North Ecliptic Pole Wide Field Survey of AKARI: Survey Strategy and Data Characteristics

Abstract

Abstract We present the survey strategy and the data characteristics of the North Ecliptic Pole (NEP) Wide Survey of AKARI. The survey was carried out for about one year starting from 2006 May with 9 passbands from 2.5 to 24 $\mu$m and the areal coverage of about 5.8 degree$^2$ centered on NEP. The survey depth reaches to 21.8 AB magnitude near infrared (NIR) bands, and $\sim$18.6 AB magnitude at the mid infrared (MIR) bands such as 15 and 18 $\mu$m. The total number of sources detected in this survey is about 104000, with more sources in NIR than in the MIR. We have cross matched infrared sources with optically identified sources in CFHT imaging survey which covered about 2 degree$^2$ within NEP-Wide survey region in order to characterize the nature of infrared sources. The majority of the MIR sources at 15 and 18 $\mu$m bands are found to be star forming disk galaxies, with smaller fraction of early type galaxies and AGNs. We found that a large fraction (60%–80%) of bright sources in 9 and 11 $\mu$m is stars while stellar fraction decreases toward fainter sources. We present the histograms of the sources at MIR bands at 9, 11, 15, and 18 $\mu$m. The number of sources per magnitude thus varies as $m^{0.6}$ for longer wavelength sources while shorter wavelength sources show steeper variation with $m$, where $m$ is the AB magnitude.