systematically underestimated (for more details of PSC and FSC, please read IRAS Explanatory Supplement[^5]). As flux density is the key parameter of our study, we use the IRAS Scan Processing and Integration tool[^6] (Scanpi, version 6.0) to get better measurements. Scanpi is an interactive set of tools to extract, display and measure flux density from calibrated scan data (the basic data format of IRAS). It provides tools to perform more detailed photometry, which offers several advantages. First, it is possible to measure the flux density of highly extended sources, up to around 15 arcmin in radius, suitable for LVHIS galaxies. Second, the sensitivity is a factor of 2-5 better than that of PSC. It allows us to measure lower flux densities. Third, de-blending nearby sources and removing foreground or background emission can be done interactively. This again helps to detect weaker objects and improve signal-to-noise ratio.

Usually we use the default parameter set in Scanpi. For data extraction, we use all the scans with “cross-scan distance” (the distance of scan from the source) less than 1.7 arcmin and the median coadding method, which is robust to outliers. For background fitting, we use all the data points within 30 arcmin radius 