Astr212 Galaxy Projects, Spring 2007

Blackeye Galaxy (M64), Brian Vanderwal

This is an image of the Blackeye Galaxy (M64), which is about 19 million lightyears (5.8 megaparsecs) away. It is about 16 kiloparsecs in diameter.

Galaxies are classified as one of three types: elliptical, spiral, or barred spiral. Ellipticals appear just as the name sounds - like some type of ellipse. Spirals are more circular and generally have arm-shaped structures emanating from the core. Barred spirals are similar, but the arms emanate from a straight bar that passes through the core.

M64 is a spiral galaxy, though its spiral arms do not appear very pronounced. Spiral galaxies are circular, but this one appears elliptical because we are viewing it at an angle (very few galaxies are oriented in a perpendicular direction relative to our line of sight). M64 happens to have an inclination angle of approximately 63 degrees away from us (the "southern" side is closer).

Two things make M64 different from many other galaxies. For one thing, many have observed that the inner part is actually spinning in the opposite direction as the outer (this is very rare). This counter-rotation could be the cause for much of the star formation which can be seen taking place near the core.
Secondly, it has a dark dust cloud obscuring a large region near the core, from which it gets the name "Blackeye Galaxy." Both the unusual rotation and apparent black eye have been attributed to a collision with another galaxy. The prominent blue color near the core is evidence of a high amount of new star formation.

Spiral galaxies are classified based on three parameters developed by Hubble

• The size of the bulge relative to the disk length
• The tightness of the winding of the spiral arms
• The degree of resolution of the disk in stars and HII regions

Different letters correspond to certain values within those three main areas, though extra letters have been inserted over the years to cover more specific features. The official classification of M64 is (R)SA(rs)ab. This can be broken down to determine the features of the galaxy:

• (R) - it has a pseudo-ring shape
• S - spiral galaxy
• A - ordinary (not barred)
• (rs) - intermediate ring shape
• ab - moderately tight spiral arm windings

Images at other wavelengths

To the right is an infrared image of M64 taken by the Hubble Space Telescope. The black eye dust cloud is not as visible since the infrared light can pass through it. The prominent red patches in this image are glowing hydrogen (the Paschen alpha spectral line), which is the raw material for star formation. Without the obstruction of the black dust, it is somewhat possible to see the slight ring-shape, particularly near the core of the galaxy.

Light Profile

The above brightness profile shows how the perceived brightness of the galaxy falls off as you move away from the central bulge. The far left of the graph is the brightest point directly in the center of the galaxy. This graph plots the brightness along the minor axis, so you can see that as the brightness begins to drop off, there is a large dip. This is where the black eye dust lane causes extinction on one side.

Comparing the brightness profiles in the green and blue filters makes it possible to determine the amount of extinction caused by the dust lane. It is especially convenient for M64 since the dust only occurs on one side, making it easier to compare against light on the opposite side. By doing this, I found the extinction to be about 3.4 magnitudes.

The calculated scale length of the major axis is 0.781± 0.005 kpc, and of the minor axis is 0.348± 0.003 kpc. The surface brightness measured along the major axis came out to 3470± 60 counts/pixel, and along the minor axis 5500± 100 counts/pixel. This means that M64 is among the smaller galaxies observed by the class, whose scale lengths ranged from 0.6 to 1.8 kpc.

I reduced the data collected for this project by doing the following:

1. Open all images taken with the same exposure time in Maxim
2. Go to Process | Set Calibration. At the top of the calibration dialog, make sure only Calibrate Bias, Calibrate Dark, and Calibrate Flat are checked.
3. Add a group for Dark, and add the dark file to the group. Use auto-optimize for Dark Frame Scaling, and sigma clip for Combine Type.
4. Add a group for Flat, and add the flat file to the group. Use sigma clip for Combine Type.
5. Add a group for Bias, and add the bias file to the group. Use sigma clip again for the Combine Type.
6. Click OK, then go to Process | Calibrate All and wait as Maxim calibrates the images.

References:
Frommert, Hartmut and Kronberg, Christine
Messier Object 64
<http://seds.lpl.arizona.edu/messier/m/m064.html>

Frommert, Hartmut and Kronberg, Christine
Messier 64 HST Images
<http://www.seds.org/messier/more/m064_hst.html>

Caltech Cool Cosmos
<http://coolcosmos.ipac.caltech.edu/cosmic_classroom/
multiwavelength_astronomy/multiwavelength_museum/m64.html>

This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.