Mission and instrumentation concept for the baryonic structure probe

Abstract

There is a growing consensus that a substantial fraction of the matter in the universe, especially what we think of as normal baryonic matter, exists in a tenuous, hot filamentary intergalactic medium often referred to as the Cosmic Web. Improving our understanding of the web has been a high priority scientific goal in NASA's planning and roadmapping activities. NASA recently supported an Origins Probe study that explored the observable phenomenology of the web in detail and developed concepts for the instrumentation and mission. The Baryonic Structure Probe operates in the ultraviolet spectral region, using primarily O VI (λλ 1032, 1038Å) and HI Ly α (λ 1216 Å) as tracers of the web. A productive investigation requires both moderate resolution (R = λ/∆λ ~ 30000) absorption line spectroscopy using faint background quasars as continuum sources, and imaging of the diffuse filaments in emission lines of the same ions. Spectroscopic sensitivity to quasars as faint as V ~ 19 will probe a large number of sight lines to derive physical diagnostics over the redshift range 0 < z < 1. Spectral imaging with a wide field of view and sensitivity to a redshift range 0 < z < 0.3 will map the filaments in a large volume of the universe after the web had evolved to near its modern structure. This paper summarizes the scientific goals, identifies the measurement requirements derived from them, and describes the instrument concepts and overall mission architecture developed by the BSP study team.