The deepest image of the Universe at a wavelength of 15 microns

TL;DR

This paper presents the deepest 15 micron infrared image of the universe, resolving a significant portion of the cosmic infrared background and providing insights into galaxy formation and evolution at high redshifts.

Contribution

It provides the deepest 15 micron image of the universe using gravitational lensing, resolving the cosmic infrared background beyond previous surveys and analyzing galaxy evolution.

Findings

Resolved over 80% of the CIRB at 15 microns

Detected 565 sources in the deepest image to date

Observed strong galaxy evolution consistent with downsizing models

Abstract

We present photometry, photometric redshifts and extra galactic number counts for ultra deep 15 micron mapping of the gravitational lensing cluster Abell 2218 (A2218), which is the deepest image taken by any facility at this wavelength. This data resolves the cosmic infrared background (CIRB) beyond the 80% that blank field AKARI surveys aim to achieve. To gain an understanding of galaxy formation and evolution over the age of the Universe a necessary step is to fully resolve the CIRB, which represents the dust-shrouded cosmic star formation history. Observing through A2218 gives magnifications of up to a factor of 10, thus allowing the sampling of a more representative spread of high redshift galaxies, which comprise the bulk of the CIRB. 19 pointed observations were taken by AKARIs IRC MIR-L channel, and a final combined image with an area of 122.3 square arcminutes and effective integration time of 8460 seconds was achieved. The 5 sigma sensitivity limit is estimated at 41.7 uJy. An initial 5 sigma catalogue of 565 sources was extracted giving 39 beams per source, which shows the image is confusion limited. Our 15 micron number counts show strong evolution consistent with galaxy evolution models that incorporate downsizing in star formation.