This collaborative award will fund continuation of a project to measure distances to the Galactic high velocity clouds (HVCs), massive clouds of neutral hydrogen gas moving at velocities incompatible with a simple model of differential galactic rotation. Since they stand out from the gas in the Galactic Disk, they can be used as test particles for energetic phenomena in the Milky Way. The program will study HVC metallicities and distances using interstellar absorption lines in the spectra of stars projected against the clouds. The results of this project will be important for estimates of several fundamental parameters of Galactic evolution, including the rate of infall of low metallicity gas, the potential of the dark matter halo, the rate of circulation of gas between Disk and Halo, and the fraction of ionizing photons escaping the Disk.
The Broader Impacts of this program include training of graduate and undergraduate students.
This grant was a collaborative research grant to determine the distances to high velocity gas clouds in the halo of our Galaxy. The project included collaborators from the Univeristy of Wisconsin-Madison, University of Kentucky, Michigan State University and the University of Chicago. The University of Kentucky's portion of the grant was to determine distances to stars that fall along the line-of-sight up to and beyond the high velocity clouds. By detecting signatures of the the high velcity gas in the stellar spectra of the stars it is possible to bracket the distance to the clouds and ultimately use that distance to determine important cloud parameters such as the mass of the cloud. During the period of the grant the Co-PI and a graduate student at University of Kentucky shared in photometric observations completed at the WIYN 0.9 meter telescope located at Kitt Peak, Arizona. The photometry was necessary to determine the class of the star and ultimately its distance. Analysis of the ultraviolet magnitudes from this data showed various systematic problems which added complications to the distance determinations. As a result the Kentucky Co-PI, reworked his calibrations to give greater weight in the distance determination, to the strength of the hydogen Balmer lines. This helped to minimize the effects of the anomalous ultraviolet magnitudes. We have also taken more data, of standard stars, with known ultraviolet magnitudes in order to help remove the systematic errors in our data. This attempt is still ongoing, as the head PI for this collaborative reaseach has asked for a one year, no cost extention (NCE) to his portion of the grant to allow us to finalize the removal of the systematic errors. Once the NCE period is complete we will compute distance to various high velocity clouds and this will allow us to better constrain the contribution these clouds have to the overall evolution of the Milky Way galaxy.
