KiDS DR3 file types and formats

Data product types

The following types of data products are provided only for the 292 newly released tiles:

  • Coadds: photometrically and astrometrically calibrated, stacked images (1 per filter per tile)
  • Weights: weight frames (1 for each Coadd)
  • Flag images: FITS images with pixel flags in areas affected by bright stars (saturated pixels, diffraction spikes, etc.) (1 for each Coadd)
  • Source lists: lists of sources detected in single Coadds

This corresponds to a total of 4672 files and a total data volume is 4.0 TB.

The multi-band source catalog covers 440 tiles (the aggregate of all tiles released so far) and is distributed over multiple files: a metadata file describing the catalog contents and one catalog data file per tile. Thus, the total number of files making up the catalog is 441. New in the multi-band catalog are Gaussian Aperture and Photometry (GAaP) magnitudes, photometric homogenization, and photometric redshifts. In total the catalog contains 48,736,591 sources and the data volume is 37 GB.

Naming convention

The naming convention used for all data products is the following:
KiDS_DR3.0_R.R_D.D_F_TTT.fits,
where R.R and D.D are the RA and DEC of the tile center in degrees (J2000.0) with 1 decimal place, F is the filter (u, g, r, or i), and TTT is the data product type. The value of TTT for the different data products is given in column 4 of the table below.

For example: the r-band stacked image of the tile "KIDS_140.0_0.5" is called KiDS_DR3.0_140.0_0.5_r_sci.fits and the catalog data file of the same tile KiDS_DR3.0_140.0_0.5_ugri_src.fits.

The following table lists the types of data products provided in this release, together with descriptions of the file types and naming conventions used.

Data productESO product category nameFile typeTTT
Calibrated, stacked imagesSCIENCE.IMAGEFITS imagesci
Weight framesANCILLARY.WEIGHTMAPFITS imagewei
MasksANCILLARY.MASKFITS imagemsk
Single-band source listsSCIENCE.SRCTBLBinary FITS tablesrc
Multi-band catalogue data fileSCIENCE.MCATALOGBinary FITS tablesrc

 

Image data format

The final calibrated, coadded images have a uniform pixel scale of 0.2 arcsec. The pixel units are fluxes relative to the flux corresponding to magnitude = 0. This means that the effective zeropoint is equal to 0 and the magnitude m corresponding to a pixel value f is:

m = -2.5 log10 f.

The gain varies slightly over the field-of-view because of the zeropoint offsets applied to individual CCDs to homogenize the photometry. An average effective gain is provided in the data table.

An example of a FITS header of a coadded image can be viewed here.

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Single-band catalog columns

The following table lists the columns that are present in the single-band source lists provided in KiDS-ESO-DR3. In the following we provide additional information on certain columns:

