Two Peaks and a Valley: The Bolometric Division of the Background Between Starlight and Dust

This paper addresses a specific question in the accounting of the cosmic optical and infrared backgrounds: how is the total extragalactic background divided, bolometrically, between the stellar peak near one micron and the dust peak near one hundred microns? The approach is a transparent computation from stated inputs drawn from the published literature, carried through in a deposited script whose output supplies every number quoted here. The principal computed values are: peak stellar nW = 11; peak dust nW = 14; peak ratio dust to stellar = 1.27; bolometric stellar nW = 26.6; bolometric dust nW = 30.7; bolometric total nW = 57.3; stellar frac bolometric = 0.465; valley at 8um nW = 1.37. These are compared with published measurements and budgets at the same wavelengths, and the agreement or disagreement is stated in each case. The study is computed from stated assumptions, not a new measurement; its contribution is arithmetic that can be checked line by line, with sensitivities reported wherever an input is uncertain.