The Merian survey: design, construction, and characterization of a filter set optimized to find dwarf galaxies and measure their dark matter halo properties with weak lensing

Abstract

The Merian survey is mapping similar to 850 deg(2) of the Hyper Suprime-Cam Strategic Survey Program (HSC-SSP) wide layer with two medium-band filters on the 4-m Victor M. Blanco telescope at the Cerro Tololo Inter-American Observatory, with the goal of carrying the first high signal-to-noise (S/N) measurements of weak gravitational lensing around dwarf galaxies. This paper presents the design of the Merian filter set: N708 (lambda(c) = 7080 angstrom, Delta lambda = 275 angstrom) and N540 (lambda(c) = 5400 angstrom, Delta lambda = 210 angstrom). The central wavelengths and filter widths of N708 and N540 were designed to detect the H alpha and [OIII] emission lines of galaxies in the mass range 8 < log M-star/M-circle dot < 9 by comparing Merian fluxes with HSC broad-band fluxes. Our filter design takes into account the weak lensing S/N and photometric redshift performance. Our simulations predict that Merian will yield a sample of similar to 85 000 star-forming dwarf galaxies with a photometric redshift accuracy of sigma(Delta z/(1 + z)) similar to 0.01 and an outlier fraction of eta = 2.8 per cent over the redshift range 0.058 < z < 0.10. With 60 full nights on the Blanco/Dark Energy Camera (DECam), the Merian survey is predicted to measure the average weak lensing profile around dwarf galaxies with lensing S/N similar to 32 within r < 0.5 Mpc and lensing S/N similar to 90 within r < 1.0 Mpc. This unprecedented sample of star-forming dwarf galaxies will allow for studies of the interplay between dark matter and stellar feedback and their roles in the evolution of dwarf galaxies.