KiDS DR4 quasar catalog
We present a catalog of photometrically selected quasars candidates with their corresponding photometric redshifts and redshift uncertainties. The catalog and methodology is described in Nakoneczny et al. (2021, A&A, 649, id.A81; arXiv:2010.13857).
The catalog results from applying artificial neural networks to process the KiDS data limited to 9- band detections. The machine learning (ML) models are trained on KiDS objects cross-matched with the spectroscopic SDSS survey. We address the problem of extrapolation to KiDS objects fainter than the SDSS limit by properly generalising ML models, and creating inference subsets which describe the reliability of estimations: safe, extrapolation, unsafe. We provide the suggested cuts on magnitude and probability of photometric classification, which are derived from validating the catalog with several methods. For details, please refer to Nakoneczny et al. (2021, A&A, 649, id.A81; arXiv:2010.13857).
Catalog format
| Column name | Description |
|---|---|
| ID | ESO ID |
| RAJ2000 | Centroid sky position right ascension (J2000) |
| DECJ2000 | Centroid sky position declination (J2000) |
| MAG_GAAP_r | r-band GAaP magnitude with optimal MIN_APER (extinction corrected) |
| CLASS_STAR | SExtractor star-galaxy classifier |
| MASK | 9-band mask information |
| {CLASS}_PHOTO | Probability that the source is in one of the three classes: GALAXY, QSO, STAR |
| CLASS_PHOTO | Object class with the highest probability |
| Z_PHOTO_QSO | Photometric redshift for quasars |
| Z_PHOTO_STDDEV_QSO | Uncertainty of photometric redshift for quasars |
| SUBSET | ML inference subset (see Section 2.2 in the paper). Values: safe, extrapolation, unsafe |
Data access
1. Catalog of quasar candidates
File: KiDS_DR4_QSO_candidates.fits
File size: 110 MB
Number of objects: 1,095,711
Data limited to:
- 9-band detections
- r < 25
- CLASS_STAR < 0.2 or CLASS_STAR > 0.
- QSO_PHOTO > 0.9
Suggested cut for the extrapolation subset: 22 < r < 23.5 and QSO_PHOTO > 0.98.
2. Catalog of all machine learning estimates
Online catalog at CDS: https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/649/A81
Number of objects: 45,469,955
Data limited to 9-band detections.
Acknowledgements
Please cite Nakoneczny et al. (2021, A&A, 649, id.A81; arXiv:2010.13857) and include the KiDS DR4 acknowledgments.
Contact
szymon[dot]nakoneczny[at]ncbj[dot]gov[dot]pl