Published in MNRAS, 312, L9, 2000
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ABSTRACT. We assess the constraints imposed by the observed
extragalactic
background light (EBL) on the cosmic history of star formation and the
stellar mass density today. The logarithmic slope of the galaxy
number-magnitude relation from the Southern Hubble Deep Field
imaging survey is flatter than 0.4
in all seven UBVIJHK optical bandpasses, i.e. the light from
resolved galaxies has converged from the UV to the near-IR. We find a
lower limit to the surface brightness
of the optical extragalactic sky of about 15 n W m-2
sr-1, comparable to the
intensity of the far-IR background from COBE data.
Assuming a Salpeter initial mass function with a lower cutoff consistent
with observations of M subdwarf disk stars, we set a lower limit of
Ωg+s
h2 > 0.0013 I50
to the visible (processed gas + stars) mass density required to generate an
EBL at a level of 50 I50 n W m-2
sr-1; our ``best-guess'' value is
Ωg+s
h2 0.0031
I50. Motivated by
the recent microlensing results
of the MACHO collaboration, we consider the possibility that massive
dark halos around spiral galaxies are composed of faint white dwarfs, and
show that only a small fraction (
5%) of the nucleosynthetic baryons
can be locked in the remnants of intermediate-mass stars forming at
zF
5, as the bright early phases of such halos would otherwise overproduce the
observed EBL.
Key Words: cosmology: miscellaneous - dark matter - diffuse radiation - galaxies: evolution - Galaxy: halo
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