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WEAVE-QSO

Team Lead: Matthew Pieri

 

The WEAVE-QSO survey is designed to optimise quasar absorption science through the measurement of Lyman-alpha absorption and other intergalactic medium (IGM) absorbers. The science objectives form two pillars; probing cosmological parameters through measurements of baryon acoustic oscillations through quasar absorption, and a wider variety of IGM science and smaller-scale structure cosmology. The former is contingent on WEAVE-QSO's unrivalled number density of Lyman-alpha forest quasars, the latter rests on unprecedented resolution and signal-to-noise massive spectroscopic survey.

One of the challenges of our time is determining the cause of this acceleration in the expansion of the universe that we term 'dark energy'. One way to explore this phenomenon is to measure the expansion history of the Universe. There is a convenient standard ruler to achieve this, called Baryon Acoustic Oscillations (BAOs; e.g. Seo & Eisenstein 2003). Measuring the scale of BAOs in the distribution of large-scale structure at various epochs allows us to probe the expansion of the Universe.


Figure 1: Illustration of the expansion of the universe (from right to left) probed by high redshift quasars (see as white points). Credit: Paul Hooper at http://www.spirit-design.com/ with material from Gongbo Zhao. 


In quasar absorption spectroscopy, we measure large-scale structure in skewers of density through the Universe. In this way we can measure the large-scale 3D distribution of gas in correlations between skewers, allowing a measurement of BAO and so expansion. This emergent method was first demonstrated with the recently complete BOSS survey (e.g. Busca et al 2013, Bautista et al 2017), which is being extended by eBOSS to reach over 200,000 quasars with z>2. WEAVE will more than double this number, but the key determinant for the cosmological precision, in a massive spectroscopy IGM survey, is not in fact the number of spectra but the number density of sight-lines through the universe. In this regard WEAVE-QSO will surpass all other surveys concurrent surveys producing competitive BAO constraints at z>2.

In addition, WEAVE-QSO will offer unparalleled spectral resolution (mostly R=5000, but also R=20,000) in a large-scale spectroscopic survey of the IGM, and will provide very high signal-to-noise data through high levels of completeness to bright quasars. Such data will be impactful for a wide range of science, including constraints on (other) cosmology through the use of the Lyman-alpha flux power spectrum in measuring neutrino masses and possible effects of warm dark matter. Also since IGM properties are sensitive to density, temperature, UV radiation, metallicity and abundance pattern, quasars spectra constrains galaxy formation in a variety of ways. Inflowing/outflowing gas associated with nearby galaxies will be studied in a cosmic web context. Of particular interest are HETDEX fields, which will provide higher resolution mapping and Lyman-alpha emitting galaxies. The WEAVE-QSO survey resolution and signal-to-noise will be uniquely capable of studying absorbers through a dynamic range spanning more than 8 orders of magnitude in hydrogen column density with thermal properties and accompanying narrow metal lines.

 

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