Piero Madau
Published 1999-07-20Version 1
I review the constraints imposed by the observed extragalactic background light (EBL) on the history of the stellar birthrate in galaxies. At faint magnitudes, the logarithmic slope of the galaxy counts is flatter than 0.4 in all seven UBVIJHK optical bandpasses of the Hubble Deep Field-South imaging survey. The integration of the number counts provides a lower limit to the surface brightness of the optical extragalactic sky of 15 nW/m2/sr, comparable to the intensity of the far-IR background from COBE data. If the initial mass function has a Salpeter slope with a lower mass cutoff consistent with observations of M subdwarf disk stars, a lower limit of Omega_*>0.005 (at Hubble constant 50 km/s/Mpc) is derived for the visible (processed gas + stars) mass density needed to generate an extragalactic background light (EBL) at a level of 50 nW/m2/sr. The current `best-guess' estimate to Omega_* is 0.012, about 16% of the nucleosynthetic baryon density. The contribution of quasar activity to the observed EBL is unlikely to exceed 20%.
Comments: LaTeX, 9 pages, 4 figures, invited review at the VLT Opening Symposium, Antofagasta, Chile 1-4 March 1999
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