Halos In Galaxy Clusters Research Articles

Probing the dark-matter halos of cluster galaxies with weak lensing

Context: Understanding the evolution of the dark matter halos of galaxies after they become part of a cluster is essential for understanding the evolution of these satellite galaxies. Aims: We investigate the potential of galaxy-galaxy lensing to map the halo density profiles of galaxies in clusters. Methods: We propose a method that separates the weak-lensing signal of the dark-matter halos of galaxies in clusters from the weak-lensing signal of the cluster's main halo. Using toy cluster models as well as ray-tracing through N-body simulations of structure formation along with semi-analytic galaxy formation models, we test the method and assess its performance. Results: We show that with the proposed method, one can recover the density profiles of the cluster galaxy halos in the range 30 - 300 kpc. Using the method, we find that weak-lensing signal of cluster member galaxies in the Millennium Simulation is well described by an Navarro-Frenk-White (NFW) profile. In contrast, non-singular isothermal mass distribution (like PIEMD) model provide a poor fit. Furthermore, we do not find evidence for a sharp truncation of the galaxy halos in the range probed by our method. Instead, there is an observed overall decrease of the halo mass profile of cluster member galaxies with increasing time spent in the cluster. This trend, as well as the presence or absence of a truncation radius, should be detectable in future weak-lensing surveys like the Dark Energy Survey (DES) or the Large Synoptic Survey Telescope (LSST) survey. Such surveys should also allow one to infer the mass-luminosity relation of cluster galaxies with our method over two decades in mass. Conclusions: It is possible to recover in a non-parametric way the mass profile of satellite galaxies and their dark matter halos in future surveys, using our proposed weak lensing method.

Neutrino halos in clusters of galaxies and their weak lensing signature

We study whether non-linear gravitational effects of relic neutrinos on the development of clustering and large-scale structure may be observable by weak gravitational lensing. We compute the density profile of relic massive neutrinos in a spherical model of a cluster of galaxies, for several neutrino mass schemes and cluster masses. Relic neutrinos add a small perturbation to the mass profile, making it more extended in the outer parts. In principle, this non-linear neutrino perturbation is detectable in an all-sky weak lensing survey such as EUCLID by averaging the shear profile of a large fraction of the visible massive clusters in the universe, or from its signature in the general weak lensing power spectrum or its cross-spectrum with galaxies. However, correctly modeling the distribution of mass in baryons and cold dark matter and suppressing any systematic errors to the accuracy required for detecting this neutrino perturbation is severely challenging.

Fractional polarization as a probe of magnetic fields in the intra-cluster medium

The aim of this work is to investigate the average properties of the intra-cluster medium (ICM) magnetic fields, and to search for possible correlations with the ICM thermal properties and cluster radio emission. We have selected a sample of 39 massive galaxy clusters from the HIghest X-ray FLUx Galaxy Cluster Sample, and used Northern VLA Sky Survey data to analyze the fractional polarization of radio sources out to 10 core radii from the cluster centers. Following Murgia et al (2004), we have investigated how different magnetic field strengths affect the observed polarized emission of sources lying at different projected distances from the cluster center. In addition, statistical tests are performed to investigate the fractional polarization trends in clusters with different thermal and non-thermal properties. We find a trend of the fractional polarization with the cluster impact parameter, with fractional polarization increasing at the cluster periphery and decreasing toward the cluster center. Such trend can be reproduced by a magnetic field model with central value of few $\mu$G. The logrank statistical test indicates that there are no differences in the depolarization trend observed in cluster with and without radio halo, while the same test indicates significant differences when the depolarization trend of sources in clusters with and without cool core are compared. The comparison between clusters with high and low temperatures does not yields significant differences. Although therole of the gas density should be better accounted for, these results give important indications for models that require a role of the ICM magnetic field to explain the presence of cool core and radio halos in galaxy clusters.

