The bahamas project: effects of a running scalar spectral index on large-scale structure

Monthly Notices of the Royal Astronomical Society

Stafford

et al. 2020

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In this work we consider the impact of spatially-uniform but time-varying dark energy (or ‘dynamical dark energy’, DDE) on large-scale structure in a spatially flat universe, using large cosmological hydrodynamical simulations that form part of the BAHAMAS project. As DDE changes the expansion history of the universe, it impacts the growth of structure. We explore variations in DDE that are constrained to be consistent with the cosmic microwave background. We find that DDE can affect the clustering of matter and haloes at the $\sim 10\%$ level (suppressing it for so-called ‘freezing’ models, while enhancing it for ‘thawing’ models), which should be distinguishable with upcoming large-scale structure surveys. DDE cosmologies can also enhance or suppress the halo mass function (with respect to ΛCDM) over a wide range of halo masses. The internal properties of haloes are minimally affected by changes in DDE, however. Finally, we show that the impact of baryons and associated feedback processes is largely independent of the change in cosmology and that these processes can be modelled separately to typically better than a few percent accuracy.

Section: Discussion and Summarymentioning

confidence: 91%

Section: Large-scale Structurementioning

confidence: 99%

The BAHAMAS project: effects of dynamical dark energy on large-scale structure

Pfeifer

Monthly Notices of the Royal Astronomical Society

Stafford

et al. 2020

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“…Next, we use the BAHAMAS simulations to model the impact of baryons on cosmological constraints. We make the assumption that the fractional effect of baryonic processes is independent of cosmology, which has been shown to be true for the power spectrum within a few per cent (Mead et al 2015(Mead et al , 2016Mummery et al 2017;Stafford et al 2019;van Daalen et al 2019). To include baryonic effects, we introduce into our emulator a new parameter A baryon , which linearly interpolates the fractional effect of baryons between no baryonic effects (A baryon = 0) to the BAHAMAS high-AGN model A baryon = 3, with A baryon = 2 for the fiducial model and A baryon = 1 for the low-AGN model.…”

Section: M Pac T O F Ba Ryo N Smentioning

confidence: 99%

Weak lensing minima and peaks: Cosmological constraints and the impact of baryons

Coulton

Liu

Monthly Notices of the Royal Astronomical Society

et al. 2020

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We present a novel statistic to extract cosmological information in weak lensing data: the lensing minima. We also investigate the effect of baryons on cosmological constraints from peak and minimum counts. Using the MassiveNuS simulations, we find that lensing minima are sensitive to non-Gaussian cosmological information and are complementary to the lensing power spectrum and peak counts. For an LSST-like survey, we obtain $95{{\ \rm per\ cent}}$ credible intervals from a combination of lensing minima and peaks that are significantly stronger than from the power spectrum alone, by $44{{\ \rm per\ cent}}$, $11{{\ \rm per\ cent}}$, and $63{{\ \rm per\ cent}}$ for the neutrino mass sum ∑mν, matter density Ωm, and amplitude of fluctuation As, respectively. We explore the effect of baryonic processes on lensing minima and peaks using the hydrodynamical simulations BAHAMAS and Osato15. We find that ignoring baryonic effects would lead to strong (≈4σ) biases in inferences from peak counts, but negligible (≈0.5σ) for minimum counts, suggesting lensing minima are a potentially more robust tool against baryonic effects. Finally, we demonstrate that the biases can in principle be mitigated without significantly degrading cosmological constraints when we model and marginalize the baryonic effects.

“…Lovell et al 2017;Hellwing et al 2016) and a running of the spectral index (e.g. Garrison-Kimmel et al 2014;Stafford et al 2020b) to name but a few possible extensions (see Stafford et al 2020a for a recent comparison of the effects of these extensions along with baryonic processes).…”

Section: Introductionmentioning

confidence: 99%

Connecting the structure of dark matter haloes to the primordial power spectrum

Brown

Monthly Notices of the Royal Astronomical Society

Diemer

et al. 2020

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A large body of work based on collisionless cosmological N-body simulations going back over two decades has advanced the idea that collapsed dark matter (DM) haloes have simple and approximately universal forms for their mass density and pseudo-phase-space density (PPSD) distributions. However, a general consensus on the physical origin of these results has not yet been reached. In the present study, we explore to what extent the apparent universality of these forms holds when we vary the initial conditions (i.e. the primordial power spectrum of density fluctuations) away from the standard CMB-normalized case, but still within the context of lambda cold dark matter with a fixed expansion history. Using simulations that vary the initial amplitude and shape, we show that the structure of DM haloes retains a clear memory of the initial conditions. Specifically, increasing (lowering) the amplitude of fluctuations increases (decreases) the concentration of haloes and, if pushed far enough, the density profiles deviate strongly from the NFW form that is a good approximation for the CMB-normalized case. Although, an Einasto form works well. Rather than being universal, the slope of the PPSD (or pseudo-entropy) profile steepens (flattens) with increasing (decreasing) power spectrum amplitude and can exhibit a strong halo mass dependence. Our results therefore indicate that the previously identified universality of the structure of DM haloes is mostly a consequence of adopting a narrow range of (CMB-normalized) initial conditions for the simulations. Our new suite provides a useful test-bench against which physical models for the origin of halo structure can be validated.