week before! I was looking over the OOTWs in Hydra on Adventures in Deep Space and was surprised to see it so short and missing M83, so I have seized the opportunity to present a well-known object that is perhaps just a bit neglected due to its southern declination.
STScI-01EVT37HAEB2WGQ0DDR0A67PCY.jpg
M83 from the Hubble Space Telescope
The galaxy was discovered by Nicolas-Louis de Lacaille in 1751, before Charles Messier observed and recorded it as M83¹. It lies about 16 million light-years away from us². It is a grand design spiral galaxy. M83 is obviously very well-studied and the Wikipedia page happens to be well-written. The one interesting thing that stood out to me while reading that page was the potential interaction with NGC 5253, on which see Scott Harrington's OOTW post. M 83 is part of the Centaurus A–M83 galaxy group, which Scott helpfully annotated in his OOTW as consisting of Centaurus A, M83, NGC 4945 (Tweezers), NGC 5102 (iota's Ghost), NGC 5253 etc.
M83_POSSIBlue.jpeg
M83, POSS I Blue Image (it is overexposed on POSSII Blue)
Visually, the striking feature of M83 is certainly its beautiful grand design spiral arms, studded with star-forming knots and its prominent bar.
I first looked at this galaxy on December 27th 2005 from a village south of Bangalore, where I logged it through my ATM'd 8" f/8 as "Terribly faint face-on spiral" and noted that its surface brightness was similar to M 33. Three nights later, we were prospecting a new observing site in a village north of Bangalore where we encountered much better conditions. My logs show a lot of excitement around the sky, and the entry on M83 reflects that: "Significantly brighter! We could probably see the spiral arms!" I vaguely remember having seen it through 10×50 binoculars, but have no log entry.
Those of us who were on the field of Texas Star Party (TSP) 2012 (I spy Jimi, Alvin and others) will remember those special nights. It being my first ever time at TSP, I thought it was just another night and was very very impressed with the views. It certainly wasn't your average TSP night. The reason I mention this is that I still remember being very impressed by M83 that night – great conditions really make a difference. I logged, with my 18", "Bar, lots of spiral arms, mottling! Was not a uniform glow even in 8×50 finder."
My most recent observation was from a SAC site near Phoenix, Arizona. The sketch through my 18" shows a bright core with a bar running SE-NW. The bar gets brighter where it meets the spiral arms, and the galaxy appeared heavily mottled all over. Two tight spiral arms were discerned, going counterclockwise from the ends of the bar. The starting portions of two other spiral arms were also picked up. Here is my sketch:
M83_knots.jpeg
(I renamed A as #1, B as #2, C as #3 below so my designations are not confused with any official designations)
As you can see, I logged three knots, but it's hard to correlate the rough sketch to images and identify exactly which knots on the image correspond to the sketch. My best guess is the following:
Knot #1: 13:36:43.3 -29:52:19 ~ [RK83] 266
Knot #2: 13:37:04.2 -29:49:23 ~ [RK83] 113
Knot #3 (suspected): 13:37:01 -29:54:24 ~ [RK83] 144
M83Knots.jpg
Above knots marked on the POSSII Red image
The designations are HII regions plotted in SIMBAD or NED from Rumstay and Kaufman 1983 that were roughly aligned within the knots. Knot #1 was most prominent followed by knot #2.
Out of curiosity, I looked up the M83 Group in SIMBAD and it lists 13 members. I wanted to know what is the nearest dwarf galaxy towards M83 to see if it was tractable. It happens to be PGC 166170 which I wish you the very best of luck with, because there seems to be nothing visible on the DSS2 imagery! The next closest one seems to be ESO 444-78 which seems to have some hope of yielding.
GIVE IT A GO AND LET US KNOW
References:
1. Courtney Seligman's website on NGC 5236
2. Redshift-independent distances for M83 from NED
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