The Leo triplet of galaxies
AAO image reference AAT 103.    « Previous || Next »

The Leo triplet of galaxies, NGC 3628, NGC 3627 (M66) and NGC 3623 (M65)
Top left is NE. Image width is about 50 arc min
Image and text © 1991-2010, Australian Astronomical Observatory, photograph by David Malin.

This picture is almost a degree across on the sky and shows three members of a small group of galaxies in the northern constellation of Leo. These galaxies are together in space at a distance of about 30 million light years. Two of the galaxies were bright enough for Messier to see and he catalogued them as M65 and M66. Probably the most interesting member of the Leo triplet was too faint for Messier to notice, so it does not appear in his catalogue. This is NGC 3628, which is seen as an edge-on spiral galaxy at the top of the picture.

Galaxies seen edge-on are unusual, but NGC 3628 has other peculiarities that tell us something of the nature of the group as a whole. The dust lane is distinctly askew and the ends of the spiral arms are obviously puffed out, with some evidence of star formation. The bright bulge of the galaxy also has an unusual 'peanut' shape. All of this confirms observations made at radio wavelengths that reveal the galaxies of the Leo group are physically associated, gradually pulling each other apart as they engage their partners in a gravitational waltz from which there is no escape. The galaxies will eventually merge, losing their identity in a massive burst of star formation.

The rectangular pattern at the top of the picture is from the projection calibration sensitometer built into the photographic camera on the AAT. This pattern appears on every plate and is used to provide photometric and colour balance information, but is normally cropped off the final images.

Related Images
AAT 61.   Messier 65 (NGC 3627) spiral galaxy in Leo
AAT 62.   Messier 66 (NGC 3627) spiral galaxy in Leo
AAT 63 .  Edge-on spiral galaxy NGC 3628 in Leo
Constellation of Leo (external site)

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Updated by David Malin, 2011, November 17