Large-scale Structure Formation Research Articles

WSPEC: A Waveguide Filter-Bank Focal Plane Array Spectrometer for Millimeter Wave Astronomy and Cosmology

Imaging and spectroscopy at (sub-)millimeter wavelengths are key frontiers in astronomy and cosmology. Large area spectral surveys with moderate spectral resolution (R=50-200) will be used to characterize large scale structure and star formation through intensity mapping surveys in emission lines such as the CO rotational transitions. Such surveys will also be used to study the SZ effect, and will detect the emission lines and continuum spectrum of individual objects. WSPEC is an instrument proposed to target these science goals. It is a channelizing spectrometer realized in rectangular waveguide, fabricated using conventional high-precision metal machining. Each spectrometer is coupled to free space with a machined feed horn, and the devices are tiled into a 2D array to fill the focal plane of the telescope. The detectors will be aluminum Lumped-Element Kinetic Inductance Detectors (LEKIDs). To target the CO lines and SZ effect, we will have bands at 135-175 GHz and 190-250 GHz, each Nyquist-sampled at R~200 resolution. Here we discuss the instrument concept and design, and successful initial testing of a WR10 (i.e. 90 GHz) prototype spectrometer. We recently tested a WR5 (180 GHz) prototype to verify that the concept works at higher frequencies, and also designed a resonant backshort structure that may further increase the optical efficiency. We are making progress towards integrating a spectrometer with a LEKID array and deploying a prototype device to a telescope for first light.

Multi-fractal analysis and lacunarity spectrum of the dark matter haloes in the SDSS-DR7

The dark matter halo distribution of the nearby universe is used to study the fractal behaviour in the proximate universe. The data, which is based on four volume-limited galaxy samples was obtained by Muñoz-Cuartas and Mueller (2012) from the Seventh Data Release of the Sloan Digital Sky Survey (SDSS-DR7). In order to know the fractal behaviour of the observed universe, from the initial sample which contains 412,468 galaxies and 339,505 dark matter haloes were used as input for the fractal calculations. Using this data we use the sliding-window technique for the dark matter distribution and compute the multi-fractal dimension and the lacunarity spectrum and use it to study its dependence on radial distance in every sample.The transition to homogeneity is not observed in the dark matter halo distribution obtained from the SDSS-DR7 volume-limited galaxy samples; in its place the dark matter halo distribution exhibits a persistent multi-fractal behaviour where the measured dimension does not arrive at the value of the physical dimension of the space, for all structure parameter values of the analysed set, at least up to radial distances of the ordered from 165 Mpc/h from the available centres of each sample. Our results and their implications are discussed in the context of the formation of large-scale structures in the universe.

RADIO AND X-RAY SHOCKS IN CLUSTERS OF GALAXIES

Radio relics detected in the outskirts of galaxy clusters are thought to trace radio-emitting relativistic electrons accelerated at cosmological shocks. In this study, using the cosmological hydrodynamic simulation data for the large-scale structure formation and adopting a diffusive shock acceleration (DSA) model for the production of cosmic-ray (CR) electrons, we construct mock radio and X-ray maps of simulated galaxy clusters that are projected in the sky plane. Various properties of shocks and radio relics, including the shock Mach number, radio spectral index and luminosity are extracted from the synthetic maps and compared with observations. A substantial fraction of radio and X-ray shocks identified in these maps involve multiple shock surfaces along line of sights (LoSs), and the morphology of shock distributions in the maps depends on the projection direction. Among multiple shocks in a given LoS, radio observations tend to pick up stronger shocks with flatter radio spectra, while X-ray observations preferentially select weaker shocks with larger kinetic energy flux. As a result, the shock Mach numbers and locations derived from radio and X-ray observations could differ from each other in some cases. We also find that the distributions of the spectral index and radio power of the synthetic radio relics are somewhat inconsistent with those of observed real relics; a bit more radio relics have been observed closer to the cluster core and with steeper spectral indices. We suggest the inconsistency could be explained, if very weak shocks with $M_s \la 2$ accelerate CR electrons more efficiently, compared to the DSA model adopted here.

