ISOPHOT was used to survey the sky at 90 and 170 µm , mainly
(plus a few surveys at 60, 120, 150 and 180 µm, see
Juvela et al. 2000;
Linden-Voernle et
al. 2000;
cf review by
Dole 2002).
At 90 µm,
the 46 arcseconds pixels and FWHM of ISOPHOT represented a significant
improvement with respect to IRAS, however due to k-correction and
sensitivity limitations, only the local universe could be probed at
such wavelengths. The 170 µm band was more favorable for the
detection of distant ULIRGs as shown in the
Fig. 1 where
the peak emission of a ULIRG of 4 × 1012
L and redshifted
at z = 1 is shown (normalized SED of Arp 220). A major issue at these
wavelengths with a 60 cm telescope is obviously the identification of
optical counterparts for the determination of a redshift and the
separation of local and distant galaxies.