DESI mock challenge: constructing DESI galaxy catalogues based on FastPM simulations

Together with larger spectroscopic surveys such as the Dark Energy Spectroscopic Instrument (DESI), the precision of large scale structure studies and thus the constraints on the cosmological parameters are rapidly improving. Therefore, one must buildrealistic simulations and robust covariance matrices. We build galaxy catalogues by applying a halo occupation distribution(HOD) model upon the FASTPM simulations, such that the resulting galaxy clustering reproduces high-resolution N-bodysimulations. While the resolution and halo finder are different from the reference simulations, we reproduce the reference galaxytwo-point clustering measurements – monopole and quadrupole – to a precision required by the DESI Year 1 emission line galaxysample down to non-linear scales, i.e. k 10 Mpc h−1. Furthermore, we compute covariance matrices basedon the resulting FASTPM galaxy clustering – monopole and quadrupole. We study for the first time the effect of fitting on Fourierconjugate (e.g. power spectrum) on the covariance matrix of the Fourier counterpart (e.g. correlation function). We estimate theuncertainties of the two parameters of a simple clustering model and observe a maximum variation of 20 per cent for the differentcovariance matrices. Nevertheless, for most studied scales the scatter is between 2 and 10 per cent. Consequently, using thecurrent pipeline we can precisely reproduce the clustering of N-body simulations and the resulting covariance matrices providerobust uncertainty estimations against HOD fitting scenarios. We expect our methodology will be useful for the coming DESIdata analyses and their extension for other studies

Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: Cosmological implications from two decades of spectroscopic surveys at the Apache Point Observatory

We present the cosmological implications from final measurements of clustering using galaxies, quasars, and Ly α forests from the completed Sloan Digital Sky Survey (SDSS) lineage of experiments in large-scale structure. These experiments, composed of data from SDSS, SDSS-II, BOSS, and eBOSS, offer independent measurements of baryon acoustic oscillation (BAO) measurements of angular-diameter distances and Hubble distances relative to the sound horizon, r_{d}, from eight different samples and six measurements of the growth rate parameter, fσ_{8}, from redshift-space distortions (RSD). This composite sample is the most constraining of its kind and allows us to perform a comprehensive assessment of the cosmological model after two decades of dedicated spectroscopic observation. We show that the BAO data alone are able to rule out dark-energy-free models at more than eight standard deviations in an extension to the flat, Λ CDM model that allows for curvature. When combined with Planck Cosmic Microwave Background (CMB) measurements of temperature and polarization, under the same model, the BAO data provide nearly an order of magnitude improvement on curvature constraints relative to primary CMB constraints alone. Independent of distance measurements, the SDSS RSD data complement weak lensing measurements from the Dark Energy Survey (DES) in demonstrating a preference for a flat Λ CDM cosmological model when combined with Planck measurements. The combined BAO and RSD measurements indicate σ_{8} = 0.85 ± 0.03, implying a growth rate that is consistent with predictions from Planck temperature and polarization data and with General Relativity. When combining the results of SDSS BAO and RSD, Planck, Pantheon Type Ia supernovae (SNe Ia), and DES weak lensing and clustering measurements, all multiple-parameter extensions remain consistent with a Λ CDM model. Regardless of cosmological model, the precision on each of the three parameters, Ω_{Λ}, H_{0}, and σ_{8}, remains at roughly 1%, showing changes of less than 0.6% in the central values between models. In a model that allows for free curvature and a time-evolving equation of state for dark energy, the combined samples produce a constraint Ω_{k} = −0.0022 ± 0.0022. The dark energy constraints lead to w_{0} = −0.909 ± 0.081 and w_{a} = −0.49^{+0.35}_{-0.30}, corresponding to an equation of state of w_{p} = 1.018 ± 0.032 at a pivot redshift z_{p} = 0.29 and a Dark Energy Task Force Figure of Merit of 94. The inverse distance ladder measurement under this model yields H_{0} = 68.18 ± 0.79 km s^{-1} Mpc^{-1}, remaining in tension with several direct determination methods; the BAO data allow Hubble constant estimates that are robust against the assumption of the cosmological model. In addition, the BAO data allow estimates of H_{0} that are independent of the CMB data, with similar central values and precision under a Λ CDM model. Our most constraining combination of data gives the upper limit on the sum of neutrino masses at ∑m_{v} < 0.115 eV (95% confidence). Finally, we consider the improvements in cosmology constraints over the last decade by comparing our results to a sample representative of the period 2000–2010. We compute the relative gain across the five dimensions spanned by w, Ω_{k}, ∑m_{v}, H_{0}, H_{0}, and σ_{8} and find that the SDSS BAO and RSD data reduce the total posterior volume by a factor of 40 relative to the previous generation. Adding again the Planck, DES, and Pantheon SN Ia samples leads to an overall contraction in the five-dimensional posterior volume of 3 orders of magnitude

