CFHT MegaPrime/MegaCam $u$-band source catalogue of the $AKARI$ North Ecliptic Pole Wide field

TL;DR

This paper presents a comprehensive u-band optical source catalogue for the AKARI NEP-Wide field, enhancing IR source studies with improved photometric redshifts and UV data, based on CFHT MegaPrime/MegaCam observations covering 3.6 square degrees.

Contribution

The work provides the first extensive u-band optical catalogue for the AKARI NEP-Wide field, enabling better multi-wavelength analysis of IR sources with new UV and optical data.

Findings

Catalogue includes 351,635 sources with high-quality photometry.

Achieved limiting magnitudes of 25.38 and 25.79 in shallow and deep regions.

Improves photometric redshift accuracy and UV characterization of IR sources.

Abstract

The $AKARI$ infrared (IR) space telescope conducted two surveys (Deep and Wide) in the North Ecliptic Pole (NEP) field to find more than 100,000 IR sources using its Infrared Camera (IRC). IRC's 9 filters, which cover wavebands from 2 to 24 $\mu$m continuously, make $AKARI$ unique in comparison with other IR observatories such as $Spitzer$ or $WISE$. However, studies of the $AKARI$ NEP-Wide field sources had been limited due to the lack of follow-up observations in the ultraviolet (UV) and optical. In this work, we present the Canada-France-Hawaii Telescope (CFHT) MegaPrime/MegaCam $u$-band source catalogue of the $AKARI$ NEP-Wide field. The observations were taken in 7 nights in 2015 and 2016, resulting in 82 observed frames covering 3.6 deg$^2$. The data reduction, image processing and source extraction were performed in a standard procedure using the \textsc{Elixir} pipeline and the \textsc{AstrOmatic} software, and eventually 351,635 sources have been extracted. The data quality is discussed in two regions (shallow and deep) separately, due to the difference in the total integration time (4,520 and 13,910 seconds). The 5$\sigma$ limiting magnitude, seeing FWHM, and the magnitude at 50 per cent completeness are 25.38 mag (25.79 mag in the deep region), 0.82 arcsec (0.94 arcsec) and 25.06 mag (25.45 mag), respectively. The u-band data provide us with critical improvements to photometric redshifts and UV estimates of the precious infrared sources from the $AKARI$ space telescope.