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 product | ESO product category name | File type | TTT |
|---|---|---|---|
| Calibrated, stacked images | SCIENCE.IMAGE | FITS image | sci |
| Weight frames | ANCILLARY.WEIGHTMAP | FITS image | wei |
| Masks | ANCILLARY.MASK | FITS image | msk |
| Single-band source lists | SCIENCE.SRCTBL | Binary FITS table | src |
| Multi-band catalogue data file | SCIENCE.MCATALOG | Binary FITS table | src |
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.
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.
| Label | Format | Unit | Description |
|---|---|---|---|
| 2DPHOT | J | Source | classification (see section on star/galaxy separation) |
| X_IMAGE | E | pixel | Object position along x |
| Y_IMAGE | E | pixel | Object position along y |
| NUMBER | J | Running object number | |
| CLASS_STAR | E | S-Extractor S/G classifier | |
| FLAGS | J | Extraction flags | |
| IMAFLAGS_ISO | J | FLAG-image flags OR'ed over the iso. profile | |
| NIMAFLAG_ISO | J | Number of flagged pixels entering | |
| FLUX_RADIUS | E | pixel | Fraction-of-light radii |
| KRON_RADIUS | E | pixel | Kron apertures in units of A or B |
| FWHM_IMAGE | E | pixel | FWHM assuming a gaussian core |
| ISOAREA_IMAGE | J | pixel2 | Isophotal area above Analysis threshold |
| ELLIPTICITY | E | 1 - B_IMAGE/A_IMAGE | |
| THETA_IMAGE | E | deg | Position angle (CCW/x) |
| MAG_AUTO | E | mag | Kron-like elliptical aperture magnitude |
| MAGERR_AUTO | E | mag | RMS error for AUTO magnitude |
| ALPHA_J2000 | D | deg | Right ascension of baryleft (J2000) |
| DELTA_J2000 | D | deg | Declination of baryleft (J2000) |
| FLUX_APER_2 | E | count | Flux vector within circular aperture of 2 pixels |
| ... | ... | ... | ... |
| FLUX_APER_200 | E | count | Flux vector within circular aperture of 200 pixels |
| FLUXERR_APER_2 | E | count | RMS error vector for flux within aperture of 2 pixels |
| ... | ... | ... | ... |
| FLUXERR_APER_200 | E | count | RMS error vector for flux within aperture of 200 pixels |
| MAG_ISO | E | mag | Isophotal magnitude |
| MAGERR_ISO | E | mag | RMS error for isophotal magnitude |
| MAG_ISOCOR | E | mag | Corrected isophotal magnitude |
| MAGERR_ISOCOR | E | mag | RMS error for corrected isophotal magnitude |
| MAG_BEST | E | mag | Best of MAG_AUTO and MAG_ISOCOR |
| MAGERR_BEST | E | mag | RMS error for MAG_BEST |
| BACKGROUND | E | count | Background at centroid position |
| THRESHOLD | E | count | Detection threshold above background |
| MU_THRESHOLD | E | arcsec-2 | Detection threshold above background |
| FLUX_MAX | E | count | Peak flux above background |
| MU_MAX | E | arcsec-2 | Peak surface brightness above background |
| ISOAREA_WORLD | E | deg2 | Isophotal area above Analysis threshold |
| XMIN_IMAGE | J | pixel | Minimum x-coordinate among detected pixels |
| YMIN_IMAGE | J | pixel | Minimum y-coordinate among detected pixels |
| XMAX_IMAGE | J | pixel | Maximum x-coordinate among detected pixels |
| YMAX_IMAGE | J | pixel | Maximum y-coordinate among detected pixels |
| X_WORLD | D | deg | Baryleft position along world x axis |
| Y_WORLD | D | deg | Baryleft position along world y axis |
| XWIN_IMAGE | E | pixel | Windowed position estimate along x |
| YWIN_IMAGE | E | pixel | Windowed position estimate along y |
