Many of the sample objects are rather distant and have weak far-infrared fluxes
(see Sect. 3).
The detection limit of the IRAS satellite
(
and 
Jy)
implies that at radial velocities
larger than 
, only galaxies with a FIR luminosity higher than
1010 
could be detected by IRAS.
Similarly, an observational bias was introduced in the CO and 
data,
the choice of a reasonable integration time setting a limit to the
and H2 gas masses which could be detected.
On the average, an integration time of 4 hours has been spent on each galaxy,
which corresponds
to a noise level of about 3 mK (in 
) in the CO data
and 3 mJy in the data for the velocity resolutions of our spectra.
An upper limit to the emission can be determined as 
.
Using a linewidth 
=150 km s-1.
this means that
within 4 hours of integration
a limit of 109 
(108 respectively) on the H2 mass is reached
only for galaxies with 
(
respectively).
For , a limit of 109 is reached within 4 hours for galaxies
with 
.