Sterile neutrinos with secret interactions—lasting friendship with cosmology

Sterile neutrinos with mass ≃ 1 eV and order 10% mixing with active neutrinos have been proposed as a solution to anomalies in neutrino oscillation data, but are tightly constrained by cosmological limits. It was recently shown that these constraints are avoided if sterile neutrinos couple to a new MeV-scale gauge boson A′. However, even this scenario is restricted by structure formation constraints when A′-mediated collisional processes lead to efficient active-to-sterile neutrino conversion after neutrinos have decoupled. In view of this, we reevaluate in this paper the viability of sterile neutrinos with such ``secret'' interactions. We carefully dissect their evolution in the early Universe, including the various production channels and the expected modifications to large scale structure formation. We argue that there are two regions in parameter space—one at very small A′ coupling, one at relatively large A′ coupling—where all constraints from big bang nucleosynthesis (BBN), cosmic microwave background (CMB), and large scale structure (LSS) data are satisfied. Interestingly, the large A′ coupling region is precisely the region that was previously shown to have potentially important consequences for the small scale structure of dark matter halos if the A′ boson couples also to the dark matter in the Universe.

Mapping stellar content to dark matter haloes using galaxy clustering and galaxy–galaxy lensing in the SDSS DR7

The mapping between the distributions of the observed galaxy stellar mass and the underlying dark matter halos provides the crucial link from theories of large-scale structure formation to interpreting the complex phenomena of galaxy formation and evolution. We develop a novel statistical method, based on the Halo Occupation Distribution model (HOD), to solve for this mapping by jointly fitting the galaxy clustering and the galaxy-galaxy lensing measured from the Sloan Digital Sky Survey (SDSS). The method, called the iHOD model, extracts maximum information from the survey by including ~80% more galaxies than the traditional HOD methods, and takes into account the incompleteness of the stellar mass samples in a statistically consistent manner. The derived stellar-to-halo mass relation not only explains the clustering and lensing of SDSS galaxies over almost four decades in stellar mass, but also successfully predicts the stellar mass functions observed in SDSS. Due to its capability of modelling significantly more galaxies, the iHOD is able to break the degeneracy between the logarithmic scatter in the stellar mass at fixed halo mass and the slope of the stellar-to-halo mass relation at high mass end, without the need to assume a strong prior on the scatter and/or use the stellar mass function as an input. We detect a decline of the scatter with halo mass, from 0.22 dex at below 10^{12} Msun to 0.18 dex at 10^{14} Msun. The model also enables stringent constraints on the satellite stellar mass functions at fixed halo mass, predicting a departure from the Schechter functional form in high mass halos. The iHOD model can be easily applied to existing and future spectroscopic datasets, greatly improving the statistical constraint on the stellar-to-halo mass relation compared to the traditional HOD methods within the same survey.

Examining the Emergence of Large-scale Structures in Collaboration Networks: Methods in Sociological Analysis

This article introduces a number of methods that can be useful for examining the emergence of large-scale structures in collaboration networks. The study contributes to sociological research by investigating how clusters of research collaborators evolve and sometimes percolate in a collaboration network. Typically, we find that in our networks, one cluster among the leading ones eventually wins the growth race by percolating through the network, spanning it and rapidly filling up a significant volume of it. We show how this process is governed by the dynamics of cluster growth in the network. When operating in a percolating regime, this class of networks possesses many useful functional properties, which have important sociological implications. We first develop the methodological tools to perform a study of the intrinsic clustering process. Then, to understand the actual large-scale structure formation process in the network, we apply the theoretical methods to simulate a number of realistic scenarios, including one based on actual data on the collaboration behavior of a sample of researchers. From the perspective of social science research, our methods can be adapted to suit the application domains of many other types of real social processes.

