When people think of galaxies, they might think of a large group of stars spinning around a point in a shape similar to a top. While this idea is not entirely inaccurate it does not fully describe the many different features that can be seen and studied within the many types of galaxies. The galaxy that I chose to study for this Galactic Astronomy and Cosmology class is formally named M98. This name is given because it is number ninety-eight in the set of astronomical figures that Charles Messier catalogued. This galaxy has also been catalogued in the New General Catalogue as NGC 4192. Neither of these names do anything for describing anything about the galaxy. The M 98 galaxy is located approximately 16 megaparsecs, 55 megalight years, or for those not accustomed to astronomical units 500 quintillion kilometers, or 300 quintillion miles. This galaxy is also about 35 kiloparsecs in diameter,seen in the picture from bottom left to top right..
The official classification of this galaxy is SAB(s)ab. This classification means that it fits about halfway between a spiral galaxy and a bar galaxy and has a relatively large core. M98 looks similar to our galaxy to the average person. When looking for this galaxy in the night sky you will first need a rather large telescope because of the apparent magnitude of about 10, which is just dimmer than objects can be seen with a pair of decent binoculars on a clear night. The M98 galaxy is located in the Coma Berenices constellation in a group of galaxies called the Virgo cluster. An interesting feature about this galaxy is that it is blue shifted and by definition is traveling towards us. The redshift is -0.000474, which means that this galaxy is traveling towards us at 141.1 km/s. This is largely due to it being located in a very large cluster of galaxies and its relative movement is more influenced by the Virgo cluster than the expansion of the universe
One of the more striking features of this galaxy is the color that it produces. In the center the bulge produces a more whitish yellow light while in the disk and arm section it has more of a bluish hue. When researching galaxies light is the most important source of information and differences in wavelength and color can be used to predict many features about galaxies. The bluish hue around the edge and throughout the disk shows that newer younger stars are being formed. Blue stars are much hotter than red stars and burn through their resources faster. This lets us know that the blue regions contain much younger stars. Also notable are the blurred sections near the center that appear to block out some of the light. These are dust regions and are important in the formation of new stars.
Figure 1. From  Distefano et al.: "Rotational curve folded with respect to the dynamical center and the systemic velocity. Full dots and open circles are the two opposite sides. The solid line is the polynomial fitted to the curve. The optical spectral line was used for these points. (not corrected for inclination)."
Figure 1 shows the rotation curve of the galaxy. This shows that if a measurement of velocity around the center of the galaxy is taken of individual stars, as the distance increases from the center, velocity neither increases nor decreases dramatically. This rotation curve is very consistent with what is known about most spiral galaxies. Stars that are located farther away from the center of the galaxy do not travel slower than stars located closer. This is counterintuitive when looking at systems such as our solar system where Pluto travels around the Sun much slower than Mercury. Astronomers' explanation for this vast difference in observations is that galaxies contain a large amount of dark matter which moves with the stars around the galaxy.
Figure 2. From  Distefano et al.: "Comparison between optical (full dots) and radio curves (open circles: Guhathakurta et al., 1988)"
In figure 2 another rotational curve is shown but this one includes radio wave observations as well as visual observations. This result shows that not only are the stars traveling at the same speed but items such as neutral gas in the thin disk and most of the objects well out into the galaxy's "halo" are all traveling near 250 km/s and that this speed is independent of their distance to the center of the galaxy.
Figure 3. UV image taken by GALEX (via NED on M98).
When studying galaxies and other deep space objects it is important to not just view them at an optical wave length but to use other wavelengths to learn more about a galaxy. Seen in Figure 3 is a UV capture of the M98 galaxy taken by the telescope GALEX. From this image the spiral arms can be very clearly seen. The UV part of the spectrum reveals emissions from very young OB stars (hot massive stars in the OB sections of stellar classification). These stars are located within the spiral arms. The arms of galaxies contain many of the ingredients needed to form stars as well as the gravitational pressure waves and this can be seen in the image above with all the young stars residing mostly in the spiral arms.
Shown here is another beautiful image of the galaxy M98. The credit for this picture goes to Astrofotografia and astroguia.org.
 Distefano, A; Rampazzo, R; Chincarini, G; de Souza, R. "Optical studies of galaxies in clusters. II- Observations of spirals in Virgo" Astronomy and Astrophysics Supplement Series (1990), 86, 7. <http://adsabs.harvard.edu/abs/1990A&AS...86....7D>
 "Astrofotografía - Galería de imágenes astronómicas" Astroguia. 2007-04-02. Web. Accessed April 2011. <http://astroguia.org/astroalbum/displayimage.php?pos=-309>
 Kutner, Marc L. Astronomy: A Physical Perspective, 2nd ed. Cambridge: Cambridge University Press, 2003.
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.
|Right Ascension (J2000)||12:13:48|
|Filters used||blue(B), green(V), red(R), and clear(C)|
|Exposure time per filter||
11x300 seconds in C
2,4 2011 (C)