Galaxy Clusters

We use gas-dynamical simulations of galaxy clusters to compare their X-ray and strong lensing properties. Special emphasis is laid on mass estimates. The cluster masses range between 6x10^14 and 4x10^15 M_solar, and they are examined at redshifts between 1 and 0. We compute the X-ray emission of the intracluster gas by thermal bremsstrahlung, add background contamination, and mimic imaging and spectral observations with current X-ray telescopes. Although the beta model routinely provides excellent fits to the X-ray emission profiles, the derived masses are typically biased low because of the restricted range of radii within which the fit can be done. For beta values of ~2/3, which is the average in our numerically simulated sample, the mass is typically underestimated by ~40 per cent. The masses of clusters that exhibit pronounced substructure are often substantially underestimated. We suggest that the ratio between peak temperature and emission-weighted average cluster temperature may provide a good indicator for ongoing merging and, therefore, for unreliable mass estimates. X-ray mass estimates are substantially improved if we fit a King density profile rather than the beta model to the X-ray emission, thereby dropping the degree of freedom associated with beta. Clusters selected for their strong lensing properties are typically dynamically more active than typical clusters. Bulk flows in the intracluster gas contain a larger than average fraction of the internal energy of the gas in such objects, hence the measured gas temperatures are biased low. The bulk of the optical depth for arc formation is contributed by clusters with intermediate rather than high X-ray luminosity. Arcs occur predominantly in clusters that exhibit substructure and are not in an equilibrium state. Finally, we explain why the X-ray emission of some observed arc clusters is cooler than predicted from the arc geometry. All clusters for which this happens in our simulations show structure in velocity space, indicating ongoing merging along the line of sight. The temperature discrepancy is probably a projection effect.

In this paper we study scalar perturbations of the metric for nonlinear f(R) models. We consider the Universe at the late stage of its evolution and deep inside the cell of uniformity. We investigate the astrophysical approach in the case of Minkowski spacetime background and two cases in the cosmological approach, the large scalaron mass approximation and the quasi-static approximation, getting explicit expressions for scalar perturbations for both these cases. In the most interesting quasi-static approximation, the scalar perturbation functions depend on both the nonlinearity function f(R) and the scale factor a. Hence, we can study the dynamical behavior of the inhomogeneities (e.g., galaxies and dwarf galaxies) including into consideration their gravitational attraction and the cosmological expansion, and also taking into account the effects of nonlinearity. Our investigation is valid for functions f(R) which have stable de Sitter points in future with respect to the present tim...

My work here is the Determine Age of Open Star Clusters. Star clusters, as the name suggests are very large group of stars that are gravitationally bound. They are at the same distance from earth and are of the same age. By analyzing them we can find information about the evolution of different type of stars and clusters. There can be two types of clusters; Open star clusters and Globular star clusters. On comparison with Globular star clusters, Open star clusters are gravitationally loosely bound and young, mainly consisting of blue stars. Open clusters will often disrupt due to the gravitational influence of nearby giant molecular cloud even before the stars in it die. It will be having a few hundreds of stars and they are confined to the galactic planes, in the spiral arms of the galaxies. In this project I am using the data from Gaia DR2, which comprises of 46 open star clusters. I find the age of these clusters using two methods; Using theory of stellar evolution and Stellar isochrone fitting methods with the help of Excel and TOPCAT software.

I present the latest form of the Tully fisher relation (TFR) which evolves with cosmic time.This so called evolving bTFR provides information about mass, age and velocity of a galaxy sample and is a necessary tool in studying galactic, cluster and cosmic evolution.

The following assumptions of the Big Bang theory are challenged and found to be false: the cosmological principle, the assumption that all matter formed at the same time and the assumption regarding the cause of the cosmic microwave background radiation (CMBR).

The evolution of the universe is described based on the conclusion that the universe is finite with a space boundary. The CMBR is coming from a source located within the event horizon of the universe. There is sufficient mass in the universe to create an event horizon at the Schwarzschild radius.

Galaxies form over time due to the energy released by the expansion of space. When a galaxy forms the matter formation is in the form of neutrons. Pairs of neutrons bond to form dark matter (dineutrons) and single neutrons decay to form protons and electrons which combine to form hydrogen.

Conservation of energy must consider total energy which is mass (+ve) plus energy (+ve) plus spacetime curvature (-ve) so that the total energy of the universe is always zero. The predominant position of galaxy formation moves over time from the centre of the universe towards the boundary so that today the majority of new galaxy formation is taking place beyond our horizon of observation at 14 billion light years.

