Power spectrum of the extragalactic background light.

Abstract

The extragalactic background light (EBL) is the surface brightness of the integrated light from distant unresolved galaxies. Because galaxies tend to cluster, the EBL is anisotropic, and this clustering is reflected in the power spectrum of the extragalactic background light (PSEBL). To measure the PSEBL, observations have been made on four pairs of fields near the galactic poles with a CCD imaging system on angular scales from 2$\sp\prime$ to 25$\sp\prime$ at 4400, 5500 and 7000 A. In total, 13 hours of data were collected. In order to collect information from as large a redshift as possible, foreground stars and galaxies brighter than 20.5 magnitudes have been removed from the data. To be sure that the final data is only characteristic of the EBL, specific checks have been made on the contributions to the power spectrum due to instrumental effects, atmospheric variations and zodiacal light, scattering halos of stars and galaxies, and the diffuse galactic light. Most of the data was taken at 7000 A, and the observed PSEBL is well fit by a power law with index $-$0.84 $\pm$ 0.11. The measured power spectra are compared to a simple model which is based on the two-point galaxy correlation function $\xi(r)$. A power law shape for the spatial correlation function, $\xi$(r) $\propto$ r$\sp{-1.8}$, implies a power law shape for the angular power spectrum with index $-$1.2. The amplitude of the observed PSEBL corresponds to fluctuations in the surface brightness which are about 70% larger than predicted by the model. However, the amplitude of the power spectra can be explained by including modest luminosity evolution of the galaxy light. Based on the model, it is expected that half of the contributions to the PSEBL comes from beyond a redshift of z $\sim$ 0.55.