Cosmology with the MaunaKea Spectroscopic Explorer

This document summarizes the science cases related to cosmology studies with the MaunaKea Spectroscopic Explorer (MSE), a highly-multiplexed (4332 fibers), wide FOV (1.5 sq deg), large aperture (11.25 m in diameter), optical/NIR (360nm to 1300nm) facility. The MSE High-z Cosmology Survey is designed to probe a large volume of the Universe with a galaxy density sufficient to measure the extremely-large-scale density fluctuations required to explore primordial non-Gaussianity and therefore inflation. We expect a measurement of the local parameter $f_{NL}$ to a precision $\sigma(f_{NL}) = 1.8$. Combining the MSE High-z Cosmology Survey data with data from a next generation CMB stage 4 experiment and existing DESI data will provide the first $5\sigma$ confirmation of the neutrino mass hierarchy from astronomical observations. In addition, the Baryonic Acoustic Oscillations (BAO) observed within the sample will provide measurements of the distance-redshift relationship in six different redshift bins between $z=1.6$ and 4.0, each with an accuracy of $\sim0.6\%$. The simultaneous measurements of Redshift Space Distortions (RSD) constrain the amplitude of the fluctuations, at a level ranging from $1.9\%$ to $3.6\%$. The proposed survey covers 10,000 ${\rm deg}^2$, measuring redshifts for three classes of target objects: Emission Line Galaxies (ELGs) with $1.6<z<2.4$, Lyman Break Galaxies (LBGs) with $2.4<z<4.0$, and quasars $2.1<z<3.5$. The ELGs and LBGs will be used as direct tracers of the underlying density field, while the Lyman-$\alpha$ forests in the quasar spectra will be utilized to probe structure. Exposures of duration 1,800sec will guarantee a redshift determination efficiency of $90\%$ for ELGS and at least $50\%$ for LBGs. The survey will represent 100 nights per year for a 5-year MSE program. Finally, three ideas for additional projects of cosmological interest are proposed

The DESI N-body Simulation Project-II. Suppressing sample variance with fast simulations

Dark Energy Spectroscopic Instrument (DESI) will construct a large and precise three-dimensional map of our Universe. The survey effective volume reaches ∼ 20 h-3, Gpc3. It is a great challenge to prepare high-resolution simulations with a much larger volume for validating the DESI analysis pipelines. AbacusSummit is a suite of high-resolution dark-matter-only simulations designed for this purpose, with 200,-3}, Gpc3 (10 times DESI volume) for the base cosmology. However, further efforts need to be done to provide a more precise analysis of the data and to cover also other cosmologies. Recently, the CARPool method was proposed to use paired accurate and approximate simulations to achieve high statistical precision with a limited number of high-resolution simulations. Relying on this technique, we propose to use fast quasi-N-body solvers combined with accurate simulations to produce accurate summary statistics. This enables us to obtain 100 times smaller variance than the expected DESI statistical variance at the scales we are interested in, e.g. k &lt; 0.3h Mpc-1 for the halo power spectrum. In addition, it can significantly suppress the sample variance of the halo bispectrum. We further generalize the method for other cosmologies with only one realization in AbacusSummit suite to extend the effective volume ∼20 times. In summary, our proposed strategy of combining high-fidelity simulations with fast approximate gravity solvers and a series of variance suppression techniques sets the path for a robust cosmological analysis of galaxy survey data

VizieR Online Data Catalog: 12 massive lensing clusters MUSE observations (Richard+, 2021)

International audienc

VizieR Online Data Catalog: 12 massive lensing clusters MUSE observations (Richard+, 2021)

International audienc

VizieR Online Data Catalog: 12 massive lensing clusters MUSE observations (Richard+, 2021)

International audienc

VizieR Online Data Catalog: 12 massive lensing clusters MUSE observations (Richard+, 2021)

International audienc

VizieR Online Data Catalog: 12 massive lensing clusters MUSE observations (Richard+, 2021)

International audienc

Suppressing the Sample Variance of DESI-Like Galaxy Clustering with Fast Simulations

International audienceOngoing and upcoming galaxy redshift surveys, such as the Dark Energy Spectroscopic Instrument (DESI) survey, will observe vast regions of sky and a wide range of redshifts. In order to model the observations and address various systematic uncertainties, $N$-body simulations are routinely adopted, however, the number of large simulations with sufficiently high mass resolution is usually limited by available computing time. Therefore, achieving a simulation volume with the effective statistical errors significantly smaller than those of the observations becomes prohibitively expensive. In this study, we apply the Convergence Acceleration by Regression and Pooling (CARPool) method to mitigate the sample variance of the DESI-like galaxy clustering in the AbacusSummit simulations, with the assistance of the quasi-$N$-body simulations FastPM. Based on the halo occupation distribution (HOD) models, we construct different FastPM galaxy catalogs, including the luminous red galaxies (LRGs), emission line galaxies (ELGs), and quasars, with their number densities and two-point clustering statistics well matched to those of AbacusSummit. We also employ the same initial conditions between AbacusSummit and FastPM to achieve high cross-correlation, as it is useful in effectively suppressing the variance. Our method of reducing noise in clustering is equivalent to performing a simulation with volume larger by a factor of 5 and 4 for LRGs and ELGs, respectively. We also mitigate the standard deviation of the LRG bispectrum with the triangular configurations k_2=2k_1=0.2\hMpc by a factor of 1.6. With smaller sample variance on galaxy clustering, we are able to constrain the BAO scale parameters to higher precision. The CARPool method will be beneficial to better constrain the theoretical systematics of BAO, redshift space distortions (RSD) and primordial non-Gaussianity