The distribution of galaxies in a finite universe is such that there is a variation in gravitational acceleration depending on the distance from the centre of the universe. This gravitational acceleration results in the difference in the recession velocity of galaxies previously attributed to dark energy.

Galaxy clusters provide us with key information based on their characteristics such as they evolve slowly so they retain information of how the universe formed. From the time of its discovery, galaxy clusters have been studied and observed with many different instruments, such as the Hubble Space Telescope (HST), using multiwavelength astronomy. X-ray emissions from galaxy clusters provide information about the environment and physical processes occurring in that galaxy group. X-ray surveys offer an advantage since they provide a correlation between X-ray observables and mass due to their purity and completeness. The primary disadvantage of X-ray cluster surveys is that they can only be carried out from space, which is expensive. Optical and Near-Infrared (NIR) emission from galaxy clusters comes mostly from starlight (usually the central regions of clusters). The main observables from optical surveys include richness, luminosity, and color. Projection of filamentary structures along the line of sight greatly impacts optical catalogs, adding a degree of uncertainty. The Sunyaev-Zel'dovich (SZ) effect arises due to the inverse Compton scattering off hot ICM electrons, causing a shift in the CMB spectrum. The advantage of SZ surveys is that, unlike optical and X-ray measurements, the SZ signal does not undergo surface dimming. Challenges for these catalogs include determining the low signal-to-noise ratio (SNR) regime. Gravitational lensing arises due to the bending of light around the distribution of matter as light travels from the source to the observer. If the cluster and background galaxy redshifts are known, galaxy lensing can be used to calculate the cluster mass using gravitational shear. The future of multiwavelength galaxy cluster observations looks bright with cluster catalogs set to expand in size with new projects and surveys underway.

The accelerating expansion of the universe is the most surprising cosmological discovery in many decades, implying that the universe is dominated by some form of "dark energy" with exotic physical properties, or that Einstein's theory of gravity breaks down on cosmological scales. The profound implications of cosmic acceleration have inspired ambitious experimental efforts to measure the history of expansion and growth of structure with percent-level precision or higher. We review in detail the four most well established methods for making such measurements: Type Ia supernovae, baryon acoustic oscillations (BAO), weak gravitational lensing, and galaxy clusters. We pay particular attention to the systematic uncertainties in these techniques and to strategies for controlling them at the level needed to exploit "Stage IV" dark energy facilities such as BigBOSS, LSST, Euclid, and WFIRST. We briefly review a number of other approaches including redshift-space distortions, the Alcock-Paczynski test, and direct measurements of H_0. We present extensive forecasts for constraints on the dark energy equation of state and parameterized deviations from GR, achievable with Stage III and Stage IV experimental programs that incorporate supernovae, BAO, weak lensing, and CMB data. We also show the level of precision required for other methods to provide constraints competitive with those of these fiducial programs. We emphasize the value of a balanced program that employs several of the most powerful methods in combination, both to cross-check systematic uncertainties and to take advantage of complementary information. Surveys to probe cosmic acceleration produce data sets with broad applications, and they continue the longstanding astronomical tradition of mapping the universe in ever greater detail over ever larger scales.

The paper describes One among the Cluster Development Projects in Tanzania that promotes national socio-economic development. The project used Cluster Based Approach that engaged academia, research and development organization in stimulating, catalyzing and promoting the development of innovation systems and innovative clusters in Tanzania.  The programme started in 2006 by piloting eight (8) Cluster Initiatives (CI). As of December 2015, the programme has facilitated the establishment of more than 70 clusters.
The project interventions included business support services, training of cluster facilitators, providing and advising new technologies/techniques on business development and provision of entrepreneurship and business skills.
The project has notable achievements, challenges as well as opportunities and recommendations towards cluster development initiatives in Tanzania.
The project has noted one important aspect of having a Cluster Development Guideline for Tanzania that will enable various Cluster Development Practitioners to use in Cluster Development initiatives.