HOW TO IDENTIFY AND SEPARATE BRIGHT GALAXY CLUSTERS FROM THE LOW-FREQUENCY RADIO SKY

In this work we simulate the $50-200$ MHz radio sky that is constrained in the field of view ($5^{\circ}$ radius) of the 21 Centimeter Array (21CMA), by carrying out Monte-Carlo simulations to model redshifted cosmological reionization signals and strong contaminating foregrounds, including emissions from our Galaxy, galaxy clusters, and extragalactic point sources. As an improvement of previous works, we consider in detail not only random variations of morphological and spectroscopic parameters within the ranges allowed by multi-band observations, but also evolution of radio halos in galaxy clusters, assuming that relativistic electrons are re-accelerated in the ICM in merger events and lose energy via both synchrotron emission and inverse Compton scattering with CMB photons. By introducing a new approach designed on the basis of independent component analysis (ICA) and wavelet detection algorithm, we prove that, with a cumulative observation of one month with the 21CMA array, about $80\%$ of galaxy clusters with central brightness temperatures of $> 10~{\rm K}$ at 65 MHz can be safely identified and separated from the overwhelmingly bright foreground. We find that the morphological and spectroscopic distortions are extremely small as compared to the input simulated clusters, and the reduced $\chi^2$ of brightness temperature profiles and spectra are controlled to be $\lesssim 0.5$ and $\lesssim 1.3$, respectively. These results robustly indicate that in the near future a sample of dozens of bright galaxy clusters will be disentangled from the foreground in 21CMA observations, the study of which will greatly improve our knowledge about cluster merger rates, electron acceleration mechanisms in cluster radio halos, and magnetic field in the ICM.

Unveiling radio halos in galaxy clusters in the LOFAR era

Giant radio halos are mega-parsec scale synchrotron sources detected in a fraction of massive and merging galaxy clusters. Radio halos provide one of the most important pieces of evidence for non-thermal components in large scale structure. Statistics of their properties can be used to discriminate among various models for their origin. Therefore, theoretical predictions of the occurrence of radio halos are important as several new radio telescopes are about to begin to survey the sky at low frequencies with unprecedented sensitivity. In this paper we carry out Monte Carlo simulations to model the formation and evolution of radio halos in a cosmological framework. We extend previous works on the statistical properties of radio halos in the context of the turbulent re-acceleration model. First we compute the fraction of galaxy clusters that show radio halos and derive the luminosity function of radio halos. Then, we derive differential and integrated number count distributions of radio halos at low radio frequencies with the main goal to explore the potential of the upcoming LOFAR surveys. By restricting to the case of clusters at redshifts <0.6, we find that the planned LOFAR all sky survey at 120 MHz is expected to detect about 350 giant radio halos. About half of these halos have spectral indices larger than 1.9 and substantially brighten at lower frequencies. If detected they will allow for a confirmation that turbulence accelerates the emitting particles. We expect that also commissioning surveys, such as MSSS, have the potential to detect about 60 radio halos in clusters of the ROSAT Brightest Cluster Sample and its extension (eBCS). These surveys will allow us to constrain how the rate of formation of radio halos in these clusters depends on cluster mass.

Hydro-Gravitational Dynamics of Planets and Dark Energy

Self gravitational fluid mechanical methods termed hydro-gravitational-dynamics (HGD) predict plasma fragmentation 0.03 Myr after the turbulent big bang to form protosuperclustervoids, turbulent protosuperclusters, and protogalaxies at the 0.3 Myr transition from plasma to gas. Linear protogalaxyclusters fragment at 0.003 Mpc viscous-inertial scales along turbulent vortex lines or in spirals, as observed. The plasma protogalaxies fragment on transition into white-hot planet-mass gas clouds (PFPs) in million-solar-mass clumps (PGCs) that become globular-star-clusters (GCs) from tidal forces or dark matter (PGCs) by freezing and diffusion into 0.3 Mpc halos with 97% of the galaxy mass. The weakly collisional non-baryonic dark matter diffuses to > Mpc scales and fragments to form galaxy cluster halos. Stars and larger planets form by binary mergers of the trillion PFPs per PGC, mostly on 0.03 Mpc galaxy accretion disks. Stars deaths depend on rates of planet accretion and internal star mixing. Moderate accretion rates pro-duce white dwarfs that evaporate surrounding gas planets by spin-radiation to form planetary nebulae before Supernova Ia events, dimming some events to give systematic distance errors, the dark energy hypothesis, and overestimates of the universe age.

