We use the EAGLE (Evolution and Assembly GaLaxies and their Environments) simulations, with the 50 co-moving Mpc a side box, with and without the effect of active galactic nuclei (AGN) to study dark ...matter distribution and stellar density in central galaxies. The simulations allow us to study cosmological structures at various redshifts which are chosen at 0, 0.27 and 0.87. We study the brightest cluster galaxy (BCG) in the largest galaxy cluster at these redshifts. The dark matter profile of the galaxy in the simulation with AGN exhibits a flat core, while its counterpart in the simulation without AGN is cuspy at all redshifts. The stellar density in the galaxy resembles the corresponding dark matter profile at all radii. At outer radii, the stellar density profile in the simulation with AGN changes dramatically from high to low redshift. We conclude that the energetic process of AGN in the simulation can effect both the stellar and dark matter components in central galaxies. As the box size is relatively small and the result is based on only central galaxies of small clusters, the study does not cover a wide dynamic range. The baryonic feedback effect on dark matter needs to be further explored on larger scales for cosmologists to correctly constrain cosmological parameters.
Abstract
Feedback from active galactic nuclei (AGN) plays an important role on the formation and matter distribution in haloes. We investigate the effect of AGN feedback on shape of dark haloes ...formed in the EAGLE simulations, and trace the evolution. We select three mass ranges of haloes; low (10
11
− 10
11.5
M
⨀
), intermediate (10
12
− 10
12.5
M
⨀
) and high (10
13
− 10
14.5
M
⨀
) mass, the last range is of small cluster scale. We find the median profile of triaxiality in each mass range at three redshifts (0, 0.27 and 0.87) from two simulations, with and without AGN. The difference of triaxiality in both simulations of low mass haloes at all redshifts is relatively not apparent while the most apparent difference exhibits in high mass haloes. The shape of dark matter haloes in the simulation with AGN is more prolate than that in the simulation without AGN. We also use the ratio between blackhole and dark matter mass, relating to AGN energy output relative to halo potential depth to explain the result. Since the mass ratio between blackhole and dark matter mass in the high and intermediate mass is much larger and extends to the larger radii than that of low mass haloes, the difference is more prominent out to the outer region. We conclude that the shape of dark matter haloes of small cluster scale can be affected by AGN feedback through the evolution. However, this study focuses on an extreme AGN feedback model with a relatively small dynamical range.
Abstract
We calculate X-ray properties of present-day galaxy clusters from hydrodynamical cosmological simulations of the ΛCDM cosmology and compare these with recent X-ray observations. Results from ...three simulations are presented, each of which uses the same initial conditions: Non-radiative, a standard adiabatic, non-radiative model; Radiative, a radiative model that includes radiative cooling of the gas; and Preheating, a preheating model that also includes cooling but in addition impulsively heats the gas prior to cluster formation. At the end of the simulations, the global cooled baryon fractions in the latter two runs are 15 and 0.4 per cent, respectively, which bracket the recent result from the K-band luminosity function. We construct cluster catalogues that consist of over 500 clusters and are complete in mass down to 1.18 × 1013, h
−1 M⊙. While clusters in the Non-radiative simulation behave in accord with the self-similar picture, those of the other two simulations reproduce key aspects of the observed X-ray properties: namely, the core entropy, temperature-mass and luminosity-temperature relations are all in good agreement with recent observations. This agreement stems primarily from an increase in entropy with respect to the Non-radiative clusters. Although the physics affecting the intracluster medium is very different in the latter two models, the resulting cluster entropy profiles are very similar.
We investigate the redshift dependence of X-ray cluster scaling relations drawn from three hydrodynamic simulations of the CDM cosmology: a "Radiative" model that incorporates radiative cooling of ...the gas, a "Preheating" model that additionally heats the gas uniformly at high redshift, and a "Feedback" model that self-consistently heats cold gas in proportion to its local star formation rate. While all three models are capable of reproducing the observed local L sub(X)-T sub(X) relation, they predict substantially different results at high redshift (to z = 1.5), with the Radiative, Preheating, and Feedback models predicting strongly positive, mildly positive, and mildly negative evolution, respectively. The physical explanation for these differences lies in the structure of the intracluster medium. All three models predict significant temperature fluctuations at any given radius due to the presence of cool subclumps and, in the case of the Feedback simulation, reheated gas. The mean gas temperature lies above the dynamical temperature of the halo for all models at z = 0, but differs between models at higher redshift, with the Radiative model having the lowest mean gas temperature at z = 1.5. We have not attempted to model the scaling relations in a manner that mimics the observational selection effects, nor has a consistent observational picture yet emerged. Nevertheless, evolution of the scaling relations promises to be a powerful probe of the physics of entropy generation in clusters. First indications are that early, widespread heating is favored over an extended period of heating, as is associated with galaxy formation.
We have extracted over 400 clusters, covering more than two decades in mass, from three simulations of the τCDM cosmology. This represents the largest uniform catalogue of simulated clusters ever ...produced. The clusters exhibit a wide variety of density profiles. Only a minority are well-fitted in their outer regions by the widely used density profile of Navarro, Frenk & White (NFW), which is applicable to relaxed haloes. Others have steeper outer density profiles, show sharp breaks in their density profiles, or have significant substructure. If we force a fit to the NFW profile, then the best-fitting concentrations decline with increasing mass, but this is driven primarily by an increase in substructure as one moves to higher masses. The temperature—mass relations for properties measured within a sphere enclosing a fixed overdensity all follow the self-similar form, T∝M2/3; however, the normalization is lower than the value inferred for observed clusters. The temperature—mass relations for properties measured within a fixed physical radius are significantly steeper then this. Both can be accurately predicted using the NFW model.
The amplitude of density perturbations, for the currently-favoured ΛCDM cosmology, is constrained using the observed properties of galaxy clusters. The catalogue used is that of Ikebe et al. The ...relation of cluster temperature to mass is obtained via N-body/hydrodynamical simulations including radiative cooling and pre-heating of cluster gas, which we have previously shown to reproduce well the observed temperature–mass relation in the innermost parts of clusters. We generate and compare mock catalogues via a Monte Carlo method, which allows us to constrain the relation between X-ray temperature and luminosity, including its scatter, simultaneously with cosmological parameters. We find a luminosity–temperature relation in good agreement with the results of Ikebe et al., while for the matter power spectrum normalization, we find σ8= 0.78+0.30−0.06 at 95 per cent confidence for Ω0= 0.35. Scaling to the Wilkinson Microwave Anisotropy Probe central value of Ω0= 0.27 would give a best-fitting value of σ8≃ 0.9.
It has become increasingly apparent that traditional hydrodynamical simulations of galaxy clusters are unable to reproduce the observed properties of galaxy clusters, in particular overpredicting the ...mass corresponding to a given cluster temperature. Such overestimation may lead to systematic errors in results using galaxy clusters as cosmological probes, such as constraints on the density perturbation normalization σ8. In this paper we demonstrate that inclusion of additional gas physics, namely radiative cooling and a possible pre-heating of gas prior to cluster formation, is able to bring the temperature—mass relation in the innermost parts of clusters into good agreement with recent determinations by Allen, Schmidt & Fabian using Chandra data.
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