  We present 1.25 mm continuum data for a southern galaxy sample selected from
the IRAS PSC and complete to S_60=2 Jy. Two thirds of the galaxies have been
detected and significant limits on the remaining objects have been set. We
find, on a statistical basis, indications that the dust emission in these
galaxies is somewhat more centrally concentrated than that of the optical
light, possibly tracing a higher metal content in the inner galactic regions.
This result also allows to estimate the aperture corrections to the millimetric
data. The latter, together with IRAS photometric data, have been used to
compare the broad-band FIR/mm spectra with a simple dust model. According to
their far-IR/mm spectrum, the sample galaxies show a dichothomy: almost half of
the objects, those displaying bright 25-60um fluxes ascribed to warm dust
residing in 'starburst' regions, are characterized by higher values of the
bolometric (optical + FIR) luminosity, of the dust-to-gas mass ratio, of the
dust optical depths and of the overall extinction. A complementary class of
objects dominated by cold dust ('cirrus') shows opposite trends. Because of the
favourable observational setup, selection wavelength and completeness, we
believe these data provide an exhaustive and unbiased view of dust properties
in spiral galaxies.
