The HectoMAP Redshift Survey: First Data Release

TL;DR

HectoMAP's first data release provides a dense, red-selected galaxy redshift survey over 8.7 square degrees, enabling improved cluster membership analysis and assessment of photometric redshift accuracy, with 17,313 redshifts and derived galaxy properties.

Contribution

This work presents the initial data release of HectoMAP, a dense redshift survey that combines spectroscopic data with imaging, facilitating new applications in galaxy cluster studies and photometric redshift validation.

Findings

17,313 redshifts obtained in the first data release.

Identification of a remarkable strong lensing system in the survey.

Systematic issues found in photometric redshifts when compared with spectroscopic data.

Abstract

HectoMAP is a dense, red-selected redshift survey to a limiting $r = 21.3$ covering 55 square degrees in a contiguous 1.5$^\circ$ strip across the northern sky. This region is also covered by the Subaru/Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP) photometric survey enabling a range of applications that combine a dense foreground redshift survey with both strong and weak lensing maps. The median redshift of HectoMAP exceeds 0.3 throughout the survey region and the mean density of the redshift survey is $\sim 2000$ galaxies deg$^{-2}$. Here we report a total of 17,313 redshifts in a first data release covering 8.7 square degrees. We include the derived quantities D$_{n}4000$ and stellar mass for nearly all of the objects. Among these galaxies, 8117 constitute a 79\% complete red-selected subsample with $r \leq 20.5$ and an additional 4318 constitute a 68\% complete red-selected subsample with $20.5 < r < 21.3$. As examples of the strengths of HectoMAP data we discuss two applications: refined membership of redMaPPer photometrically selected clusters and a test of HSC photometric redshifts. We highlight a remarkable redMaPPer strong lensing system. The comparison of photometric redshifts with spectroscopic redshifts in a dense survey uncovers subtle systematic issues in the photometric redshifts.