PROBING THE TRUNCATION OF GALAXY DARK MATTER HALOS IN HIGH-DENSITY ENVIRONMENTS FROM HYDRODYNAMICALN-BODY SIMULATIONS

We analyze high-resolution, N-body hydrodynamical simulations of fiducial galaxy clusters to probe tidal stripping of the dark matter subhalos. These simulations include a prescription for star formation allowing us to track the fate of the stellar component as well. We investigate the effect of tidal stripping on cluster galaxies hosted in these dark matter subhalos as a function of projected cluster-centric radius. To quantify the extent of the dark matter halos of cluster galaxies, we introduce the half-mass radius r 1/2 as a diagnostic, and study its evolution with projected cluster-centric distance R as a function of redshift. We find a well-defined trend for (r 1/2, R): the closer the galaxies are to the center of the cluster, the smaller the half-mass radius. Interestingly, this trend is inferred in all redshift frames examined in this work ranging from z = 0 to z = 0.7. At z = 0, galaxy halos in the central regions of clusters are found to be highly truncated, with the most compact half-mass radius of 10 kpc. We also find that r 1/2 depends on luminosity and we present scaling relations of r 1/2 with galaxy luminosity. The corresponding total mass of the cluster galaxies is also found to increase with projected cluster-centric distance and luminosity, but with more scatter than the (r 1/2, R) trend. Comparing the distribution of stellar mass to total mass for cluster galaxies, we find that the dark matter component is preferentially stripped, whereas the stellar component is much less affected by tidal forces. We compare these results with galaxy-galaxy lensing probes of r 1/2 and find qualitative agreement. Future surveys with space-based telescopes such as DUNE and SNAP, that combine wide-field and high-resolution imaging, will be able to probe the predicted (r 1/2, R) relation observationally.

The tidal streams of disrupting subhaloes in cosmological dark matter haloes

We present a detailed analysis of the properties of tidally stripped material from disrupting substructure haloes or subhaloes in a sample of high-resolution cosmological N-body host haloes ranging from galaxy- to cluster-mass scales. We focus on devising methods to recover the infall mass and infall eccentricity of subhaloes from the properties of their tidally stripped material (i.e. tidal streams). Our analysis reveals that there is a relation between the scatter of stream particles about the best-fitting debris plane and the infall mass of the progenitor subhalo. This allows us to reconstruct the infall mass from the spread of its tidal debris in space. We also find that the spread in radial velocities of the debris material (as measured by an observer located at the centre of the host) correlates with the infall eccentricity of the subhalo, which allows us to reconstruct its orbital parameters. We devise an automated method to identify the leading and trailing arms that can, in principle at least, be applied to observations of stellar streams from satellite galaxies. This method is based on the energy distribution of material in the tidal stream. Using this method, we show that the masses associated with the leading and trailing arms differ. While our analysis indicates that tidal streams can be used to recover certain properties of their progenitor subhaloes (and consequently satellites), we do not find strong correlations between host halo properties and stream properties. This likely reflects the complicated relationship between the stream and the host, which in a cosmological context is characterized by a complex mass accretion history, an asymmetric mass distribution and the abundance of substructure. Finally, we confirm that the so-called ‘backsplash’ subhalo population is present not only in galaxy cluster haloes but also in galaxy haloes. The orbits of backsplash subhaloes brought them inside the virial radius of their host at some earlier time, but they now reside in its outskirts at the present-day, beyond the virial radius. Both backsplash and bound subhaloes experience similar mass loss, but the contribution of the backsplash subhaloes to the overall tidal debris field is negligible.

Cosmic Rays and Radio Halos in Galaxy Clusters: New Constraints from Radio Observations

Clusters of galaxies are sites of acceleration of charged particles and sources of nonthermal radiation. We report on new constraints on the population of cosmic rays in the intracluster medium (ICM) obtained via radio observations of a fairly large sample of massive, X-ray-luminous galaxy clusters in the redshift interval 0.2-0.4. The bulk of the observed galaxy clusters does not show any hint of megaparsec-scale synchrotron radio emission at the cluster center (radio halo). We obtained solid upper limits to the diffuse radio emission and discuss their implications for the models for the origin of radio halos. Our measurements allow us to also derive a limit to the content of cosmic-ray protons in the ICM. Assuming spectral indices of these protons ? = 2.1-2.4 and ?G level magnetic fields, as from rotation measures, these limits are 1 order of magnitude deeper than present EGRET upper limits, while they are less stringent for steeper spectra and lower magnetic fields.

