The Dust Peak of the Cosmic Infrared Background: A Spectrum from a Single Evolving Emissivity

This paper addresses a specific question in the accounting of the cosmic optical and infrared backgrounds: can one evolving dust emissivity, with a single temperature and emissivity index, reproduce the observed shape and peak wavelength of the cosmic infrared background? 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 lambda um = 160; I160 nW = 14; I250 nW = 13.2; ratio 250 to 160 = 0.945; ratio 850 to 160 = 0.103. 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.