ABSTRACT
The degree of turbulent pressure support by residual gas motions in galaxy clusters is not well known. Mass modelling of combined X-ray and Sunyaev–Zel’dovich observations provides an ...estimate of turbulent pressure support in the outer regions of several galaxy clusters. Here, we test two different filtering techniques to disentangle bulk from turbulent motions in non-radiative high-resolution cosmological simulations of galaxy clusters using the cosmological hydrocode enzo. We find that the radial behaviour of the ratio of non-thermal pressure to total gas pressure as a function of cluster-centric distance can be described by a simple polynomial function. The typical non-thermal pressure support in the centre of clusters is ∼5 per cent, increasing to ∼15 per cent in the outskirts, in line with the pressure excess found in recent X-ray observations. While the complex dynamics of the intracluster medium makes it impossible to reconstruct a simple correlation between turbulent motions and hydrostatic bias, we find that a relation between them can be established using the median properties of a sample of objects. Moreover, we estimate the contribution of radial accelerations to the non-thermal pressure support and conclude that it decreases moving outwards from 40 per cent (in the core) to 15 per cent (in the cluster’s outskirts). Adding this contribution to one provided by turbulence, we show that it might account for the entire observed hydrostatic bias in the innermost regions of the clusters, and for less than 80 per cent of it at r > 0.8 r200,m.
Observations of galaxy clusters both in the radio and X-ray bands probe a direct link between cluster mergers and giant radio halos, suggesting that these sources can be used as probes of the cluster ...merging rate with cosmic time. While all giant radio halos are found in merging clusters, not every merging cluster hosts a giant radio halo. In this paper we carry out an explorative study that combines the observed fractions of merging clusters and radio halos with the merging rate predicted by cosmological simulations, and we attempt to infer constraints on merger properties of clusters that appear disturbed in X-rays and clusters that host radio halos. We used classical morphological parameters to identify merging systems and analysed the largest current (mass-selected M500 ≳ 6 × 1014M⊙ and 0.2 ≤ z ≤ 0.33) sample of galaxy clusters with radio and X-ray data; we extracted this sample from the Planck Sunyaev-Zeldovich cluster catalogue. We found that the fraction of merging clusters in this sample is fm ~ 62−67%, while that of clusters with radio halos is fRH ~ 44−51%. We assume that the morphological disturbance measured in the X-rays is driven by the merger with the largest mass ratio, ξ (ξ = Mi/M1< 1, where Mi and M1 are the progenitor masses), which is still ongoing in the cluster at the epoch of observation. Results from theoretical studies allow us to derive the fraction of mergers with mass ratio above a minimum threshold (those with \hbox{$\xi\gtsim\xi_{\rm min}$} ξ ξ min > ~ ) in our sample, under the assumption of a timescale τm for the duration of merger-induced disturbance. The comparison of the theoretical merger fraction with the observed merger fraction allows us to constrain a region in the (ξmin, τm) plane. We find that under the assumption of τm ~ 2−3 Gy, as constrained by simulations, the observed merger fraction matches the theoretical value for ξmin ~ 0.1−0.18. This is consistent with optical and near-infrared (IR) observations of galaxy clusters in the sample that constrain ξmin ≃ 0.14−0.16 through weak lensing analysis or study of the velocity distribution of galaxies in the clusters. The fact that radio halos are only found in a fraction of merging galaxy clusters may suggest that merger events generating radio halos are characterized by larger mass ratios; this seems to be supported by optical/near-IR observations of radio halo clusters in the sample that indeed allow us to constrain ξmin ~ 0.2−0.25. Alternatively, radio halos may be generated in all mergers but their lifetime is shorter (by ~fRH/fm) than the timescale of the merger-induced disturbance. We stress that this is an explorative study, however it suggests that follow-up studies using the forthcoming radio surveys and adequate numerical simulations have the potential to derive quantitative constraints on the link between cluster merging rate and radio halos at different cosmic epochs and for different cluster masses.
ABSTRACT We explore the possibility of measuring the mass accretion rate (MAR) of galaxy clusters from their mass profiles beyond the virial radius R200. We derive the accretion rate from the mass of ...a spherical shell whose inner radius is 2R200, whose thickness changes with redshift, and whose infall velocity is assumed to be equal to the mean infall velocity of the spherical shells of dark matter halos extracted from N-body simulations. This approximation is rather crude in hierarchical clustering scenarios where both smooth accretion and aggregation of smaller dark matter halos contribute to the mass accretion of clusters. Nevertheless, in the redshift range z = 0, 2, our prescription returns an average MAR within 20%-40% of the average rate derived from the merger trees of dark matter halos extracted from N-body simulations. The MAR of galaxy clusters has been the topic of numerous detailed numerical and theoretical investigations, but so far it has remained inaccessible to measurements in the real universe. Since the measurement of the mass profile of clusters beyond their virial radius can be performed with the caustic technique applied to dense redshift surveys of the cluster outer regions, our result suggests that measuring the mean MAR of a sample of galaxy clusters is actually feasible. We thus provide a new potential observational test of the cosmological and structure formation models.
