Astronomy & Astrophysics manuscript no. ms c ESO 2019 February 25, 2019 The fourth data release of the Kilo-Degree Survey: ugri imaging and nine-band optical-IR photometry over 1000 square degrees K. Kuijken1, C. Heymans2, A. Dvornik1, H. Hildebrandt3; 4, J.T.A. de Jong5, A.H. Wright4, T. Erben4, M. Bilicki1; 6, B. Giblin2, H.-Y. Shan4; 7, F. Getman8, A. Grado8, H. Hoekstra1, L. Miller9, N. Napolitano10; 8, M. Paolilo11, M. Radovich12, P. Schneider4, W. Sutherland13, M. Tewes4, C. Tortora14, E.A. Valentijn5, and G.A. Verdoes Kleijn5 1 Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, the Netherlands e-mail: [email protected] 2 Scottish Universities Physics Alliance, Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK 3 Astronomisches Institut, Ruhr-Universität Bochum, Universitätsstrasse 150, 44801 Bochum, Germany 4 Argelander-Institut für Astronomie, Auf dem Hügel 71, D-53121 Bonn, Germany 5 Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700 AV Groningen, the Netherlands 6 Center for Theoretical Physics, Polish Academy of Sciences, al. Lotników 32/46, 02-668, Warsaw, Poland 7 Shanghai Astronomical Observatory, Nandan Road 80, Shanghai 200030, China 8 INAF - Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Napoli, Italy 9 Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK 10 School of Physics and Astronomy, Sun Yat-sen University, Guangzhou 519082, Zhuhai Campus, P.R. China 11 Dept.of Physics “Ettore Pancini”, Università Federico II, 80126 Napoli, Italy 12 INAF - Osservatorio Astronomico di Padova, via dell’Osservatorio 5, 35122 Padova, Italy 13 School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London E1 4NS, UK 14 INAF - Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy Received ???; accepted ??? ABSTRACT Context. The Kilo-Degree Survey (KiDS) is an ongoing optical wide-field imaging survey with the OmegaCAM camera at the VLT Survey Telescope, specifically designed for measuring weak gravitational lensing by galaxies and large-scale structure. When completed it will consist of 1350 square degrees imaged in four filters (ugri). Aims. Here we present the fourth public data release which more than doubles the area of sky covered by data release 3. We also include aperture-matched ZYJHKs photometry from our partner VIKING survey on the VISTA telescope in the photometry catalogue. We illustrate the data quality and describe the catalogue content. Methods. Two dedicated pipelines are used for the production of the optical data. The Astro-WISE information system is used for the production of co-added images in the four survey bands, while a separate reduction of the r-band images using the theli pipeline is used to provide a source catalogue suitable for the core weak lensing science case. All data have been re-reduced for this data release using the latest versions of the pipelines. The VIKING photometry is obtained as forced photometry on the theli sources, using a re-reduction of the VIKING data that starts from the VISTA pawprints. Modifications to the pipelines with respect to earlier releases are described in detail. The photometry is calibrated to the Gaia DR2 G band using stellar locus regression. Results. In this data release a total of 1006 square-degree survey tiles with stacked ugri images are made available, accompanied by weight maps, masks, and single-band source lists. We also provide a multi-band catalogue based on r-band detections, including homogenized photometry and photometric redshifts, for the whole dataset. Mean limiting magnitudes (5σ in a 200 aperture) and the tile-to-tile rms scatter are 24:23 ± 0:12, 25:12 ± 0:14, 25:02 ± 0:13, 23:68 ± 0:27 in ugri, respectively, and the mean r-band seeing is 000:70. Key words. observations: galaxies: general – astronomical data bases: surveys – cosmology: large-scale structure of Universe 1. Introduction: the Kilo-Degree and VIKING focal plane contains the square 268-million pixel CCD mosaic Surveys camera OmegaCAM (Kuijken 2011) that covers a 1◦:013 × 1◦:020 area at 000:213 pitch, and the site and telescope optics (with ac- High-fidelity images of the sky are one of the most fundamental tively controlled primary and secondary mirrors) ensure an im- kinds of data for astronomy research. While for many decades age quality that is sub-arcsecond most of the time, and that does photographic plates dominated optical sky surveys, the advent of not degrade towards the corners of the field. Since starting op- large-format CCD detectors for astronomy opened up the era of erations in October 2011, more than half of the available time digital, high resolution, high sensitivity, linear-response