Press Release

Subaru Reveals History of Star Formation in M33

March 6, 2009

The Subaru Telescope in Hawai’i has produced a beautiful high-resolution view of the nearby galaxy M33 that reveals fine structure in its spiral shape. The image, which covers an area of sky roughly equivalent to eight full moons and shows details in a region measuring 90,000 x 60,000 light-years across, shows the spatial distribution of stars, star clusters, and star-forming regions in M33 in detail.

This galaxy, which lies about 2.5 million light-years away in the constellation Triangulum, is one of the closest galaxies to our own Milky Way. That proximity -- plus its nearly face-on view -- makes M33 a suitable target for the detailed study of spiral structure. There have been no other high-resolution images that cover M33 so widely and deeply.

The Subaru/Suprime-Cam image of M33 was taken by an international research group of astronomers from the National Astronomical Observatory of Japan, the Institute of Physics of Lithuania, the Gunma Astronomical Observatory, and other institutes in Japan, France, and the UK.

Zooming in on the Details

Most of M33’s light comes from stars in its disk. While many spiral galaxies, including the Milky Way, boast central structures called bulges, M33 does not seem to have one. Instead, it appears that the central region of the galaxy has a rich history of star-birth activity. One burst of star formation took place in M33’s central region approximately 10 million years ago.

Out in the disk, away from the central areas of star birth, there are numerous open clusters and star-forming regions containing massive young stars. The analysis of high-resolution images of this galaxy makes it very straightforward to map the spatial distribution of stars formed at different epochs of M33’s evolution. For example, star-forming activity in the disk seems to propagate from the central part to the outer disk. This new image will help astronomers map the star-formation history of each individual region in this galaxy.

In addition, the disk of this galaxy is surrounded by a halo containing a sparse distribution of stars and globular clusters. A detailed analysis of M33 reveals that old halo stars are spread all over the place.

There is also a difference in M33’s globular cluster population. While globulars in the Milky Way are older than 10 billion years, those in M33 are estimated to be a few billion years younger, suggesting that there was a different formation history for clusters in M33 than those belonging to the Milky Way. Such differences may arise from the fact that the mass of M33 is an order of magnitude less than the Milky Way.

The research group also discovered an extended globular cluster at M33. It is considerably different from the normal compact globular clusters we see in the Milky Way and could well be the remnant of a dwarf galaxy that merged with M33 in the past. Finding such a cluster indicates that M33 has a complex merger history.

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Object Name: The spiral galaxy M33
Telescope: Subaru Telescope / Prime Focus
Instrument: Suprime-Cam
Filter: B, V, Hα
Color: Blue (B), Green (V), Red (Hα)
Date: UT Nov. 20, 21, 2001; Nov. 4, 2002
Exposure: 7.5 min. (V), 15min. (Hα), 9.2 min. (B) for each field of view.
Field of View: Approx. 100' x 65' (8 fields of the Suprime-Cam' field of view)
Orientation: West-northwest is up, South-southwest is left
Position: RA(J2000.0)=1h34,
Dec(J2000.0)= +30°39'

Zoomable Images:Spiral Galaxy M33



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