Jeffrey Alan Willick (1959–2000)

Jeff Willick, 40, assistant professor of physics at Stanford University, was tragically killed by a runaway car while working at a coffee-shop on June 18, 2000. Jeff was an observational cosmologist who had done important work in mapping the peculiar velocity field of galaxies and comparing the results with the large-scale distribution of galaxies. He is survived by his wife, Ellen Schneider, and three children, Jason, Emily, and Julia.

Jeff did his undergraduate studies in physics and chemistry at Harvard, and obtained his PhD in physics in 1991 from Berkeley, after taking a year off from his studies to teach high school physics in his home town of Englewood, New Jersey. He was a postdoctoral fellow at the Carnegie Observatories in Pasadena for four years before joining the faculty at Stanford.

He carried out a peculiar velocity survey of spiral galaxies in the Perseus-Pisces supercluster for his PhD thesis. Measurement of the "peculiar" velocity of a spiral galaxy, or residual motion above and beyond that due to the uniform expansion of the universe, uses an empirical relation between the internal rotation speed of the galaxy and its intrinsic luminosity (known as the Tully-Fisher relation). Further measurement of the apparent brightness of the galaxy then allows determination of its distance via the inverse square law.

Comparison of the inferred distance with the spectroscopic redshift of a galaxy allows one to infer its peculiar velocity. The substantial scatter of the Tully-Fisher relation requires that exquisite care be taken to avoid systematic effects and biases in the interpretation of peculiar velocity data. Jeff was one of the world experts in the development of both observational techniques and mathematical formalisms to extract unbiased statistics about the large-scale peculiar velocity field. His papers on Malmquist bias in particular are a model of clarity in what had been a very confused field.

Jeff had always been fascinated by the question of the coherence scale of the cosmic velocity field. The coherence scale is directly related to the mean density of the universe and the distribution of the largest cosmological structures; as such, it yields important constraints on cosmological models for the formation of these structures. His thesis work gave hints that the Perseus-Pisces supercluster of galaxies was undergoing a large-scale flow in a direction close to that of our Milky Way's motion relative to the inertial frame defined by the cosmic microwave background. Indeed, Jeff's thesis provided a clear demonstration for large-scale low-amplitude density fluctuations in the universe. In collaboration with one of us (Courteau), David Burstein, Avishai Dekel, Sandy Faber, and others, Jeff combined peculiar velocity data from a variety of "Tully-Fisher" surveys, and put them on a common basis to give a single unified dataset, the Mark III Catalog of Galaxy Peculiar Velocities which quickly became the work horse for exploration of the large-scale velocity field.

Understanding the limitations of stitching together heterogeneous surveys, he undertook two new, uniform all-sky surveys, one by himself, and the other in collaboration with Courteau, Strauss, David Schlegel, and Marc Postman. In particular, the latter, dubbed "Shellflow," showed conclusively that the velocity field has a coherence length of less than 60 Mpc, a result which is in accord with currently popular cosmological models. He developed statistically rigorous techniques for quantitative comparison of the peculiar velocity data with large-scale redshift surveys, yielding perhaps the best limits to date of the Cosmological Density Parameter Ω from cosmic velocity fields.

At the time of his death, Jeff was leading a vibrant group of undergraduate students, graduate students, and postdoctoral fellows at Stanford, working on a variety of exciting projects in cosmology. With Puneet Batra, he explored various systematic effects which bedevil the determination of the Hubble Constant (which gives the rate of expansion of our universe), showing that its value might be somewhat larger than many previous workers had found. With Ben Mathiesen and Keith Thompson, he had started a major new survey for distant clusters of galaxies, using the newly commissioned 11-meter Hobby-Eberly Telescope to obtain red shifts. As Jeff had shown in a theoretical paper published shortly before his death, the evolution of cluster number density is a powerful probe both of the value of Ω, and of any possible non-Gaussian tail in the distribution of density fluctuations in the early universe, as might be expected, e.g., in certain models of inflation.

Jeff had also a keen interest in undergraduate education and in general public understanding of science and its influence on environment and society. In only a few years at Stanford, he had already inspired a number of undergraduate students with his scientific abilities, his excitement for astronomy, his compassion and his integrity. He had also established a distinguished teaching and advising record, and was highly valued as an academic mentor. Those of us lucky enough to collaborate with Jeff were impressed by his broad knowledge of physics, his keen intuition, his attention to detail, and his desire to do things right from the beginning. He was a warm human being, a deep thinker and an outstanding husband and father. We miss him greatly; his death is a great personal loss and a professional loss to the world of astronomy.

Photo, Stanford University Visual Arts Services. with permission from the Stanford University Physics Department