APPENDIX: THE EXTENDED SOURCE CORRECTION

The flux calibration of the LWS instrument is based on observations of Uranus, a point source in the LWS aperture. The telescope is diffraction limited at about 110 µm, beyond which a fraction of the flux of an on-axis point source may be diffracted out of the standard aperture. Significant diffraction loss does not occur in sources that appear extended in the LWS beam. Therefore, an extended source correction must be applied to put these fluxes on a point source calibration scale. In order to apply this correction, the LWS beam of each detector and the telescope PSF must be well known. The extended source correction also assumes that the source is infinitely extended and uniformly bright. None of these galaxies are either, so applying the correction requires great caution. From tests done by the LWS instrument team, the extended source correction works well for sources larger than 3'-4' (Gry et al. 2003) when compared to IRAS at 100 µm.

The fluxes quoted in Tables 2, 4, and 5 are those which have been measured according to the point source flux calibration. The current understanding of the LWS beam is still not complete, and the extended source correction may change in the future as more work is done. Therefore, the extended source correction has not been applied to the line fluxes listed in this paper, but those galaxies that may require an extended source correction have been noted in Tables 2, 4, and 5. The most up-to-date effective apertures and corrections are listed in Table 7, taken from the ISO LWS Handbook Volume III (Gry et al. 2003).