Michael Dorris
Graduate Student, Physics (Astronomy Program)

Office
Varian Physics Building, Room 302a
382 Via Pueblo Ave.
Stanford, CA 94305-4060
650-723-8025
My current research project involves producing models and fitting data that describe the evolution of galaxy types through the history of the universe. In particular, I am looking at the kinds of bias that are inherent to observing nearby and distant galaxies. Well-known is the bias toward bright galaxies; at large distances, one is likely only to see the brightest galaxies. Somewhat more difficult to quantify is the bias due to surface brightness, i.e. how centrally concentrated the light is. If nearly all of the light in a galaxy comes from the innermost regions, then the observed point of light in the sky may be so small that we cannot tell if it is a galaxy or a point source (e.g. a star). If the light in a galaxy is greatly spread out, then even though the galaxy may be bright enough in total for us to detect it, each individual point in our image may be too faint to be able to detect the shape of the galaxy.

This kind of bias analysis has been done before, in different degrees of detail. What makes this project new is that only recently have galaxies' surface brightness functions been begun to be measured with good accuracy. A surface brightness distribution is a statistical quantity, describing how many galaxies are observed for a given surface brightness. Combined with the simpler luminosity function, which describes how many galaxies are seen for a given total brightness, one can obtain a better description of the numbers of different kinds of galaxies. Additionally, one gets a better estimate of the number of galaxies most likely to be affected by the biases I am investigating.

Using this combined bivariate brightness function to predict and then fit these biases, one can try to describe how astronomers see the relative numbers of elliptical shaped galaxies and spiral shaped galaxies change with the history of the universe. A good understanding of the observational bias allows us to know how much of the observed change is artificially caused by bias, and how much is due to the inherent evolution of the universe.

In addition to this research, I have taken up the responsibility for maintaining the astronomy group web pages and mailing lists (particularly after a hacking incident on one of the astronomy computers left the pages and mailing list in disarray).

Poster Presentations
Influence of Surface Brightness Dimming and the K-correction on Observed Morphological Evolution of Distant Galaxies
Dorris, M., Petrosian, V. Poster submitted for AAS Meeting #203 (Jan 2004)
A Magnitude-Redshift Relation for Distant Clusters of Galaxies
Dorris, M., McNamara, B.R., Vikhlinin, A. Poster #106.05 at AAS Meeting #191 (Jan 1998)

Unpublished review essay (March 1998): Observational Evidence for a Cosmological Constant
PostScript / gzipped PostScript / HTML


Michael Dorris - contact address (Personal page)