We present an improved determination of the total mass distribution of three massive clusters from the Cluster Lensing and Supernova Survey with Hubble and Hubble Frontier Fields, MACS J1206.2−0847 ...(z = 0.44), MACS J0416.1−2403 (z = 0.40), Abell S1063 (z = 0.35). We specifically reconstructed the sub-halo mass component with robust stellar kinematics information of cluster galaxies, in combination with precise strong lensing models based on large samples of spectroscopically identified multiple images. We used integral-field spectroscopy in the cluster cores, from the Multi Unit Spectroscopic Explorer on the Very Large Telescope, to measure the stellar velocity dispersion, σ, of 40−60 member galaxies per cluster, covering four to five magnitudes to mF160W ≃ 21.5. We verified the robustness and quantified the accuracy of the velocity dispersion measurements with extensive spectral simulations. With these data, we determined the normalization and slope of the galaxy L–σ Faber–Jackson relation in each cluster and used these parameters as a prior for the scaling relations of the sub-halo population in the mass distribution modeling. When compared to our previous lens models, the inclusion of member galaxies’ kinematics provides a similar precision in reproducing the positions of the multiple images. However, the inherent degeneracy between the central effective velocity dispersion, σ0, and truncation radius, rcut, of sub-halos is strongly reduced, thus significantly alleviating possible systematics in the measurements of sub-halo masses. The three independent determinations of the σ0 − rcut scaling relation in each cluster are found to be fully consistent, enabling a statistical determination of sub-halo sizes as a function of σ0, or halo masses. Finally, we derived the galaxy central velocity dispersion functions of the three clusters projected within 16% of their virial radius, finding that they are well in agreement with each other. We argue that such a methodology, when applied to high-quality kinematics and strong lensing data, allows the sub-halo mass functions to be determined and compared with those obtained from cosmological simulations.
We study the characteristics of the galaxy cluster samples expected from the European Space Agency's Euclid satellite and forecast constraints on parameters describing a variety of cosmological ...models. In this paper we use the same method of analysis already adopted in the Euclid
Red
Book, which is based on the Fisher matrix approach. Based on our analytical estimate of the cluster selection function in the photometric Euclid survey, we forecast the constraints on cosmological parameters corresponding to different extensions of the standard Λ cold dark matter model. Using only Euclid clusters, we find that the amplitude of the matter power spectrum will be constrained to Δσ8 = 0.0014 and the mass density parameter to ΔΩm = 0.0011. The dynamical evolution of dark energy will be constrained to Δw
0 = 0.03 and Δw
a
= 0.2 with free curvature Ω
k
, resulting in a (w
0, w
a
) figure of merit (FoM) of 291. In combination with Planck cosmic microwave background (CMB) constraints, the amplitude of primordial non-Gaussianity will be constrained to Δf
NL ≃ 6.6 for the local shape scenario. The growth factor parameter γ, which signals deviations from general relativity, will be constrained to Δγ = 0.02, and the neutrino density parameter to ΔΩν = 0.0013 (or Δ∑m
ν = 0.01). Including the Planck CMB covariance matrix improves dark energy constraints to Δw
0 = 0.02, Δw
a
= 0.07, and a FoM = 802. Knowledge of the observable–cluster mass scaling relation is crucial to reach these accuracies. Imaging and spectroscopic capabilities of Euclid will enable internal mass calibration from weak lensing and the dynamics of cluster galaxies, supported by external cluster surveys.
Abstract
Gravitational lensing by clusters of galaxies offers a powerful probe of their structure and mass distribution. Several research groups have developed techniques independently to achieve ...this goal. While these methods have all provided remarkably high-precision mass maps, particularly with exquisite imaging data from the Hubble Space Telescope (HST), the reconstructions themselves have never been directly compared. In this paper, we present for the first time a detailed comparison of methodologies for fidelity, accuracy and precision. For this collaborative exercise, the lens modelling community was provided simulated cluster images that mimic the depth and resolution of the ongoing HST Frontier Fields. The results of the submitted reconstructions with the un-blinded true mass profile of these two clusters are presented here. Parametric, free-form and hybrid techniques have been deployed by the participating groups and we detail the strengths and trade-offs in accuracy and systematics that arise for each methodology. We note in conclusion that several properties of the lensing clusters are recovered equally well by most of the lensing techniques compared in this study. For example, the reconstruction of azimuthally averaged density and mass profiles by both parametric and free-form methods matches the input models at the level of ∼10 per cent. Parametric techniques are generally better at recovering the 2D maps of the convergence and of the magnification. For the best-performing algorithms, the accuracy in the magnification estimate is ∼10 per cent at μtrue = 3 and it degrades to ∼30 per cent at μtrue ∼ 10.
Aims.