images. on the telescope has been used for a set of three wide-area ‘Pub- lic Imaging Surveys’ for the ESO community. The Kilo-Degree The ESO VLT Survey Telescope (VST; Capaccioli & Schipani 2011; Capaccioli et al. 2012) at ESO’s Paranal observa- tory was specifically designed for wide-field, optical imaging. Its Article number, page 1 of 25 A&A proofs: manuscript no. ms Table 1. KiDS observing strategy: observing condition constraints and exposure times. Filter Max. lunar Min. moon Max. seeing Max. airmass Sky transp. Dithers Total Exp. illumination distance [deg] [arcsec] time [s] u 0.4 90 1.1 1.2 CLEAR 4 1000 g 0.4 80 0.9 1.6 CLEAR 5 900 r 0.4 60 0.8 1.3 CLEAR 5 1800 i 1.0 60 1.1 2.0 CLEAR 5 1200 Table 2. Appriximate boundaries of the KiDS fields (see also Fig. 1). Northern patch, KiDS-N, contains two additional smaller areas: KiDS-N-W2, which coincides with the G9 patch of the GAMA Field RA range Dec range survey (Driver et al. 2011), and KiDS-N-D2, a single pointing KiDS-S [330◦:0; 52◦:5] [−35◦:6; −26◦:6] on the COSMOS field. In a coordinated effort over the same part of the sky, the VISTA Kilo-degree INfrared Galaxy sur- ◦ ◦ ◦ ◦ KiDS-N [155:5; 225:5] [−4:0; +4:0] vey (VIKING; Edge et al. 2013) on the nearby VISTA telescope [225◦:5; 238◦:5] [−2◦:0; +3◦:0] added the five bands Z, Y, J, H and Ks. VIKING observations are 4 5 KiDS-N-W2 [128◦:5; 141◦:5] [−2◦:0; +3◦:0] complete and available in the ESO archive . Table 2 and Fig. 1 show the full KiDS footprint on the sky, as well as the part that KiDS-N-D2 [149◦:5; 150◦:5] [+1◦:7; +2◦:7] is covered by the data contained in this data release (KiDS-ESO- DR4, or DR4 for short). The fields that were previously released under DR1+2+3 are also indicated: this is the area that was used 1 Survey (KiDS; de Jong et al. 2013) is the deepest of these, and for the [KiDS450] cosmic shear analysis, with the corresponding the one that exploits the best observing conditions. shape/photometric redshift catalogue released as DR3.1. KiDS was designed as a cosmology survey, to study the In order to improve the fidelity of the photometric redshift- galaxy population out to redshift ∼1 and in particular to mea- based tomography, and to enable inclusion of high-value sources sure the effect on galaxy shapes due to weak gravitational lens- in the redshift range 0.9–1.2, Hildebrandt et al. (2018) added ing by structure along the line of sight. By combining galaxy VIKING photometry to the KiDS-450 data set, as described in shapes with photometric redshift estimates it is possible to lo- Wright et al. (2018). The resulting cosmological parameter con- cate the redshift at which the gravitational lensing signal orig- straints of this new analysis, dubbed ‘KV450’, are fully con- inates, and hence to map out the growth of large-scale struc- sistent with [KiDS450]. DR4 incorporates the methodology de- ture, an important aspect of the evolution of the Universe and a veloped for KV450 and includes VIKING photometry for all key cosmology probe. Together with KiDS, two other major sur- sources. Of all wide-area surveys, this makes it the one with by veys are engaged in such measurements: the Dark Energy Sur- far the deepest near-IR data. vey (DES; Dark Energy Survey Collaboration 2005)2 and the Though designed for the primary cosmology science case HyperSuprimeCam survey (HSC; Aihara et al. 2018)3, and all ([KiDS450]; Joudaki et al. 2017; van Uitert et al. 2018; Köh- three have reported intermediate cosmology results (Hildebrandt linger et al. 2017; Harnois-Déraps et al. 2017; Amon et al. 2018; et al. 2017, henceforth [KiDS450]; Troxel et al. 2018; Hikage Shan et al. 2018; Martinet et al. 2018; Giblin et al. 2018; As- et al. 2018). Their precision is already such that the measure- gari et al. 2018), KiDS data are also being used for a variety of ments can constrain some parameters in the cosmological model other studies, including the galaxy-halo connection (van Uitert to a level that is comparable to what is achieved from the cos- et al. 2016, 2017), searches for strongly lensed galaxies (Petrillo mic microwave background anisotropies (Planck Collaboration et al. 2019) and quasars (Spiniello et al. 2018; Sergeyev et al. 2018). Since ground-based surveys are limited fundamentally by 2018), solar system objects (Mahlke et al. 2018), photometric the atmospheric disturbance on galaxy shapes and photometry, redshift machine learning method development (Amaro et al. space missions Euclid (Laureijs et al. 2011) and later WFIRST 2019; Bilicki et al. 2018), studies of galaxy evolution (Tortora (Spergel et al. 2015) are planned to increase the fidelity of such et al.