AKARI and IRAS: From Beam Corrections to SEDs
  There is significant scientific value to be gained from combining AKARI
fluxes with data at other far-IR wavelengths from the IRAS and Herschel
missions. To be able to do this we must ensure that there are no systematic
differences between the datasets that need to be corrected before the fluxes
are compatible with each other. One such systematic effect identified in the
BSCv1 data is the issue of beam corrections. We determine these for the BSCv2
data by correlating ratios of appropriate IRAS and AKARI bands with the
difference in 2MASS J band extended and point source magnitudes for sources
cross matched between the IRAS FSC, AKARI BSCv2 and 2MASS catalogs. We find
significant correlations (p<< 10^-13) indicating that beam corrections are
necessary in the 65 and 90 micron bands. We then use these corrected fluxes to
supplement existing data in spectral energy distribution (SED) fits for
ultraluminous infrared galaxies in the HERUS survey. The addition of AKARI
fluxes makes little difference to the results of simple (T,beta) fits to the
SEDs of these sources, though there is a general decrease in reduced chi^2
values. The utility of the extra AKARI data, however, is in allowing physically
more realistic SED models with more parameters to be fit to the data. We also
extend our analysis of beam correction issues in the AKARI data by examining
the Herschel Reference Sample, which have Herschel photometry from 100 to 500
microns and which are more spatially extended than the HERUS ULIRGs.
Thirty-four of the HRS sources have good Herschel SEDs and matching data from
AKARI. This investigation finds that our simple 2MASS-based beam correction
scheme is inadequate for these larger and more complex sources. There are also
indications that additional beam corrections at 140 and 160 microns are needed
for these sources, extended on scales >1 arcminute.
