  Investigations of the point spread functions (PSFs) and flux calibrations for
stacking analysis have been performed with the far-infrared (wavelengths range
of 60 to 140 um all-sky maps taken by the Far-Infrared Surveyor (FIS) onboard
the AKARI satellite. The PSFs are investigated by stacking the maps at the
positions of standard stars with their fluxes of 0.02 -10 Jy. The derived full
widths at the half maximum (FWHMs) of the PSFs are ~ 60 arcsec at 65 and 90 um
and ~ 90 arcsec at 140 um, which are much smaller than that of the previous
all-sky maps obtained with IRAS (~ 6 arcmin). Any flux dependence in the PSFs
is not seen on the investigated flux range. By performing the flux
calibrations, we found that absolute photometry for faint sources can be
carried out with constant calibration factors, which range from 0.6 to 0.8.
After applying the calibration factors, the photometric accuracies for the
stacked sources in the 65, 90, and 140 um bands are 9, 3, and 21 %,
respectively, even below the detection limits of the survey. Any systematic
dependence between the observed flux and model flux is not found. These results
indicate that the FIS map is a useful dataset for the stacking analyses of
faint sources at far-infrared wavelengths.