Scalar-fluid theories: cosmological perturbations and large-scale structure

Recently a new Lagrangian framework was introduced to describe interactions between scalar fields and relativistic perfect fluids. This allows two consistent generalizations of coupled quintessence models: non-vanishing pressures and a new type of derivative interaction. The implications of these to the formation of cosmological large-scale structure are uncovered here at the linear order. The full perturbation equations in the two cases are derived in a unified formalism and their Newtonian, quasi-static limit is studied analytically. Requiring the absence of an effective sound speed term in the coupled dark matter fluid restricts the Lagrangian to be a linear function of the matter number density. This leaves new potentially viable classes of both algebraically and derivatively interacting models wherein the coupling may impact the background expansion dynamics and imprint new signatures into the large-scale structure.

Precision Measurements of the Cosmic Microwave Background

Fifty years after the first detection, we are now in the era of precision measurements of the Cosmic Microwave Background (CMB). The spectrum, anisotropy and polarization of the CMB have been measured with outstanding precision. The results support the hot big bang theory, and the adiabatic inflationaly scenario for the formation of large-scale structures in the Universe, with cold dark matter and dark energy. This is a short report on the latest experimental results, with mention of their impact on fundamental physics, and in particular on neutrino physics, the subject of this conference. We focus on spaceborne experiments, aimed at measuring the finest details of the CMB with final precision and accuracy.

Emission-line-selected galaxies atz= 0.6–2 in GOODS South: Stellar masses, SFRs, and large-scale structure

We have obtained deep NIR narrow and broad (J and Y) band imaging data of the GOODS-South field. The narrow band filter is centered at 1060 nm corresponding to redshifts $z = 0.62, 1.15, 1.85$ for the strong emission lines H$\alpha$, $[$OIII$]$/H$\beta$ and $[$OII$]$, respectively. From those data we extract a well defined sample ($M(AB)=24.8$ in the narrow band) of objects with large emission line equivalent widths in the narrow band. Via SED fits to published broad band data we identify which of the three lines we have detected and assign redshifts accordingly. This results in a well defined, strong emission line selected sample of galaxies down to lower masses than can easily be obtained with only continuum flux limited selection techniques. We compare the (SED fitting-derived) main sequence of star-formation (MS) of our sample to previous works and find that it has a steeper slope than that of samples of more massive galaxies. We conclude that the MS steepens at lower (below $M_{\star} = 10^{9.4} M_{\odot}$) galaxy masses. We also show that the SFR at any redshift is higher in our sample. We attribute this to the targeted selection of galaxies with large emission line equivalent widths, and conclude that our sample presumably forms the upper boundary of the MS. We briefly investigate and outline how samples with accurate redshifts down to those low stellar masses open a new window to study the formation of large scale structure in the early universe. In particular we report on the detection of a young galaxy cluster at $z=1.85$ which features a central massive galaxy which is the candidate of an early stage cD galaxy, and we identify a likely filament mapped out by $[$OIII$]$ and $H\beta$ emitting galaxies at $z=1.15$.

Large-scale structure and integrated Sachs–Wolfe effect in decaying vacuum cosmology

The concordance particle creation model - a class of $\Lambda(t)$CDM cosmologies - is studied using large scale structure (LSS) formation, with particular attention to the integrated Sachs-Wolfe (ISW) effect. The evolution of the gravitational potential and the amplitude of the cross-correlation of the cosmic microwave background (CMB) signal with LSS surveys are calculated in detail. We properly include in our analysis the peculiarities involving the baryonic dynamics of the $\Lambda(t)$CDM model which were not included in previous works. Although both the $\Lambda(t)$CDM and the standard cosmology are in agreement with available data for the CMB-LSS correlation, the former presents a slightly higher signal which can be identified with future data.