The accelerating expansion of the universe is the most surprising cosmological discovery in many decades. In this short review, we briefly summarize theories for the origin of cosmic acceleration and the observational methods being used to test these theories. We then discuss the current observational state of the field, with constraints from the cosmic microwave background (CMB), baryon acoustic oscillations (BAO), Type Ia supernovae (SN), direct measurements of the Hubble constant (H0), and measurements of galaxy and matter clustering. Assuming a flat universe and dark energy with a constant equation-of-state parameter w=P/ρ, the combination of Planck CMB temperature anisotropies, WMAP CMB polarization, the Union2.1 SN compilation, and a compilation of BAO measurements yields w=−1.10+0.08−0.07, consistent with a cosmological constant (w=−1). However, with these constraints the cosmological constant model predicts a value of H0 that is lower than several of the leading recent estimates, and it predicts a parameter combination σ8(Ωm)0.5 that is higher than many estimates from weak gravitational lensing, galaxy clusters, and redshift-space distortions. Individually these tensions are only significant at the ~2σ level, but they arise in multiple data sets with independent statistics and distinct sources of systematic uncertainty. The tensions are stronger with Planck CMB data than they were with WMAP because of the smaller statistical errors and the higher central value of Ωm. With the improved measurements expected from the next generation of data sets, these tensions may diminish, or they may sharpen in a way that points towards a more complete physical understanding of cosmic acceleration.

We consider the Universe deep inside the cell of uniformity. At these scales, the Universe is filled with inhomogeneously distributed discrete structures (galaxies, groups and clusters of galaxies), which perturb the background Friedmann model. Here, the mechanical approach (Eingorn & Zhuk, 2012) is the most appropriate to describe the dynamics of the inhomogeneities which is defined, on the one hand, by gravitational potentials of inhomogeneities and, on the other hand, by the cosmological expansion of the Universe. In this paper, we present additional arguments in favor of this approach. First, we estimate the size of the cell of uniformity. With the help of the standard methods of statistical physics and for the galaxies of the type of the Milky Way and Andromeda, we get that it is of the order of 190 Mpc which is rather close to observations. Then, we show that the nonrelativistic approximation (with respect to the peculiar velocities) is valid for $z \lesssim 10$, i.e. approximately for 13 billion years from the present moment. We consider scalar perturbations and, within the $\Lambda$CDM model, justify the main equations. Moreover, we demonstrate that radiation can be naturally incorporated into our scheme. This emphasizes the viability of our approach. This approach gives a possibility to analyze different cosmological models and compare them with the observable Universe. For example, we indicate some problematic aspects of the spatially flat models. Such models require a rather specific distribution of the inhomogeneities to get a finite potential at any points outside gravitating masses. We also criticize the application of the Schwarzschild-de Sitter solution to the description of the motion of test bodies on the cosmological background.

The article gives a brief exposition of the solution of cosmological problems. The problem of stability and shortage of mass in galaxies, huge velocities of galactic clusters is solved. The law of formation of fundamental constants, the law of nonlinear expansion of the Universe, the law of gravitational interaction is found. Proof of the hypothesis of large Dirac numbers.

The cosmological many-body problem is effectively an infinite system of gravitationally interacting masses in an expanding universe. Despite the interactions' long-range nature, an analytical theory of statistical mechanics describes the spatial and velocity distribution functions which arise in the quasi-equilibrium conditions that apply to many cosmologies. Consequences of this theory agree well with the observed distribution of galaxies. Further consequences such as thermodynamics provide insights into the physical properties of this system, including its robustness to mergers, and its transition from a grand canonical ensemble to a collection of microcanonical ensembles with negative specific heat.

The nearby cluster Abell194 hosts two luminous, distorted radio galaxies. Both reside within the cluster's core region, being separated in projection by only 100 kpc. It is often suggested that tailed radio galaxies such as these reside in clusters that are under formation and are accreting new material from their outskirts. In this paper, we study the intriguing appearance of Abell 194, and test whether the cluster and radio source dynamics are consistent with the cluster formation/merger model. We analyse data from the XMM-Newton satellite and previously unpublished observations with the Very Large Array as well as present new data from the Giant Metre-Wave Radio Telescope (GMRT). The shape of the jets, and the lack of significant stripping of the galaxies' interstellar media, indicates that the radio galaxies are not moving at the large velocities they would have had if they were falling into the cluster from its outskirts; galaxy velocities of <=300kms-1 are adequate instead. A plausible scenario that could explain the observations is that the dynamics of the cluster centre are relatively quiescent, with the dominant system of massive galaxies being bound and orbiting the cluster centre of mass. For plausible jet/plume speeds and densities and the galaxy dynamics implied by this picture of the cluster, we show that the observed jet structures can be explained without invoking a major cluster merger event.

