Astronomical Observatory: Cool Images

Astr212 Galaxy Projects, Spring 2005

M85: A Lenticular Galaxy, Kristin Datema

Galaxies are large groupings of stars that can contain hundreds of billions of stars. One such galaxy is M85
(right), which is a lenticular (SO) galaxy. Lenticular galaxies are galaxies that are neither completely elliptical
nor spiral galaxies. Elliptical galaxies appear to be smooth and have an elliptical shape, but have no spiral structure. Spiral galaxies, on the other hand, have disks and a spiral structure within their disks. A lenticular
galaxy is a combination of an elliptical and a spiral galaxy. Lenticular galaxies have a disk, but do not have a
spiral structure in the disk. Often lenticular galaxies are misclassified as ellipticals because then tend to
appear more as ellipticals than spirals. In this image the disk structure is hard to see, but it has a vertical orientation. Some lenticular galaxies have a much more prominent disks. For example, NGC 5866 has a
clearly visible disk. Also in the image NGC 4394 (left) is a small barred spiral galaxy. From the image it is
apparent that NGC 4394 has a spiral structure whereas M85 does not. These galaxies do have similarities,
for instance both M85 and NGC 4394 have disks even though it is not so apparent in the image.

M85 was discovered in 1781 by Pierre Mechain. The name M85 came from Charles Messier who added the
galaxy to his famous catalogue. M85 is located approximately 59 million light years away from the earth. This particular galaxy is the northernmost member of the Virgo Cluster of galaxies and it can be found in the constellation Coma Berenices. In the image, M85 appears to have a yellowish tint because it contains an old
yellow stellar population. The stars are yellow because they are long-lived stars which are low temperature
stars and are therefore towards the red end of the spectrum.

Multi-wavelength images:

In the above image the contours are x-ray and the gray scale is the optical negative. M85 is the dark spot in
the middle. This x-ray image shows the supernova remnants and ionized hydrogen. The light detected by this image is emitted through synchrotron radiation. This means that there were supernovae in M85 in the past.
In fact, according to S.E.D.S., there was a supernova in M85 and it appeared in 1960.

The above image is a Near Infrared image of M85. The colors in this image show three infrared wavelengths:
1.25, 2.2, and 3.5 microns. The objects seen in this image come from the blackbody emission of the K, F,
and M stars. These are the older and cooler stars in the bulge of the galaxy. This image therefore shows that
M85 does indeed contain older stars.

Light Profile:

This graph is the light profile for the major axis of M85. A light profile is a plot of the brightness of a galaxy at certain radii. This is important for an elliptical galaxy because it can be used to determine an effective radius.
The effective radius is of interest because inside that radius, half the total light given off by the galaxy is
emitted. The data was analyzed and a light curve was created using Microsoft Excel. The equation of best fit
was y = -1.251x + 5.774, where y = log(surface brightness) and x = (radius)^(1/4). From this data the effective radius and the ellipticity can be calculated. The effective radius of the major axis was 100.54 arc seconds
with an uncertainty of .06 arc seconds. The ellipticity of M85 was calculated to be n=1.2.

References:
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)

Students for the Exploration and Development of Space, M85.

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.