We calculate X-ray properties of present-day galaxy clusters from hydrodynamical cosmological simulations of the LCDM cosmology and compare these with recent X-ray observations. Results from three ...simulations are presented, each of which uses the same initial conditions: a standard adiabatic, Non-radiative model, a Radiative model that includes radiative cooling of the gas, and 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 per cent and 0.4 per cent respectively which bracket the recent result from the K-band luminosity function. We construct cluster catalogues which consist of over 500 clusters and are complete in mass down to 1.18*10^{13} Msun/h. While clusters in the Non-radiative model behave in accord with the self-similar picture, those of the other two models reproduce key aspects of the observed X-ray properties: 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 intra-cluster medium is very different in the two models, the resulting cluster entropy profiles are very similar.
On Arcs and Omega Bartelmann, Matthias; Huss, Andreas; Colberg, Joerg M ...
09/1997
Journal Article
Odprti dostop
The gravitational lens effect of galaxy clusters can produce large arcs from
source galaxies in their background. Typical source redshifts of ~ 1 require
clusters at z ~ 0.3 for arcs to form ...efficiently. Given the cluster abundance
at the present epoch, the fewer clusters exist at z ~ 0.3 the higher Omega_0
is, because the formation epoch of galaxy clusters strongly depends on Omega_0.
In addition, at fixed Omega_0, clusters are less concentrated, and hence less
efficient lenses, when the cosmological constant is positive, Omega_Lambda > 0.
Numerical cluster simulations show that the expected number of arcs on the sky
is indeed a sensitive function of Omega_0 and Omega_Lambda. The numerical
results are compatible with the statistics of observed arcs only in a universe
with low matter density, Omega_0 ~ 0.3, and zero cosmological constant. Other
models fail by one or two orders of magnitude, rendering arc statistics a
sensitive probe for cosmological parameters.
We investigate phenomenological models of star formation and supernova feedback in N-body/SPH simulations of galaxy formation. First, we compare different prescriptions in the literature for turning ...cold gas into stars neglecting feedback effects. We find that most prescriptions give broadly similar results: the ratio of cold gas to stars in the final galaxies is primarily controlled by the range of gas densities where star formation is allowed to proceed efficiently. In the absence of feedback, the fraction of gas that cools is much too high resulting, for example, in a K-band luminosity function that is much brighter than observed. This problem is ameliorated by including a feedback model which either imparts radial kinetic perturbations to galactic gas or directly reheats such material and prevents it from cooling for a certain period of time. In both these models, a significant fraction of cold gas is heated and expelled from haloes with an efficiency that varies inversely with with halo circular velocity. Increasing the resolution of a simulation allows a wider dynamic range in mass to be followed, but the average properties of the resolved galaxy population remain largely unaffected. However, as the resolution is increased, more and more gas is reheated by small galaxies; our results suggest that convergence requires the full mass range of galaxies to be resolved.
Astron.Astrophys. 330 (1998) 1-9 We use numerical simulations of galaxy clusters in different cosmologies to
study their ability to form large arcs. The cosmological models are: Standard
CDM (SCDM; ...Omega_0=1, Omega_Lambda=0); tauCDM with reduced small-scale power
(parameters as SCDM, but with a smaller shape parameter of the power spectrum);
open CDM (OCDM; Omega_0=0.3, Omega_Lambda=0); and spatially flat, low-density
CDM (LambdaCDM; Omega_0=0.3, Omega_Lambda=0.7). All models are normalised to
the local number density of rich clusters. Simulating gravitational lensing by
these clusters, we compute optical depths for the formation of large arcs. For
large arcs with length-to-width ratio >= 10, the optical depth is largest for
OCDM. Relative to OCDM, the optical depth is lower by about an order of
magnitude for LambdaCDM, and by about two orders of magnitude for S/tauCDM.
These differences originate from the different epochs of cluster formation
across the cosmological models, and from the non-linearity of the strong
lensing effect. We conclude that only the OCDM model can reproduce the observed
arc abundance well, while the other models fail to do so by orders of
magnitude.
We compare the results of two techniques used to calculate the evolution of cooling gas during galaxy formation: Smooth Particle Hydrodynamics (SPH) simulations and semi-analytic modelling. We ...improve upon the earlier statistical comparison of Benson et al. by taking halo merger histories from the dark matter component of the SPH simulation, which allows us to compare the evolution of galaxies on an object-by-object basis in the two treatments. We use a ``stripped-down'' version of the semi-analytic model described by Helly et al. which includes only shock heating and radiative cooling of gas and which is adjusted to mimic the resolution and other parameters of a comparison SPH simulation as closely as possible. We compare the total mass of gas that cools in halos of different mass as a function of redshift as well as the masses and spatial distribution of individual ``galaxies.'' At redshift z=0, the cooled gas mass in well-resolved halos agrees remarkably well (to better than ~20%) in the SPH simulation and stripped-down semi-analytic model. At high redshift, resolution effects in the simulation become increasingly important and, as a result, more gas tends to cool in low mass halos in the SPH simulation than in the semi-analytic model. The cold gas mass function of individual galaxies in the two treatments at z=0 also agrees very well and, when the effects of mergers are accounted for, the masses of individual galaxies and their 2-point correlation functions are also in excellent agreement in the two treatments. Thus, our comparison confirms and extends the earlier conclusion of Benson et al. that SPH simulations and semi-analytic models give consistent results for the evolution of cooling galactic gas.
