Nature of infrared sources in 11 μm selected sample from early data of the AKARI north ecliptic pole deep survey

Abstract

We present the properties of 11 μm selected sources detected in the early data of the North Ecliptic Pole Deep (NEP-Deep) Survey of AKARI. The data set covers 6 wavelength bands from 2.5 to 11 μm, with exposure times of 10-20 minutes. This field lies within the CFHT survey with four filter bands (g′, r′, i′, z′), enabling us to establish nearly continuous spectral energy distributions (SEDs) for wavelengths ranging from 0.4 to 11 μm. The main sample studied here consists of 72 sources whose 11 μm AB magnitudes are equal to or brighter than 18.5 (144 μJy), which is complete to more than 90%. The 11 μm band has an advantage of sampling star-forming galaxies with low-to-medium redshifts, since the prominent PAH feature shifts into this band. As expected, we find that the majority (71%) of 11 μm bright sources are star-forming galaxies at 0.2 ≲ z ≲ 0.7 with LIR ∼ 1010-1012 L⊙ based on detailed modelling of the SEDs. We also find four AGNs lying at various redshifts in the main sample. In addition, we discuss a few sources that have non-typical SEDs of the main sample, including a brown-dwarf candidate, a steep power-law source, a flat-spectrum object, and an early-type galaxy at moderate redshift. © 2007. Astronomical Society of Japan.