We are surveying the entire galaxy M33, a spiral galaxy in the Local Group, with several ground-based telescopes and space observatories. The multi-wavelength imaging will provide un unprecedented complete view of the stellar populations and diffuse medium in this galaxy, and their physical conditions.

Click to see a multi-wavelength view of the entire galaxy M33. The different colors (filters) or energy bands show the different components of the galaxy: interstellar gas, heated dust, young stars and old stars.

Here is a sample from our HST multi-band photometric survey of M33,
showing the center of the galaxy:



In the image below you can explore the center of the nearby spiral galaxy M33, observed with the Hubble Space Telescope WFPC2 (Wide Field and Planetary Camera 2). The false-color image is a combination of data in three different filters: F555W, approximately V (visual) = GREEN, F439W (BLUE), F336W (U, visible Ultraviolet) and F170W, a space ultraviolet (UV) band not visible from the ground and recording flux emitted at higher energies.
Scroll the cursor on the navigation buttons on the right, to see how the appearance of the galaxy changes with color (i.e. frequency, or energy). The images taken in the visible colors (V, B) show the galaxy ``bulge'', a diffuse dense population of old and middle-age stars, numerous and not particularly bright. As you go towards bluer colors (---> U, ---> UV), younger and hotter stars are revealed. In the UV (F170W) filter, the old population (bulge) desappears entirely, and an inner spiral arm structure is delineated. These are the hottest, youngest and most massive stars formed. They are much more sparse than the older, fainter stars in the bulge, because massive stars are rare (read here if you want to find out why).







The image is about 150 arcseconds on a side. At the distance of M33, this corresponds to an extent of 615 parsecs across the center of the galaxy, (a bit more than the distance from us to the Orion nebula). The galaxy M33 is at a distance of 817,000 parsecs (that is about 2.5 million light years, or 15.5 billion times the distance Sun-Earth). At the distance of M33, 1 arcsecond on the sky corresponds to about 4 parsecs, hence this Hubble Image (0.1arcsec resolution) is resolving details down to a scale of 0.4pc (1.2 light year), allowing us to study the individual stars in this galaxy as well as its global stellar population.

This image was taken with a Hubble Space Telescope program led by L.Bianchi




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