KiDS-450 Weak Lensing data
The weak lensing data set based on the KiDS DR3 data set is also called the "KiDS-450" data set and has been released as KiDS DR3.1. Based on the same input data set as the main DR3 release, the KiDS-450 data set encompasses 454 survey tiles. Masking of bright stars, satellite trails and other image defects is already applied in the release catalog, resulting in an effective area of 360.3 sq.deg. Only galaxies with reliable shape measurements are included in this catalog. Unreliable sources have been rejected based on several criteria listed in Hildebrandt & Viola et al. (2017, MNRAS, 465, 1454). The faint limit of the catalog is r = 25.0, corresponding to a typical signal- to-noise of 5σ. The catalog contains a total of 14,650,348 sources, is made up of 455 files (454 data files and 1 metadata file), and has a total data volume of 4.14 GB
For the galaxy shape measurements, the r-band data was processed using a lensing optimized pipeline based on the THELI data reduction system and the lensfit shape measurement software. Source detection was done on stacked r-band images, after which galaxy shapes were measured on individual sub-exposures. The included photometry and photometric redshifts are based on the 4-band ugri image stacks from the main DR3 release.
Note: Hildebrandt & Viola et al. (2017, MNRAS, 465, 1454) found in their cosmic shear analysis that small residual c-terms (non-zero average shear) are present in the catalog. These were subtracted per patch and per tomographic bin before computing the shear-shear correlation functions. Any science analysis for which c-terms are important should determine these from the data, using the lensfit weights to compute the averages.
Release notes
For further details regarding the catalog and its creation please see the release notes.
Data access
The weak lensing data set based on the KiDS DR3 data set is also called the "KiDS-450" data set. The shear catalog was released as KiDS DR3.1 and is publicly available via ESO, CADC and direct download. A binary mask of the footprint is available as well, as are the THELI-reduced images. Links and information for all access routes are provided in the following table.
| Link | Data type | Description |
|---|---|---|
| ESO Catalogue Facility query interface | ||
| Webpage | Catalog |
Query the catalog using ESO's catalog interface. Use "The Kilo-Degree Survey: Weak lensing shear measurements", version 1 (ESO Portal account required) |
| Canadian Astronomy Data Center (CADC) | ||
| KiDS-450 query page | Catalog, images |
Query the catalog hosted at the CADC. Via the "Graphical Search Tool" the THELI-reduced r-band image stacks and their weight, sum and flag maps can also be retrieved. Single exposure data is available on request. |
| Catalog download | ||
|
wget input file md5 sums |
Catalog |
Download the full catalog as FITS tables using wget. FITS files with the catalog data can be downloaded with wget using the input file linked on the left. For these files the catalog has been split into the five patches (G9, G12, G15, G23 and GS) used in Hildebrandt et al. 2017 (see KiDS-450 cosmic shear), so there are five separate FITS files. The md5sums file can be used to verify your downloaded files with the command "md5sum -c kids_dr3.1_shear_md5sums.txt". |
| KiDS-450 footprint mask | ||
| FITS file | Footprint mask |
Download the KiDS-450 footprint mask. This is a N=2048 Healpix map that provides a simple binary mask of the KiDS-450 footprint. |
| KiDS-450 cosmic shear data | ||
| KiDS-450 Cosmic Shear | Cosmic shear data | Scientific data products specific to the cosmic shear analysis in Hildebrandt & Viola et al. (2017). |
Acknowledgements
Users of these data should include the following acknowledgment to the source of the data:
Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme IDs 177.A-3016, 177.A-3017 and 177.A-3018.
and should cite Hildebrandt & Viola et al. (2017), Fenech Conti et al. (2016) and accompanying papers as follows:
We use cosmic shear measurements from the Kilo-Degree Survey (Kuijken et al. 2015, Hildebrandt & Viola et al. 2017, Fenech Conti et al. 2016), hereafter referred to as KiDS. The KiDS data are processed by THELI (Erben et al. 2013) and Astro-WISE (Begeman et al. 2013, de Jong et al 2015). Shears are measured using lensfit (Miller et al. 2013), and photometric redshifts are obtained from PSF-matched photometry and calibrated using external overlapping spectroscopic surveys (see Hildebrandt et al. 2016).
Catalog format
Please note that the source ID's in this catalog are not always identical to those in the DR3 multi-band catalog, due to the independent astrometric solution used for the lensing analysis.The table below lists the columns provided in the KiDS-450 or KiDS-DR3.1 lensing shear catalog. For a number of columns additional information is provided:
- KIDS_TILE: name of the KiDS survey tile in which the source is located. Searching the ESO archive with this OBJECT name will link to further data products for this tile.
