Abstract
Observational cosmology in the next decade will rely on probes of the distribution of matter in the redshift range between $0<z<3$ to elucidate the nature of dark matter and dark energy. In this redshift range, galaxy formation is known to have a significant impact on observables such as two-point correlations of galaxy shapes and positions, altering their amplitude and scale dependence beyond the expected statistical uncertainty of upcoming experiments at separations under 10 Mpc. Successful extraction of information in such a regime thus requires, at the very least, unbiased models for the impact of galaxy formation on the matter distribution, and can benefit from complementary observational priors. This work reviews the current state of the art in the modelling of baryons for cosmology, from numerical methods to approximate analytical prescriptions, and makes recommendations for studies in the next decade, including a discussion of potential probe combinations that can help constrain the role of baryons in cosmological studies. We focus, in particular, on the modelling of the matter power spectrum, $P(k,z)$, as a function of scale and redshift, and of the observables derived from this quantity. This work is the result of a workshop held at the University of Oxford in November of 2018.
Highlights
Over the past two decades, observational cosmology has become an effective tool for learning about the past, present and fate of the Universe
Most modern cosmological simulations are initialized at early times, with the initial distribution of dark matter and baryons being set to reproduce the matter power spectrum calculated by Boltzmann codes using cosmological parameter values determined from the cosmic microwave background [e.g. 87]
Reference [65] explains that the approach taken for Illustris was to establish the values of the ∼ 15 free parameters of the subgrid model [67] based on their physical meaning in as much as possible, but clarify that a subset of these had to be tuned based on smaller volume (35.5 Mpc on each side) simulations, whose predictions were compared against the history of cosmic star-formation rate density and the z = 0 stellar mass function
Summary
Over the past two decades, observational cosmology has become an effective tool for learning about the past, present and fate of the Universe. This figure assumes the information is directly extracted from the matter power spectrum, evaluated in the expected median redshift of future optical surveys (0 < z < 3). A third approach proposes to model the Universe by modifying the profiles of dark matter haloes in cosmological N-body simulations with a prescription to displace particles based on observational constraints of the distributions and abundances of gas and stars in haloes [25, 29] This approach can be tested self-consistently in hydrodynamical simulations.
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