Michelle Griffin

B.S. Physics, Rice University, 1995
Ph.D. Department of Astronomy 2003
Thesis Advisor: Laird Thompson

Thesis Title: The Mt. Laguna Infrared Cluster Survey: A Search for Galaxy Clusters Beyond z = 1

Michelle Griffin undertook an ambitious program to survey a large number of blank fields to identify galaxy clusters at redshifts in the vicinity of z = 1. It is widely known that the identification of galaxy clusters in this redshift range will place significant constraints on hierarchical models of structure formation. Ms Griffin's cluster search was done in the JHK bands with a 256x256 NICMOS-3 detector mounted at Cassegrain focus of the Mt. Laguna 1-m Telescope. This near-IR camera -- which is called NIRIM -- was built for the 1-m telescope by Meixner, Young-Owl, and Leach to take best advantage of the wide-field characteristics of the Mt. Laguna Observatory f/7.6 1-m telescope.

Images from NIRIM were analyzed with techniques pioneered by Julianne Dalcanton. Dalcanton's method was devised to identify distant clusters based on their low surface brightness extended emission. That is, highly smoothed images of galaxy clusters reveal the extended emission associated with an entire cluster even though the same images do not resolve the light from individual galaxies. By imaging the survey fields in three colors and demanding that all cluster candidates be centered on a bright galaxy with colors that match the colors of first-brightest cluster members (predicted from the observed colors of known high-redshift galaxy clusters), moderately deep JHK band images on a 1-m telescope are sufficient for the survey images.

To further enhance the chances of success of this project, Monte Carlo simulations were used to model the detection process. These simulations involved the insertion of test galaxy clusters into the JHK band image frames (with appropriate color shifts and (1+z)^4 surface brightness dimming) to check the viability of the search methods.