Gus Oemler

Director Emeritus


Since stepping down as Observatories director, Gus Oemler has been a part-time member of the research staff. He divides his time between writing a data pipeline, to reduce data for the Inamori Magellan Areal Camera and Spectrograph (IMACS), and conducting a new long-term study of galaxy evolution in clusters.

IMACS produces vast amounts of data. Reducing even minimal multi-slit spectroscopic data is a difficult task. However, without an efficient pipeline the data would overwhelm observers. Oemler volunteered for the job basing his pipeline on software written by Ken Clardy. It models the IMACS optics, and transforms positions on the slit-mask to positions on the CCD focal plane. A generally reliable and efficient first version is complete and used by Magellan consortium and outside observers. Oemler is now improving the software and extending it to support the LDSS3 spectrograph, in both its original and new configurations. He spends some time helping new users of the software, work that will eventually be accomplished by others.

Galaxy clusters are the most massive units in the universe. Oemler has studied the evolution of the galaxies in the clusters for years. Although it has been established that cluster galaxies do, indeed, evolve—almost certainly from spirals to S0s (galaxies that are in-between spiral and elliptical)—the mechanisms driving that evolution are still undetermined. At least half a dozen candidate processes have been proposed, each supported by some of the work that has been done. The uncertainty is (as usual) the lack of adequate data. Alan Dressler, Mike Gladders, and Oemler are using IMACS for a long-term project to follow the evolution of galaxies as they move out of the supercluster environment, through in-falling groups and filaments, and finally into the cluster core. Using well-selected clusters from the Gladders and Yee Red-Sequence Cluster survey, they pick those that best exemplify the successive stages of a single cluster. This selection, plus a very dense data set, should allow them to follow the detailed evolutionary tracks of galaxies as they interact with the successive environments they occupy.


A.B., 1969, Princeton University; M.S. and Ph.D., 1974, California Institute of Technology

Data reduction, evolution of galaxies in clusters