We present a cosmological analysis of abundances and stacked weak lensing profiles of galaxy clusters, exploiting the AMICO KiDS-DR3 catalogue. The sample consists of 3652 galaxy clusters with ...intrinsic richness
λ
*
≥ 20, over an effective area of 377 deg
2
, in the redshift range
z
∈ 0.1, 0.6.
Methods.
We quantified the purity and completeness of the sample through simulations. The statistical analysis has been performed by simultaneously modelling the co-moving number density of galaxy clusters and the scaling relation between the intrinsic richnesses and the cluster masses, assessed through stacked weak lensing profile modelling. The fluctuations of the matter background density, caused by super-survey modes, have been taken into account in the likelihood. Assuming a flat Λ cold dark matter (ΛCDM) model, we constrained Ω
m
,
σ
8
,
S
8
≡
σ
8
(Ω
m
/0.3)
0.5
, and the parameters of the mass-richness scaling relation.
Results.
We obtained Ω
m
= 0.24
−0.04
+0.03
,
σ
8
= 0.86
−0.07
+0.07
, and
S
8
= 0.78
−0.04
+0.04
. The constraint on
S
8
is consistent within 1
σ
with the results from WMAP and Planck. Furthermore, we got constraints on the cluster mass scaling relation in agreement with those obtained from a previous weak lensing only analysis.
We propose a new approach to the problem of the missing baryons. Building on the common assumption that the missing baryons are in the form of the warm hot intergalactic medium (WHIM), we also assume ...here that the galaxy luminosity density can be used as a tracer of the WHIM. This last assumption is supported by our discovery of a significant correlation between the WHIM density and the galaxy luminosity density in recent hydrodynamical simulations. We also found that the percentage of the gas mass in the WHIM phase is substantially higher (by a factor of ~1.6) within large-scale galactic filaments, i.e. ~70%, compared to the average in the full simulation volume of ~0.1 Gpc3. The relation between the WHIM overdensity and the galaxy luminosity overdensity within the galactic filaments is consistent with a linear one: δwhim = 0.7 ± 0.1 × δLD0.9±0.2. We then applied our procedure to the line of sight towards the blazar H2356-309 and found evidence of WHIM that corresponds to the Sculptor Wall (SW) (z ~ 0.03 and log NH = 19.9+ 0.1-0.3) and Pisces-Cetus (PC) superclusters (z ~ 0.06 and log NH = 19.7+ 0.2-0.3), in agreement with the redshifts and column densities of the X-ray absorbers identified recently. This agreement indicates that the galaxy luminosity density and galactic filaments are reliable signposts for the WHIM and that our method is robust for estimating WHIM density. The signal that we detected cannot originate in the halos of nearby galaxies because they cannot account for the high WHIM column densities that our method and X-ray analysis consistently find in the SW and PC superclusters.
ABSTRACT
Galaxy clusters and cosmic voids, the most extreme objects in our Universe in terms of mass and size, trace two opposite sides of the large-scale matter density field. By studying their ...abundance as a function of their mass and radius, respectively, i.e. the halo mass function (HMF) and void size function (VSF), it is possible to achieve fundamental constraints on the cosmological model. While the HMF has already been extensively exploited, providing robust constraints on the main cosmological model parameters (e.g. Ωm, σ8, and S8), the VSF is still emerging as a viable and effective cosmological probe. Given the expected complementarity of these statistics, in this work, we aim at estimating the costraining power deriving from their combination. To this end, we exploit realistic mock samples of galaxy clusters and voids extracted from state-of-the-art large hydrodynamical simulations, in the redshift range 0.2 ≤ z ≤ 1. We perform an accurate calibration of the free parameters of the HMF and VSF models, needed to take into account the differences between the types of mass tracers used in this work and those considered in previous literature analyses. Then, we obtain constraints on Ωm and σ8 by performing a Bayesian analysis. We find that cluster and void counts represent powerful independent and complementary probes to test the cosmological framework. In particular, the constraining power of the HMF on Ωm and σ8 improves with the VSF contribution, increasing the S8 constraint precision by a factor of about 60 per cent.
Context.
In metric theories of gravity with photon number conservation, the luminosity and angular diameter distances are related via the Etherington relation, also known as the distance duality ...relation (DDR). A violation of this relation would rule out the standard cosmological paradigm and point to the presence of new physics.
Aims.
We quantify the ability of
Euclid
, in combination with contemporary surveys, to improve the current constraints on deviations from the DDR in the redshift range 0 <
z
< 1.6.
Methods.
We start with an analysis of the latest available data, improving previously reported constraints by a factor of 2.5. We then present a detailed analysis of simulated
Euclid
and external data products, using both standard parametric methods (relying on phenomenological descriptions of possible DDR violations) and a machine learning reconstruction using genetic algorithms.
Results.
We find that for parametric methods
Euclid
can (in combination with external probes) improve current constraints by approximately a factor of six, while for non-parametric methods
Euclid
can improve current constraints by a factor of three.
Conclusions.
Our results highlight the importance of surveys like
Euclid
in accurately testing the pillars of the current cosmological paradigm and constraining physics beyond the standard cosmological model.
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