Deep CFHT Y-band imaging of VVDS-F22 field: I. data products and photometric redshifts

TL;DR

This paper presents deep Y-band imaging data of a 2-square-degree field, combining it with optical and near-infrared data to derive accurate photometric redshifts for galaxies and quasars, aiding in faint quasar selection and redshift estimation.

Contribution

The study provides new deep Y-band imaging data and demonstrates improved photometric redshift accuracy, especially at z~1-2, by including near-infrared bands, which was not extensively done before.

Findings

Detected ~80,000 galaxies down to Y=22.86 mag.

Photometric redshifts have small systematic offsets and low catastrophic failure rates.

Including Y-band improves redshift accuracy at z~1-2.

Abstract

We present our deep $Y$-band imaging data of a two square degree field within the F22 region of the VIMOS VLT Deep Survey. The observations were conducted using the WIRCam instrument mounted at the Canada--France--Hawaii Telescope (CFHT). The total on-sky time was 9 hours, distributed uniformly over 18 tiles. The scientific goals of the project are to select faint quasar candidates at redshift $z>2.2$, and constrain the photometric redshifts for quasars and galaxies. In this paper, we present the observation and the image reduction, as well as the photometric redshifts that we derived by combining our $Y$-band data with the CFHTLenS $u^*g'r'i'z'$ optical data and UKIDSS DXS $JHK$ near-infrared data. With $J$-band image as reference total $\sim$80,000 galaxies are detected in the final mosaic down to $Y$-band $5\sigma$ point source limiting depth of 22.86 mag. Compared with the $\sim$3500 spectroscopic redshifts, our photometric redshifts for galaxies with $z<1.5$ and $i'\lesssim24.0$ mag have a small systematic offset of $|\Delta{z}|\lesssim0.2$, 1$\sigma$ scatter $0.03<\sigma_{\Delta z} < 0.06$, and less than 4.0% of catastrophic failures. We also compare to the CFHTLenS photometric redshifts, and find that ours are more reliable at $z\gtrsim0.6$ because of the inclusion of the near-infrared bands. In particular, including the $Y$-band data can improve the accuracy at $z\sim 1.0-2.0$ because the location of the 4000\AA-break is better constrained. The $Y$-band images, the multi-band photometry catalog and the photometric redshifts are released at \url{http://astro.pku.edu.cn/astro/data/DYI.html}.