Involved people at OAB: Ciliegi.
In collaboration with Lagache G. and Puget J.L. (Institute d'Astrophysique
Spatiale, Orsay, France), Ciliegi is working on the identification of
the FIRBACK sources. FIRBACK is one of the deepest surveys performed
at 175 
m with ISOPHOT onboard ISO, and is aimed at the study
of cosmic far infrared background sources. About 300 galaxies are
detected in an area of four square degree. Preliminary FIRBACK integral
source counts at 175 
m show a strong slope of 2.2 between 120
and 500 mJy. This strong slope is not explained by a K correction or
cosmological evolution alone: both must be present. Moreover, SCUBA
follow up of FIRBACK sources shown that they are generally detectable
in the sub-mm; those with somewhat higher 850 
m flux density
may be at z 
1, while those which are fainter in the sub-mm
may be more normal galaxies at z 
0. Model of evolving galaxy
populations which provide a fit to the 175 
m counts predict that the
median redshift of the FIRBACK sources is around 1. An intensive
programme of spectroscopic optical identification of the FIRBACK sources
will be carried out during May 2000 at the William
Herschel Telescope (WHT) in La Palma (Spain).