The First Detections of the Extragalactic Background Light at 3000, 5500, and 8000å (iii): Cosmological Implications

We have used the Hubble Space Telescope Wide–Field and Planetary Camera 2, in combination with ground–based spectroscopy, to measure the integrated flux of galaxies at optical wavelengths — the extragalactic background light (EBL). We have also computed the integrated light from individual galaxy counts in the images used to measure the EBL and in the Hubble Deep Field. We find that flux in galaxies as measured by standard galaxy photometry methods has generally been underestimated by about 50%, resulting from missed flux in the outer, lower surface–brightness parts of galaxies and from associated errors in the estimated sky level. Comparing the corrected, integrated flux from individual galaxies with our total EBL measurement, we find that there is yet further light that contributes to the background that is not represented by galaxy counts, and that the total flux in individually detected sources is a factor of 2 to 3 less than the EBL from 8000 to 3000 Å. We show that a significant fraction of the EBL may come from normal galaxies at z < 4, which are simply undetectable as a result of K-corrections and cosmological surface brightness dimming. This result is consistent with results from recent redshift surveys at z < 4. In the context of some simple models, we discuss the constraints placed by the EBL on evolution in the luminosity density at z > 1; while significant flux comes from galaxies beyond the current detection limits, this evolution cannot be tightly constrained by our data. Based on our measurements of the optical EBL, combined with previously published measurements of the UV and IR EBL, we estimate that the total EBL from 0.1–1000 μm is 100±20 nW m sr. If the total EBL were produced entirely by stellar nucleosynthesis, then we estimate that the total baryonic mass processed through stars is Ω∗ = 0.0062(±0.0022)h−2 in units of the critical density. For currently favored values of the baryon density, ΩB, this corresponds to 0.33 ± 0.12ΩB. This estimate is smaller by roughly 7% if we allow for a contribution of 7h0.7 nW m −2 sr to the total EBL from accretion onto central black holes. This estimate of Ω∗ suggests that the universe has been enriched to a total metal mass of 0.21(±0.13)Z⊙ΩB, which is consistent with other observational estimates of the cumulative metal mass fraction of stars, stellar remnants, and the intracluster medium of galaxy clusters in the local universe. Subject headings: Diffuse radiation — cosmology: observations — galaxies: evolution — galaxies: photometry