We analyse environmental correlations using mark clustering statistics with the mock galaxy catalogue constructed by Muldrew et al. (Paper I). We find that mark correlation functions are able to ...detect even a small dependence of galaxy properties on the environment, quantified by the overdensity 1 + δ, while such a small dependence would be difficult to detect by traditional methods. We then show that rank ordering the marks and using the rank as a weight is a simple way of comparing the correlation signals for different marks. With this we quantify to what extent fixed-aperture overdensities are sensitive to large-scale halo environments, nearest-neighbour overdensities are sensitive to small-scale environments within haloes and colour is a better tracer of overdensity than luminosity.
We present a study of a comparison of spin distributions of subhaloes found associated with a host halo. The subhaloes are found within two cosmological simulation families of Milky Way-like ...galaxies, namely the Aquarius and GHALO simulations. These two simulations use different gravity codes and cosmologies. We employ 10 different substructure finders, which span a wide range of methodologies from simple overdensity in configuration space to full 6D phase space analysis of particles. We subject the results to a common post-processing pipeline to analyse the results in a consistent manner, recovering the dimensionless spin parameter. We find that spin distribution is an excellent indicator of how well the removal of background particles (unbinding) has been carried out. We also find that the spin distribution decreases for substructures the nearer they are to the host haloes, and that the value of the spin parameter rises with enclosed mass towards the edge of the substructure. Finally, subhaloes are less rotationally supported than field haloes, with the peak of the spin distribution having a lower spin parameter.
Revisiting the cosmic cooling crisis Balogh, Michael L.; Pearce, Frazer R.; Bower, Richard G. ...
Monthly notices of the Royal Astronomical Society,
10/2001, Letnik:
326, Številka:
4
Journal Article
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Recent measurements of the K-band luminosity function now provide us with strong, reliable constraints on the fraction of baryons which have cooled. Globally, this fraction is only about 5 per cent, ...and there is no strong evidence that it is significantly higher in clusters. Without an effective subgrid feedback prescription, the cooled gas fraction in any numerical simulation exceeds these observational constraints, and increases with increasing resolution. This compromises any discussion of galaxy and cluster properties based on results of simulations which include cooling but do not implement an effective feedback mechanism.
We study the shapes of subhalo distributions from four dark-matter-only simulations of Milky Way-type haloes. Comparing the shapes derived from the subhalo distributions at high resolution to those ...of the underlying dark matter fields, we find the former to be more triaxial if the analysis is restricted to massive subhaloes. For three of the four analysed haloes, the increased triaxiality of the distributions of massive subhaloes can be explained by a systematic effect caused by the low number of objects. Subhaloes of the fourth halo show indications for anisotropic accretion via their strong triaxial distribution and orbit alignment with respect to the dark matter field. These results are independent of the employed subhalo finder. Comparing the shape of the observed Milky Way satellite distribution to those of high-resolution subhalo samples from simulations, we find agreement for samples of bright satellites, but significant deviations if faint satellites are included in the analysis. These deviations might result from observational incompleteness.
We present a study of the substructure finder dependence of subhalo clustering in the Aquarius Simulation. We run 11 different subhalo finders on the haloes of the Aquarius Simulation and study their ...differences in the density profile, mass fraction and two-point correlation function of subhaloes in haloes. We also study the mass and v
max dependence of subhalo clustering. As the Aquarius Simulation has been run at different resolutions, we study the convergence with higher resolutions. We find that the agreement between finders is at around the 10 per cent level inside R
200 and at intermediate resolutions when a mass threshold is applied, and better than 5 per cent when v
max is restricted instead of mass. However, some discrepancies appear in the highest resolution, underlined by an observed resolution dependence of subhalo clustering. This dependence is stronger for the smallest subhaloes, which are more clustered in the highest resolution, due to the detection of subhaloes within subhaloes (the sub-subhalo term). This effect modifies the mass dependence of clustering in the highest resolutions. We discuss implications of our results for models of subhalo clustering and their relation with galaxy clustering.
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 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.
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.
ABSTRACT We compare the l-galaxies semi-analytic model to deep observational data from the UKIDSS Ultra Deep Survey (UDS) across the redshift range 0.5 < z < 3. We find that the overabundance of ...low-mass, passive galaxies at high redshifts in the model can be attributed solely to the properties of ‘orphan’ galaxies, i.e. satellite galaxies where the simulation has lost track of the host dark matter sub-halo. We implement a simple model that boosts the star formation rates in orphan galaxies by matching them to non-orphaned satellite galaxies at a similar evolutionary stage. This straightforward change largely addresses the discrepancy in the low-mass passive fraction across all redshifts. We find that the orphan problem is somewhat alleviated by higher resolution simulations, but the preservation of a larger gas reservoir in orphans is still required to produce a better fit to the observed space density of low-mass passive galaxies. Our findings are also robust to the precise definition of the passive galaxy population. In general, considering the vastly different prescriptions used for orphans in semi-analytic models, we recommend that they are analysed separately from the resolved satellite galaxy population, particularly with JWST observations reigniting interest in the low-mass regime in which they dominate.
We present deep, large-area B and r′ imaging for a sample of 49 brightest cluster galaxies (BCGs). The clusters were selected by their X-ray luminosity and redshift to form two volume-limited ...samples, one with 〈z〉∼ 0.07 and the other at 〈z〉∼ 0.17. For each cluster, the data cover 41 × 41 arcmin2. We discuss our data-reduction techniques in detail, and show that we can reliably measure the surface brightness at the levels of μ
B
∼ 29 and μ
r′∼ 28. For each galaxy, we present the B and r′ images together with the surface brightness profile, B−r′ colour, eccentricity and position angle as a function of radius.
We investigate the distribution of positional offsets between the optical centroid of the BCG and the centre of the X-ray emission, and conclude that the mass profiles are cuspy, and do not have extended cores. We also introduce a method to objectively identify the transition from BCG to extended envelope of intracluster light, using the Petrosian index as a function of radius.
We investigate the internal structure of clusters of galaxies in high-resolution N-body simulations of four different cosmologies. There is a higher proportion of disordered clusters in ...critical-density than in low-density universes, although the structure of relaxed clusters is very similar in each case. Crude measures of substructure, such as the shift in the position of the centre-of-mass as the density threshold is varied, can distinguish the two in a sample of just 20 or so clusters; it is harder to differentiate between clusters in open and flat models with the same density parameter. Most clusters are in a quasi-steady state within the virial radius and are well-described by the density profile of Navarro, Frenk & White.
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