  • 2DPHOT: KiDS-CAT star/galaxy classification bitmap based on the source morphology (see e.g. de Jong et al., 2015). Values are: 1 = high confidence star candidate; 2 = unreliable source (e.g. cosmic ray); 4 = star according to star/galaxy separation criteria; 0 = all other sources (e.g. including galaxies). Sources identified as stars can thus have a flag value of 1, 4 or 5.
  • IMAFLAGS_ISO: Bitmap of mask flags indicating the types of masked areas that intersect with each source's isophotes, as identified by the Pulecenella software (de Jong et al., 2015). Different flag values indicate different types of areas: 1 = readout spike; 2 = saturation core; 4 = diffraction spike; 8 = primary reflection halo; 16 = secondary reflection halo; 32 = tertiary reflection halo; 64 = bad pixel.
  • FLUX_APER_* and FLUXERR_APER_*: aperture flux measurements are included for 27 different aperture sizes. In the table only the smallest (2 pixels or 0.4 arcsec diameter) and the largest (200 pixels or 40 arcsec diameter) are listed; the label for the aperture of 28.5 pixels is FLUX_APER_28p5.
LabelFormatUnitDescription
2DPHOTJSourceclassification (see section on star/galaxy separation)
X_IMAGEEpixelObject position along x
Y_IMAGEEpixelObject position along y
NUMBERJRunning object number
CLASS_STARES-Extractor S/G classifier
FLAGSJExtraction flags
IMAFLAGS_ISOJFLAG-image flags OR'ed over the iso. profile
NIMAFLAG_ISOJNumber of flagged pixels entering
FLUX_RADIUSEpixelFraction-of-light radii
KRON_RADIUSEpixelKron apertures in units of A or B
FWHM_IMAGEEpixelFWHM assuming a gaussian core
ISOAREA_IMAGEJpixel2Isophotal area above Analysis threshold
ELLIPTICITYE1 - B_IMAGE/A_IMAGE
THETA_IMAGEEdegPosition angle (CCW/x)
MAG_AUTOEmagKron-like elliptical aperture magnitude
MAGERR_AUTOEmagRMS error for AUTO magnitude
ALPHA_J2000DdegRight ascension of baryleft (J2000)
DELTA_J2000DdegDeclination of baryleft (J2000)
FLUX_APER_2EcountFlux vector within circular aperture of 2 pixels
............
FLUX_APER_200EcountFlux vector within circular aperture of 200 pixels
FLUXERR_APER_2EcountRMS error vector for flux within aperture of 2 pixels
............
FLUXERR_APER_200EcountRMS error vector for flux within aperture of 200 pixels
MAG_ISOEmagIsophotal magnitude
MAGERR_ISOEmagRMS error for isophotal magnitude
MAG_ISOCOREmagCorrected isophotal magnitude
MAGERR_ISOCOREmagRMS error for corrected isophotal magnitude
MAG_BESTEmagBest of MAG_AUTO and MAG_ISOCOR
MAGERR_BESTEmagRMS error for MAG_BEST
BACKGROUNDEcountBackground at centroid position
THRESHOLDEcountDetection threshold above background
MU_THRESHOLDEarcsec-2Detection threshold above background
FLUX_MAXEcountPeak flux above background
MU_MAXEarcsec-2Peak surface brightness above background
ISOAREA_WORLDEdeg2Isophotal area above Analysis threshold
