ULTRA DEEP AKARI OBSERVATIONS OF ABELL 2218: RESOLVING THE 15 μm EXTRAGALACTIC BACKGROUND LIGHT

We present extragalactic number counts and a lower limit estimate for the cosmic infrared background (CIRB) at 15 mu m from AKARI ultra deep mapping of the gravitational lensing cluster Abell 2218. These data are the deepest taken by any facility at this wavelength and uniquely sample 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 mu Jy. The resulting 15 mu m galaxy number counts are a factor of 3 fainter than previous results, extending to a depth of similar to 0.01 mJy and providing a stronger lower limit constraint on the CIRB at 15 mu m of 1.9 +/- 0.5 nW m(-2) sr(-1).