Accurate Realizations of the Ionized Gas in Galaxy Clusters: Calibrating Feedback

Using the full, three-dimensional potential of galaxy cluster halos (drawn from an N-body simulation of the current, most favored cosmology), the distribution of the X-ray emitting gas is found by assuming a polytropic equation of state and hydrostatic equilibrium, with constraints from conservation of energy and pressure balance at the cluster boundary. The resulting properties of the gas for these simulated redshift zero clusters (the temperature distribution, mass-temperature and luminosity-temperature relations, and the gas fraction) are compared with observations in the X-ray of nearby clusters. The observed properties are reproduced only under the assumption that substantial energy injection from non-gravitational sources has occurred. Our model does not specify the source, but star formation and AGN may be capable of providing this energy, which amounts to 3 to 5 x10^{-5} of the rest mass in stars (assuming ten percent of the gas initially in the cluster forms stars). With the method described here it is possible to generate realistic X-ray and Sunyaev-Zel'dovich cluster maps and catalogs from N-body simulations, with the distributions of internal halo properties (and their trends with mass, location, and time) taken into account.

The Sizes of Galaxy Halos in Galaxy Cluster Abell 1689

The multiple images observed in galaxy cluster Abell 1689 provide strong constraints not only on the mass distribution of the cluster but also on the ensemble properties of the cluster galaxies. Using parametric strong lensing models for the cluster, and by assuming well motivated scaling laws between the truncation radius s and the velocity dispersion sigma of a cluster galaxy we are able to derive sizes of the dark matter halos of cluster galaxies. For the scaling law expected for galaxies in the cluster environment (s propto sigma), we obtain s = 64^{+15}_{-14} (sigma / 220 km/s) kpc. For the scaling law used for galaxies in the field with s propto sigma^2 we find s = 66^{+18}_{-16} (sigma / 220 km/s)^2 kpc. Compared to halos of field galaxies, the cluster galaxy halos in Abell 1689 are strongly truncated.

The spin and shape of dark matter haloes in the Millennium simulation of a Λ cold dark matter universe

We investigate the spins and shapes of over a million dark matter haloes identified at z = 0 in the Millennium simulation. Our sample spans halo masses ranging from dwarf galaxies to rich galaxy clusters. The very large dynamic range of this A cold dark matter cosmological simulation enables the distribution of spins and shapes and their variation with halo mass and environment to be characterized with unprecedented precision. We compare results for haloes identified using three different algorithms, and investigate (and remove) biases in the estimate of angular momentum introduced both by the algorithm itself and by numerical effects. We introduce a novel halo definition called the TREE halo, based on the branches of the halo merger trees, which is more appropriate for comparison with real astronomical objects than the traditional 'friends-of-friends' and 'spherical overdensity' (SO) algorithms. We find that for this many objects, the traditional lognormal function is no longer an adequate description of the distribution, P(λ), of the dimensionless spin parameter λ, and we provide a different function that gives a better fit for TREE and SO haloes. The variation in spin with halo mass is weak but detectable, although the trend depends strongly on the halo definition used. For the entire population of haloes, we find median values of λ med = 0.0367-0.0429, depending on the definition of a halo. The haloes exhibit a range of shapes, with a preference for prolateness over oblateness. More-massive haloes tend to be less spherical and more prolate. We find that the more-spherical haloes have less coherent rotation in the median, and those closest to being spherical have a spin independent of mass (λ med ≈0.033). The most-massive haloes have a spin independent of shape (λ med ≈0.032). The majority of haloes have their angular momentum vector aligned with their minor axis and perpendicular to their major axis. We find a general trend for higher spin haloes to be more clustered, with a stronger effect for more-massive haloes. For galaxy cluster haloes, this can be larger than a factor of∼2.

