The HSC photo-z team computed photometric redshifts using several independent codes for this public release. As described in detail in the photo-z release paper, we first constructed a training sample by combining public spectroscopic redshifts, HST grism redshifts, and high-quality many-band photometric redshifts in COSMOS with weights to each objects to reproduce the color-magnitude distributions of the HSC objects. We then performed a 5-fold cross-validation (validation technique depends on the code) to train and validate our codes. The held-out test sample is used to evaluate the performance. The trained codes are then run on the target catalogs for production.
Our catalog products are stored in the database and the schema browser gives the details of the catalogs. As discussed in the PDR1 photo-z paper, we suggest that zbest should be used for point estimates and zrisk as an indicator of reliability. In addition to the catalogs, we also release the redshift probability distribution functions in the fits format below. Further description of our training procedure, data products, explanation of the statistics plots below can be found in the PDR2 photo-z release paper. When you use the photo-z products, please quote the photo-z release papers (both PDR1 and PDR2) and the relevant code papers linked below.
We have computed photo-z’s using several independent codes. Here is a brief summary of our codes.
DEmP: Combination of nearest neighbor technique and polynomial (actually linear) fitting. Redshift of each object is estimated using the 40 nearest neighbors in the nine-dimensional space (5 magnitude axes and g-r, r-i, i-z, z-y color axes using the PSF-matched aperture photometry) with a linear function.
Mizuki: Template fitting with Bayesian priors on physical properties of galaxies. In addition to redshifts, physical parameters such as stellar mass and SFRs are computed. The code uses CModel. Photo-z’s are available only for objects with i<25 in the Wide layer. All objects in Deep+UltraDeep have photo-z’s.
Here are some basic statistics plots for the COSMOS wide-depth median seeing stack. The accuracy here represents the average accuracy of our photo-z in the Wide and Deep/UltraDeep layers. More details can be found in the PDR2 photo-z release paper.
Probability Distribution Functions
Our P(z) files are available for each field in the fits format. Note these are massive files! Some important notes:
- One fits file for one tract. The file name gives the tract number.
- The 1st HDU contains P(z) and the 2nd HDU defines the redshift grids.
- Please do not use the header keywords to define the redshift grids. Please always use the 2nd HDU.