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.
Collaborative Research: Distances to High Velocity Clouds Federal Award ID 0907743 End date: 07/31/2012 Intellectual Merit: Our goal is to determine the distances to a set of neutral hydrogen clouds, of unknown origin, in the halo of the Milky Way. They fill about 10 % of the sky with hydrogen emission at the radio wavlength of 21 cm. As far as we can tell, there are no stars associated with these clouds. The motion of the large aggregates of gas are peculiar compared to the large scale rotation of the Galaxy: it is assumed that the origins of the large peculiar motions lies in the origin of the clouds. The mystery of the origin of these clouds and of their place in the overall system of the Galaxy has been with astronomers for almost 50 years. The understanding of the origin of the high velocity clouds affects many areas of the study of the detailed origin of the Milky Way itself. For instance, if a portion of the clouds represent infalling material of gas that is not enriched in metals from star formation (i.e., if the parent gas is the intergalactic medium where very few stars are formed that produce heavy elements) the "rain" of metal poor gas will dilute the abundances we observe in the main gas of the Milky Way and our study of the history of the star formation in the Milky Way and of the subseqent production of metals will be compromised. If some part of the system involves the loss of material blown out of the Galaxy as new stars form ("winds"), it would imply that fresh material from which to form new stars will be depleleted and star formation will cease in the Galaxy (or any galaxy with a similar phenomenon). The clouds represent a unique source of information for understanding the history of the Milky Way galaxy. Broader Impacts: The study of these clouds provides a critical training ground for students in college. The fundametal concepts are anchored in practical spectroscopy and are easy to understand. There is a wealth of relevant data which students can become involved in analyzing. Many students learn their first programming languages while working on the straightforward practical aspects of problems like this. It is a great launching point for discussing the question of how we got here, ultimately, and how little we actually know about the detailed answer to that question. The field is a good training ground for students who later decide to go into a non-science field, because it involves rigid, quantitative rules of nature that we think we understand and enhances critical thinking skills in the face of real data. The students of the PI are employed in things they like to do using skills they learned doing research and facing the awesome truth of the facts, whether in science or non-science fields.. The PI mentors an average of 2 undergraduate student and one post-doc at a time. Beyond that, he is engaged in a $500,000 a year program to enhance teaching and learning through appropriate use of computers in education in the public schools of Chicago.In over 17 years of involvement, about 3000 teachers and 30,000 students have been impacted through this work, in an urban setting that is short on resources and opportunity. In addition, the group (CUIP, Chicago Public Schools Internet Project) provides summer programs of teachers and students for high schools in Chicago. The work includes use of on-line data bases and creative use of computers for students to evaluate, discuss, commnicate,and learn by using data, as co-learners with their teachers. The investigations are done in small group settings that simulate the problem solving environments of both science labs, hospitals and buisnesses. Outcomes: We have engaged in the study of high velocity clouds, with NSF funding, over a period of six years. In that time, we have enriched the field by producing exact or preliminary distances to 13 clouds, where only one distance was known when we started. This small sample already shows a wide range of properties of the clouds. If they can be described by a single story, it must be one involving process that creates a range of elements and a range of motions, not unlike an evolving picture that galaxies form from small, merging galaxies producing renants of gas clouds and stars that meander through the Galaxy. Astonomers have postulated another population of material, the mysterious dark matter that dominates over all other forms of matter and has very simple properties. Perhaps the two are related: the study of high velocity clouds may provide one of the best ways to understand one of the biggest unknowns of the Universe: the where, why and whence of the dark matter that shapes the Universe.
