Messier 83

Discovered 1752 by Abbe Nicholas Louis de la Caille.

Messier 83 (M83, NGC 5236) is one of the most conspicuous spiral galaxies in the sky. Situated in constellation Hydra, it is the southernmost galaxy in Messier's catalog.

M83 was discovered by Abbe Nicholas Louis de la Caille at the Cape of Good Hope on February 23, 1752; it was his object Lacaille I.6. Thus it became the first galaxy to be discovered beyond the Local Group, and the third of all galaixes, after M31 and M32. It was next cataloged by Charles Messier on February 17, 1781; from his mid-northern location in Paris (at 49 degrees Northern latitude), it is such a difficult object that he stated that: "One is only able with the greatest concentration to see it at all." The present author can confirm it is one of the most difficult Messier objects from South Germany. Due to this fact, older Northern-compiled catalogs tended to underestimate its brightness considerably; e.g., Becvar has it at a mere 10.1 mag only.

Early 19th century Australian observer James Dunlop has it as No. 628 in his catalog. Its spiral structure was noted and sketched by William Lassell who described it as a "three-branched spiral."

M83 was classified as intermediate between normal and barred spiral galaxies by G. de Vaucouleurs, in his classification this is SAB(s)c. It is magnificient in our image, has very well defined spiral arms and displays a very dynamic appearance, appealing by the red and blue knots tracing the arms. The red knots are apparently diffuse gaseous nebulae in which star formation is just taking place, and which are excited to shine by its very hot young stars. The blue regions represent young stellar populations which have formed shortly (i.e., some million or some dozens of million years ago). Between the pronounced spiral arms are regions with fewer stars. Dark dust lanes follow the spiral structure throughout the disk, and may be traced well into the central region to the nucleus, which has only 20" diameter. This nucleus shows strong emission lines. It is composed of an older yellowish stellar population which dominates the whole central region, and extends along the barlike structure.

Our image was obtained by David Malin with the 3.9-meter Anglo-Australian Telescope of the Anglo-Australian Observatory. Interested parties can get more detailed information on this image. Also available are more images of M83 with the same telescope.

David Malin, in his older publications, always gave a distance of about 25 million light years, as he does in his book A View of the Universe in chapter 4, while in his Galaxies chapter 8, he joins the lot of those claiming a distance of about 10 million light years, and gives an argument, namely that the brightest stars can be viewed as individuals over this distance. M83 recedes at 337 km/sec, implying a bit larger distance from Hubble's law (H0=75 yields about 15 million light years, uncorrected for the disturbation by the Virgo cluster of galaxies, the Virgo centric flow, but in excellent agreement with the value of 15.3 million light years given in R. Brent Tully's Nearby Galaxies Catalog). Kepple/Sanner give another deviating distance value of 22 million ly.

This galaxy is sometimes called the "Southern Pinwheel". It forms a small physical group, the M83 group, with the peculiar radio galaxy Centaurus A (NGC 5128) and the unusual galaxy NGC 5253 in Centaurus. R. Brent Tully also lists the following smaller and fainter presumable (or possible) members of this group: NGC 4945, NGC 5102, NGC 5164, NGC 5408, ESO 381-20 (MCG-6-28-017; 1243-33), ESO 324-24 (MCG-6-30-003; 1324-41), ESO 444-84 (MCG-5-32-000; 1334-27), ESO 325-11 (1342-41), and ESO 383-87 (MCG-6-30-025; 1346-35).

Five or six supernovae were reported in M83 up to now, more than in any other Messier galaxy:

• 1923A was observed by C.O. Lampland at Lowell Observatory at mag 14.
• 1945B appeared on July 13, 1945 and reached mag 14.2). This supernova was only detected in 1990 by W. Liller on photographic plates taken at Harvard's station at Bloemfontein (South Africa), and could be traced from July 13 to August 7 (see IAU Circular 5091).
• 1950B was observed by G. Haro and reached mag 14.5 in its maximum,
• 1957D was discovered by H.S. Gates on December 13, 1957 and reached only mag 15.0, it was about 3' NNE of the nucleus.
• Supernova 1968L was discovered visually by amateur astronomer Jack C. Bennett of Pretoria, South Africa, when sweeping for comets; this was a type I, located 5" preceding the nucleus and reached mag 11 to 12.
• 1983N appeared on July 3, 1983 and became as bright as 12.5 mag.

For years, M83 had been the galaxy with most discovered supernovae, but semi-recently NGC 6946 passed this mark and holds the current record with a total number of 8.

M83 is one of the showpieces in the southern deep sky, but difficult for mid-northern observers, as already stated. It is even rather difficult to find: First locate one of the stars Gamma or Pi Hydrae. It can be found either by star hopping from Gamma Hydrae (mag 3.00, spectral type G5 III) which is 6.5 deg N and 3deg 15' (19 min in RA) W, or from Pi Hydrae (3.27 mag, spectral type K2 III) from which M83 is about 3deg 15' S and 6deg 20' W. Following a trail of 5th to 7th mag stars, one arrives at a yellowish 5.83-mag star of spectral type F6 and a mag 7.0 white star (spectrum A5 V) which lie about 30' NE of M83. Star hopping from Gamma will bring you close to NGC 5061 (H 1.138), an elliptical galaxy of mag 10.2.

Southerners may find it easier by locating M83 from the constellation Centaurus, as it is just north of the border from Hydra to this constellation. From Iota and Theta Centauri, in the Head of the Centaurus figure, locate the stars i, h and k (mentioned by Messier) as well as g Centauri, all between mag 4 and 5; they are also known as 1 i Cen, 2 g Cen, 3 k Cen, and 4 h Cen. g and i just point to M83 (and further to Gamma Hydrae); the galaxy comes beyond i, at double distance from it than has g.

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