- THELI_NAME: name for the survey tile in the THELI pipeline; for scripting reasons the '.' and '-' characters are replaced with 'p' and 'm', respectively.
- MASK: bit mask indicating sources affected by different types of defects. Automatic and manual masks produced during data processing flag areas affected by bright stars (e.g. saturated pixels, reflection halos, diffraction and readout spikes) and other severe image defects. In the released catalog the most strongly affected regions are already removed, leaving only sources with reliable measurements. As a result, only the bit mask values 2 (faint stellar reflection halo), 64 (u-band Astro-WISE manual mask), 128 (g-band Astro-WISE manual mask), 256 (r-band Astro-WISE manual mask) and 512 (i-band manual mask) are present.
- Flag: SExtractor extraction flag. Many sources that are flagged during source detection are removed from the catalog based on the lensfit results because they do not provide reliable shape measurements. The flag values that are still present in the catalog are 1 (the object has neighbors, bright and close enough to significantly bias the photometry, or bad pixels (more than 10% of the integrated area affected), 2 (the object was originally blended with another one) and 16 (objects aperture data are incomplete or corrupted).
- SG_FLAG: star-galaxy separator based on analysis of the second and fourth order image moments of the source; 0 = star, 1 = galaxy
- MAG_u/g/r/i: the magnitudes are based on Gaussian Aperture and Photometry (GAaP) measurements and are dereddened and color-calibrated using stellar locus regression. Note: these aperture magnitudes are mainly intended for color measurements, since they only probe the central regions of the source. They are not total magnitudes, except in the case of unresolved or point sources.
- MAG_LIM_u/g/r/i: local limiting magnitude, defined as the magnitude corresponding to a flux equal to the 1σ flux error.
- ZPT_offset: the magnitudes reported in this catalog have been color-calibrated, but their absolute calibration has only been homogenized per survey tile, not over the full area. Based on a comparison of the $r$-band magnitudes with the GAIA DR1 \citep{gaia/etal:2016} we provide these additional photometric offsets that can be used to homogenize the photometry over the whole catalog. The reported offsets are with respect to the GAIA photometry, but can be used to calibrate the photometry to the SDSS photometric system as follows:
mag_u/g/r/i_homogenized = mag_u/g/r/i - ZPT_offset + 0.049
Note: if used, these offsets must be applied to the magnitudes in all filters! - T_B: the best-fit spectral template for each source; these values correspond to the following types, where fractional types can occur because the templates are interpolated: 1=CWW-Ell, 2=CWW-Sbc, 3=CWW-Scd, 4=CWW-Im, 5=KIN-SB3, 6=KIN-SB2 (Capak, 2004, PhD. thesis, Univ. Hawai'i).
- ODDS: a measure of the uni-modality of the redshift Probability Distribution Function; a higher value indicates a higher reliability of the best photo-z estimate.
- fitclass: lensfit object class; the only classes included in the catalog are 0 (galaxy, no issues) and -9 (large galaxy, overfills 48 pixel postage stamp size). The latter class is retained to avoid ellipticity selection bias in the brightest galaxy sample.
- n_exposures_used: the number of r-band sub-exposures for which lensfit measured the shape of the source. Due to the dither pattern, or near tile edges, some sources are only present in a subset of the 5 sub-exposures.
- e1 or e2: lensfit shear estimators. Note: the e2 component is defined relative to the RAJ2000, DECJ2000 grid; depending on the user's definition of angles in this reference frame, the sign of \verb e2 may need to be changed.
- PSF_e1 and PSF_e1_exp[k]: model PSF ellipticities at the location of the object, in this case the real part of εPSF. PSF_e1_exp[k] is the PSF ellipticity in sub-exposure number k, while PSF_e1 refers to the average over all exposures used.
- m: the multiplicative shear calibration correction which should be applied in an ensemble average, rather than on a galaxy-by-galaxy basis \citep[see ][]{fenechconti/etal:2016}. Averaged catalogd ellipticities should be divided by 1+
, where the ellipticities should be weighted with the lensfit weight.
