ABSTRACT
Upcoming weak lensing surveys require a detailed theoretical understanding of the matter power spectrum in order to derive accurate and precise cosmological parameter values. While galaxy ...formation is known to play an important role, its precise effects are currently unknown. We present a set of 92 matter power spectra from the OWLS, cosmo-OWLS, and BAryons and HAloes of MAssive Systems simulation suites, including different ΛCDM cosmologies, neutrino masses, subgrid prescriptions, and AGN feedback strengths. We conduct a detailed investigation of the dependence of the relative difference between the total matter power spectra in hydrodynamical and collisionless simulations on the effectiveness of stellar and AGN feedback, cosmology, and redshift. The strength of AGN feedback can greatly affect the power on a range of scales, while a lack of stellar feedback can greatly increase the effectiveness of AGN feedback on large scales. We also examine differences in the initial conditions of hydrodynamic and N-body simulations that can lead to an $\sim 1{{\ \rm per\ cent}}$ discrepancy in the large-scale power, and furthermore show our results to be insensitive to cosmic variance. We present an empirical model capable of predicting the effect of galaxy formation on the matter power spectrum at z = 0 to within $1{{\ \rm per\ cent}}$ for $k\lt 1\, h\, \mathrm{Mpc}^{-1}$, given only the mean baryon fraction in galaxy groups. Differences in group baryon fractions can also explain the quantitative disagreement between predictions from the literature. All total and dark matter only power spectra in this library will be made publicly available at powerlib.strw.leidenuniv.nl.
The evolution of the large-scale distribution of matter is sensitive to a variety of fundamental parameters that characterize the dark matter, dark energy, and other aspects of our cosmological ...framework. Since the majority of the mass density is in the form of dark matter that cannot be directly observed, to do cosmology with large-scale structure, one must use observable (baryonic) quantities that trace the underlying matter distribution in a (hopefully) predictable way. However, recent numerical studies have demonstrated that the mapping between observable and total mass, as well as the total mass itself, are sensitive to unresolved feedback processes associated with galaxy formation, motivating explicit calibration of the feedback efficiencies. Here, we construct a new suite of large-volume cosmological hydrodynamical simulations (called bahamas, for BAryons and HAloes of MAssive Systems), where subgrid models of stellar and active galactic nucleus feedback have been calibrated to reproduce the present-day galaxy stellar mass function and the hot gas mass fractions of groups and clusters in order to ensure the effects of feedback on the overall matter distribution are broadly correct. We show that the calibrated simulations reproduce an unprecedentedly wide range of properties of massive systems, including the various observed mappings between galaxies, hot gas, total mass, and black holes, and represent a significant advance in our ability to mitigate the primary systematic uncertainty in most present large-scale structure tests.
ABSTRACT
Models of cold dark matter (CDM) predict that the distribution of dark matter in galaxy clusters should be cuspy, centrally concentrated. Constant density cores would be strong evidence for ...beyond CDM physics, such as self-interacting dark matter (SIDM). An observable consequence would be oscillations of the brightest cluster galaxy (BCG) in otherwise relaxed galaxy clusters. Offset BCGs have indeed been observed – but only interpreted via a simplified, analytic model of oscillations. We compare these observations to the BAryons and HAloes of MAssive Sysmtes (BAHAMAS)–SIDM suite of cosmological simulations, which include SIDM and a fully hydrodynamical treatment of star formation and feedback. We predict that the median offset of BCGs increases with the SIDM cross-section, cluster mass, and the amount of stellar mass within 10 kpc, while CDM exhibits no trend in mass. Interpolating between the simulated cross-sections, we find that the observations (of 10 clusters) are consistent with CDM at the ∼1.5σ level, and prefer cross-section σ/m < 0.12(0.39) cm2 g−1 at 68 per cent (95 per cent) confidence level. This is on the verge of ruling out velocity-independent dark matter self-interactions as the solution to discrepancies between the predicted and observed behaviour of dwarf galaxies, and will be improved by larger surveys by Euclid or Super-pressure Balloon-borne Imaging Telescope (SuperBIT).
