Astronomical Observatory: Cool Images

Astr212 Galaxy Projects, Spring 2005

M59: Elliptical Galaxy (E5), Samuel VanScoter

M-59 (which is the reddish disk near the center) is an elliptical galaxy that is about 60 million lightyears away. Galaxies are huge structures in the universe that are comprised of millions of stars held together by
gravitational force. There are mainly two types of galaxies that can be found, spiral and elliptical galaxies.
Spiral galaxies have a lot of dust and gas that rotates around the central core and can create spiral arms. Although the stars in elliptical galaxies do revolve around the core of the galaxy, spiral arms do not form.
Some reasons are because the stars in elliptical galaxies do not always revolve in the same direction and
elliptical galaxies contain much less gas and dust than spiral galaxies.

The light in the photograph above is emitted mainly by stars. The reddish color around the core of the galaxy
is from numerous old stars in the galaxy. Since there is very little gas and dust in ellipticals, new star
formation is pretty rare. The formation of new stars would give off a blue color because short-lived stars are
much hotter and can burn through their fuel faster. Therefore, Spiral galaxies tend to be more blueish in
color and Elliptical galaxies tend to be more reddish.

M-59 is classified as an E5 elliptical because its major axis is twice as long as its minor axis. The classification
of elliptical galaxies is a measure of their deviation from a perfect circle, or their ellipticity. Ellipticity is
calculated by e = 1 - (b/a), where b is the length of the minor axis and a is the length of the major axis. The classification number comes by muliplying e by 10 and that result is put after an 'E' and called the galaxies classification. To calculate e for M-59, I used the b and a as the minor effective radius and the major effective radius respectively (See light profile below).

M-59 is the only galaxy in the photograph, all of the other dots are stars.

Images taken from non-visual parts of the spectrum:

Near Infared:

This image was taken in the near infared part of the spectrum with the 2MASS 1.3m telescope. The
resolution was 2.5 arc seconds. The wavelengths of the image range from 1.11 to 2.32 micro meters. The
size of this image is 7.0 by 7.0 arc minutes. This image shows the blackbody radiation emitted from cool,
low-mass stars. As you can see, there are many cool, low-mass stars around the core of M-59. Since new
stars are hot, these are older stars.

X-Ray:

This image was taken in the X-ray part of the specturm by the Einstein Observatory telescope. The
wavelengths of the image range from 0.2 to 3.5 kilo electron volts. The image shows X-ray image
superimposed over an optical image translated to a grey scale. The X-rays are shown as contour lines and represent the syncotron radiation emmitted by Super Nova remnants and also can be from binary stars.

Light Profile:

A light profile is a method for measuring and then determining a model for the surface brightness of a galaxy.
This model is then able to reveal to us the internal structure of the galaxy and also reveal to us their
formation and mass distribution. Since elliptical galaxies are very bright near the core and fairly faint out in
the envelope, I calculated the radial profile for M-59. Radial light profiles for elliptical galaxies are generally represented by "de Vaucouleurs r ^ (1/4) law" because the surface brightness of most elliptical galaxies
decreases as r ^ (1/4) goes out from the center.

Major Axis:

The above graph shows the brightness as a function of radius, as measured along the major axis of M-59.
As you can see the brightness falls off at an exponential rate, and the effective radius of the major axis is
between 3 and 4 kpc. When I calculated the effective radius for the major axis of M-59 I got the value 3.86
kpc.

The above graph show the Log of the surface brightness as a function of radius to the (1/4) [in pixels]. Since
the plot graphs the line y = -1.4x - 6.0, the surface brightness along the major axis of M-59 falls off as radius
^ (1/4). This is common to most elliptical galaxies and confirms "de Vaucouleurs r ^ (1/4) law."

Minor Axis:

The above graph shows the brightness as a function of radius, as measured along the minor axis of M-59.
As you can see the brightness falls off at an exponential rate, and the effective radius of the minor axis is
between 2 and 3 kpc. When I calculated the effective radius for the minor axis of M-59 I got the value 1.62
kpc.

The above graph show the Log of the surface brightness as a function of radius to the (1/4) [in pixels]. Since
the plot graphs the line y = -0.7x - 6.2, the surface brightness along the minor axis of M-59 falls off as radius
^ (1/4). This is common to most elliptical galaxies and confirms "de Vaucouleurs r ^ (1/4) law."

References:
Bannister, Nigel. "Elliptical Galaxies" University of Leicester, Physics and Astronomy. 2003

Elmegreen, D.M. 1998, Galaxies and Galactic Structure (New Jersey: Prentice Hall)

Fabbiano, G.; Kim, D.-W.; Trinchieri, G., "An X-ray catalog and atlas of galaxies", 1992, Astrophysical Journal Supplement Series, 80, 531

Jarrett, T. H; Chester, T.; Cutri, R.; Schneider, S. E.; Huchra, J. P."The 2MASS Large Galaxy Atlas", 2003, Astronomical Journal, 125, 525

Kutner, M. L. 2003, Astronomy: A Physical Perspective, 2nd ed. (Cambridge: Cambridge University Press)

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.