Galaxy cluster cosmology from X-ray surveys of the hot and energetic Universe (original) (raw)
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X-ray clusters of galaxies as tracers of structure in the Universe
Nature, 2001
Clusters of galaxies are visible tracers of the network of matter in the Universe, marking the high-density regions where filaments of dark matter join together. When observed at X-ray wavelengths these clusters shine like cosmic lighthouses, as a consequence of the hot gas trapped within their gravitational potential wells. The X-ray emission is linked directly to the total mass of a cluster, and so can be used to investigate the mass distribution for a sizeable fraction of the Universe. The picture that has emerged from recent studies is remarkably consistent with the predictions for a low-density Universe dominated by cold dark matter.
Probing dark energy with the next generation X-ray surveys of galaxy clusters
Monthly Notices of the Royal Astronomical Society, 2012
We present forecasts on the capability of future wide-area high-sensitivity X-ray surveys of galaxy clusters to yield constraints on the parameters defining the dark energy (DE) equation of state. Our analysis is carried out for future X-ray surveys which have enough sensitivity to provide accurate measurements of X-ray mass proxies and Fe-line-based redshifts for about 2 × 10 4 clusters. We base our analysis on the Fisher matrix formalism, by combining information on the cluster number counts and power spectrum, also including, for the first time in the analysis of the large-scale cluster distribution, the effect of linear redshift-space distortions. This study is performed with the main purpose of dissecting the cosmological information provided by geometrical and growth tests, which are both included in the analysis of number counts and clustering of galaxy clusters. We compare cosmological constraints obtained by assuming different levels of prior knowledge of the parameters which define the relation between cluster mass and X-ray observables. This comparison further demonstrates the fundamental importance of having a well calibrated observable-mass relation and, most importantly, its redshift evolution. Such a calibration can be achieved only by having at least ∼10 3 net photon counts for each cluster included in the survey, with sufficient angular resolution. We show that redshift-space distortions in the power spectrum analysis carry important cosmological information also when traced with galaxy clusters. We find that the DE figure of merit increases by a factor of 8 when including the effect of such distortions. Besides confirming the potential that large cluster surveys have in constraining the nature of DE, our analysis emphasizes that a full exploitation of the cosmological information carried by such surveys requires not only a large statistic but also a robust measurement of the mass proxies and redshift for a significant fraction of the cluster sample, which ought to be derived from the same X-ray survey data. This will be possible with future X-ray surveys, such as those envisioned with the Wide Field X-ray Telescope, with an adequate combination of survey area, sensitivity and angular resolution.
An X-ray Galaxy Cluster Survey for Investigations of Dark Energy
2005
The amount and nature of dark energy (DE) can be tightly constrained by measuring the spatial correlation features and evolution of a sample of ∼ 100, 000 galaxy clusters over the redshift range 0 < z < ∼ 1.5. Such an X-ray survey will discover all collapsed structures with mass above 3.5 × 10 14 h −1 M ⊙ at redshifts z < 2 (i.e. the full range where such objects are expected) in the high Galactic latitude sky. Above this mass threshold the tight correlations between X-ray observables and mass allow direct interpretation of the data.
Constraining the dark energy with galaxy cluster x-ray data
Physical Review D, 2003
The equation of state characterizing the dark energy component is constrained by combining Chandra observations of the X-ray luminosity of galaxy clusters with independent measurements of the baryonic matter density and the latest measurements of the Hubble parameter as given by the HST key project. By assuming a spatially flat scenario driven by a "quintessence" component with an equation of state px = ωρx we place the following limits on the cosmological parameters ω and Ωm: (i) −1 ≤ ω ≤ −0.55 and Ωm = 0.32 +0.027 −0.014 (1σ) if the equation of state of the dark energy is restricted to the interval −1 ≤ ω < 0 (usual quintessence) and (ii) ω = −1.29 +0.686 −0.792 and Ωm = 0.31 +0.037 −0.034 (1σ) if ω violates the null energy condition and assume values < −1 (extended quintessence or "phantom" energy). These results are in good agreement with independent studies based on supernovae observations, large-scale structure and the anisotropies of the cosmic background radiation.
Unveiling the Galaxy Cluster - Cosmic Web Connection with X-ray Observations in the Next Decade
BAAS 51, 2019
In recent years, the outskirts of galaxy clusters have emerged as one of the new frontiers and unique laboratories for studying the growth of large scale structure in the universe. Modern cosmological hydrodynamical simulations make firm and testable predictions of the thermody-namic and chemical evolution of the X-ray emitting intracluster medium. However, recent X-ray and Sunyaev-Zeldovich effect observations have revealed enigmatic disagreements with theoretical predictions, which have motivated deeper investigations of a plethora of astrophysical processes operating in the virialization region in the cluster outskirts. Much of the physics of cluster out-skirts is fundamentally different from that of cluster cores, which has been the main focus of X-ray cluster science over the past several decades. A next-generation X-ray telescope, equipped with sub-arcsecond spatial resolution over a large field of view along with a low and stable instrumental background, is required in order to reveal the full story of the growth of galaxy clusters and the cosmic web and their applications for cosmology.
X-ray Clusters of Galaxies as Cosmological Tools
Arxiv preprint arXiv:0908.2955, 2009
This paper was written as part of a book entitled: "Questions of Modern Cosmology -Galileo's Legacy" which is a celebrative book dedicated to Galileo Galilei. The book is published in 2009, the International Year of Astronomy, since it is intended to be a modern tribute to the astronomer who, 400 years ago, first pointed a telescope towards the night sky. The book is written in the form of interviews between the editors and many physicists, astrophysicists and cosmologists from all over the world. The editors engaged in several discussions on the formation and evolution of the Universe with the aim of summarizing the most important and significative advances made by cosmology over the past century and at the beginning of the new millennium. This paper deals with X-ray clusters of galaxies and how they can be used to constrain fundamental cosmological parameters.