Abstract
Recent studies have presented evidence for tension between the constraints on Ωm and σ8 from the cosmic microwave background (CMB) and measurements of large-scale structure (LSS). This ...tension can potentially be resolved by appealing to extensions of the standard model of cosmology and/or untreated systematic errors in the modelling of LSS, of which baryonic physics has been frequently suggested. We revisit this tension using, for the first time, carefully calibrated cosmological hydrodynamical simulations, which thus capture the backreaction of the baryons on the total matter distribution. We have extended the BAryons and HAloes of MAssive Sysmtes simulations to include a treatment of massive neutrinos, which currently represents the best-motivated extension to the standard model. We make synthetic thermal Sunyaev–Zel'dovich effect, weak galaxy lensing, and CMB lensing maps and compare to observed auto- and cross-power spectra from a wide range of recent observational surveys. We conclude that: (i) in general, there is tension between the primary CMB and LSS when adopting the standard model with minimal neutrino mass; (ii) after calibrating feedback processes to match the gas fractions of clusters, the remaining uncertainties in the baryonic physics modelling are insufficient to reconcile this tension; and (iii) if one accounts for internal tensions in the Planck CMB data set (by allowing the lensing amplitude, ALens, to vary), invoking a non-minimal neutrino mass, typically of 0.2–0.4 eV, can resolve the tension. This solution is fully consistent with separate constraints from the primary CMB and baryon acoustic oscillations.
ABSTRACT
We introduce the Assembly of high-ResoluTion Eagle-simulations of MIlky Way-type galaxieS (artemis) simulations, a new set of 42 zoomed-in, high-resolution (baryon particle mass of $\approx ...2\times 10^4 \, {\rm M}_{\odot }\, h^{-1}$), hydrodynamical simulations of galaxies residing in haloes of Milky Way mass, simulated with the eagle galaxy formation code with re-calibrated stellar feedback. In this study, we analyse the structure of stellar haloes, specifically the mass density, surface brightness, metallicity, colour, and age radial profiles, finding generally very good agreement with recent observations of local galaxies. The stellar density profiles are well fitted by broken power laws, with inner slopes of ≈−3, outer slopes of ≈−4, and break radii that are typically ≈20–40 kpc. The break radii generally mark the transition between in situ formation and accretion-driven formation of the halo. The metallicity, colour, and age profiles show mild large-scale gradients, particularly when spherically averaged or viewed along the major axes. Along the minor axes, however, the profiles are nearly flat, in agreement with observations. Overall, the structural properties can be understood by two factors: that in situ stars dominate the inner regions and that they reside in a spatially flattened distribution that is aligned with the disc. Observations targeting both the major and minor axes of galaxies are thus required to obtain a complete picture of stellar haloes.
Abstract
We use the cosmo-OWLS and bahamas suites of cosmological hydrodynamical simulations to explore the separate and combined effects of baryon physics (particularly feedback from active galactic ...nuclei, AGN) and free streaming of massive neutrinos on large-scale structure. We focus on five diagnostics: (i) the halo mass function, (ii) halo mass density profiles, (iii) the halo mass–concentration relation, (iv) the clustering of haloes and (v) the clustering of matter, and we explore the extent to which the effects of baryon physics and neutrino free streaming can be treated independently. Consistent with previous studies, we find that both AGN feedback and neutrino free streaming suppress the total matter power spectrum, although their scale and redshift dependences differ significantly. The inclusion of AGN feedback can significantly reduce the masses of groups and clusters, and increase their scale radii. These effects lead to a decrease in the amplitude of the mass–concentration relation and an increase in the halo autocorrelation function at fixed mass. Neutrinos also lower the masses of groups and clusters while having no significant effect on the shape of their density profiles (thus also affecting the mass–concentration relation and halo clustering in a qualitatively similar way to feedback). We show that, with only a small number of exceptions, the combined effects of baryon physics and neutrino free streaming on all five diagnostics can be estimated to typically better than a few per cent accuracy by treating these processes independently (i.e. by multiplying their separate effects).
We present results from a subset of simulations from the ‘Evolution and Assembly of GaLaxies and their Environments’ (eagle) suite in which the formulation of the hydrodynamics scheme is varied. We ...compare simulations that use the same subgrid models without recalibration of the parameters but employing the standard gadget flavour of smoothed particle hydrodynamics (SPH) instead of the more recent state-of-the-art anarchy formulation of SPH that was used in the fiducial eagle runs. We find that the properties of most galaxies, including their masses and sizes, are not significantly affected by the details of the hydrodynamics solver. However, the star formation rates of the most massive objects are affected by the lack of phase mixing due to spurious surface tension in the simulation using standard SPH. This affects the efficiency with which AGN activity can quench star formation in these galaxies and it also leads to differences in the intragroup medium that affect the X-ray emission from these objects. The differences that can be attributed to the hydrodynamics solver are, however, likely to be less important at lower resolution. We also find that the use of a time-step limiter is important for achieving the feedback efficiency required to match observations of the low-mass end of the galaxy stellar mass function.