Regular and chaotic dynamics of non-spherical bodies. Zeldovich’s pancakes and emission of very long gravitational waves

In this paper we review a recently developed approximate method for investigation of dynamics of compressible ellipsoidal figures. Collapse and subsequent behaviour are described by a system of ordinary differential equations for time evolution of semi-axes of a uniformly rotating, three-axis, uniform-density ellipsoid. First, we apply this approach to investigate dynamic stability of non-spherical bodies. We solve the equations that describe, in a simplified way, the Newtonian dynamics of a self-gravitating non-rotating spheroidal body. We find that, after loss of stability, a contraction to a singularity occurs only in a pure spherical collapse, and deviations from spherical symmetry prevent the contraction to the singularity through a stabilizing action of nonlinear non-spherical oscillations. The development of instability leads to the formation of a regularly or chaotically oscillating body, in which dynamical motion prevents the formation of the singularity. We find regions of chaotic and regular pulsations by constructing a Poincaré diagram. A real collapse occurs after damping of the oscillations because of energy losses, shock wave formation or viscosity. We use our approach to investigate approximately the first stages of collapse during the large scale structure formation. The theory of this process started from ideas of Ya. B. Zeldovich, concerning the formation of strongly non-spherical structures during nonlinear stages of the development of gravitational instability, known as ‘Zeldovich’s pancakes’. In this paper the collapse of non-collisional dark matter and the formation of pancake structures are investigated approximately. Violent relaxation, mass and angular momentum losses are taken into account phenomenologically. We estimate an emission of very long gravitational waves during the collapse, and discuss the possibility of gravitational lensing and polarization of the cosmic microwave background by these waves.

Do Newtonian large-scale structure simulations fail to include relativistic effects?

The Newtonian simulations describing the formation of large-scale structures do not include relativistic effects. A new approach to this problem is proposed, which consists of splitting the Hawking-Hayward quasilocal energy of a closed spacelike 2-surface into a ``Newtonian'' part due to local perturbations and a ``relativistic'' part due to the cosmology. It is found that the Newtonian part dominates over the relativistic one as time evolves, lending support to the validity of Newtonian simulations.

NEUTRINO CONSTRAINTS TO THE DIFFUSE GAMMA-RAY EMISSION FROM ACCRETION SHOCKS

Accretion of gas during the large scale structure formation has been thought to give rise to shocks that can accelerate cosmic rays. This process then results in an isotropic extragalactic gamma-ray emission contributing to the extragalactic gamma-ray background observed by the Fermi-LAT. Unfortunately this emission has been difficult to constrain and thus presents an uncertain foreground to any attempts to extract potential dark matter signal. Recently, IceCube has detected high-energy isotropic neutrino flux which could be of an extragalactic origin. In general, neutrinos can be linked to gamma rays since cosmic-ray interactions produce neutral and charged pions where neutral pions decay into gamma rays, while charged pions decay to give neutrinos. By assuming that isotropic high-energy IceCube neutrinos are entirely produced by cosmic rays accelerated in accretion shocks during the process of structure formation, we obtain the strongest constraint to the gamma-ray emission from large scale structure formation (strong) shocks and find that they can make at best ~20% of the extragalactic gamma-ray background, corresponding to neutrino flux with spectral index 2, or ~10% for spectral index 2.46. Since typical objects where cosmic rays are accelerated in accretion shocks are galaxy clusters, observed high-energy neutrino fluxes can then be used to determine the gamma-ray emission of a dominant cluster type and constrain acceleration efficiency, and thus probe the process of large scale structure formation.

Use of Methods of Mathematical Modeling to Analyze Low-Frequency Pressure Pulsations in the Continuous Run of High-Head HPP

