Dr. Oka and his team study the properties of warm, diffuse gas in the Galactic center by measuring (H3)+ and CO infrared absorption towards the Central Molecular Zone. Protonated molecular hydrogen, (H3)+, is a tracer of the density, temperature, ionization rate, and volume filling factor of the large regions containing this molecular ion. It is also a tracer for other polyatomic molecules that are difficult to measure in the diffuse interstellar medium. The (H3)+ discovery and observations along 14 sight lines showed that warm diffuse gas (T about 250 K, density of 100-1000 particles per cubic centimeter) indicates the presence of a warm, diffuse component to the longer known components of dense-molecular, hot-ionized, and ultra-hot plasma. The researchers found that the volume filling factor of this gas appears to be very high, and the ionization rate for the warm diffuse gas an order of magnitude higher values for these sight lines near the Galactic Center than expected for these regions. The present work investigates more sight lines towards the Galactic center using new background stars that are selected from the Spitzer GLIMPSE (Galactic Legacy Infrared Mid-Plane Survey Extraordinaire) database and CO observations. The data are compared with new Herschel observations of (H2O)+ and radio and infrared spectra of CO to fully characterize the physical properties of the warm diffuse gas and the other components in the complex and dynamical regions at the Galactic center. This project trains a post-doctoral fellow in observational infrared astronomy and molecular astrophysics.
