What wavelengths are best for trying to observe baryonic matter?
Probing the baryonic content of the universe as it evolves requires a broad imaging and spectroscopic capability from the ultraviolet to the infrared. For objects like brown dwarfs and dwarf galaxies, sensitive imaging in the infrared with moderate spatial resolution (D ~ 0.15″) over wide fields of view (many square arcminutes) will be needed. Studies of black holes will benefit from even better spatial resolution, but only modest spectral resolution (R ~ 1000) is required. Tracing the gas content of the universe requires spectroscopic observations over a wide wavelength range, from the ultraviolet to the infrared, with low spatial resolution (D ~ 1″); both the ultraviolet and thermal infrared require space missions. Modest spectral resolution (R ~ 1000) is required for studying emission from gas clouds, but R 2 x 104 is needed for many studies of absorbing gas, like the Lyman-alpha clouds that we observe in the light from distant quasars. Hot baryonic gas surrounding galaxies and in c