We use hydrodynamical simulations to assess the impact of radiative cooling and `pre-heating' on predictions for the Sunyaev--Zel'dovich (SZ) effect. Cooling significantly reduces both the mean SZ ...signal and its angular power spectrum, while pre-heating can give a higher mean distortion while leaving the angular power spectrum below that found in a simulation without heating or cooling. We study the relative contribution from high and low density gas, and find that in the cooling model about 60 per cent of the mean thermal distortion arises from low overdensity gas. We find that haloes dominate the thermal SZ power spectrum in all models, while in the cooling simulation the kinetic SZ power spectrum originates predominantly in lower overdensity gas.
On Arcs and Omega Bartelmann, Matthias; Huss, Andreas; Colberg, Joerg M ...
arXiv.org,
09/1997
Paper
Odprti dostop
The gravitational lens effect of galaxy clusters can produce large arcs from source galaxies in their background. Typical source redshifts of ~ 1 require clusters at z ~ 0.3 for arcs to form ...efficiently. Given the cluster abundance at the present epoch, the fewer clusters exist at z ~ 0.3 the higher Omega_0 is, because the formation epoch of galaxy clusters strongly depends on Omega_0. In addition, at fixed Omega_0, clusters are less concentrated, and hence less efficient lenses, when the cosmological constant is positive, Omega_Lambda > 0. Numerical cluster simulations show that the expected number of arcs on the sky is indeed a sensitive function of Omega_0 and Omega_Lambda. The numerical results are compatible with the statistics of observed arcs only in a universe with low matter density, Omega_0 ~ 0.3, and zero cosmological constant. Other models fail by one or two orders of magnitude, rendering arc statistics a sensitive probe for cosmological parameters.
We use numerical simulations of galaxy clusters in different cosmologies to study their ability to form large arcs. The cosmological models are: Standard CDM (SCDM; Omega_0=1, Omega_Lambda=0); tauCDM ...with reduced small-scale power (parameters as SCDM, but with a smaller shape parameter of the power spectrum); open CDM (OCDM; Omega_0=0.3, Omega_Lambda=0); and spatially flat, low-density CDM (LambdaCDM; Omega_0=0.3, Omega_Lambda=0.7). All models are normalised to the local number density of rich clusters. Simulating gravitational lensing by these clusters, we compute optical depths for the formation of large arcs. For large arcs with length-to-width ratio >= 10, the optical depth is largest for OCDM. Relative to OCDM, the optical depth is lower by about an order of magnitude for LambdaCDM, and by about two orders of magnitude for S/tauCDM. These differences originate from the different epochs of cluster formation across the cosmological models, and from the non-linearity of the strong lensing effect. We conclude that only the OCDM model can reproduce the observed arc abundance well, while the other models fail to do so by orders of magnitude.
The star formation history (SFH) of galaxies is critical for understanding galaxy evolution. Hydrodynamical simulations enable us to precisely reconstruct the SFH of galaxies and establish a link to ...the underlying physical processes. In this work, we present a model to describe individual galaxies' SFHs from three simulations: TheThreeHundred, Illustris-1 and TNG100-1. This model divides the galaxy SFH into two distinct components: the "main sequence" and the "variation". The "main sequence" part is generated by tracing the history of the \(SFR-M_*\) main sequence of galaxies across time. The "variation" part consists of the scatter around the main sequence, which is reproduced by fractional Brownian motions. We find that: 1) The evolution of the main sequence varies between simulations; 2) fractional Brownian motions can reproduce many features of SFHs, however, discrepancies still exist; 3) The variations and mass-loss rate are crucial for reconstructing the SFHs of the simulations. This model provides a fair description of the SFHs in simulations. On the other hand, by correlating the fractional Brownian motion model to simulation data, we provide a 'standard' against which to compare simulations.
We introduce the THE THREE HUNDRED project, an endeavour to model 324 large galaxy clusters with full-physics hydrodynamical re-simulations. Here we present the data set and study the differences to ...observations for fundamental galaxy cluster properties and scaling relations. We find that the modelled galaxy clusters are generally in reasonable agreement with observations with respect to baryonic fractions and gas scaling relations at redshift z = 0. However, there are still some (model-dependent) differences, such as central galaxies being too massive, and galaxy colours (g - r) being bluer (about 0.2 dex lower at the peak position) than in observations. The agreement in gas scaling relations down to 10^{13} h^{-1} M_{\odot} between the simulations indicates that particulars of the sub-grid modelling of the baryonic physics only has a weak influence on these relations. We also include - where appropriate - a comparison to three semi-analytical galaxy formation models as applied to the same underlying dark-matter-only simulation. All simulations and derived data products are publicly available.