| X2_IMAGE | D | pixel2 | Variance along x |
| Y2_IMAGE | D | pixel2 | Variance along y |
| XY_IMAGE | D | pixel2 | Covariance between x and y |
| X2_WORLD | E | deg2 | Variance along X-WORLD (alpha) |
| Y2_WORLD | E | deg2 | Variance along Y-WORLD (delta) |
| XY_WORLD | E | deg2 | Covariance between X-WORLD and Y-WORLD |
| CXX_IMAGE | E | pixel-2 | Cxx object ellipse parameter |
| CYY_IMAGE | E | pixel-2 | Cyy object ellipse parameter |
| CXY_IMAGE | E | pixel-2 | Cxy object ellipse parameter |
| CXX_WORLD | E | deg-2 | Cxx object ellipse parameter (WORLD units) |
| CYY_WORLD | E | deg-2 | Cyy object ellipse parameter (WORLD units) |
| CXY_WORLD | E | deg-2 | Cxy object ellipse parameter (WORLD units) |
| A_IMAGE | D | pixel | Profile RMS along major axis |
| B_IMAGE | D | pixel | Profile RMS along minor axis |
| A_WORLD | E | deg | Profile RMS along major axis (WORLD units) |
| B_WORLD | E | deg | Profile RMS along minor axis (WORLD units) |
| THETA_WORLD | E | deg | Position angle (CCW/world-x) |
| THETA_J2000 | E | deg | Position angle (east of north) (J2000) |
| ELONGATION | E | deg | A_IMAGE/B_IMAGE |
| ERRX2_IMAGE | E | pixel2 | Variance of position along x |
| ERRY2_IMAGE | E | pixel2 | Variance of position along y |
| ERRXY_IMAGE | E | pixel2 | Covariance of position between x and y |
| ERRX2_WORLD | E | deg2 | Variance of position along X-WORLD (alpha) |
| ERRY2_WORLD | E | deg2 | Variance of position along Y-WORLD (delta) |
| ERRXY_WORLD | E | deg2 | Covariance of position X-WORLD/Y-WORLD |
| ERRCXX_IMAGE | E | pixel-2 | Cxx error ellipse parameter |
| ERRCYY_IMAGE | E | pixel-2 | Cyy error ellipse parameter |
| ERRCXY_IMAGE | E | pixel-2 | Cxy error ellipse parameter |
| ERRCXX_WORLD | E | deg-2 | Cxx error ellipse parameter (WORLD units) |
| ERRCYY_WORLD | E | deg-2 | Cyy error ellipse parameter (WORLD units) |
| ERRCXY_WORLD | E | deg-2 | Cxy error ellipse parameter (WORLD units) |
| ERRA_IMAGE | E | pixel | RMS position error along major axis |
| ERRB_IMAGE | E | pixel | RMS position error along minor axis |
| ERRA_WORLD | E | deg | World RMS position error along major axis |
| ERRB_WORLD | E | deg | World RMS position error along minor axis |
| ERRTHETA_IMAGE | E | deg | Error ellipse pos. angle (CCW/x) |
| ERRTHETA_WORLD | E | deg | Error ellipse pos. angle (CCW/world-x) |
| ERRTHETA_J2000 | E | deg | J2000 error ellipse pos. angle (east of north) |
| FWHM_WORLD | E | deg | FWHM assuming a gaussian core |
| ISO0 | J | pixel2 | Isophotal area at level 0 |
| ISO1 | J | pixel2 | Isophotal area at level 1 |
| ISO2 | J | pixel2 | Isophotal area at level 2 |
| ISO3 | J | pixel2 | Isophotal area at level 3 |
| ISO4 | J | pixel2 | Isophotal area at level 4 |
| ISO5 | J | pixel2 | Isophotal area at level 5 |
| ISO6 | J | pixel2 | Isophotal area at level 6 |
| ISO7 | J | pixel2 | Isophotal area at level 7 |
| SLID | K | Source list ID | |
| SID | K | Source ID within the source list | |
| HTM | K | Hierarchical Triangular Mesh (level 25) | |
| FLAG | K | Not used |
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.
- EXT_SFD_<F>: galactic foreground extinction based on the E(B-V) maps and coefficients from Schlegel, Finkbeiner & Davis (1998, ApJ, 500, 525)
- 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.
