The First Detections of the Extragalactic Background Light at 3000, 5500, and 8000å (ii): Measurement of Foreground Zodiacal Light

We present a measurement of the absolute surface brightness of the zodiacal light (3900–5100Å) toward a fixed extragalactic target at high ecliptic latitude based on moderate resolution (∼1.3Å per pixel) spectrophotometry obtained with the du Pont 2.5m telescope at Las Campanas Observatory in Chile. This measurement and contemporaneous Hubble Space Telescope data from WFPC2 and FOS comprise a coordinated program to measure the mean flux of the diffuse extragalactic background light (EBL). The zodiacal light at optical wavelengths results from scattering by interplanetary dust, so that the zodiacal light flux toward any extragalactic target varies seasonally with the position of the Earth. This measurement of zodiacal light is therefore relevant to the specific observations (date and target field) under discussion. To obtain this result, we have developed a technique that uses the strength of the zodiacal Fraunhofer lines to identify the absolute flux of the zodiacal light in the multiple–component night sky spectrum. Statistical uncertainties in the result are 0.6% (1σ). However, the dominant source of uncertainty is systematic errors, which we estimate to be 1.1% (1σ). We discuss the contributions included in this estimate explicitly. The systematic errors in this result contribute 25% in quadrature to the final error in our coordinated EBL measurement, which is presented in the first paper of this series. Subject headings: Diffuse radiation — cosmology: observations — techniques: spectroscopic — interplanetary medium