Galmatheia: A Galactic Plasma Explorer

Galmatheia is a broad bandpass (900-1800 Angstrom), far-ultraviolet (FUV) nebular spectrograph (lambda /delta lambda ~ 650) for the study of the evolution of galactic plasma with a temperature of 10^4.5 - 10^6 K. Galmatheia will survey the FUV sky with 5' imaging and conduct hundreds of deep 8 degree x 5' field pointings during its proposed two-year mission. Unprecedented sensitivity is achieved by careful exclusion of FUV-bright stars and airglow background. The emission-line sensitivity for a single-day exposure and for a one-year sky survey 3 degree x 3 degree bin yields 50 sigma and 10-15 sigma detections, respectively, of both the predicted radiation from hot Galactic gas and previously-observed diffuse FUV emission. The continuum sensitivity provides 15-25 sigma detections of the predicted flux from unresolved extra-galactic sources.