RUI: Emission Line Studies of High-Velocity Interstellar Clouds using the WHAM Spectrometer

Lewis And Clark College, Portland OR

Investigators

Abstract

AST 0206349 Tufte High-Velocity Clouds (HVCs) are an important component of the Milky Way's interstellar medium, covering a significant fraction of the sky and containing considerable mass and kinetic energy. HVCs are by definition peculiar; they are the material with velocities not explainable by the differential rotation of the galaxy. Despite over thirty-five years of study, their origin and nature remain a mystery. Proposed explanations of HVCs span a broad range. One picture envisions a galactic fountain. In this model, powerful supernova explosions in the disk of the galaxy vent hot material into regions high above the plane. The gas then cools, condenses into clouds, and then rains back down upon the disk. Another prominent model purports that the HVCs are dispersed throughout the Local Group of galaxies, the remnants of its creation. It appears that some of the high-velocity material was tidally torn from the Magallenic clouds, and now streams behind them in their orbit around our galaxy. Recent evidence suggests that one major complex of high-velocity material has low metallicity and is accreting onto the disk from high in the halo. This is especially interesting because such fresh fuel for star formation has long been required by models of the chemical evolution of the Galaxy. Current observational efforts to distinguish between these models will enhance present understandings of the formation of the Milky Way galaxy and its subsequent chemical evolution, as well as illuminate long debated issues concerning the connection of processes in the disk of our Galaxy to the halo. The vast majority of previous investigations of HVCs have used radio telescopes to study the 21- cm line, and thus only probe the neutral hydrogen present in the clouds. Dr. Stephen Tufte, at Lewis and Clark College, will investigate ionized material associated with HVCs by making measurements of optical emission lines using the Wisconsin H-Alpha Mapper (WHAM) Observatory. WHAM is a Fabry-Perot based spectroscopic instrument that sits atop Kitt Peak in Arizona and is completely remote-operable. The observations will take place from the principal investigator's laboratory on the campus of Lewis & Clark College, by way of the Internet. This project will measure the intensities of emission lines of hydrogen, nitrogen, sulfur, and oxygen from various HVCs. The observations will provide information on the locations and metal abundances of HVCs, will yield new insights into the nature of compact HVCs, and will reveal the physical conditions present in the clouds such as their temperature and ionization state. The principal investigator has already proven WHAM to be a uniquely powerful instrument for these studies. The new measurements have the ability to distinguish between the vastly different models that have been proposed to explain HVCs, and therefore significantly advance our understanding of their origin and nature. This award is made under the auspices of the Research in Undergraduate Institutions (RUI) program at NSF. ***