Nature of Infrared Sources in 11 micron Selected Sample from Early Data of the AKARI North Ecliptic Pole Deep Survey

TL;DR

This paper analyzes 11 micron selected sources from the AKARI NEP-Deep survey, revealing that most are star-forming galaxies at moderate redshifts, with some AGNs and unusual objects, based on detailed spectral energy distribution modeling.

Contribution

It provides a detailed characterization of 11 μm sources, including their redshift distribution and properties, using multi-wavelength data and SED modeling, which is novel for this survey.

Findings

Majority (~68%) are star-forming galaxies at 0.2<z<0.7

Detected four AGNs at various redshifts

Identified unusual objects like brown dwarf candidate

Abstract

We present the properties of 11 $\mu$m 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 $\mu$m, with the exposure time 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 $\mu$m. The main sample studied here consists of 71 sources whose 11 $\mu$m AB magnitudes are equal to or brighter than 18.5 (251 $\mu$Jy), which is complete to more than 90%. The 11 $\mu$m 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 (~68%) of 11 $\mu$m bright sources are star forming galaxies at 0.2 < z < 0.7 with $L_{IR} ~ 10^{10}$ -- $10^{12} L_{\odot}$ based on the detailed modelling of SEDs. We also find four AGNs lying at various redshifts in the main sample. In addition, we discuss a few sources which have non-typical SEDs of the main sample, including a brown dwarf candidate, a steep power-law source, flat spectrum object, and an early-type galaxy at moderate redshift.