A multi--wavelength study of the IRAS Deep Survey galaxy sample II. The far-IR properties

We derive the 60\mu local LF to sensitivity levels 10 times deeper than before, to investigate evolutionary effects up to a redshift of 0.37, and, using the 60/15\mu bi-variate method, the poorly known 15\mu local LF of galaxies. We exploited our ISOCAM observations of the IRAS Deep Survey (IDS) fields (Hacking and Houck 1987), to correct the $60mu fluxes for confusion effects and observational biases. We find indications of a significant incompleteness of the IDS sample, still one of the deepest far-IR selected galaxy samples, below \simeq 80mJy (Mazzei et al. 2001). We have reliable identifications and spectroscopic redshifts for 100% of a complete subsample comprising 56 sources with S(60mu(m))> 80mJy. With our spectroscopic coverage we construct the 60mu LF for a sample complete down to 80 mJy. This LF extends over three orders of magnitude in luminosity, from 9 up to more than 12 in log(L_(60)/L_(\odot)). Despite the fact that the redshift range of our sample exceeds z=0.3, the V/V_{max} test gives <V/V_{max}>=0.51\pm 0.06, consistent with a uniform distribution of sources. A more direct test, whereby the LF was measured in each of four different redshift intervals, does not point out any signature of evolution. On the other hand, the rest--frame 15\mu local LF we derive, extends up to log(L_{15}/L_{\odot})=12 and predicts 10 times more sources at log(L_{15}/L_{\odot})=11 than are seen by Pozzi et al. (2004).