Ultra deep AKARI observations of Abell 2218: resolving the 15 um extragalactic background light

TL;DR

This paper uses ultra deep AKARI observations of Abell 2218 to resolve faint 15 um galaxy sources, providing new insights into the cosmic infrared background and galaxy populations beyond previous limits.

Contribution

It presents the deepest 15 um galaxy counts to date, resolving sources below previous sensitivity limits and refining the lower limit estimate of the cosmic infrared background.

Findings

Galaxy counts are three times fainter than previous results.

Extended galaxy counts down to ~0.01 mJy.

Lower limit on cosmic infrared background at 15 um is 1.9 +/- 0.5 nW m^-2 sr^-1.

Abstract

We present extragalactic number counts and a lower limit estimate for the cosmic infrared background at 15 um from AKARI ultra deep mapping of the gravitational lensing cluster Abell 2218. This data is the deepest taken by any facility at this wavelength, and uniquely samples the normal galaxy population. We have de-blended our sources, to resolve photometric confusion, and de-lensed our photometry to probe beyond AKARI's blank-field sensitivity. We estimate a de-blended 5 sigma sensitivity of 28.7 uJy. The resulting 15 um galaxy number counts are a factor of three fainter than previous results, extending to a depth of ~ 0.01 mJy and providing a stronger lower limit constraint on the cosmic infrared background at 15 um of 1.9 +/- 0.5 nW m^-2 sr^-1.