Linear bias and halo occupation distribution of emission-line galaxies from Nancy Grace Roman Space Telescope

Abstract

We present measurements of the linear galaxy bias of Hα and [O III] emission-line galaxies (ELGs) for the High Latitude Spectroscopic Survey (HLSS) of Nancy Grace Roman Space Telescope (or Roman), using galaxy mocks constructed using semi-analytical model for galaxy formation, Galacticus, with a large cosmic volume and redshift coverage. We compute the two-point statistics of galaxies in configuration space and measure linear bias within scales of 10–50 h⁻¹ Mpc. We adopt different selection algorithms to investigate the impact of the Roman line flux cut, as well as the effect of dust model used to calibrate Galacticus, on the bias measurements. We consider galaxies with Hα and [O III] emissions over the redshift range 1 < z < 3, as specified by the current baseline for the Roman HLSS. We find that the linear bias for the Hα and [O III] ELGs can be expressed as a linear function with respect to redshift: b ≃ 0.9z + 0.5 for Hα (1 < z < 2), and b ≃ z + 0.5 for [O III] (2 < z < 3). We have also measured the halo occupation distributions of these Hα and [O III] ELGs to understand their distribution within dark matter haloes. Our results provide key input to enable the reliable forecast of dark energy and cosmology constraints from Roman.