Observational requirements for Lyα forest tomographic mapping of large-scale structure at z ∼ 2

Abstract

The z ≳ 2 Lyα forest traces the underlying dark matter distribution on large scales and, given sufficient sightlines, can be used to create three-dimensional (3D) maps of large-scale structures. We examine the observational requirements to construct such maps and estimate the signal-to-noise as a function of exposure time and sightline density. Sightline densities at z = 2.25 are n los [360, 1200, 3300] deg-2 at limiting magnitudes of g = [24.0, 24.5, 25.0], resulting in transverse sightline separations of 〈d 〉 [3.6, 1.9, 1.2] h -1 Mpc, which roughly sets the reconstruction scale. We simulate these reconstructions using mock spectra with realistic noise properties and find that spectra with S/N 4 per angstrom can be used to generate maps that clearly trace the underlying dark matter at overdensities of ρ/〈ρ〉 ∼ 1. For the VLT/VIMOS spectrograph, exposure times t exp = [4, 6, 10] hr are sufficient for maps with spatial resolution ε3D = [5.0, 3.2, 2.3] h -1 Mpc. Assuming ∼250 h -1 Mpc is probed along the line of sight, 1 deg 2 of survey area would cover a comoving volume of 106 h -3 Mpc3 at 〈z〉 ∼ 2.3, enabling the efficient mapping of large volumes with 8-10 m telescopes. These maps could be used to study galaxy environments, the topology of large-scale structures at high z, and to detect proto-clusters. © 2014. The American Astronomical Society. All rights reserved..