High-redshift post-reionization cosmology with 21cm intensity mapping

We investigate the possibility of performing cosmological studies in the redshift range 2.5<z<5 through suitable extensions of existing and upcoming radio-telescopes like CHIME, HIRAX and FAST. We use the Fisher matrix technique to forecast the bounds that those instruments can place on the growth rate, the BAO distance scale parameters, the sum of the neutrino masses and the number of relativistic degrees of freedom at decoupling, Neff. We point out that quantities that depend on the amplitude of the 21cm power spectrum, like f\u3c38, are completely degenerate with \u3a9HI and bHI, and propose several strategies to independently constrain them through cross-correlations with other probes. Assuming 5% priors on \u3a9HI and bHI, kmax=0.2 h Mpc-1 and the primary beam wedge, we find that a HIRAX extension can constrain, within bins of \u394 z=0.1: 1) the value of f\u3c38 at 4%, 2) the value of DA and H at 1%. In combination with data from Euclid-like galaxy surveys and CMB S4, the sum of the neutrino masses can be constrained with an error equal to 23 meV (1\u3c3), while Neff can be constrained within 0.02 (1\u3c3). We derive similar constraints for the extensions of the other instruments. We study in detail the dependence of our results on the instrument, amplitude of the HI bias, the foreground wedge coverage, the nonlinear scale used in the analysis, uncertainties in the theoretical modeling and the priors on bHI and \u3a9HI. We conclude that 21cm intensity mapping surveys operating in this redshift range can provide extremely competitive constraints on key cosmological parameters

The quijote simulations

The Quijote simulations are a set of 44,100 full N-body simulations spanning more than 7000 cosmological models in the hyperplane. At a single redshift, the simulations contain more than 8.5 trillion particles over a combined volume of 44,100 each simulation follows the evolution of 2563, 5123, or 10243 particles in a box of 1 h -1 Gpc length. Billions of dark matter halos and cosmic voids have been identified in the simulations, whose runs required more than 35 million core hours. The Quijote simulations have been designed for two main purposes: (1) to quantify the information content on cosmological observables and (2) to provide enough data to train machine-learning algorithms. In this paper, we describe the simulations and show a few of their applications. We also release the petabyte of data generated, comprising hundreds of thousands of simulation snapshots at multiple redshifts; halo and void catalogs; and millions of summary statistics, such as power spectra, bispectra, correlation functions, marked power spectra, and estimated probability density functions

Overview of the instrumentation for the Dark Energy Spectroscopic Instrument

The Dark Energy Spectroscopic Instrument (DESI) embarked on an ambitious 5 yr survey in 2021 May to explore the nature of dark energy with spectroscopic measurements of 40 million galaxies and quasars. DESI will determine precise redshifts and employ the baryon acoustic oscillation method to measure distances from the nearby universe to beyond redshift z > 3.5, and employ redshift space distortions to measure the growth of structure and probe potential modifications to general relativity. We describe the significant instrumentation we developed to conduct the DESI survey. This includes: a wide-field, 3.°2 diameter prime-focus corrector; a focal plane system with 5020 fiber positioners on the 0.812 m diameter, aspheric focal surface; 10 continuous, high-efficiency fiber cable bundles that connect the focal plane to the spectrographs; and 10 identical spectrographs. Each spectrograph employs a pair of dichroics to split the light into three channels that together record the light from 360–980 nm with a spectral resolution that ranges from 2000–5000. We describe the science requirements, their connection to the technical requirements, the management of the project, and interfaces between subsystems. DESI was installed at the 4 m Mayall Telescope at Kitt Peak National Observatory and has achieved all of its performance goals. Some performance highlights include an rms positioner accuracy of better than 0.″1 and a median signal-to-noise ratio of 7 of the [O ii] doublet at 8 × 10−17 erg s−1 cm−2 in 1000 s for galaxies at z = 1.4–1.6. We conclude with additional highlights from the on-sky validation and commissioning, key successes, and lessons learned

Ingredients for 21 cm Intensity Mapping

© 2018. The American Astronomical Society. All rights reserved. Current and upcoming radio telescopes will map the spatial distribution of cosmic neutral hydrogen (H i) through its 21 cm emission. In order to extract the maximum information from these surveys, accurate theoretical predictions are needed. We study the abundance and clustering properties of H i at redshifts z ≤ 5 using TNG100, a large state-of-the-art magnetohydrodynamic simulation of a 75 h -1 Mpc box size, which is part of the IllustrisTNG Project. We show that most of the H i lies within dark matter halos, and we provide fits for the halo H i mass function, i.e., the mean H i mass hosted by a halo of mass M at redshift z. We find that only halos with circular velocities larger than ≃30 km s-1 contain H i. While the density profiles of H i exhibit a large halo-to-halo scatter, the mean profiles are universal across mass and redshift. The H i in low-mass halos is mostly located in the central galaxy, while in massive halos the H i is concentrated in the satellites. Our simulation reproduces the bias value of damped Lyα systems from observations. We show that the H i and matter density probability distribution functions differ significantly. Our results point out that for small halos, the H i bulk velocity goes in the same direction and has the same magnitude as the halo peculiar velocity, while in large halos, differences show up. We find that halo H i velocity dispersion follows a power law with halo mass. We find a complicated H i bias, with H i already becoming nonlinear at k = 0.3 h Mpc-1 at z 3. The clustering of H i can, however, be accurately reproduced by perturbative methods. We find a new secondary bias by showing that the clustering of halos depends not only on mass but also on H i content. We compute the amplitude of the H i shot noise and find that it is small at all redshifts, verifying the robustness of BAO measurements with 21 cm intensity mapping. We study the clustering of H i in redshift space and show that linear theory can explain the ratio between the monopoles in redshift and real space down to 0.3, 0.5, and 1 h Mpc-1 at redshifts 3, 4, and 5, respectively. We find that the amplitude of the Fingers-of-God effect is larger for H i than for matter, since H i is found only in halos above a certain mass. We point out that 21 cm maps can be created from N-body simulations rather than full hydrodynamic simulations. Modeling the one-halo term is crucial for achieving percent accuracy with respect to a full hydrodynamic treatment. Although our results are not converged against resolution, they are, however, very useful as we work at the resolution where the model parameters have been calibrated to reproduce galaxy properties

UNESCO's communication policies as discourse: how change, human development and knowledge relate to communication

While the 1970s and 1980s as turbulent decades for the United Nations Educational, Scientific and Cultural Organization (UNESCO) have been well covered by international communication scholars, UNESCO's communication policies during the past decade have received less attention. Examining UNESCO's communication policies as discourse from a social constructivist and post-positivist standpoint, we found that discourses concerning change, human development and knowledge which popped up in the last decade can be regarded as giving a specific interpretation to the discourse on communication. These entwining discourses share a neglect of existing power relations and inequalities. Focusing on the individual, they offer an incomplete answer to structural inequalities and imbalances. As such, a specific interpretation of change, human development and knowledge reinforces the shift of the organization's communication policies which has been consolidated ever since its 1989 New Communication Strategy was adopted. In this process the organization has grown closer to the World Bank's neoliberal (and depoliticizing) approaches