The wide-field, multiplexed, spectroscopic facility WEAVE: Survey design, overview, and simulated implementation

WEAVE, the new wide-field, massively multiplexed spectroscopic survey facility for the William Herschel Telescope, will see first light in late 2022. WEAVE comprises a new 2-degree field-of-view prime-focus corrector system, a nearly 1000-multiplex fibre positioner, 20 individually deployable 'mini' integral field units (IFUs), and a single large IFU. These fibre systems feed a dual-beam spectrograph covering the wavelength range 366\(-\)959\,nm at \(R\sim5000\), or two shorter ranges at \(R\sim20\,000\). After summarising the design and implementation of WEAVE and its data systems, we present the organisation, science drivers and design of a five- to seven-year programme of eight individual surveys to: (i) study our Galaxy's origins by completing Gaia's phase-space information, providing metallicities to its limiting magnitude for \(\sim\)3 million stars and detailed abundances for \(\sim1.5\) million brighter field and open-cluster stars; (ii) survey \(\sim0.4\) million Galactic-plane OBA stars, young stellar objects and nearby gas to understand the evolution of young stars and their environments; (iii) perform an extensive spectral survey of white dwarfs; (iv) survey \(\sim400\) neutral-hydrogen-selected galaxies with the IFUs; (v) study properties and kinematics of stellar populations and ionised gas in \(z1\) million spectra of LOFAR-selected radio sources; (viii) trace structures using intergalactic/circumgalactic gas at \(z>2\). Finally, we describe the WEAVE Operational Rehearsals using the WEAVE Simulator.