Involved people at OAB: Pozzetti.
In collaboration with P. Madau (IoA, Cambridge),
have been investigated the constraints imposed by the observed extragalactic
background light (EBL) on the cosmic history of star formation and the
stellar mass density today. From galaxy number counts
in the UV to K bands (including the Southern Hubble Deep Field)
a lower limit to the optical EBL of about 15
was derived, comparable to the intensity of the far-IR
background from COBE data. A lower limit of 
can be set to the visible (processed gas + stars) mass density
required to generate an EBL at a level of 
;
our ``best-guess'' value is 
(Madau & Pozzetti 2000).