GMRT radio halo survey in galaxy clusters atz= 0.2–0.4

Aims.We present the first results of an ongoing project devoted to the search of giant radio halos in galaxy clusters located in the redshift range –0.4. One of the main goals of our study is to measure the fraction of massive galaxy clusters in this redshift interval hosting a radio halo, and to constrain the expectations of the particle re-acceleration model for the origin of non-thermal radio emission in galaxy clusters.

On spatial distributions of old globular clusters in clusters of galaxies

We investigate structural properties of old, metal-poor globular clusters (GCs) formed at high redshifts (z>6) and located inside and outside virialized galaxy-scale halos in clusters of galaxies with the total masses of M_CL based on high-resolution cosmological simulations with models of GC formation. We mainly derive the parameter dependences of physical properties of intracluster GCs (ICGCs) based on the results of 14 models. Our principle results are summarized as follows. (1) The projected radial density profiles (Sigma_GC) of ICGCs in clusters with different M_CL can be diverse, though ICGCs have inhomogeneous, asymmetric, and somewhat elongated distributions in most models. If Sigma_GC (R) ~ R^alpha, alpha ranges from -1.5 to -2.5 for GCs in clusters. (2) Although total number of GCs within the central 0.05 Mpc (N_GC,0.05) and 0.2 Mpc (N_GC,0.2) are diverse in different clusters, they can depend weakly on M_CL in such a way that both N_GC,0.05 and N_GC,0.2 are likely to be larger for clusters with larger M_CL. (3) Total number of GCs per cluster masses (specific frequency of GCs for clusters of galaxies) are more likely to be larger in more massive clusters, mainly because a larger number of earlier virialized objects can be located in more massive clusters. (4) Spatial distributions of old GCs in clusters can depend on the truncation epoch of GC formation (z_trun) such that they can be steeper and more compact in the models with higher z_trun. (5) The mean metallicity of ICGCs in a cluster can be smaller than that of GCs within the cluster member galaxy-scale halos by ~ 0.3 in [Fe/H]. Metallicity distribution functions (MDFs) of ICGCs show peak values around [Fe/H] ~ -1.6 and do not have remarkable bimodality.

Shapes and Alignments of Galaxy Cluster Halos

We present distribution functions and mark correlations of the shapes of massive dark matter halos derived from Hubble volume simulations of a ?CDM universe. We measure both position and velocity shapes within spheres that encompass a mean density 200 times the critical value and calibrate small-N systematic errors using Poisson realizations of isothermal spheres and higher resolution simulations. For halos more massive than 3 ? 1014 h-1 M?, the shape distribution function peaks at (minor/major, intermediate/major) axial ratios of (0.64, 0.76) in position and is rounder in velocity, peaking at (0.72, 0.82). Halo shapes are rounder at lower mass and/or redshift; the mean minor-axis ratio in position follows c/a(M,z) = c15,0[1 - ? ln(M/1015 h-1 M?)](1 + z)-, with c15,0 = 0.631 ? 0.001, ? = 0.023 ? 0.002, and = 0.086 ? 0.004. Position and velocity principal axes are well aligned in direction, with median alignment angle 22?, and the axial ratios in these spaces are correlated in magnitude. We investigate mark correlations of halo pair orientations using two measures: a simple scalar product shows ?1% alignment extending to 30 h-1 Mpc, while a filamentary statistic exhibits nonrandom alignment extending to scales ~200 h-1 Mpc, 10 times the sample two-point correlation length and well into the regime of negative two-point correlation. Shapes of cluster halos are little affected by the large-scale environment; the distribution of supercluster member minor-axis ratios differs from that of the general population at only the few percent level.

SECONDARY ELECTRONS IN CLUSTERS OF GALAXIES AND GALAXIES

We investigate the role of secondary electrons in galaxy clusters and in ultra-luminous infrared galaxies (ULIGs). The radio emission in galaxy clusters and ULIGs is believed to be produced by the synchrotron radiation of relativistic electrons. Nonetheless, the sources of these relativistic electrons are still unclear. Relativistic secondary electrons can be produced from the hadronic interactions of cosmic-ray nuclei with the intra-cluster media (ICM) of galaxy clusters and the dense molecular clouds of ULIGs. We estimate the contribution of the secondary electrons in galaxy clusters and ULIGs by comparing observational results with theoretical calculations for the radio emission in these sources. We find that the radio halos of galaxy clusters can not be produced from the secondary electrons; on the other hand, at least for some ULIGs, the radio emission can be dominated by the synchrotron emission of the secondary electrons.