Anumerical procedure is presented for analysis of pressure pulsations in hydraulic turbines. Results of its use for description of unsteady turbulent flow in the continuous run of a hydraulic turbine are presented. The nu- merical method is adapted for results of modeling of turbulent unsteady flow in the continuous rune of a high-head HPP. The structure of the flow beyond the impeller and its effect on the intensity of unsteady pro- cesses are examined. Results of the analysis are compared with full-scale data. Good agreement is obtained between the computed and experimental results. Capacity regulation in the power system is a critical problem of hydroelectric power plants. When the load varies, the generating sets pass repeatedly through non-standard loading regimes. In such regimes, a significant portion of the swirling remains in the flow after passing through the impel- ler of the hydraulic turbine. Development of vigorous low- frequency hydrodynamic pulsations, which presents a threat to the reliability of turbine structures, is associated with the unsteady nature of the convoluted flow. An increase in operating stability and an increase in the efficiency of the hydraulic machines is impossible without study of the physical mechanisms of the hydrodynamic pro- cesses, among which unstable phenomena associated with formation of large-scale eddy structures play a major role. Some of the mechanisms responsible for generation of flow pulsations is precession of the vortex core that forms beyond the impeller of the hydraulic turbine in under-loaded or over-loaded operating regimes of the hydraulic turbine, when the flow after passing through the hydraulic turbine has suffi- ciently large residual swirl (1 - 2). Precession of the vortex core presents a serious risk to

S3T Stability of the Homogeneous State of Barotropic Beta-Plane Turbulence

Abstract Zonal jets and nonzonal large-scale flows are often present in forced–dissipative barotropic turbulence on a beta plane. The dynamics underlying the formation of both zonal and nonzonal coherent structures is investigated in this work within the statistical framework of stochastic structural stability theory (S3T). Previous S3T studies have shown that the homogeneous turbulent state undergoes a bifurcation at a critical parameter and becomes inhomogeneous with the emergence of zonal and/or large-scale nonzonal flows and that these statistical predictions of S3T are reflected in direct numerical simulations. In this paper, the dynamics underlying the S3T statistical instability of the homogeneous state as a function of parameters is studied. It is shown that, for weak planetary vorticity gradient β, both zonal jets and nonzonal large-scale structures form from upgradient momentum fluxes due to shearing of the eddies by the emerging infinitesimal flow. For large β, the dynamics of the S3T instability differs for zonal and nonzonal flows but in both the destabilizing vorticity fluxes decrease with increasing β. Shearing of the eddies by the mean flow continues to be the mechanism for the emergence of zonal jets while nonzonal large-scale flows emerge from resonant and near-resonant triad interactions between the large-scale flow and the stochastically forced eddies. The relation between the formation of large-scale structure through modulational instability and the S3T instability of the homogeneous state is also investigated and it is shown that the modulational instability results are subsumed by the S3T results.

A graph of dark energy significance on different spatial and mass scales

The current cosmological paradigm sees the formation and evolution of the cosmic large-scale structure as governed by the gravitational attraction of the Dark Matter (DM) and the repulsion of the Dark Energy (DE). We characterize the relative importance of uniform and constant dark energy, as given by the Lambda term in the standard LCDM cosmology, in galaxy systems of different scales, from groups to superclusters. An instructive "Lambda significance graph" is introduced where the matter-DE density ratio <rho_M>/rho_Lambda for different galaxy systems is plotted against the radius R. This presents gravitation and DE dominated regions and shows directly the zero velocity radius, the zero-gravity radius, and the Einstein-Straus radius for any fixed value of mass. Example galaxy groups and clusters from the local universe illustrate the use of the Lambda significance graph. These are generally located deep in the gravity-dominated region <rho_M}>/rho_Lambda > 2, being virialized. Extended clusters and main bodies of superclusters can reach down near the border line between gravity-dominated and DE dominated regions <rho_M>/rho_Lambda = 2. The scale--mass relation from the standard 2-point correlation function intersects this balance line near the correlation lenght. The log <rho_M>/rho_Lambda vs. log R diagram is a useful and versatile way to characterize the dynamical state of systems of galaxies within the Lambda dominated expanding universe.

