[M79]

Canis Major Dwarf

Irregular Galaxy Canis Major Dwarf, centered in Canis Major

[CMa Dw in IR]
Right Ascension 07 : 15 (h : m)
Declination -28: (deg : m)
Distance 25.0 (kly)
Apparent Dimension 720 (arc min)

Discovered in November 2003 by Martin, Ibata, Bellazzini, Irwin, Lewis, and Dehnen.

This small galaxy, or galaxy remnant, was discovered only in 2003 by a team of astronomers from France, Italy, the UK, and Australia. It was found from the analysis of data on asymmetries in the population of Galactic red giant stars (of spectral type M) in the 2MASS All Sky catalog. These stars show several large-scale asymmetries, the most significant of which is a strong elliptical-shaped over-density close to the Galactic plane, around the position l=240deg, b=-8deg in Galactic coordinates, or about RA=07:20, Dec=-30, with an extension in Galactic longitude of about 12 deg (720 arc min). The distance of this concentration was estimated at 25,000 light-years from us and 42,000 light-years from the center of our Milky Way Galaxy.

The authors find that this concentration is the nucleus of a dwarf galaxy which is in a progressive state of disruption, as it orbits our Milky Way Galaxy. This galaxy is thus our nearest known intergalactic neighbor, and a new dwarf member of the Local Group. The major part of its matter has been distributed along its orbit, and forms arc structures around the Milky Way. It may have been a considerable though small galaxy at one time, having of the order of one billion stars, and may have contributed up to about one percent of the matter of our Milky Way.

The image on the right shows the Canis Major Dwarf's nucleus just below the stellar band indicating the equatorial plane of our Milky Way. This is an infrared view, composed from the Two-Micron All Sky Survey (2MASS).

In many respects such as size, orbit and the process of dissolution, the Canis Major Dwarf is similar to SagDEG, which had been discovered in 1994 and taken the place as the nearest known neighbor for nine years.

Some Milky Way globular clusters are loosely grouped around the nucleus of the Canis Major dwarf, and at least some of them may have their origin in the halo of this small galaxy, and may represent the remnant of its former globular cluster system: M79, NGC 1851, NGC 2298, and NGC 2808. Open clusters AM-2 and Tombaugh 2 are strong candidates for being physically associated with the Canis Major Dwarf.

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References:


Hartmut Frommert
Christine Kronberg
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Last Modification: November 22, 2003