Optical – near-infrared catalog for the AKARI north ecliptic pole Deep field

Oi, Nagisa; Matsuhara, Hideo; Murata, Kazumi; Goto, Tomotsugu; Wada, Takehiko; Takagi, Toshinobu; Ohyama, Youichi; Malkan, Matthew; Im, Myungshin; Shim, Hyunjin; Serjeant, Stephen and Pearson, Chris (2014). Optical – near-infrared catalog for the AKARI north ecliptic pole Deep field. Astronomy & Astrophysics, 566 A60.

DOI: https://doi.org/10.1051/0004-6361/201322561

Abstract

Aims. We present an 8-band (u∗, g′, r′, i′, z′, Y, J, Ks) optical to near-infrared deep photometric catalog based on the observations made with MegaCam and WIRCam at the CFHT, and compute photometric redshifts, zp in the north ecliptic pole (NEP) region. AKARI infrared satellite carried out a deep survey in the NEP region at near- to mid-infrared wavelengths. Our optical to near-infrared catalog allows us to identify the counterparts and zp for the AKARI sources.

Methods. We obtained seven-band (g′, r′, i′, z′, Y, J, Ks) imaging data, and we crossmatched them with existing u∗-band data (limiting magnitude = 24.6 mag [5σ; AB]) to design the band-merged catalog. We included all z′-band sources with counterparts in at least one of the other bands in the catalog. We used a template-fitting methods to compute zp for all the cataloged sources.

Results. The estimated 4σ detection limits within a 1 arcsec aperture radius are 26.7, 25.9, 25.1, and 24.1 mag [AB] for the optical g′, r′, i′, and z′-bands and 23.4, 23.0, and 22.7 mag for the near-infrared Y, J, and Ks-bands, respectively. There are a total of 85 797 sources in the band-merged catalog. An astrometric accuracy of this catalog determined by examining coordinate offsets with regard to 2MASS is 0.013 arcsec with a root mean square offset of 0.32 arcsec. We distinguish 5441 secure stars from extended sources using the u∗ − J versus g′ − Ks colours, combined with the SExtractor stellarity index of the images. Comparing with galaxy spectroscopic redshifts, we find a photometric redshift dispersion, σΔz/(1 + z), of 0.032 and catastrophic failure rate, Δz/(1 + z) > 0.15, of 5.8% at z< 1, while a dispersion of 0.117 and a catastrophic failure rate of 16.6% at z> 1. We extend the estimate of the zp uncertainty over the full magnitude/redshift space with a redshift probability distribution function and find that our redshifts are highly accurate with z′ < 22 at zp< 2.5 and for fainter sources with z′ < 24 at zp< 1. From the investigation of photometric properties of AKARI infrared sources (23 354 sources) using the g′z′Ks diagram, < 5% of AKARI sources with optical counterparts are classified as high-z (1.4 <z< 2.5) star-forming galaxies. Among the high-z star-forming galaxies, AKARI mid-infrared detected sources seem to be affected by stronger dust extinction compared with sources with non-detections in the AKARI mid-infrared bands.

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