The AKARI NEP-Deep survey: a mid-infrared source catalogue

Abstract

We present a new catalogue of mid-IR sources using the AKARI NEP-Deep survey. The InfraRed Camera (IRC) onboard AKARI has a comprehensive mid-IR wavelength coverage with 9 photometric bands at 2-24 μm. We utilized all of these bands to cover a nearly circular area adjacent to the north ecliptic pole (NEP). We designed the catalogue to include most of sources detected in 7, 9, 11, 15 and 18 μm bands, and found 7284 sources in a 0.67 deg 2 area. From our simulations, we estimate that the catalogue is ∼80 per cent complete to 200 μJy at 15-18 μm, and ∼10 per cent of sources are missed, owing to source blending. Star-galaxy separation is conducted using only AKARI photometry, as a result of which 10 per cent of catalogued sources are found to be stars. The number counts at 11, 15, 18, and 24 μm are presented for both stars and galaxies. A drastic increase in the source density is found in between 11 and 15 μm at the flux level of ∼300 μJy. This is likely due to the redshifted PAH emission at 8 μm, given our rough estimate of redshifts from an AKARI colour-colour plot. Along with the mid-IR source catalogue, we present optical-NIR photometry for sources falling inside a Subaru/Sprime-cam image covering part of the AKARI NEP-Deep field, which is deep enough to detect most of AKARI mid-IR sources, and useful to study optical characteristics of a complete mid-IR source sample.

AKARI North Ecliptic Pole Deep Survey

“…The corresponding 50% completeness limits for these bands are 56,55,38,29,34,50,86,94, and 247 μJy, respectively. The number of MIR objects was increased by ∼2000 to 9560 compared with Takagi et al (2012). Furthermore, the false-detection rate has been much reduced, making the new catalogue reliable at 99.7% even in the single-band detection.…”

“…Previous versions of the NEP-deep catalogues have been created by Wada et al (2008) and Takagi et al (2012). The former created nine single-band catalogues, the latter a MIR-merged catalogue with NIR photometry.…”

“…A comparison between these previous catalogues and our revised catalogue is necessary to assess the merits and the demerits in our analysis. In the following we compare our NIR catalogue with that of Wada et al (2008) and our MIR catalogue with that of Takagi et al (2012).…”

“…The catalogue from this survey has been created by Wada et al (2008) and Takagi et al (2012). The former created single-band catalogues for all nine bands, while the latter created a mid-infrared (MIR) based bandmerged catalogue.…”

Overview of the North Ecliptic Pole Deep Multi-Wavelength Survey (Nep-Deep)

“…The IRC image processing and the source extraction are described in Wada et al (2008), and the band-merged catalog based on the resulted mosaiced images are presented in Takagi et al (2012). The near-IR false-color image is shown in Figure 1.…”