COBE FIRAS observations of Galactic Lines

The COBE Far InfraRed Absolute Spectrophotometer (FIRAS) observations constitute an unbiased survey over the wavelength range from 100 μm to 1 cm over 99% of the sky. Improved calibration of the FIRAS instrument and the inclusion of all of the FIRAS data allow an improved signal to noise determination of the spectral lines by a factor of ∼ 2 over our previous results. The resolution is low (0.45 cm) so only the strongest lines are observable. The CO chain from J = 1− 0 to J = 8− 7 is observed towards the Galactic center. The line ratios are roughly consistent with a 40 K excitation temperature. The 157.7 μm C ii and 205.3 μm N ii lines are observable over most of the sky. The 370.4 μm and 609.1 μm lines of C i, and the 121.9 μm line of N ii are observed in the Galactic plane. The line ratios at the Galactic center are consistent with a density of n0 ∼ 30 cm −3 and a UV flux of G0 ≈ 15 μW m −2 sr (10 Habing units). The 269 μm H2O line is observed toward the Galactic center in absorption. Subject headings: ISM: atoms, bubbles, general, molecules — line: identification Galaxy: general