Scaling relations for galaxy clusters: properties and evolution

Well-calibrated scaling relations between the observable properties and the total masses of clusters of galaxies are important for understanding the physical processes that give rise to these relations. They are also a critical ingredient for studies that aim to constrain cosmological parameters using galaxy clusters. For this reason much effort has been spent during the last decade to better understand and interpret relations of the properties of the intra-cluster medium. Improved X-ray data have expanded the mass range down to galaxy groups, whereas SZ surveys have openened a new observational window on the intracluster medium. In addition,continued progress in the performance of cosmological simulations has allowed a better understanding of the physical processes and selection effects affecting the observed scaling relations. Here we review the recent literature on various scaling relations, focussing on the latest observational measurements and the progress in our understanding of the deviations from self similarity.Comment: 38 pages. Review paper. Accepted for publication in Space Science Reviews (eds: S. Ettori, M. Meneghetti). This is a product of the work done by an international team at the International Space Science Institute (ISSI) in Bern on "Astrophysics and Cosmology with Galaxy Clusters: the X-ray and Lensing View

The Sunyaev-Zel'dovich temperature of the intracluster medium

The relativistic Sunyaev-Zel'dovich (SZ) effect offers a method, independent of X-ray, for measuring the temperature of the intracluster medium (ICM) in the hottest systems. Here, using N-body/hydrodynamic simulations of three galaxy clusters, we compare the two quantities for a non-radiative ICM, and for one that is subject both to radiative cooling and strong energy feedback from galaxies. Our study has yielded two interesting results. Firstly, in all cases, the SZ temperature is hotter than the X-ray temperature and is within ten per cent of the virial temperature of the cluster. Secondly, the mean SZ temperature is less affected by cooling and feedback than the X-ray temperature. Both these results can be explained by the SZ temperature being less sensitive to the distribution of cool gas associated with cluster substructure. A comparison of the SZ and X-ray temperatures (measured for a sample of hot clusters) would therefore yield interesting constraints on the thermodynamic structure of the intracluster gas.Comment: This version accepted for publication in MNRAS following minor revisio

The XMM Cluster Outskirts Project (X-COP): Physical conditions to the virial radius of Abell 2142

Context. Galaxy clusters are continuously growing through the accretion of matter in their outskirts. This process induces inhomogeneities in the gas density distribution (clumping) which need to be taken into account to recover the physical properties of the intracluster medium (ICM) at large radii. Aims. We studied the thermodynamic properties in the outskirts (R > R500) of the massive galaxy cluster Abell 2142 by combining the Sunyaev Zel'dovich (SZ) effect with the X-ray signal. Methods. We combined the SZ pressure profile measured by Planck with the XMM-Newton gas density profile to recover radial profiles of temperature, entropy and hydrostatic mass out to 2R500. We used a method that is insensitive to clumping to recover the gas density, and we compared the results with traditional X-ray measurement techniques. Results. When taking clumping into account, our joint SZ/X-ray entropy profile is consistent with the predictions from pure gravitational collapse, whereas a significant entropy flattening is found when the effect of clumping is neglected. The hydrostatic mass profile recovered using joint X-ray/SZ data agrees with that obtained from spectroscopic X-ray measurements and with mass reconstructions obtained through weak lensing and galaxy kinematics. Conclusions. We found that clumping can explain the entropy flattening observed by Suzaku in the outskirts of several clusters. When using a method insensitive to clumping for the reconstruction of the gas density, the thermodynamic properties of Abell 2142 are compatible with the assumption that the thermal gas pressure sustains gravity and that the entropy is injected at accretion shocks, with no need to evoke more exotic physics. Our results highlight the need for X-ray observations with sufficient spatial resolution, and large collecting area, to understand the processes at work in cluster outer regions.Comment: 22 pages, 32 figures, accepted in the journal A&

The X-IFU end-to-end simulations performed for the TES array optimization exercise

Trabajo presentado a la Conferencia: Exploring the Hot and Energetic Universe: The first scientific conference dedicated to the Athena X-ray observatory; celebrada en Madrid (España) del 8 a 10 de septiembre de 2015.-- et al.The focal plane assembly of the Athena X-ray Integral Field Unit (X-IFU) includes as the baseline an array of ~4000 single size calorimeters based on Transition Edge Sensors (TES). Other sensor array configurations could however be considered, combining TES of different properties (e.g. size). In attempting to improve the X-IFU performance in terms of field of view, count rate performance, and even spectral resolution, two alternative TES array configurations to the baseline have been simulated, each combining a small and a large pixel array. With the X-IFU end-to-end simulator, a sub-sample of the Athena core science goals, selected by the X-IFU science team as potentially driving the optimal TES array configuration, has been simulated for the results to be scientifically assessed and compared. In this contribution, we will describe the simulation set-up for the various array configurations, and highlight some of the results of the test cases simulated.Peer Reviewe

Reconstruction of Gas Temperature and Density Profiles of the Galaxy Cluster RX J1347.5-1145

