Dipolar modulation in the size of galaxies: The effect of Doppler magnification

archiveprefix: arXiv primaryclass: astro-ph.CO slaccitation: %%CITATION = ARXIV:1610.05946;%%archiveprefix: arXiv primaryclass: astro-ph.CO slaccitation: %%CITATION = ARXIV:1610.05946;%%archiveprefix: arXiv primaryclass: astro-ph.CO slaccitation: %%CITATION = ARXIV:1610.05946;%%archiveprefix: arXiv primaryclass: astro-ph.CO slaccitation: %%CITATION = ARXIV:1610.05946;%%archiveprefix: arXiv primaryclass: astro-ph.CO slaccitation: %%CITATION = ARXIV:1610.05946;%

Cosmology with Phase 1 of the Square Kilometre Array Red Book 2018: Technical specifications and performance forecasts

We present a detailed overview of the cosmological surveys that we aim to carry out with Phase 1 of the Square Kilometre Array (SKA1) and the science that they will enable. We highlight three main surveys: a medium-deep continuum weak lensing and low-redshift spectroscopic HI galaxy survey over 5 000 deg2; a wide and deep continuum galaxy and HI intensity mapping (IM) survey over 20 000 deg2 from to 3; and a deep, high-redshift HI IM survey over 100 deg2 from to 6. Taken together, these surveys will achieve an array of important scientific goals: measuring the equation of state of dark energy out to with percent-level precision measurements of the cosmic expansion rate; constraining possible deviations from General Relativity on cosmological scales by measuring the growth rate of structure through multiple independent methods; mapping the structure of the Universe on the largest accessible scales, thus constraining fundamental properties such as isotropy, homogeneity, and non-Gaussianity; and measuring the HI density and bias out to . These surveys will also provide highly complementary clustering and weak lensing measurements that have independent systematic uncertainties to those of optical and near-infrared (NIR) surveys like Euclid, LSST, and WFIRST leading to a multitude of synergies that can improve constraints significantly beyond what optical or radio surveys can achieve on their own. This document, the 2018 Red Book, provides reference technical specifications, cosmological parameter forecasts, and an overview of relevant systematic effects for the three key surveys and will be regularly updated by the Cosmology Science Working Group in the run up to start of operations and the Key Science Programme of SKA1

Observational signatures of modified gravity on ultra-large scales

Extremely large surveys with future experiments like Euclid and the SKA will soon allow us to access perturbation modes close to the Hubble scale, with wavenumbers $k\sim {\mathcal{H}}.$ If a modified gravity (MG) theory is responsible for cosmic acceleration, then the Hubble scale is a natural regime for deviations from General Relativity (GR) to become manifest. However, the majority of studies to date have concentrated on the consequences of alternative gravity theories for the subhorizon, quasi-static regime. In this paper, we investigate how modifications to the gravitational field equations affect perturbations around the Hubble scale. We choose functional forms to represent the generic scale-dependent behavior of gravity theories that modify GR at long wavelengths, and study the resulting deviations of ultra-large-scale relativistic observables from their GR behavior. We find that these are small unless modifications to the field equations are drastic. The angular dependence and redshift evolution of the deviations is highly parameterization- and survey-dependent, however, and so they are possibly a rich source of MG phenomenology if they can be measured

Testing General Relativity with the Doppler magnification effect

archiveprefix: arXiv primaryclass: astro-ph.CO slaccitation: %%CITATION = ARXIV:1810.12793;%%archiveprefix: arXiv primaryclass: astro-ph.CO slaccitation: %%CITATION = ARXIV:1810.12793;%%archiveprefix: arXiv primaryclass: astro-ph.CO slaccitation: %%CITATION = ARXIV:1810.12793;%%archiveprefix: arXiv primaryclass: astro-ph.CO slaccitation: %%CITATION = ARXIV:1810.12793;%

The environmental dependence of neutral hydrogen in the GIMIC simulations

We use the Galaxies-Intergalactic Medium Interaction Calculation (GIMIC) cosmological hydrodynamic simulation at z = 0 to study the distribution and environmental dependence of neutral hydrogen (H I) gas in the outskirts of simulated galaxies. This gas can currently be probed directly in, for example, Lyα absorption via the observation of background quasars. Radio facilities, such as the Square Kilometre Array, will provide a complementary probe of the diffuse H I in emission and will constrain the physics underpinning the complex interplay between accretion and feedback mechanisms which affect the intergalactic medium. We extract a sample of 488 galaxies from a resimulation of the average cosmic density GIMIC region. We estimate the neutral hydrogen content of these galaxies and the surrounding intergalactic medium within which they reside. We investigate the average H I radial profiles by stacking the individual profiles according to both mass and environment. We find high H I column densities at large impact parameters in group environments and markedly lower H I densities for non-group galaxies. We suggest that these results likely arise from the combined effects of ram pressure stripping and tidal interactions present in group environments

HIFLOW: Generating Diverse HI Maps and Inferring Cosmology while Marginalizing over Astrophysics Using Normalizing Flows

International audienceA wealth of cosmological and astrophysical information is expected from many ongoing and upcoming large-scale surveys. It is crucial to prepare for these surveys now and develop tools that can efficiently extract most information. We present HIFLOW: a fast generative model of the neutral hydrogen (HI) maps that is conditioned only on cosmology (Ω m and σ 8) and designed using a class of normalizing flow models, the masked autoregressive flow. HIFLOW is trained on the state-of-the-art simulations from the Cosmology and Astrophysics with MachinE Learning Simulations (CAMELS) project. HIFLOW has the ability to generate realistic diverse maps without explicitly incorporating the expected two-dimensional maps structure into the flow as an inductive bias. We find that HIFLOW is able to reproduce the CAMELS average and standard deviation HI power spectrum within a factor of ≲2, scoring a very high R 2 > 90%. By inverting the flow, HIFLOW provides a tractable high-dimensional likelihood for efficient parameter inference. We show that the conditional HIFLOW on cosmology is successfully able to marginalize over astrophysics at the field level, regardless of the stellar and AGN feedback strengths. This new tool represents a first step toward a more powerful parameter inference, maximizing the scientific return of future HI surveys, and opening a new avenue to minimize the loss of complex information due to data compression down to summary statistics