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Astr212 Project: Light profile of Galaxy M32

M32 GalaxyM32 is a member of the Local Group of galaxies, and is an elliptical dwarf galaxy of the type E2. It is a companion of the Great Andromeda Galaxy, M31.
M32 was the first elliptical galaxy ever discovered and was discovered by Le Gentil in 1749. Since then there have been more observations of this galaxy. It is among the most investigated elliptical galaxies since it is one of the closest brightest elliptical galaxies to us. Messier who is famous for grouping the galaxies into a catalogue, first observed this object in 1757, 8 years after it was first discovered. It appears as a round, bright patch, and is situated south of the central region of Andromeda, M31.

M32 was first resolved into stars by Baade in 1944, when he also resolved the nucleus of M31. It was Baade who recognized that the stars of M32 were population 2 stars.

Outside links to other images of M32:

Contents of the image:

The image is oriented with the North being straight up in the image, East is to the left. The major axis is located about 25 degrees east of north.
For cases of observation, M32 can be found in the constellation Pegasus, near the hind feet of the horse.

Right Ascension 00h 42' 51"
Declination + 40° 53' 01"
Distance 2.5 Million Light Years
Size 221 Pc
Mass 3 million M solar
Linear Diameter 8000 Light Years
Apparent Magnitude 8.6

1 Solar mass = 1.99 X 10^30 kg

Although M32 is a dwarf galaxy, it resembles a much larger elliptical galaxy. Therefore there are beliefs that M32 was at one time a large elliptical galaxy, but lost its outer stars to the Halo of Andromeda, in past encounters. Proof for these encounters is suggested in the disturbed spiral pattern of M31.

M32 consist mainly of old population 2 stars, which are red old stars that were formed near the beginning of the universe. However, there seem to be intermediate stars of heavier elements. These are typical population 1 stars, which were formed later and are hotter, bluer and brighter stars. The presence of these heavier intermediate stars may be responsible for the difference in characteristics of M32 from other dwarf galaxies of comparable size. M32 is a lot brighter than other dwarf galaxies and its apparent color is not normally associated with its age.

Light Profile:
The light profile of the galaxy is shown below. The light profile is a plot of the brightness versus the radius of the galaxy (distance from the center to the point in consideration). This of importance because the light profile of an elliptical galaxy can be used to determine the mass enclosed in an effective radius. The effective radius (re) is also an effect of the galaxy light profile. The equation below shows a relationship for the brightness and radius.

r = distance (radius)
re = effective radius
E(r) = Brightness at distance r
Ee =Brightness at the effective radius re

The main characteristics of an elliptical galaxy light profile are:

  • The brightness decreases with increasing radius
  • The log of the brightness is directly proportional to the (radius)^(1/4)

It's nucleus contains about one-third of this mass

M32 contours M32 light profile

The image above shows contour lines of M32, and clearly shows its elliptical structure.

M32 light profile

The typical effective radius for bulges of spirals is between 0.5 to 5 kpc. The value for this experiment is 0.22kpc which is slightly lower than the expected radius. However, this is because the brightness of M32 peaks rapidly as you move in toward the center. This phenomenon can be seen on the graph of the brightness versus the radius. The more light that a galaxy gives off, the heavier it is. This is without the effects of dark matter. Since the brightness of M32 peaks off rapidly around the center we would expect a lot of its mass to be enclosed in a small radius.

Observing Process:
The above image was compiled from 15 raw images by Andrew Vache, taken with a CCD camera mounted to the 16" Schmidt-Cassegrain telescope in the Calvin College Observatory. All the observing was completed on November 12, 2002 between 7:30PM and 8:30PM. Corresponding dark images (images taken with the camera shutter closed) and flat images (images taken of diffuse incandescent light through the telescope) were also taken on November 12.

M32 galaxy
Each raw and dark image was taken with a 9.25 second exposure.
After aligning the raw images, and subtracting the dark and flat images from the aligned image looked as it does above.
Further image processing using the computer program DS9 led to the image below, with the light in the galaxy fit to a squared scale, showing the actual structure of the ellipse. A "heat" filter led to the orange color.

Team: Joel Eigege and Andrew Vache