Sound speed of scalar field dark energy: Weak effects and large uncertainties

The possibility of reconstruction of Lagrangian for the scalar field dark energy with constant effective sound speed $c_s$ is analyzed. It is found that such reconstruction can be made with accuracy up to an arbitrary constant. The value of $c_s$ is estimated together with other dark energy parameters ($\Omega_{de}$, $w_0$, $c_a^2$) and main cosmological ones on the basis of data including Planck-2013 results on CMB anisotropy, BAO distance ratios from recent galaxy surveys, galaxy power spectrum from WiggleZ, magnitude-redshift relations for distant SNe Ia from SNLS3 and Union2.1 compilations, the HST determination of the Hubble constant. It is shown that no value of $c_s$ from the range [0,1] is preferred by the used data because of very weak influence of dark energy perturbations on the large scale structure formation and CMB temperature fluctuations.

Searching for primordial localized features with CMB and LSS spectra

Inspired by the study of mild transient reductions in the speed of sound of the adiabatic mode during inflation, we search for a primordial localized feature imprinted in cosmic microwave background and large-scale structure formation observables. We find some common oscillatory patterns both in the Planck CMB temperature-temperature power spectrum and the WiggleZ galaxy spectrum. By performing independent searches with these two data sets, we find a coincidence in the most significant mode previously found by Ach\'ucarro et al. 2013 by using only Planck data. Furthermore, the joint data analysis shows that the oscillation frequency of the feature gets better constrained, and the amplitude marginally deviates from zero, unlike what was observed using only Planck data. Besides the parameter estimation, we also discuss the Bayesian evidence. The addition of WiggleZ data mildly enhances the significance of the best mode found in the Planck data.

Temporal Development of HF-Excited Langmuir and Ion Turbulence at Arecibo

The Arecibo high-power, high-frequency (HF) facility and 430 MHz radar are used to examine the temporal development of the HF-induced Langmuir and ion turbulences from 1 ms to many minutes after the turn-on of the HF beam in the F region. All HF observations begin in a smooth, stratified, stable plasma. “Cold start” HF transmissions are employed to avoid remnant irregularities from prior HF transmissions. HF-excited plasma line (HFPL) and ion line echoes are used to monitor the evolution of the turbulence. In the evening/nighttime the HFPL develops in three reproducible stages. Over time scales of 0 to 10–20 ms (possibly 40 ms), the smooth plasma conditions are maintained, and the results are consistent with theoretical models of the excitation of strong Langmuir turbulence near HF reflection. This entails the initiation of the so-called “caviton production cycle.” The turbulence from the parametric decay instability is detected at lower altitudes where the radar wave vector matches those of the HF-enhanced waves. The data suggests that the two processes coexist in the region in between. After ~40 ms the “overshoot process” begins and consists of a downward extension of the HFPL from the HF reflection region to heights ~1.1 km below followed by a retreat back to the reflection region. The whole overshoot process takes place over a time scale of ~3 s. Thereafter the echo remains near HF reflection for 20–90 s after HF turn-on. The HFPL echo subsequently breaks up into patches because of the formation of large-scale electron density structures in the plasma. New kinetic models indicate that suprathermal electrons excited in the plasma by, for example, caviton burn-out serve to regulate plasma turbulence in the modified ionospheric volume.

Formation of large-scale structures with sharp density gradient through Rayleigh-Taylor growth in a two-dimensional slab under the two-fluid and finite Larmor radius effects

Two-fluid and the finite Larmor effects on linear and nonlinear growth of the Rayleigh-Taylor instability in a two-dimensional slab are studied numerically with special attention to high-wave-number dynamics and nonlinear structure formation at a low β-value. The two effects stabilize the unstable high wave number modes for a certain range of the β-value. In nonlinear simulations, the absence of the high wave number modes in the linear stage leads to the formation of the density field structure much larger than that in the single-fluid magnetohydrodynamic simulation, together with a sharp density gradient as well as a large velocity difference. The formation of the sharp velocity difference leads to a subsequent Kelvin-Helmholtz-type instability only when both the two-fluid and finite Larmor radius terms are incorporated, whereas it is not observed otherwise. It is shown that the emergence of the secondary instability can modify the outline of the turbulent structures associated with the primary Rayleigh-Taylor instability.