The caustic technique uses galaxy redshifts alone to measure the escape velocity and mass profiles of galaxy clusters to clustrocentric distances well beyond the virial radius, where dynamical equilibrium does not necessarily hold. We provide a detailed description of this technique and analyse its possible systematic errors. We apply the caustic technique to clusters with mass M_200>=10^{14}h^{-1} M_sun extracted from a cosmological hydrodynamic simulation of a LambdaCDM universe. With a few tens of redshifts per squared comoving megaparsec within the cluster, the caustic technique, on average, recovers the profile of the escape velocity from the cluster with better than 10 percent accuracy up to r~4 r_200. The caustic technique also recovers the mass profile with better than 10 percent accuracy in the range (0.6-4) r_200, but it overestimates the mass up to 70 percent at smaller radii. This overestimate is a consequence of neglecting the radial dependence of the filling function F_beta(r). The 1-sigma uncertainty on individual escape velocity profiles increases from ~20 to ~50 percent when the radius increases from r~0.1 r_200 to ~4 r_200. Individual mass profiles have 1-sigma uncertainty between 40 and 80 percent within the radial range (0.6-4) r_200. We show that the amplitude of these uncertainties is completely due to the assumption of spherical symmetry, which is difficult to drop. Alternatively, we can apply the technique to synthetic clusters obtained by stacking individual clusters: in this case, the 1-sigma uncertainty on the escape velocity profile is smaller than 20 percent out to 4 r_200. The caustic technique thus provides reliable average profiles which extend to regions difficult or impossible to probe with other techniques.

There are several possibilities to constrain the value of the magnetic field in the ICM, the most direct ones being the combination of inverse Compton and synchrotron observations, and the Faraday rotation measures. Here we discuss on the possibility to provide constraints on the magnetic field in the ICM from the analysis of the statistical properties of the giant radio halos, Mpc--scale diffuse radio emission in galaxy clusters. Present observations of a few well studied radio halos can be interpreted under the hypothesis that the emitting relativistic electrons are re-accelerated on their way out. By using statistical calculations carried out in the framework of the re-acceleration model we show that the observed radio--power vs cluster mass correlation in radio halos can be reproduced only by assuming $\mu$G fields in the ICM and a scaling of the magnetic field with cluster mass $B \propto M_v^b$, with $b \geq 0.6$. We also show that the expected occurrence of radio halos with mass and redshift, and their number counts are sensitive to the magnetic field intensity in massive galaxy clusters and to the scaling of B with cluster mass. Thus future deep surveys of radio halos would provide constraints on B in galaxy clusters.

We analyze the XMM dataset of the interacting cluster of galaxies Abell 3528 located westward in the core of the Shapley Supercluster, the largest concentration of mass in the nearby Universe. A3528 is formed by two interacting clumps (A3528-N at North and A3528-S at South) separated by 0.9 $h_{70}^{-1}$ Mpc at redshift 0.053. XMM data describe these clumps as relaxed structure with an overall temperature of $4.14 \pm 0.09$ and $4.29 \pm 0.07$ keV in A3528-N and A3528-S, respectively, and a core cooler by a factor 1.4--1.5 and super-solar metal abundance in the inner 30 arcsec. These clumps are connected by a X-ray soft, bridge-like emission and present asymmetric surface brightness with significant excess in the North--West region of A3528-N and in the North--East area of A3528-S. However, we do not observe any evidence of shock heated gas, both in the surface brightness and in the temperature map. Considering also that the optical light distribution is more concentrated around A3528-N and makes A3528-S barely detectable, we do not find support to the originally suggested head-on pre-merging scenario and conclude that A3528 is in a off-axis post-merging phase, where the closest cores encounter happened about 1--2 Gyrs ago.

We employ a high-resolution dissipationless N-body simulation of a galaxy cluster to investigate the impact of subhalo selection on the resulting velocity distributions. Applying a lower limit on the present bound mass of subhalos leads to high subhalo velocity dispersions compared to the diffuse dark matter (positive velocity bias) and to a considerable deviation from a Gaussian velocity distribution (kurtosis -0.6). However, if subhalos are required to exceed a minimal mass before accretion onto the host, the velocity bias becomes negligible and the velocity distribution is close to Gaussian (kurtosis -0.15). Recently it has been shown that the latter criterion results in subhalo samples that agree well with the observed number-density profiles of galaxies in clusters. Therefore we argue that the velocity distributions of galaxies in clusters are essentially un-biased. The comparison of the galaxy velocity distribution and the sound speed, derived from scaling relations of X-ray observations, results in an average Mach number of 1.24. Altogether 65% of the galaxies move supersonically and 8% have Mach numbers larger than 2 with respect to the intra cluster gas.

