KiDS+VIKING-450: A new combined optical and near-infrared dataset for cosmology and astrophysics

We present the curation and verification of a new combined optical and near infrared dataset for cosmology and astrophysics, derived by combining u gri-band imaging from the Kilo-Degree Survey (KiDS) and ZYJHK(s)-band imaging from the VISTA Kilo degree Infrared Galaxy (VIKING) survey. This dataset is unrivaled in cosmological imaging surveys due to the combination of its area (458 deg(2) before masking), depth (r <= 25), and wavelength coverage (ugriZYJHK(s)). This combination of survey depth, area, and (most importantly) wavelength coverage allows significant reductions in systematic uncertainties (i.e. reductions of between 10% and 60% in bias, outlier rate, and scatter) in photometric-to-spectroscopic redshift comparisons, compared to the optical-only case at photo-z above 0.7. The complementarity between our optical and near infrared surveys means that over 80% of our sources, across all photo-z, have significant detections (i.e. not upper limits) in our eight reddest bands. We have derived photometry, photo-z, and stellar masses for all sources in the survey, and verified these data products against existing spectroscopic galaxy samples. We demonstrate the fidelity of our higher-level data products by constructing the survey stellar mass functions in eight volume-complete redshift bins. We find that these photometrically derived mass functions provide excellent agreement with previous mass evolution studies derived using spectroscopic surveys. The primary data products presented in this paper are made publicly available through the KiDS survey website.