December 3, 1998 CfA Colloquium

Title: Exploring Diffuse Ionized Gas in the Milky Way

Speaker: Ron Reynolds

Abstract: Warm ionized hydrogen is widespread throughout our Galaxy. Although the nature of this gas is not well understood, its existence appears to challenge the traditional picture of the interstellar medium, including the morphology of the medium and the mechanisms of ionization and heating. It also is a potentially significant source of contamination in observations of various astrophysical backgrounds. The Wisconsin H-alpha Mapper (WHAM) is a new facility dedicated to the study of this gas through observations of faint optical emission lines at high spectral resolution. WHAM has recently completed a northern sky survey of the interstellar H-alpha emission, providing for the first time a detailed picture of the distribution and kinematics of the diffuse ionized hydrogen through the H-alpha line that is comparable to surveys of the neutral hydrogen obtained through the 21 cm line. In addition to the survey, WHAM has detected faint emission lines from a variety of interstellar ions and atoms that probe properties of the gas and radiation field within the Galactic disk and halo.

Reference for students: Faint, Large-Scale H-alpha Filaments in the Milky Way (ApJ 501, L83,1998); Science 277, 1446, 1997. Lunch on Thursday at 1:00pm in the classroom.