The first and second data releases of the Kilo-Degree Survey

Abstract

Context. The Kilo-Degree Survey (KiDS) is an optical wide-field imaging survey carried out with the VLT Survey Telescope and the OmegaCAM camera. KiDS will image 1500 square degrees in four filters (ugri), and together with its near-infrared counterpart VIKING will produce deep photometry in nine bands. Designed for weak lensing shape and photometric redshift measurements, its core science driver is mapping the large-scale matter distribution in the Universe back to a redshift of ∼0.5. Secondary science cases include galaxy evolution, Milky Way structure, and the detection of high-redshift clusters and quasars. Aims. KiDS is an ESO Public Survey and dedicated to serving the astronomical community with high-quality data products derived from the survey data. Public data releases, the first two of which are presented here, are crucial for enabling independent confirmation of the survey's scientific value. The achieved data quality and initial scientific utilization are reviewed in order to validate the survey data. Methods. A dedicated pipeline and data management system based on A-WISE, combined with newly developed masking and source classification tools, is used for the production of the data products described here. Science projects based on these data products and preliminary results are outlined. Results. For 148 survey tiles (≈160 sq.deg.) stacked ugri images have been released, accompanied by weight maps, masks, source lists, and a multi-band source catalogue. Limiting magnitudes are typically 24.3, 25.1, 24.9, 23.8 (5σ in a 2 aperture) in ugri, respectively, and the typical r-band PSF size is less than 0.7 . The photometry prior to global homogenization is stable at the ∼2% (4%) level in gri (u) with some outliers due to non-photometric conditions, while the astrometry shows a typical 2D rms of 0.03 . Early scientific results include the detection of nine high-z QSOs, fifteen candidate strong gravitational lenses, high-quality photometric redshifts and structural parameters for hundreds of thousands of galaxies.

The third data release of the Kilo-Degree Survey and associated data products

“…The large range of limiting magnitudes in i-band reflects the variety in both seeing and sky illumination conditions. The overall data quality of the DR3 release is very similar to the data quality of DR1 and DR2, as described in de Jong et al (2015) and Kuijken et al (2015). The most striking and serious issues with the KiDS data are caused by stray light that scatters into the light path and onto the focal plane (see de Jong et al 2015, for some examples).…”

On the Dearth of Ultra-faint Extremely Metal-poor Galaxies

“…If the completeness function is assumed to have the functional form of the SDSS completeness, then the half-completeness, SB r , fully describes it. We carried out the exercise of estimating N QXMP for a number of ongoing and forthcoming large area surveys, specifically, for the the Dark Energy Survey (DES; The DES Collaboration 2005), the Galaxy and Mass Assembly survey (GAMA; Liske et al 2015), the Kilo-Degree Survey (KIDS; de Jong et al 2015), and the Large Synoptic Survey Telescope (LSST; Ivezic et al 2008). The parameters that define the surveys are given in Table 3.…”

A cooperative approach among methods for photometric redshifts estimation: an application to KiDS data

“…KiDS is an optical survey (de Jong et al 2015), carried out with the VST-OmegaCAM camera (Kuijken 2011), dedicated mainly to studies for gravitational lensing, galaxy evolution, searches for high-z quasars and galaxy clusters. The KiDS data releases consist of tiles which are observed in u, g, r, and i bands.…”

“…Data are processed using a distributed Oracle-based environment through the Astro-WISE (AW) optical pipeline (McFarland et al 2013). Source extraction is performed using the algorithm KiDSCAT within the AW environment, where tile stacking, photometric calibration and astrometry are performed (see de Jong et al 2015).…”

“…The sample of galaxies on which we performed our analysis is mostly extracted from the second data release of KiDS (KiDS-DR2;de Jong et al 2015) which contains 148 tiles observed in all filters during the first two years of survey regular operations. We added 29 extra tiles, not included in the DR2 at the time this was released, that will be part of the forthcoming KiDS data release, thus covering an area of 177 square degrees.…”