Calibration of the AKARI far-infrared all-sky survey maps

Abstract

We present an initial analysis of the properties of an all-sky image obtained by the Far-Infrared Surveyor (FIS) onboard the AKARI satellite, at 65μm (N60), 90μm (WIDE-S), 140μm (WIDE-L), and 160μm (N160). An absolute flux calibration was determined by comparing the data with COBE/DIRBE data sets; the intensity range was as wide as from a few MJysr-1 to >1GJysr-1. The uncertainties are considered to be the standard deviations with respect to the DIRBE data, and are less than 10% for intensities above 10, 3, 25, and 26MJysr-1 at the N60, WIDE-S, WIDE-L, and N160 bands, respectively. The characteristics of point sources in the image were also determined by stacking maps centred on photometric standard stars. The full width at half maxima of the point spread functions (PSFs) were 63", 78", and 88" at the N60, WIDE-S, and WIDE-L bands, respectively. The PSF at the N160 band was not obtained due to the sensitivity, but it is thought to be the same as that of the WIDE-L one.