| Label | Format | Unit | Description |
|---|---|---|---|
| Measurements based on r-band detection image | |||
| ID | 25A | Source identifier | |
| SCID | K | Astro-WISE SourceCollection identifier | |
| SLID | K | Astro-WISE SourceList identifier | |
| SID | K | Astro-WISE Source identifier | |
| RAJ2000 | D | deg | Right ascension |
| DECJ2000 | D | deg | Declination |
| SG2DPHOT | K | Star/galaxy separation | |
| A | D | pixel | Linear semi major axis |
| B | D | pixel | Linear semi minor axis |
| CLASS_STAR | E | SExtractor star/galaxy classifier | |
| ELLIPTICITY | E | Ellipticity | |
| KRON_RADIUS | E | pixel | Kron-radius used for MAG_AUTO |
| POSANG | E | deg | Position angle |
| A_GAAP | D | arcsec | Linear semi major axis of GAaP aperture |
| B_GAAP | D | arcsec | Linear semi minor axis of GAaP aperture |
| POSANG_GAAP | E | deg | Position angle of GAaP aperture |
| Measurements provided for each filter | |||
| FLUX_APER_4_<F> | E | count | flux in 4 pixel aperture |
| FLUX_APER_6_<F> | E | count | flux in 6 pixel aperture |
| FLUX_APER_10_<F> | E | count | flux in 10 pixel aperture |
| FLUX_APER_14_<F> | E | count | flux in 14 pixel aperture |
| FLUX_APER_25_<F> | E | count | flux in 25 pixel aperture |
| FLUX_APER_40_<F> | E | count | flux in 40 pixel aperture |
| FLUX_APER_100_<F> | E | count | flux in 100 pixel aperture |
| FLUXERR_APER_4_<F> | E | count | flux error in 4 pixel aperture |
| FLUXERR_APER_6_<F> | E | count | flux error in 6 pixel aperture |
| FLUXERR_APER_10_<F> | E | count | flux error in 10 pixel aperture |
| FLUXERR_APER_14_<F> | E | count | flux error in 14 pixel aperture |
| FLUXERR_APER_25_<F> | E | count | flux error in 25 pixel aperture |
| FLUXERR_APER_40_<F> | E | count | flux error in 40 pixel aperture |
| FLUXERR_APER_100_<F> | E | count | flux error in 100 pixel aperture |
| FLUX_APERCOR_4_<F> | E | count | corrected flux from 4 pixel aperture |
| FLUX_APERCOR_6_<F> | E | count | corrected flux from 6 pixel aperture |
| FLUX_APERCOR_10_<F> | E | count | corrected flux from 10 pixel aperture |
| FLUX_APERCOR_14_<F> | E | count | corrected flux from 14 pixel aperture |
| FLUX_APERCOR_25_<F> | E | count | corrected flux from 25 pixel aperture |
| FLUXERR_APERCOR_4_<F> | E | count | corrected flux error from 4 pixel aperture |
| FLUXERR_APERCOR_6_<F> | E | count | corrected flux error from 6 pixel aperture |
| FLUXERR_APERCOR_10_<F> | E | count | corrected flux error from 10 pixel aperture |
| FLUXERR_APERCOR_14_<F> | E | count | corrected flux error from 14 pixel aperture |
| FLUXERR_APERCOR_25_<F> | E | count | corrected flux error from 25 pixel aperture |
| FLUX_RADIUS_<F> | E | pixel | SExtractor FLUX_RADIUS |
| FWHM_IMAGE_<F> | E | pixel | SExtractor FWHM_IMAGE |
| FLAG_<F> | J | SExtractor extraction flag | |
| IMAFLAGS_ISO_<F> | J | mask flag | |
| MAGERR_AUTO_<F> | E | mag | error in MAG_AUTO |
| MAGERR_ISO_<F> | E | mag | error in MAG_ISO |
| MAG_AUTO_<F> | E | mag | MAG_AUTO1 |
| MAG_ISO_<F> | E | mag | MAG_ISO1 |
| NIMAFLAGS_ISO_<F> | J | number of masked pixels | |
| ISOAREA_IMAGE_<F> | J | pixel**2 | isophotal aperture |
| XPOS_<F> | E | pixel | X pixel position in image |
| YPOS_<F> | E | pixel | Y pixel position in image |
| MAG_GAAP_<F> | E | mag | GAaP magnitude1 |
| MAGERR_GAAP_<F> | E | mag | error in GAaP magnitude |
| ZPT_OFFSET_<F> | E | mag | photometric homogenization ZPT offset |
| EXT_SFD_<F> | E | mag | Galactic foreground extinction following Schlegel et al. maps |
| Other columns | |||
| Z_B_BPZ | E | Best-fitting BPZ photometric redshift | |
| ODDS_BPZ | E | Empirical ODDS of Z_B_BPZ | |
| T_B_BPZ | E | Best-fitting BPZ spectral type | |
| TILE_FLAG | J | Tile quality warning flag | |
| COLOR_GAAPHOM_U_G | E | mag | Homogenized and Extinction corrected GAaP u-g band color |
| COLOR_GAAPHOM_U_R | E | mag | Homogenized and Extinction corrected GAaP u-r band color |
| COLOR_GAAPHOM_U_I | E | mag | Homogenized and Extinction corrected GAaP u-i band color |
| COLOR_GAAPHOM_G_R | E | mag | Homogenized and Extinction corrected GAaP g-r band color |
| COLOR_GAAPHOM_G_I | E | mag | Homogenized and Extinction corrected GAaP g-i band color |
| COLOR_GAAPHOM_R_I | E | mag | Homogenized and Extinction corrected GAaP r-i band color |
1 these magnitudes are not extinction-corrected and not homogenized