Research Interests

Elizabeth Praton
Department of Physics & Astronomy
Franklin & Marshall College
Lancaster, PA 17604

Welcome to my research page. What follows is an introduction to areas I've worked in, with links to more detailed explanations of problems I've worked on and reference lists of my publications and presentations.

I've done work in two areas, gravitational phase transition of rotating bodies, with applications to cosmological structure formation scenarios, and redshift-space distortion. I've also dabbled in studies of the Tully-Fisher relation and the cosmic microwave background. Redshift-space distortion is my main area of interest right now.

Redshift-Space Distortion

Large-scale structure maps of galaxy distributions are made by assuming that each galaxy's spectral redshift is directly proportional to its distance, as would be true if galaxies had no motion other than that caused by the expansion of the universe. However, the gravitational influence of local structures give galaxies additional motion, called peculiar velocity. This causes a map based on redshifts to be distorted.

The simplest example of a redshift-space distortion is the one resulting from a cluster of galaxies. Because the galaxies in the cluster have randomly oriented peculiar velocities, some redshifts will be smaller and some larger than what they "should" be. If these redshifts are used as distances, the cluster will look smeared out along the line of sight, producing an artifact called a finger-of-god.

I'm interested in the morphology of redshift-space artifacts, both on large scales (the bull's-eye effect) and more local scales (infall artifacts). The following are brief descriptions.

Bull's-Eye Effect

The bull's-eye effect is a distortion in redshift-space that enhances large scale structures lying transverse to the line of sight, producing maps in which the observer seems to be ringed by concentric walls of galaxies. A bull's-eye pattern shows up in many large scale surveys, like the one at left.

  • Demo from my collaborator Adrian Melott's website.

  • More...
Redshift map of Virgo Cluster

Infall Artifacts

Peculiar velocity flows associated with infall towards large galaxy clusters can cause striking distortions. For example, simple spherical infall produces a diamond-shaped artifact with concave edges. Similar bubble-wall-like caustics show up around many clusters, like the Virgo cluster at left.

Gravitational Phase Transition

Rotating self-gravitating fluid bodies embedded in an external medium can collapse in one of two ways, according to studies of analytical approximations. They can collapse dynamically by becoming gravitationally unstable, or they can collapse via a phase transition, before dynamical instability sets in. The dual possibility arises when the equilibrium solutions have a triple-value region, as shown in the plot at left. Since the phase transition mass is often much less than the dynamical collapse mass, structure formation via phase transition represents an interesting possibility in cosmological scenarios.

Elizabeth A. Praton
Department of Physics & Astronomy
Franklin & Marshall College

Last updated July 8, 2005.