XMIN_IMAGEJpixelMinimum x-coordinate among detected pixels
YMIN_IMAGEJpixelMinimum y-coordinate among detected pixels
XMAX_IMAGEJpixelMaximum x-coordinate among detected pixels
YMAX_IMAGEJpixelMaximum y-coordinate among detected pixels
X_WORLDDdegBaryleft position along world x axis
Y_WORLDDdegBaryleft position along world y axis
XWIN_IMAGEEpixelWindowed position estimate along x
YWIN_IMAGEEpixelWindowed position estimate along y
X2_IMAGEDpixel2Variance along x
Y2_IMAGEDpixel2Variance along y
XY_IMAGEDpixel2Covariance between x and y
X2_WORLDEdeg2Variance along X-WORLD (alpha)
Y2_WORLDEdeg2Variance along Y-WORLD (delta)
XY_WORLDEdeg2Covariance between X-WORLD and Y-WORLD
CXX_IMAGEEpixel-2Cxx object ellipse parameter
CYY_IMAGEEpixel-2Cyy object ellipse parameter
CXY_IMAGEEpixel-2Cxy object ellipse parameter
CXX_WORLDEdeg-2Cxx object ellipse parameter (WORLD units)
CYY_WORLDEdeg-2Cyy object ellipse parameter (WORLD units)
CXY_WORLDEdeg-2Cxy object ellipse parameter (WORLD units)
A_IMAGEDpixelProfile RMS along major axis
B_IMAGEDpixelProfile RMS along minor axis
A_WORLDEdegProfile RMS along major axis (WORLD units)
B_WORLDEdegProfile RMS along minor axis (WORLD units)
THETA_WORLDEdegPosition angle (CCW/world-x)
THETA_J2000EdegPosition angle (east of north) (J2000)
ELONGATIONEdegA_IMAGE/B_IMAGE
ERRX2_IMAGEEpixel2Variance of position along x
ERRY2_IMAGEEpixel2Variance of position along y
ERRXY_IMAGEEpixel2Covariance of position between x and y
ERRX2_WORLDEdeg2Variance of position along X-WORLD (alpha)
ERRY2_WORLDEdeg2Variance of position along Y-WORLD (delta)
ERRXY_WORLDEdeg2Covariance of position X-WORLD/Y-WORLD
ERRCXX_IMAGEEpixel-2Cxx error ellipse parameter
ERRCYY_IMAGEEpixel-2Cyy error ellipse parameter
ERRCXY_IMAGEEpixel-2Cxy error ellipse parameter
ERRCXX_WORLDEdeg-2Cxx error ellipse parameter (WORLD units)
ERRCYY_WORLDEdeg-2Cyy error ellipse parameter (WORLD units)
ERRCXY_WORLDEdeg-2Cxy error ellipse parameter (WORLD units)
ERRA_IMAGEEpixelRMS position error along major axis
ERRB_IMAGEEpixelRMS position error along minor axis
ERRA_WORLDEdegWorld RMS position error along major axis
ERRB_WORLDEdegWorld RMS position error along minor axis
ERRTHETA_IMAGEEdegError ellipse pos. angle (CCW/x)
ERRTHETA_WORLDEdegError ellipse pos. angle (CCW/world-x)
ERRTHETA_J2000EdegJ2000 error ellipse pos. angle (east of north)
FWHM_WORLDEdegFWHM assuming a gaussian core
ISO0Jpixel2Isophotal area at level 0
ISO1Jpixel2Isophotal area at level 1
ISO2Jpixel2Isophotal area at level 2
ISO3Jpixel2Isophotal area at level 3
ISO4Jpixel2Isophotal area at level 4
ISO5Jpixel2Isophotal area at level 5
ISO6Jpixel2Isophotal area at level 6
ISO7Jpixel2Isophotal area at level 7
SLIDKSource list ID
SIDKSource ID within the source list
HTMKHierarchical Triangular Mesh (level 25)
FLAGKNot used

