Under this renewal of AST-0307489, Dr. Mendez will use a technique of narrowband imaging and slitless spectroscopy on 8-meter telescopes to find planetary nebulae in the outskirts of elliptical and S0 galaxies, and measure their radial velocities. Planetary nebulae represent the final stages in the life of a star like our Sun. They are identified by the bright emission lines of gas ionized by the hot exposed stellar core; these lines are also used to measure motion along the line of sight. The distribution and motion of the planetary nebulae will be used to study the galaxy's gravitational field, and hence its dark matter content. Dr Mendez will also use the brightness ratio of emission from hydrogen atoms with that from oxygen, to estimate how the chemical composition of the gas from which the stars were formed depends on distance from the galaxy center. Dr. Mendez and the Munich group with which he collaborates have already studied several galaxies; some show no evidence for dark matter, while others have clear signatures of its presence. Under the present proposal, the next target is M60, a flattened galaxy with a halo of hot X-ray gas that provides an alternative measure of the mass of the galaxy's dark halo. Other target galaxies will be selected to cover a range in luminosity, and to coordinate with another project using the 4-meter Herschel telescope on La Palma (Canary Islands, Spain), which can detect only the brightest planetary nebulae.
A graduate student and an undergraduate will be trained through their involvement in the research. Dr Mendez will develop a website explaining the project that will be accessible to the general public or students in elementary survey courses; it will cover topics ranging from the nature of light to evidence for dark matter around galaxies.
