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Session 12 - Cosmology, Large-Scale Structure and Distance Scales.
Display session, Monday, June 10
Great Hall,

[12.02] Shape and Orientation Studies in the Hubble Deep Field: Weak Lensing and Evolution of the Elliptical Galaxy Population

T. S. Statler, S. N. Dutta, J. Day, C. Myers (Ohio Univ.)

We measure ellipticities, orientations, and surface brightness profiles for all galaxies in the Hubble Deep Field (HDF), and report on two studies: Detection of coherent alignments due to weak gravitational lensing. We determine the ellipticity correlation function and mean shear over the full HDF and over subfields. Image polarizations of the expected magnitude for CDM, 1% -- 2%, are easily detectable with \sim2400 galaxies. The polarization is used to constrain the amplitudes of mass fluctuations on the few-Mpc scale outside of clusters. The polarization covariance function is checked for consistency with that expected from measured microwave background fluctuations on arcminute scales. (2) Evolution of the elliptical galaxy shape distribution. Using aperture photometry to pick out objects with de Vaucouleurs-like surface brightness profiles, we obtain the apparent ellipticity distributions of early-type galaxies as a function of magnitude, color, and angular size. We divide galaxies in color-magnitude-size space into distant and nearby subsamples, and test the conjecture that stellar dynamical effects drive strong secular evolution of elliptical galaxies toward rounder shapes.

Program listing for Monday