The Integrated Galaxy Light in the V Band: Which Magnitudes Actually Pay for the Optical Background

This paper addresses a specific question in the accounting of the cosmic optical and infrared backgrounds: how much of the optical extragalactic background is supplied by faint galaxies, and how much by the comparatively bright systems that were catalogued decades ago? 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: total ebl nW m2 sr = 8.03; peak mag = 20.1; peak contrib nW per mag = 1.11; frac fainter than 26 = 0.075; frac fainter than 28 = 0.0299; total faint slope 0.24 = 8.29; total faint slope 0.18 = 7.84. 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.