Abstract
ABSTRACT We propose a new method for fitting the full-shape of the Lyman-α (Ly α) forest 3D correlation function in order to measure the Alcock-Paczynski (AP) effect. Our method preserves the robustness of baryon acoustic oscillations (BAO) analyses, while also providing extra cosmological information from a broader range of scales. We compute idealized forecasts for the Dark Energy Spectroscopic Instrument (DESI) using the Ly α autocorrelation and its cross-correlation with quasars, and show how this type of analysis improves cosmological constraints. The DESI Ly α BAO analysis is expected to measure H(zeff)rd and DM(zeff)/rd with a precision of $\sim 0.9{{\ \rm per\ cent}}$, where H is the Hubble parameter, rd is the comoving BAO scale, DM is the comoving angular diameter distance, and the effective redshift of the measurement is zeff ≃ 2.3. By fitting the AP parameter from the full shape of the two correlations, we show that we can obtain a precision of $\sim 0.5-0.6{{\ \rm per\ cent}}$ on each of H(zeff)rd and DM(zeff)/rd. Furthermore, we show that a joint full-shape analysis of the Ly α auto and cross-correlation with quasars can measure the linear growth rate times the amplitude of matter fluctuations in spheres of 8 h−1Mpc, fσ8(zeff). Such an analysis could provide the first ever measurement of fσ8(zeff) at redshift zeff > 2. By combining this with the quasar autocorrelation in a joint analysis of the three high-redshift two-point correlation functions, we show that DESI could be able to measure fσ8(zeff ≃ 2.3) with a precision of $5-12{{\ \rm per\ cent}}$, depending on the smallest scale fitted.
Highlights
The vast amount of cosmological data from spectroscopic surveys is usually compressed into summary statistics such as the correlation function or power spectrum
We show the benefits of extracting more information from the Ly α forest 3D correlation functions by performing a simple cosmological analysis using the forecast measurements obtained above
We proposed to expand the cosmological information extracted from these statistics by fitting the full shape of these correlations in order to measure the Alcock–Paczynski (AP) parameter
Summary
The vast amount of cosmological data from spectroscopic surveys is usually compressed into summary statistics such as the correlation function or power spectrum. A template is first used to model the power spectrum or correlation function in order to measure a few relevant quantities that contain most of the cosmological information These measurements are used to fit cosmological parameters for some model, for example flat Cold Dark Matter ( CDM), in combination with other probes, usually the cosmic microwave background (e.g. from Planck Collaboration 2020). This approach is used because it contains minimal assumptions, and the full two-point statistic is compressed into a few well understood physical quantities. This method has been used to measure the BAO scale using the galaxy distribution at redshifts
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