The 2 to 24 micron source counts from the AKARI North Ecliptic Pole survey

TL;DR

This paper presents galaxy source counts across nine infrared bands from the AKARI NEP survey, revealing galaxy evolution and estimating the contribution to the cosmic infrared background.

Contribution

It provides new, detailed galaxy counts in the 2-24 micron range from AKARI NEP data, with corrections and comparisons to models and previous surveys.

Findings

Counts are flat at bright fluxes, consistent with Euclidean universe.

Counts deviate at faint fluxes, indicating galaxy evolution.

AKARI NEP survey accounts for 20-50% of the cosmic infrared background.

Abstract

We present herein galaxy number counts of the nine bands in the 2-24 micron range on the basis of the AKARI North Ecliptic Pole (NEP) surveys. The number counts are derived from NEP-deep and NEP-wide surveys, which cover areas of 0.5 and 5.8 deg2, respectively. To produce reliable number counts, the sources were extracted from recently updated images. Completeness and difference between observed and intrinsic magnitudes were corrected by Monte Carlo simulation. Stellar counts were subtracted by using the stellar fraction estimated from optical data. The resultant source counts are given down to the 80% completeness limit; 0.18, 0.16, 0.10, 0.05, 0.06, 0.10, 0.15, 0.16, and 0.44 mJy in the 2.4, 3.2, 4.1, 7, 9, 11, 15, 18 and 24 um bands, respectively. On the bright side of all bands, the count distribution is flat, consistent with the Euclidean Universe, while on the faint side, the counts deviate, suggesting that the galaxy population of the distant universe is evolving. These results are generally consistent with previous galaxy counts in similar wavebands. We also compare our counts with evolutionary models and find them in good agreements. By integrating the models down to the 80% completeness limits, we calculate that the AKARI NEP-survey revolves 20%-50% of the cosmic infrared background, depending on the wavebands.