Published in MNRAS, 312, L9, 2000
For a PDF version of the article, click
For a PDF version of the article, click here.
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 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
Table of Contents