Cosmic Background Explorer/FIRAS
Line Emission Maps
The Line Emission Maps cover the entire sky and give the intensity and the associated uncertainty in each of 18 emission lines: CO (115.27, 230.54, 345.80,461.04, 576.27, and 691.47 GHz), O2 (424.75 GHz), [C I] (492.23 and 809.44 GHz), H2O (556.89, 1113.3, and 1716.6 GHz), [N II] (1461.1 and 2459.4 GHz), [C II] (1900.5GHz), [O I] (2060.1 GHz), [Si I] (2311.7 GHz), and CH (2589.6 GHz).
Of the selected 18 spectral lines, the following 9 were detected (Bennett et al. 1994; included as Appendix D of the FIRAS Explanatory Supplement): the 158 micron ground state transition of C+, an important neutral interstellar gas coolant; the N+ 122 micron and 205 micron transitions, which trace extended low-density ionized gas; the 370 micron and 609 micron lines of neutral carbon, which arise in photodissociation regions; and the CO J=2-1, 3-2, 4-3, and 5-4 lines, which trace the molecular gas. As one would expect, the line emission is strongest in the Galactic plane and concentrated in the inner Galaxy.
There are three Line Emission Map FITS files. Two of these are at low spectral resolution: FIRAS_LINE_EMISSION_MAP_LOWF.FITS covers frequencies < 630 GHz; FIRAS_LINE_EMISSION_MAP_HIGH.FITS covers higher frequencies and also includes the parameters of an interstellar dust model (see below). FIRAS_LINE_EMISSION_MAP_HRES.FITS contains high spectral resolution data from 30 to 660 GHz. Synthetic spectral line profiles (FIRAS_LINE_PROFILES_*.FITS) are provided for each of the channel and scan modes or merged modes.
The synthetic profiles can be used in conjunction with a FIRAS spectrum to calculate line intensities.