Detections of the Optical EBL: Results

12. SUMMARY

We summarize our detection of the surface brightness of EBL23 from resolved and unresolved galaxies fainter than V₅₅₅ = 23 A B mag as follows (in ergs s^-1 cm^-2 sr^-1 Å^-1):

I(F300W)= 4.0 (± 2.5) × 10^-9

I(F555W)= 2.7 (± 1.4) × 10^-9

I(F814W) = 2.2 (± 1.0) × 10^-9

The quoted errors are 1 sigma combined uncertainties (statistical and systematic) corresonding to 68% confidence intervals, as described in Section 11. We can also define strict lower limits to the EBL from detected galaxies fainter than V₅₅₅ = 23 A B mag by computing the flux from all detected objects using the "aperture photometry" method described in Section 10. The lower limits for EBL23 are (in ergs s^-1 cm^-2 sr^-1 Å^-1):

I_{23 < V < 27.5}(F300W) geq

3.2 × 10^-9

I_{23 < V < 27.5}(F555W) geq

0.89 × 10^-9

I_{23 < V < 27.5}(F814W) geq

0.76 × 10^-9

For comparison with predictions of the EBL based on the local metal mass density and total star formation history of the universe, the flux from galaxies brighter than V₅₅₅ = 23 A B mag should be added to these results, as shown in Figure 23. We discuss these comparisons in Paper III.

Figure 23. The detected background light from galaxies fainter than V₅₅₅ = 23 A B mag is marked by large filled circles with 2 sigma error bars. The error bars are dotted where they extend below the flux recovered from galaxies in the range 23 < V₅₅₅ < 28 A B mag by the aperture photometry method (see Section 10) shown by the u-shaped lower limit symbols. The integrated flux from galaxies in the HDF, from 23 A B mag to the detection limit at each wavelength (29-30 A B mag), is marked by lower limit arrows connected by the thick, dashed line. The total flux in galaxy counts, HDF counts plus ground-based counts brighter than V₅₅₅ = 23 A B mag is shown by lower limit arrows connected by a thin dashed line. The open circles (displaced by 200Å for display purposes) show the EBL we detect, plus the integrated ground-based counts brighter than V₅₅₅ = 23 A B mag. We have not included uncertainties in the ground-based counts in the error bars shown.

It is a pleasure to thank A. Fruchter, R. Lyons, C. Keyes, A. Koratkar, L. Petro and D. Van Orsow for help in planning and scheduling the HST observations, and J. Christensen, H. Ferguson, and J. Keyes for help in understanding and improving the standard pipeline reduction for both the WFPC2 and FOS data. S. Baggett, S. Cassertano , R. Bohlin, and E. Smith also provided help with the WFPC2 and FOS calibration. We have also benefited greatly from discussions with J. Dalcanton, S. Shectman, T. Small, I. Smail, J. Trauger, and B. Weiner. R. Kurucz kindly provided an electronic version of the Solar Atlas. Finally, we would like to thank Carnegie Observatories and specifically L. Searle, A. Oemler, and I. Thompson for generous allocation of observing time at Las Campanas Observatory; the referee, R. Windhorst, for helpful comments; R. Blandford, A. Readhead, and W. Sargent for financial support to RAB during the first year of this work; and especially R. Williams for his support of this project. This work was supported by NASA through grants NAG LTSA 5-3254 and GO-05968.01-94A to WLF.