On Surface Brightness and Flux Calibration for Point and Compact Extended Sources in the AKARI Far-IR All-Sky Survey (AFASS) Maps

TL;DR

This paper verifies that the AKARI AFASS far-infrared all-sky maps are properly calibrated for point-source photometry using aperture correction, ensuring accurate flux measurements for both point and extended sources.

Contribution

It demonstrates the effectiveness of an empirical aperture correction method for accurate point-source flux calibration in the AKARI AFASS maps.

Findings

Fluxes in the AKARI bright source catalog are accurately recovered.

Aperture correction method is validated for point-source photometry.

Proper photometry for extended sources is confirmed using summed pixel values.

Abstract

The AKARI Infrared Astronomical Satellite produced the all-sky survey (AFASS) maps in the far-IR at roughly arc-minute spatial resolution, enabling us to investigate the whole sky in the far-IR for objects having surface brightnesses greater than a few to a couple of dozen MJy/sr. While the AFASS maps are absolutely calibrated against large-scale diffuse emission, it was uncertain whether or not an additional flux correction for point sources was necessary. Here, we verify that calibration for point-source photometry in the AFASS maps is proper. With the aperture correction method based on the empirical point-spread-function templates derived directly from the AFASS maps, fluxes in the AKARI bright source catalogue (BSC) are reproduced. The AKARI BSC fluxes are also satisfactorily recovered with the 1 sigma aperture, which is the empirical equivalent of an infinite aperture. These results confirm that in the AFASS maps far-IR photometry can be properly performed by using the aperture correction method for point sources and by summing all pixel values within an appropriately defined aperture of the intended target (i.e., the aperture photometry method) for extended sources.