Machine learning photometric redshifts
Apart from the template-fitting photometric redshifts included in the DR3 catalog, photometric redshifts based on two separate machine-learning techniques (MLPQNA and ANNz2) are also provided.
ANNz2 photometric redshifts
Photometric redshifts have been derived using the ANNz2 method (Sadeh et al. 2016, PASP, 128, 104502) for two KiDS DR3 subsets. One contains all sources with good GAaP photometry in all four filters (39,166,070 objects). The other includes bright KiDS galaxies (r<20.3 mag; 800,830 sources). Details of selections and photometric redshift derivation are provided in Bilicki et al. 2018, A&A, in press (arXiv:1709.04205). Please cite that paper together with the main KiDS DR3 one (de Jong et al. 2017, A&A, 604, A134, arXiv:1703.02991) if you use the data described here.
Full-depth catalog
Photometric redshifts were generated using a training sample from several spectroscopic fields. The released catalog contains all sources (both extended and point-like) with good GAaP photometry in all four filters (39,166,070 objects). Also included is a "fiducial" flag that identifies a more reliable subset, removing artefacts, stars and sources in parameter space not sampled by the training data; these filters result in a set of approximately 20.5 million objects. Depending on the application, additional filtering might still be needed to ensure reliable photo-zs. Please see Bilicki et al. (2018) for details.
Catalog format
Photometric redshifts derived using ANNz2 are provided in a single catalog, featuring the columns listed in the following table. Apart from the photo-z values, we provide source ID information and positions that allow straightforward association with the KiDS DR3 multi-band catalog, as well as basic photometric information, together with the fiducial flag mentioned above.
| Label | Format | Unit | Description |
|---|---|---|---|
| ID | 23A | Source identifier | |
| RAJ2000 | D | deg | Right ascension (J2000) |
| DECJ2000 | D | deg | Declination (J2000) |
| SG2DPHOT | K | Source classification | |
| IMAFLAGS_ISO_band | J | Mask flag | |
| MAG_GAAP_band_calib | E | mag | Calibrated GAaP magnitude |
| MAGERR_GAAP_band | E | mag | Error in GAaP magnitude |
| zphot_ANNz2 | D | Photometric redshift derived with ANNz2 | |
| fiducial | I | Flag defining fiducial selection |
Catalog download
The full-depth catalog can be downloaded via the following link.
- ANNz2_fullDepth_Bilicki2018.fits (4.0 GB, md5 sum:
fe428cc2c2898c5b6f7766e2ace3dd3b)
Bright-end catalog
Photometric redshifts were generated using a training sample from the Galaxy And Mass Assembly (GAMA) spectroscopic data and by applying an extended set of photometric features in photo-z derivation. The released catalog contains resolved sources (galaxies) extracted from DR3 by applying the magnitude cut of MAG_AUTO_R_calib ≤ 20.3, star-galaxy separation parameter SG2DPHOT = 0, and by requiring that all the four ugri GAaP magnitudes, and their errors, are measured; this gives 800,830 objects in total. Additional filtering, as described in Bilicki et al. (2018), is needed to remove residual artefacts.
Catalog format
Photometric redshifts derived using ANNz2 are provided in a single catalog, featuring the columns listed in the following table. Apart from the photo-z values, we provide source ID information and positions that allow straightforward association with the KiDS DR3 multi-band catalog, as well as basic photometric information.
| Label | Format | Unit | Description |
|---|---|---|---|
| ID | 23A | Source identifier | |
| RAJ2000 | D | deg | Right ascension (J2000) |
| DECJ2000 | D | deg | Declination (J2000) |
| IMAFLAGS_ISO_band | J | Mask flag | |
| MAG_AUTO_band_calib | E | mag | Calibrated Kron-like elliptical aperture magnitude |
| MAGERR_AUTO_band | E | mag | RMS error for MAG_AUTO |
| MAG_ISO_band_calib | E | mag | Calibrated isophotal magnitude |
| MAGERR_ISO_band | E | mag | RMS error for MAG_ISO |
| MAG_GAAP_band_calib | E | mag | Calibrated GAaP magnitude |
| MAGERR_GAAP_band | E | mag | Error in GAaP magnitude |
| zphot_ANNz2 | D | Photometric redshift derived with ANNz2 |
Catalog download
The bright-end catalog can be downloaded via the following link.
- ANNz2_brightEnd_Bilicki2018.fits (123 MB, md5 sum:
65a72e551974ecfb6f71d07c544c0aa5)
MLPQNA photometric redshifts and PDFs
For the DR3 data set photometric redshifts have been derived using the Multi Layer Perceptron with Quasi Newton Algorithm (MLPQNA) technique, following the a similar strategy as was done for DR2 (Cavuoti et al. 2015, MNRAS, 452, 3100). Driven by the magnitude ranges covered by the spectroscopic knowledge base (SDSS DR9 and GAMA DR2), the total number of sources with MLPQNA photo-z's is 8,582,152. Photo-z probability distribution functions (PDFs) were also derived.
Catalog format
The best-guess photometric redshifts derived using the MLPQNA technique are provided in a single catalogue, featuring the columns listed in the following table. Apart from the photo-z values the only content consists of source ID information and positions that allow straightforward association with the KiDS DR3 multi-band catalogue.
| Label | Format | Unit | Description |
|---|---|---|---|
| ID | 25A | Source identifier | |
| SLID | J | Astro-WISE SourceList identifier | |
| SID | J | Astro-WISE Source identifier | |
| RAJ2000 | D | deg | Right ascension |
| DECJ2000 | D | deg | Declination |
| Z_MLPQNA | D | Best MLPQNA predicted photometric redshift |
Also available are photo-z Probability Distribution Functions (PDFs) based on the MLPQNA technique. These are provided in separate catalog files per DR3 survey tile, and their format is specified in the following table . Again, included data is limited to the PDF bins and source ID and position information that can be used to associate to the DR3 multi-band catalogue.
| Label | Format | Unit | Description |
|---|---|---|---|
| ID | 25A | Source identifier | |
| SLID | J | Astro-WISE SourceList identifier | |
| SID | J | Astro-WISE Source identifier | |
| RAJ2000 | D | deg | Right ascension |
| DECJ2000 | D | deg | Declination |
| PDF001 | D | MLPQNA photo-z PDF bin 1 (z=0.01) | |
| ... | ... | ... | |
| PDF350 | D | MLPQNA photo-z PDF bin 350 (z=3.5) |
Catalog download
The catalog with the best photo-z estimates can be downloaded via the following link.
- KiDS_DR3.2_ugri_mlpqnaphotz.fits (467 MB, md5 sum:
d2339ba8f156027e11d3bff2ad877b9d)
The PDFs are distributed in a separate FITS catalog for each of the DR3 survey tiles; the total size of these catalogs is 23 GB. Downloading of these files is possible with wget using the input files linked below. The also provided md5sums file can be used to verify your downloaded files with the command "md5sum -c kids_dr3.2_mlpqnapdf_md5sums.txt".