On the far-IR and sub-mm spectra of spiral galaxies

Photometric measurements of three Virgo cluster spirals (NGC4254, NGC4501, and NGC4654) at 160-microns (far-infrared) and 360-microns (submillimeter) wavelengths are compared with theoretical models and observations at other wavelengths. It is shown that the data at the observed wavelengths do not fit any of interstellar dust grain models very well; four possibilities are given in order to explain discrepancies: the observed wavelength points are incorrect; previously observed data is incorrect; both data are incorrect; and the premise of the analysis is incorrect - a composite far-infrared spectrum of normal spiral galaxies is meaningless because they vary considerably in their far-infrared properties. It is also noted that the observed data are inconsistent with models having large cold grains.