We have studied primordial non-Gaussian features from a model of potential driven single field DBI Galileon inflation. We have computed the bispectrum from the three point correlation function considering all possible cross correlation between scalar and tensor modes from the proposed setup. Further, we have computed the trispectrum from four point correlation function considering the contribution from contact interaction, scalar and graviton exchange diagrams in the in-in picture. Finally we have obtained the non-Gaussian consistency conditions from the four point correlator, which results in partial violation of the Suyama-Yamaguchi four-point consistency relation. This further leads to the conclusion that sufficient primordial non-Gaussianities can be obtained from DBI Galileon inflation.

We address four physics opportunities. First, suggest new elementary particles and forces. Second, explain phenomena such as dark matter. Third, augment and unite physics theories and models. Fourth, point to opportunities for further research.
We use models based on solutions to equations featuring isotropic pairs of isotropic quantum harmonic oscillators.
First, we show solutions that match the known elementary particles. We propose that other solutions correlate with elementary particles that people have yet to detect and with dark energy forces leading to three known eras - early acceleration, subsequent deceleration, and current acceleration - pertaining to the rate of expansion of the universe.
Second, we extend solutions to encompass known conservation-law symmetries. Extended solutions correlate with known kinematics. We suggest that extended solutions describe dark matter, explain ratios of density of dark matter to density of ordinary matter, correlate with dark energy density, and explain other phenomena.
Third, we propose that our work unites, suggests details regarding, extends, suggests complements to, and suggests limits regarding aspects of traditional physics theory. Those aspects include classical physics, special relativity, general relativity, quantum mechanics, the elementary particle Standard Model, the cosmology timeline, and galaxy evolution scenarios. The work provides possible insight regarding foundation of physics topics.
Fourth, we suggest opportunities for people. We suggest opportunities for observational, experimental, and theoretical physics research. We suggest quantum field theory that features few interaction vertices, sums of few terms as alternatives to conditionally convergent sums of infinite numbers of terms, and no needs to deal with some infinities. We point to possible opportunities to further develop and apply modeling and math we use.

The SFI++ consists of ~5000 spiral galaxies which have measurements suitable for the application of the I-band Tully-Fisher (TF) relation. This sample builds on the SCI and SFI samples published in the 1990s but includes significant amounts of new data as well as improved methods for parameter determination. We derive a new I-band TF relation from a subset of this sample which consists of 807 galaxies in the fields of 31 nearby clusters and groups. This sample constitutes the largest ever available for the calibration of the TF template and extends the range of line-widths over which the template is reliably measured. Careful accounting is made of observational and sample biases such as incompleteness, finite cluster size, galaxy morphology and environment. We find evidence for a type-dependent TF slope which is shallower for early type than for late type spirals. The line-of-sight cluster peculiar velocity dispersion is measured for the sample of 31 clusters. This value is directly related to the spectrum of initial density fluctuations and thus provides an independent verification of the best fit WMAP cosmology and an estimate of Omega^0.6 sigma_8 = 0.52+/-0.06. We also provide an independent measure of the TF zeropoint using 17 galaxies in the SFI++ sample for which Cepheid distances are available. In combination with the ``basket of clusters'' template relation these calibrator galaxies provide a measure of H0 = 74+/-2 (random) +/-6 (systematic) km/s/Mpc.

The results of measurements of the Hubble's constant 0 , which characterizes the expansion rate of the universe, shows that the values of 0 vary significantly depending on Methodology. The disagreement in the values of 0 obtained by the various teams far exceeds the standard uncertainties provided with the values. This discrepancy is called the Hubble Tension. In this paper, we discuss Macrostructures of the World (Superclusters and Galaxies); explain their Origin and Evolution in frames of the developed Hypersphere World-Universe Model (WUM), which is, in fact, the Paradigm Shift in Cosmology [1]; and provide the explanation of the Hubble Tension. The main difference between WUM and Big Bang Model (BBM) is: Instead of the Infinite Homogeneous and Isotropic Universe around the Initial Singularity in BBM, in WUM, the 3D Finite Boundless World (the Hypersphere) presents a Patchwork Quilt of different Luminous Superclusters (≳10 3), which emerged in various places of the World at different Cosmological times. In WUM, the Medium of the World is Homogeneous and Isotropic. The distribution of Macroobjects in the World is spatially Inhomogeneous and Anisotropic and temporally Non-simultaneous.