Accepted for publication in ApJ 2002.
For a PDF version of the article, click
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THE FIRST DETECTIONS OF THE EXTRAGALACTIC BACKGROUND LIGHT AT 3000,
5500, AND 8000Å (III): COSMOLOGICAL IMPLICATIONS
Rebecca A. Bernstein 1,2,3
Wendy L. Freedman 2
Barry F. Madore 2,4
1) Division of Math, Physics, and Astronomy,
California Institute of
Technology, Pasadena, CA 91125
2) Carnegie
Observatories, 813 Santa Barbara St, Pasadena, CA 91101
3) rab@ociw.edu, Hubble Fellow
4) NASA/IPAC
Extragalactic Database,
California Institute of
Technology, Pasadena, CA 91125
Abstract. 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-2
sr-1.
If the total EBL were produced entirely by stellar nucleosynthesis,
then we estimate that the total baryonic mass processed through stars
is
*
= 0.0062(± 0.0022)h-2 in units of the critical
density. For currently favored values of the baryon density,
B, this
corresponds to 0.33± 0.12
B.
This estimate is smaller by roughly 7% if we allow for a
contribution of 7h0.7 nW m-2
sr-1 to the total EBL from
accretion onto central black holes. This estimate of
*
suggests that the universe has been enriched to a total metal mass of
0.21(± 0.13)
Z
B, 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.
Keywords: Diffuse radiation - cosmology: observations -
galaxies: evolution - galaxies: photometry
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