CAREER: The Interstellar Disk-Halo Connection in Edge-on Galaxies - Bringing Research to a Large Audience

University Of New Mexico, Albuquerque NM

Investigators

Abstract

AST-9986113 Rand In recent years it has been realized that the Interstellar Medium (ISM) and galaxy evolution depend pivotally on the cycling of gas between a galaxy's disk and halo. Recent discoveries of huge, vertically extended coherent structures in the ISM are called superbubbles and chimneys. The results from observations of thick layers of diffuse gas have enabled scientists to begin to form a picture of how stars energize and shape the ISM, and how, through these processes, the diffuse gas affects the future evolution of a galaxy. This "disk-halo connection" is therefore critical for star formation feedback on the ISM, chemical evolution, and possibly the escape of gas from galaxies and the production of large gaseous halos responsible for QSO metal absorption line systems. A feature of the ISM, which is now giving us a strong handle on the disk-halo connection, is the Diffuse Ionized Gas (DIG). In the Milky Way Galaxy, this vertically extended medium is known as the Reynolds layer. While it is generally accepted that the great thickness of the Reynolds layer is probably due to processes such as chimneys, we still have only a rudimentary understanding of (a) the extent of the layer and variations thereof, (b) sources of ionization and heating, (c) the kinematics of the gas far from the plane, and (d) the relation of other thick gaseous layers to the Reynolds layer and the disk-halo connection. For several reasons, many ISM issues are better addressed through studies of external galaxies, which provide a synoptic view of the emission. The relatively new area of DIG in edge-on spirals, where recent efforts have been focused, has given us a powerful tool for understanding the disk-halo connection and the ISM in general. Through imaging of edge on galaxies we are now beginning to obtain information on the structure of DIG layers and their relation to other thick gaseous layers and star formation activity. The DIG is found to be an excellent tracer of candidate chimneys. Spectroscopy of DIG layers is now being used to study the ionization, heating, kinematics and vertical extent at faint levels of this phase. Hence, such observations have great potential to address the four issues listed above. The goal of this research effort is to expand greatly these DIG observations using sensitive spectroscopy and new imaging possibilities, and to carry out searches for neutral hydrogen (HI) and cosmic ray halos. In this way it is hoped to learn about how the disk-halo connection operates in detail, as input into our larger understanding of galaxy evolution. Information on the research that is being carried out will be brought to a large audience as part of an effort to improve scientific awareness and literacy. An innovative project at the University of New Mexico (UNM), called LodeStar, combines education and outreach with information on current forefront research. LodeStar will soon open an Astronomy Science Center in Albuquerque, thus providing the infrastructure for bringing research results to the public. Through a theme called "Galaxies Across the Electromagnetic Spectrum", the interpretations and explanations of the results of this research, and results from the UNM astronomy group in general, will be used to develop programs to educate the general public and K-12 school classes about the physics of galaxies, the methods of astronomy, and the importance of astronomical research in their own State. Crucially, ethnic groups underrepresented in science, but with a strong presence in New Mexico, will be reached through these efforts. Thus the awareness of opportunities to study science at all levels will be increased. Other roles for LodeStar will be developed which will lead to effective public outreach projects. ***