Radio halos in merging clusters of galaxies

We present the preliminary results of 235 MHz, 327 MHz and 610 MHz observations of the galaxy cluster A3562 in the core of the Shapley Concentration (SC). The purpose of these observations, carried out with the Giant Metrewave Radio Telescope (GMRT, Pune, India) was to study the radio halo located at the centre of A3562 and determine the shape of its radio spectrum at low frequencies, in order to understand the origin of this source. In the framework of the re–acceleration model, the preliminary analysis of the halo spectrum suggests that we are observing a young source (few yrs) at the beginning of the re–acceleration phase.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The Evolution of Diffuse Radio Sources in Galaxy Clusters

We investigate the evolution and number distribution of radio halos in galaxy clusters. Without reacceleration or regeneration, the relativistic electrons responsible for the diffuse radio emission will lose their energy via inverse Compton and synchrotron losses in a rather short time, and radio halos will have lifetimes ~0.1 Gyr. Radio halos could last for ~Gyr if a significant level of reacceleration is involved. The lifetimes of radio halos would be comparable with the cosmological time if the radio-emitting electrons are mainly the secondary electrons generated by pion decay following proton-proton collisions between cosmic-ray protons and the thermal intracluster medium within the galaxy clusters. Adopting both observational and theoretical constraints for the formation of radio halos, we calculate the formation rates and the comoving number density of radio halos in the hierarchical clustering scheme. Comparing with observations, we find that the lifetimes of radio halos are ~Gyr. Our results indicate that a significant level of reacceleration is necessary for the observed radio halos and the secondary electrons may not be a dominant origin for radio halos.

CD galaxy contribution to the strong lensing cross-sections of galaxy clusters

We perform ray-tracing simulations evaluating the effect of a cD galaxy on the strong lensing properties of five galaxy cluster haloes obtained from N-body simulations. The cD galaxy is modelled using both axially symmetric and elliptical models and assuming several masses for its dark matter halo. The effect of the cD orientation with respect to the mass distribution of the host galaxy cluster is also investigated. The simulations are carried out in an open and a flat model universe with cosmological constant. We find that the enhancement of the cluster lensing cross-sections for long and thin arcs owing to the presence of a massive cD at the cluster centre is typically less than 100 per cent, depending on the model used for the cD galaxy and its orientation. The impact of the cD on the cluster efficiency for producing radially magnified images is larger only for those clusters with a lensing cross-section for radial arcs that is very small in absence of the central galaxy. We conclude that the presence of a cD galaxy at the cluster centre can only moderately influence the cluster efficiency for strong lensing and, in particular, fails to explain the discrepancy between the observed number of giant arcs in galaxy clusters and their abundance predicted from lensing simulations in the currently most favoured ACDM model.

The halo density profiles with non-standard N-body simulations

We propose a new numerical procedure to simulate a single dark halo of any size and mass in a hierarchical framework coupling the extended Press‐Schechter formalism (EPSF) to N-body simulations. The procedure consists of assigning cosmological initial conditions to the particles of a single halo with the EPSF technique and following only the dynamical evolution using a serial N-body code. The computational box is fixed with a side of 0.5 h −1 Mpc. This allows us to simulate galaxy cluster haloes using appropriate scaling relations, to ensure savings in computing time and code speed. The code can describe the properties of haloes composed of collisionless or collisional dark matter. For collisionless cold dark matter particles, the Navarro‐ Frenk‐White profile is reproduced for galactic haloes as well as galaxy cluster haloes. Using this numerical technique, we study some characteristics of haloes assumed to be isolated or placed in a cosmological context in the presence of weak self-interacting dark matter: the soft core formation and the core collapse. The self-interacting dark matter cross-section per unit mass is assumed to be inversely proportional to the particle collision velocity:σ/mx ∝ 1/v.