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Multi-band catalog columns

The following table lists the columns that are present in the multi-band source catalog provided in KiDS-ESO-DR3. Measurements that are provided in each of the four filters are listed only once in the second part of the table, where <F> in the label is either 'U', 'G', 'R', or 'I' for the filters u, g, r and i. In the following we provide additional information on certain columns:

  • SG2DPHOT: KiDS-CAT star/galaxy classification bitmap based on the r-band source morphology (see e.g. de Jong et al., 2015). Values are: 1 = high confidence star candidate; 2 = unreliable source (e.g. cosmic ray); 4 = star according to star/galaxy separation criteria; 0 = all other sources (e.g. including galaxies). Sources identified as stars can thus have a flag value of 1, 4 or 5.
  • IMAFLAGS_ISO_<F>: Bitmap of mask flags indicating the types of masked areas that intersect with each source's isophotes, as identified by the Pulecenella software (de Jong et al., 2015). Different flag values indicate different types of areas: 1 = readout spike; 2 = saturation core; 4 = diffraction spike; 8 = primary reflection halo; 16 = secondary reflection halo; 32 = tertiary reflection halo; 64 = bad pixel; 128 = manually masked area (tiles released in DR1 and DR2 only).
  • MAG_GAAP_<F>: these magnitudes are based on Gaussian Aperture and Photometry (GAaP) measurements and are mainly intended for colour 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.
  • ZPT_OFFSET_<F>: Zero-point offsets for each filter based on stellar locus regression (gri) and overlap photometry (ugri) that homogenize the photometry over the survey. Please note that these offsets, as well as the extinction corrections (EXT_SFD_<F>) have not been applied in the fluxes and magnitudes provided in the catalog. These corrections should be applied as:
    MAG_*_<F>_corrected = MAG_*_<F> + ZPT_OFFSET_<F> - EXT_SFD_<F>
  • 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.
  • 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)
  • TILE_FLAG: bitmap that identifies coadds that are severely affected by image defects such as scattered light features. Masking of these features is currently not available for the imaging data released in KiDS-ESO-DR3, so data tiles flagged with this flag should be used with caution. The flag values indicate which filter is affected: 1 = u; 2 = g; 3 = r; 4 = i.
LabelFormatUnitDescription
Measurements based on r-band detection image
ID25ASource identifier
SCIDKAstro-WISE SourceCollection identifier
SLIDKAstro-WISE SourceList identifier
SIDKAstro-WISE Source identifier
RAJ2000DdegRight ascension
DECJ2000DdegDeclination
SG2DPHOTKStar/galaxy separation
ADpixelLinear semi major axis
BDpixelLinear semi minor axis
CLASS_STARESExtractor star/galaxy classifier
ELLIPTICITYEEllipticity
KRON_RADIUSEpixelKron-radius used for MAG_AUTO
POSANGEdegPosition angle
A_GAAPDarcsecLinear semi major axis of GAaP aperture
B_GAAPDarcsecLinear semi minor axis of GAaP aperture
POSANG_GAAPEdegPosition angle of GAaP aperture
Measurements provided for each filter
FLUX_APER_4_<F>Ecountflux in 4 pixel aperture
FLUX_APER_6_<F>Ecountflux in 6 pixel aperture
FLUX_APER_10_<F>Ecountflux in 10 pixel aperture
FLUX_APER_14_<F>Ecountflux in 14 pixel aperture
FLUX_APER_25_<F>Ecountflux in 25 pixel aperture
FLUX_APER_40_<F>Ecountflux in 40 pixel aperture
FLUX_APER_100_<F>Ecountflux in 100 pixel aperture
FLUXERR_APER_4_<F>Ecountflux error in 4 pixel aperture
FLUXERR_APER_6_<F>Ecountflux error in 6 pixel aperture
FLUXERR_APER_10_<F>Ecountflux error in 10 pixel aperture
FLUXERR_APER_14_<F>Ecountflux error in 14 pixel aperture
FLUXERR_APER_25_<F>Ecountflux error in 25 pixel aperture
FLUXERR_APER_40_<F>Ecountflux error in 40 pixel aperture
FLUXERR_APER_100_<F>Ecountflux error in 100 pixel aperture
FLUX_APERCOR_4_<F>Ecountcorrected flux from 4 pixel aperture
FLUX_APERCOR_6_<F>Ecountcorrected flux from 6 pixel aperture
FLUX_APERCOR_10_<F>Ecountcorrected flux from 10 pixel aperture
FLUX_APERCOR_14_<F>Ecountcorrected flux from 14 pixel aperture
FLUX_APERCOR_25_<F>Ecountcorrected flux from 25 pixel aperture
FLUXERR_APERCOR_4_<F>Ecountcorrected flux error from 4 pixel aperture
FLUXERR_APERCOR_6_<F>Ecountcorrected flux error from 6 pixel aperture
FLUXERR_APERCOR_10_<F>Ecountcorrected flux error from 10 pixel aperture
FLUXERR_APERCOR_14_<F>Ecountcorrected flux error from 14 pixel aperture
FLUXERR_APERCOR_25_<F>Ecountcorrected flux error from 25 pixel aperture
FLUX_RADIUS_<F>EpixelSExtractor FLUX_RADIUS
FWHM_IMAGE_<F>EpixelSExtractor FWHM_IMAGE
FLAG_<F>JSExtractor extraction flag
IMAFLAGS_ISO_<F>Jmask flag
MAGERR_AUTO_<F>Emagerror in MAG_AUTO
MAGERR_ISO_<F>Emagerror in MAG_ISO
MAG_AUTO_<F>EmagMAG_AUTO1
MAG_ISO_<F>EmagMAG_ISO1
NIMAFLAGS_ISO_<F>Jnumber of masked pixels
ISOAREA_IMAGE_<F>Jpixel**2isophotal aperture
XPOS_<F>EpixelX pixel position in image
YPOS_<F>EpixelY pixel position in image
MAG_GAAP_<F>EmagGAaP magnitude1
MAGERR_GAAP_<F>Emagerror in GAaP magnitude
ZPT_OFFSET_<F>Emagphotometric homogenization ZPT offset
EXT_SFD_<F>EmagGalactic foreground extinction following Schlegel et al. maps
Other columns
Z_B_BPZEBest-fitting BPZ photometric redshift
ODDS_BPZEEmpirical ODDS of Z_B_BPZ
T_B_BPZEBest-fitting BPZ spectral type
TILE_FLAGJTile quality warning flag
COLOR_GAAPHOM_U_GEmagHomogenized and Extinction corrected GAaP u-g band color
COLOR_GAAPHOM_U_REmagHomogenized and Extinction corrected GAaP u-r band color
COLOR_GAAPHOM_U_IEmagHomogenized and Extinction corrected GAaP u-i band color
COLOR_GAAPHOM_G_REmagHomogenized and Extinction corrected GAaP g-r band color
COLOR_GAAPHOM_G_IEmagHomogenized and Extinction corrected GAaP g-i band color
COLOR_GAAPHOM_R_IEmagHomogenized and Extinction corrected GAaP r-i band color

1 these magnitudes are not extinction-corrected and not homogenized