We use observations of Sunyaev-Zel'dovich effect and X-ray surface brightness to reconstruct the radial profiles of gas temperature and density under the assumption of a spherically symmetric distribution of the gas. The method of reconstruction, first raised by Silk & White, depends directly on the observations of the Sunyaev-Zel'dovich effect and the X-ray surface brightness, without involving additional assumptions such as the equation of state of the gas or the conditions of hydrostatic equilibrium. We applied this method to the cluster RX J1347.5-1145, which has both the Sunyaev-Zel'dovich effect and X-ray observations with relative high precision. It is shown that it will be an effective method to obtain the gas distribution in galaxy clusters. Statistical errors of the derived temperature and density profiles of gas were estimated according to the observational uncertainties.Comment: 6 pages, 1 figure. The published version, 2008, Chin. J. Astron. Astrophys., 8, 67

The mass distribution of RX J1347-1145 from strong lensing

High resolution HST/ACS images of the galaxy cluster RX J1347-1145 have enabled us to identify several new multiple image candidates in the cluster, including a 5 image system with a central image. The multiple images allow us to construct an accurate 2-dimensional mass map of the central part of the cluster. The modelling of the cluster mass includes the most prominent cluster galaxies modelled as truncated isothermal spheres and a smooth halo component that is described with 2 parametric profiles. The mass reconstruction is done using a Markov chain Monte Carlo method that provides us with a total projected mass density as well as estimates for the parameters of interest and their respective errors. The mass profile is in reasonable agreement with previous mass estimates based on the X-ray emission from the hot intra-cluster gas, however the X-ray mass estimates are systematically lower than what we obtain with gravitational lensing.Comment: Accepted for publication in the A&

The dark matter halo of NGC 1399 - CDM or MOND?

Central galaxies in galaxy clusters may be key discriminants in the competition between the cold dark matter (CDM) paradigm and modified Newtonian dynamics (MOND). We investigate the dark halo of NGC 1399, the central galaxy of the Fornax cluster, out to a galactocentric distance of 80 kpc. The data base consists of 656 radial velocities of globular clusters obtained with MXU/VLT and GMOS/Gemini, which is the largest sample so far for any galaxy. We performed a Jeans analysis for a non-rotating isotropic model. An NFW halo with the parameters r_s = 50 kpc and rho_s = 0.0065 M_sun/pc^3 provides a good description of our data, fitting well to the X-ray mass. More massive halos are also permitted that agree with the mass of the Fornax cluster as derived from galaxy velocities. We compare this halo with the expected MOND models under isotropy and find that additional dark matter on the order of the stellar mass is needed to get agreement. A fully radial infinite globular cluster system would be needed to change this conclusion. Regarding CDM, we cannot draw firm conclusions. To really constrain a cluster wide halo, more data covering a larger radius are necessary. The MOND result appears as a small-scale variant of the finding that MOND in galaxy clusters still needs dark matter.Comment: 4 pages, 2 figures, accepted for publication as a Letter in A&

Chandra and XMM-Newton observations of the merging cluster of galaxies PLCK G036.7+14.9

We present Chandra and XMM-Newton observations of PLCK G036.7+14.9 from the Chandra-Planck Legacy Program. The high resolution X-ray observations reveal two close subclusters, G036N and G036S, which were not resolved by previous ROSAT, optical, or recent Planck observations. We perform detailed imaging and spectral analyses and use a simplified model to study the kinematics of this system. The basic picture is that PLCK G036.7+14.9 is undergoing a major merger (mass ratio close to unity) between the two massive subclusters, with the merger largely along the line-of-sight and probably at an early stage. G036N hosts a small, moderate cool-core, while G036S has at most a very weak cool-core in the central 40 kpc region. The difference in core cooling times is unlikely to be caused by the ongoing merger disrupting a pre-existing cool-core in G036S. G036N also hosts an unresolved radio source in the center, which may be heating the gas if the radio source is extended. The Planck derived mass is higher than the X-ray measured mass of either subcluster, but is lower than the X-ray measured mass of the whole cluster, due to the fact that Planck does not resolve PLCK G036.7+14.9 into subclusters and interprets it as a single cluster. This mass discrepancy could induce significant bias to the mass function if such previously unresolved systems are common in the Planck cluster sample. High resolution X-ray observations are necessary to identify the fraction of such systems and correct such a bias for the purpose of precision cosmological studies.Comment: 23 pages, 8 figures (low resolution) with additional 12 figures in the Appendix, accepted for publication in Ap

X-ray spectroscopy on Abell 478 with XMM-Newton

We report the results from a spatially resolved spectroscopy study with XMM-Newton on the relaxed cluster of galaxies Abell 478. From the EPIC data we extract a temperature profile and radial abundance profiles for Ne, Mg, Si, S, Ca, Fe and Ni. The abundance profiles follow the same trends as observed in other clusters. The spectra of the core of the cluster can be best fitted with a multi-temperature model. We argue that this multi-temperature behavior is mostly due to projection effects, because of the strong temperature gradient in the core. Contributions from other effects, for example, intrinsic temperature stratification cannot be fully excluded. For the first time we measure an underabundance of oxygen in the Galactic absorption component toward a cluster. The measured oxygen abundance in this absorber is about 0.5 times the solar oxygen abundance as determined by Anders & Grevesse (1989).Comment: 9 pages. Accepted for publication in Astronomy & Astrophysic