Monthly Notices of the Royal Astronomical Society, 2001
We use a theoretical model to predict the clustering properties of galaxy clusters. Our technique accounts for past light-cone effects on the observed clustering and follows the non-linear evolution in redshift of the underlying dark matter correlation function and cluster bias factor. A linear treatment of redshiftspace distortions is also included. We perform a maximum-likelihood analysis by comparing the theoretical predictions to a set of observational data, both in the optical (two different subsamples of the APM catalogue and the EDCC catalogue) and X-ray band (RASS1 Bright Sample, BCS, XBACs, REFLEX). In the framework of cold dark matter models, we compute the constraints on cosmological parameters, such as the matter density Ω 0m , the cosmological constant Ω 0Λ , the power-spectrum shape parameter Γ and normalisation σ 8 . Our results show that X-ray data are more powerful than optical ones, allowing smaller regions in the parameter space. If we fix Γ and σ 8 to the values suggested by different observational datasets, we obtain strong constraints on the matter density parameter: Ω 0m ≤ 0.5 and 0.2 ≤ Ω 0m ≤ 0.35, for the optical and X-ray data, respectively. Allowing the shape parameter to vary, we find that the clustering properties of clusters are almost independent of the matter density parameter and of the presence of a cosmological constant, while they appear to be strongly dependent on the shape parameter. Using the Xray data only, we obtain Γ ∼ 0.1 and 0.4 ∼ < σ 8∼ < 1.1 for the Einstein-de Sitter model, while 0.14 ∼ < Γ ∼ < 0.22 and 0.6 ∼ < σ 8∼ < 1.3 for open and flat models with Ω 0m = 0.3. Finally, we use our model to make predictions on the correlation length of galaxy clusters expected in future surveys. In particular, we show the results for an optical catalogue with characteristics similar to the EIS project and for a very deep X-ray catalogue with the characteristics of the XMM/LSS survey. We find that clusters at high redshifts are expected to have larger a correlation length than local ones.
New constraints on dark energy from the observed growth of the most X-ray luminous galaxy clusters
Monthly Notices of the Royal Astronomical Society, 2008
We present constraints on the mean matter density, Ω m , the normalization of the density fluctuation power spectrum, σ 8 , and the dark-energy equation-of-state parameter, w, obtained from measurements of the X-ray luminosity function of the largest known galaxy clusters at redshifts z < 0.7, as compiled in the Massive Cluster Survey (MACS) and the local BCS and REFLEX galaxy cluster samples. Our analysis employs an observed mass-luminosity relation, calibrated by hydrodynamical simulations, including corrections for non-thermal pressure support and accounting for the presence of intrinsic scatter. Conservative allowances for all known systematic uncertainties are included, as are standard priors on the Hubble constant and mean baryon density. We find Ω m = 0.28 +0.11 −0.07 and σ 8 = 0.78 +0.11 −0.13 for a spatially flat, cosmological-constant model, and Ω m = 0.24 +0.15 −0.07 , σ 8 = 0.85 +0.13 −0.20 and w = −1.4 +0.4 −0.7 for a flat, constant-w model (marginalized 68 per cent confidence intervals). Our findings constitute the first determination of the dark-energy equation of state from measurements of the growth of cosmic structure in galaxy clusters, and the consistency of our result with w = −1 lends additional support to the cosmological-constant model. Future work improving our understanding of redshift evolution and observational biases affecting the mass-X-ray luminosity relation have the potential to significantly tighten these constraints. Our results are consistent with those from recent analyses of type Ia supernovae, cosmic microwave background anisotropies, the X-ray gas mass fraction of relaxed galaxy clusters, baryon acoustic oscillations and cosmic shear. Combining the new Xray luminosity function data with current supernova, cosmic microwave background and cluster gas fraction data yields the improved constraints Ω m = 0.269 ± 0.016, σ 8 = 0.82 ± 0.03 and w = −1.02 ± 0.06.
The impact of galaxy formation on the X-ray evolution of clusters
Monthly Notices of the Royal Astronomical Society, 2001
We present a new model for the X-ray properties of the intracluster medium that explicitly includes heating of the gas by the energy released during the evolution of cluster galaxies. We calculate the evolution of clusters by combining the semi-analytic model of galaxy formation of Cole et al. with a simple model for the radial profile of the intracluster gas. We focus on the cluster X-ray luminosity function and on the relation between X-ray temperature and luminosity (the T-L relation). Observations of these properties are known to disagree with predictions based on scaling relations which neglect gas cooling and heating processes. We show that cooling alone is not enough to account for the flatness of the observed T-L relation or for the lack of strong redshift evolution in the observed X-ray luminosity function. Gas heating, on the other hand, can solve these two problems: in the ΛCDM cosmology, our model reproduces fairly well the T-L relation and the X-ray luminosity function. Furthermore, it predicts only weak evolution in these two properties out to z = 0.5, in agreement with recent observational data. A successful model requires an energy input of 1-2 ×10 49 ergs per solar mass of stars formed. This is comparable to the total energy released by the supernovae associated with the formation of the cluster galaxies. Thus, unless the transfer of supernovae energy to the intracluster gas is very (perhaps unrealistically) efficient, additional sources of energy, such as mechanical energy from AGN winds are required. However, the amplification of an initial energy input by the response of the intracluster medium to protocluster mergers might ease the energy requirements. Our model makes definite predictions for the X-ray properties of groups and clusters at high redshift. Some of these, such as the T-L relation at z ≃ 1, may soon be tested with data from the Chandra and Newton satellites.