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Physics & Astronomy Department

Astr212 Project: Light Profile of Galaxy M33

M33 GalaxyContents: M33, the Pinwheel Galaxy, is a Sc/Scd Spiral Galaxy. It rotates clockwise, with the northern arm moving slowly west. Its rotational period has been determined to be about 200 million years. It was probably first found by Hodierna before 1654, but was rediscovered by Charles Messier in 1764. It is about 3,000,000 light-years from earth. It covers an area of 73x45 arc minutes. Besides Andromeda (M31), it is the nearest spiral galaxy. Despite it’s proximity, it is very hard to observe because of its low surface brightness. Many amateur observers often set cannot find it because they are looking for a smaller, brighter object. It covers an area four times that of a full moon. Several supernovae remnants and 112 variable objects including 4 novae and 25 Cepheids, have been found within M33. M33 is one of only a few that does not show a redshift, it is approaching us at 7 miles per second.

The light emitted from M33 comes mostly from main sequence stars especially in the thin disk, large HII regions also contribute to the general light production. Most of the light from the spiral arms comes from blue supergiants, because of the higher amount of thes b-type supergiants, M33 seems “bluer” than most galaxies. The total integrated sprectral type is A7.

Our group set out to collect a light profile of M33 and to determine whether it fit well or poorly to theory. This was an interesting and challenging project because M33 is both large in the sky and fairly faint, but despite that we were able to create a light curve which was able to confirm that our original images were almost certainly of the bulge and that the disk must then extend off the scale of our original images.
Because M33 is so faint we were forced to be innovative in out methods. After a few false starts the method we ended up using was fairly simple. We used a piece of Astronomical software called DS9 to automatically generate two graphs of brightness per pixel along vertical and horizontal lines in our best image after rotating the image so that these lines didn’t pass through any stars and centering the crosshairs on M33. Then we printed those graphs and imported the best one into excel manually using rulers and our knowledge of proportions. Once we had this data into excel we converted pixels into kiloparsecs by using our knowledge of our original image and the distance to M33. Then we made several plots of this data to determine whether our theoretical model of the disk or the bulge fit better. As it turned out after looking at our data the bulge model fit extremely well, with a good value for the expected radius and a very good correlation to the linear fit we expected. Attached to this report you can see both our original image and two plots that show the light profile to the left and right of M33’s center with the linear trendlines we fitted to the data.

M33 Galaxy M33 Galaxy M33 Galaxy

This image is a combination of 80 images, each 20 seconds in exposure length. They were obtained on the 10th of October 2002 between the hours of 1:00am and 2:21am or 0500 and 0621 UT. The raw images had dark and flat field corrections applied to them and were aligned and then combined using the CCDSoft program by Software Bisque. The combination was done using an averaging algorithm which took the average of the aligned images thus enhancing the data and canceling out much of the noise. All of the exposures were taken with a clear filter maximizing the signal to noise ratio.

Orientation and Scale:
North is up and East is to the left. The binning for the exposures was set to 2x2 and the angular diameter of the image is 7.2x5.2 arcminutes. The galaxy core ahs celestial coordinates 01h 34m 01s +30º 40’ 37” (epoch 2000) which is 14.78 degrees South East of Andromeda (M31)

Team: Phil Ammar, David Bytwerk and Jason Kornas