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 _g+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 _g+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 z_F 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

Table of Contents

INTRODUCTION

GALAXY COUNTS FROM UV TO NEAR-IR

THE BRIGHTNESS OF THE NIGHT SKY

EBL FROM QUASAR ACTIVITY

THE STELLAR MASS DENSITY TODAY

EBL FROM MACHOS

REFERENCES