Calibration of the AKARI Far-infrared All Sky Survey Maps

TL;DR

This paper details the calibration and characterization of the AKARI Far-infrared All Sky Survey Maps across four bands, assessing flux accuracy, uncertainties, and point source properties to enhance data reliability.

Contribution

It provides the first comprehensive calibration and PSF analysis of AKARI FIS all-sky maps, improving flux accuracy and point source characterization.

Findings

Flux calibration uncertainties are below 10% for most bands.

Point spread functions have FWHMs of 63" to 88" across bands.

Calibration extends the dynamic range up to >1 GJy sr$^{-1}$.

Abstract

We present an initial analysis of the properties of the all-sky image obtained by the Far-Infrared Surveyor (FIS) onboard the AKARI satellite, at 65~$\mu$m (N60), 90~$\mu$m (WIDE-S), 140~$\mu$m (WIDE-L),and 160~$\mu$m (N160). Absolute flux calibration was determined by comparing the data with the COBE/DIRBE data sets, and the intensity range was as wide as from a few MJy~sr$^{-1}$ to $>$1~GJy~sr$^{-1}$. The uncertainties are considered to be the standard deviations with respect to the DIRBE data, and they are less than 10\% for intensities above 10, 3, 25, and 26~MJy~sr$^{-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.