# Photometric Redshifts for Hyper Suprime-Cam Subaru Strategic Program Data Release 1

## TL;DR

This paper evaluates and compares photometric redshift estimation methods for the HSC-SSP survey, introducing an improved estimator and providing publicly available redshift catalogs with quantified accuracy and uncertainties.

## Contribution

It introduces a new point estimator for photometric redshifts and thoroughly characterizes the accuracy and uncertainty calibration for HSC-SSP data.

## Key findings

- Achieves sigma(d_zphot/(1+zphot))~0.05 for galaxies with i<25
- Outlier rate is about 15% for i<25, 8% for i<24
- Provides publicly accessible photo-z catalogs with full PDFs

## Abstract

Photometric redshifts are a key component of many science objectives in the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). In this paper, we describe and compare the codes used to compute photometric redshifts for HSC-SSP, how we calibrate them, and the typical accuracy we achieve with the HSC five-band photometry (grizy). We introduce a new point estimator based on an improved loss function and demonstrate that it works better than other commonly used estimators. We find that our photo-z's are most accurate at 0.2<~zphot<~1.5, where we can straddle the 4000A break. We achieve sigma(d_zphot/(1+zphot))~0.05 and an outlier rate of about 15% for galaxies down to i=25 within this redshift range. If we limit to a brighter sample of i<24, we achieve sigma~0.04 and ~8% outliers. Our photo-z's should thus enable many science cases for HSC-SSP. We also characterize the accuracy of our redshift probability distribution function (PDF) and discover that some codes over/under-estimate the redshift uncertainties, which have implications for N(z) reconstruction. Our photo-z products for the entire area in the Public Data Release 1 are publicly available, and both our catalog products (such as point estimates) and full PDFs can be retrieved from the data release site, https://hsc-release.mtk.nao.ac.jp/.