We present results from 13 cosmological simulations that explore the parameter space of the ‘Evolution and Assembly of GaLaxies and their Environments’ (EAGLE) simulation project. Four of the ...simulations follow the evolution of a periodic cube L = 50 cMpc on a side, and each employs a different subgrid model of the energetic feedback associated with star formation. The relevant parameters were adjusted so that the simulations each reproduce the observed galaxy
stellar mass function at z = 0.1. Three of the simulations fail to form disc galaxies as extended as observed, and we show analytically that this is a consequence of numerical radiative losses that reduce the efficiency of stellar feedback in high-density gas. Such losses are greatly reduced in the fourth simulation – the EAGLE reference model – by injecting more energy in higher density gas. This model produces galaxies with the observed size distribution, and also reproduces many galaxy scaling relations. In the remaining nine simulations, a single parameter or process of the reference model was varied at a time. We find that the properties of galaxies with stellar mass ≲ M
⋆ (the ‘knee’ of the galaxy stellar mass function) are largely governed by feedback associated with star formation, while those of more massive galaxies are also controlled by feedback from accretion on to their central black holes. Both processes must be efficient in order to reproduce the observed galaxy population. In general, simulations that have been calibrated to reproduce the low-redshift galaxy stellar mass function will still not form realistic galaxies, but the additional requirement that galaxy sizes be acceptable leads to agreement with a large range of observables.
We use the BAHAMAS (BAryons and HAloes of MAssive Systems) and MACSIS (MAssive ClusterS and Intercluster Structures) hydrodynamic simulations to quantify the impact of baryons on the mass ...distribution and dynamics of massive galaxy clusters, as well as the bias in X-ray and weak lensing mass estimates. These simulations use the subgrid physics models calibrated in the BAHAMAS project, which include feedback from both supernovae and active galactic nuclei. They form a cluster population covering almost two orders of magnitude in mass, with more than 3500 clusters with masses greater than 10 super( 14) M... at z = 0. We start by characterizing the clusters in terms of their spin, shape and density profile, before considering the bias in both weak lensing and hydrostatic mass estimates. Whilst including baryonic effects leads to more spherical, centrally concentrated clusters, the median weak lensing mass bias is unaffected by the presence of baryons. In both the dark matter only and hydrodynamic simulations, the weak lensing measurements underestimate cluster masses by ...10 per cent for clusters with M200 = 10 super( 15) M... and this bias tends to zero at higher masses. We also consider the hydrostatic bias when using both the true density and temperature profiles, and those derived from X-ray spectroscopy. When using spectroscopic temperatures and densities, the hydrostatic bias decreases as a function of mass, leading to a bias of ...40 per cent for clusters with M500 greater than or equal to 10 super( 15) M... This is due to the presence of cooler gas in the cluster outskirts. Using mass weighted temperatures and the true density profile reduces this bias to 5-15 per cent. (ProQuest: ... denotes formulae/symbols omitted.)
ABSTRACT
We present bahamas-SIDM, the first large-volume, $(400 \, h^{-1} \mathrm{\, Mpc})^{3}$, cosmological simulations including both self-interacting dark matter (SIDM) and baryonic physics. ...These simulations are important for two primary reasons: (1) they include the effects of baryons on the dark matter distribution and (2) the baryon particles can be used to make mock observables that can be compared directly with observations. As is well known, SIDM haloes are systematically less dense in their centres, and rounder, than CDM haloes. Here, we find that that these changes are not reflected in the distribution of gas or stars within galaxy clusters, or in their X-ray luminosities. However, gravitational lensing observables can discriminate between DM models, and we present a menu of tests that future surveys could use to measure the SIDM interaction strength. We ray-trace our simulated galaxy clusters to produce strong lensing maps. Including baryons boosts the lensing strength of clusters that produce no critical curves in SIDM-only simulations. Comparing the Einstein radii of our simulated clusters with those observed in the CLASH survey, we find that at velocities around $1000 \mathrm{\, km \, s^{-1}}$ an SIDM cross-section of $\sigma /m \gtrsim 1 \, \mathrm{cm^2 \, g^{-1}}$ is likely incompatible with observed cluster lensing.
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