| Label | Format | Unit | Description |
|---|---|---|---|
| ID | 25A | Source identifier | |
| RAJ2000 | 1D | deg | Right ascension of barycenter (J2000) |
| DECJ2000 | 1D | deg | Declination of barycenter (J2000) |
| Patch | 3A | Patch (G9, G12, G15, G23 or GS) | |
| SeqNr | 1J | Running object number within the patch | |
| KIDS_TILE | 16A | Name of survey tile | |
| THELI_NAME | 16A | THELI name for the tile | |
| MASK | 1J | Mask value at the object position | |
| SG_FLAG | 1E | Star-galaxy separator (0=star, 1=galaxy) | |
| KRON_RADIUS | 1E | pixel | Scaling radius of the ellipse for magnitude measurements |
| Xpos | 1E | pixel | Object position along x in the r-band THELI stack (non unique) |
| Ypos | 1E | pixel | Object position along y in the r-band THELI stack (non unique) |
| FWHM_IMAGE | 1E | pixel | r-band FWHM assuming a Gaussian core |
| FWHM_WORLD | 1E | deg | r-band FWHM assuming a Gaussian core |
| Flag | 1J | r-band SExtractor extraction flags | |
| FLUX_RADIUS | 1E | pixel | r-band half-light radius |
| CLASS_STAR | 1E | r-band SExtractor S/G classifier output | |
| MAG_u | 1E | mag | Magnitude in the u-band (GAaP, dereddened) |
| MAGERR_u | 1E | mag | Magnitude error in the u-band |
| MAG_g | 1E | mag | Magnitude in the g-band (GAaP, dereddened) |
| MAGERR_g | 1E | mag | Magnitude error in the g-band |
| MAG_r | 1E | mag | Magnitude in the r-band (GAaP, dereddened) |
| MAGERR_r | 1E | mag | Magnitude error in the r-band |
| MAG_i | 1E | mag | Magnitude in the i-band (GAaP, dereddened) |
| MAGERR_i | 1E | mag | Magnitude error in the i-band |
| MAG_LIM_u | 1E | mag | Limiting magnitude in the u-band |
| MAG_LIM_g | 1E | mag | Limiting magnitude in the g-band |
| MAG_LIM_r | 1E | mag | Limiting magnitude in the r-band |
| MAG_LIM_i | 1E | mag | Limiting magnitude in the i-band |
| ZPT_offset | 1E | mag | Zeropoint offset derived from GAIA DR1 G-band photometry |
| Z_B | 1E | BPZ best redshift estimate | |
| Z_B_MIN | 1E | Lower bound of the 95% confidence interval of Z_B | |
| Z_B_MAX | 1E | Upper bound of the 95% confidence interval of Z_B | |
| T_B | 1E | Spectral type corresponding to Z_B | |
| ODDS | 1E | Empirical ODDS of Z\_B | |
| fitclass | 1I | lensfit: fit class | |
| bias_corrected_scalelength | 1E | pixel | lensfit: galaxy model scale length |
| bulge_fraction | 1E | lensfit: galaxy model bulge-fraction B/T | |
| model_flux | 1E | counts | lensfit: galaxy model flux |
| pixel_SNratio | 1E | lensfit: data S/N ratio | |
| model_SNratio | 1E | lensfit: model S/N ratio | |
| contamination_radius | 1E | pixel | lensfit: distance to nearest contaminating isophote |
| PSF_e1 | 1E | lensfit: PSF model mean ellipticity e1 | |
| PSF_e2 | 1E | lensfit: PSF model mean ellipticity e2 | |
| PSF_Strehl_ratio | 1E | lensfit: PSF model mean pseudo-Strehl ratio | |
| PSF_Q11 | 1E | lensfit: 2nd order brightness moment Q11 of the PSF | |
| PSF_Q22 | 1E | lensfit: 2nd order brightness moment Q22 of the PSF | |
| PSF_Q12 | 1E | lensfit: 2nd order brightness moment Q12 of the PSF | |
| n_exposures_used | 1E | lensfit: number of r-band exposures used in lensfit measurements | |
| PSF_e1_exp1 | 1E | lensfit: PSF model ellipticity e1 of exposure 1 | |
| PSF_e2_exp1 | 1E | lensfit: PSF model ellipticity e2 of exposure 1 | |
| PSF_e1_exp2 | 1E | lensfit: PSF model ellipticity e1 of exposure 2 | |
| PSF_e2_exp2 | 1E | lensfit: PSF model ellipticity e2 of exposure 2 | |
| PSF_e1_exp3 | 1E | lensfit: PSF model ellipticity e1 of exposure 3 | |
| PSF_e2_exp3 | 1E | lensfit: PSF model ellipticity e2 of exposure 3 | |
| PSF_e1_exp4 | 1E | lensfit: PSF model ellipticity e1 of exposure 4 | |
| PSF_e2_exp4 | 1E | lensfit: PSF model ellipticity e2 of exposure 4 | |
| PSF_e1_exp5 | 1E | lensfit: PSF model ellipticity e1 of exposure 5 | |
| PSF_e2_exp5 | 1E | lensfit: PSF model ellipticity e2 of exposure 5 | |
| e1 | 1E | lensfit: galaxy e1 expectation value | |
| e2 | 1E | lensfit: galaxy e2 expectation value | |
| weight | 1E | lensfit: inverse variance shear weight | |
| m | 1E | Multiplicative shear calibration |