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Blobrana


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Very Large Structure at Z=3.78
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Title: Discovery of a Very Large Structure at Z=3.78
Author: Kyoung-Soo Lee, Arjun Dey, Sungryong Hong, Naveen Reddy, Christian Wilson, Buell T. Jannuzi, Hanae Inami, Anthony H. Gonzalez

We report the discovery of a large-scale structure containing multiple protoclusters at z=3.78 in the Bootes field. The spectroscopic discovery of five galaxies at z=3.783+/-0.002 lying within 1 Mpc of one another led us to undertake a deep narrow- and broad-band imaging survey of the surrounding field. Within a comoving volume of 72x72x25 Mpc^3, we have identified 65 Lyman alpha emitter (LAE) candidates at z=3.795+/-0.015, and four additional galaxies at z_spec=3.730,3.753,3.780,3.835. The galaxy distribution within the field is highly non-uniform, exhibiting three large (~3-5x) overdensities separated by 8-14 Mpc (physical) and possibly connected by filamentary structures traced by LAEs. The observed number of LAEs in the entire field is nearly twice the average expected in field environments, based on estimates of the Lya luminosity function at these redshifts. We estimate that by z=0 the largest overdensity will grow into a cluster of mass 10^15 Msun; the two smaller overdensities will grow into clusters of mass (2-6)x10^14 Msun. The highest concentration of galaxies is located at the southern end of the image, suggesting that the current imaging may not map the true extent of the large scale structure. Finding three large protocluster candidates within a single 0.3 deg^2 field is highly unusual; expectations from theory suggest that such alignments should occur less than 2% of the time. Searching for and characterizing such structures and accurately measuring their volume space density can therefore place constraints on the theory of structure formation. Such regions can also serve as laboratories for the study of galaxy formation in dense environments.

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Blobrana


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RE: large scale structures
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Largest structure challenges Einstein's smooth cosmos

A collection of galaxies that is a whopping four billion light years long is the biggest cosmic structure ever seen. The group is roughly one-twentieth the diameter of the observable universe - big enough to challenge a principle dating back to Einstein, that, on large scales, the universe looks the same in every direction.
Roger Clowes of the University of Central Lancashire in Preston, UK, and colleagues discovered the structure using data from the Sloan Digital Sky Survey, the most comprehensive 3D map of the universe. They identified a cluster of 73 quasars, the brightly glowing cores found at the centre of some galaxies, far larger than any similar structure seen before.
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Blobrana


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Title: Formation of the large-scale structure of the Universe
Authors: V. N. Lukash, E. V. Mikheeva, A. M. Malinovsky

In this review, the formation, evolution, and decay of the large-scale structure of the Universe is discussed in the context of observational data, numerical simulations, and the Cosmological Standard Model (CSM). Problems concerning measuring and interpreting cosmological parameters, determining the composition of matter, and normalizing density perturbation spectra are especially highlighted.

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Blobrana


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Title: An introduction into the theory of cosmological structure formation
Authors: Christian Knobel

This text aims to give a pedagogical introduction into the main concepts of the theory of structure formation in the universe. The text is suited for graduate students of astronomy with a moderate background in general relativity. A special focus is laid on deriving the results formally from first principles. In the first chapter we introduce the homogeneous and isotropic universe defining the framework for the theory of structure formation, which is discussed in the three following chapters. In the second chapter we describe the theory in the Newtonian framework and in the third chapter for the general relativistic case. The final chapter discusses the generation of perturbations in the very early universe for the simplest models of inflation.

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Blobrana


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WiggleZ confirms the Big Picture of the Universe

Using the Anglo-Australian Telescope, Ms Morag Scrimgeour has found that on distance scales larger than 350 million light years, matter is distributed extremely evenly, with little sign of fractal-like patterns.

"We used a survey called WiggleZ which contains more than 200,000 galaxies, and probes a cosmic volume of about 3 billion light years, cubed...This makes it the largest survey ever used for this type of measurement of the large scale Universe" - Ms Morag Scrimgeour

This finding is extremely significant for cosmologists as it confirms that the tools being used to describe the Universe are the right tools for the job after all.

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Blobrana


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Title: Clustering Fossils from the Early Universe
Authors: Donghui Jeong, Marc Kamionkowski

Many inflationary theories introduce new scalar, vector, or tensor degrees of freedom that may then affect the generation of primordial density perturbations. Here we show how to search a galaxy (or 21-cm) survey for the imprint of primordial scalar, vector, and tensor fields. These new fields induce local departures to an otherwise statistically isotropic two-point correlation function, or equivalently, nontrivial four-point correlation functions (or trispectra, in Fourier space), that can be decomposed into scalar, vector, and tensor components. We write down the optimal estimators for these various components and show how the sensitivity to these modes depends on the galaxy-survey parameters. New probes of parity-violating early-Universe physics are also presented.

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Blobrana


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Title: Large Scale Structure of the Universe
Authors: Alison L. Coil

Galaxies are not uniformly distributed in space. On large scales the Universe displays coherent structure, with galaxies residing in groups and clusters on scales of ~1-3 Mpc/h, which lie at the intersections of long filaments of galaxies that are >10 Mpc/h in length. Vast regions of relatively empty space, known as voids, contain very few galaxies and span the volume in between these structures. This observed large scale structure depends both on cosmological parameters and on the formation and evolution of galaxies. Using the two-point correlation function, one can trace the dependence of large scale structure on galaxy properties such as luminosity, color, stellar mass, and track its evolution with redshift. Comparison of the observed galaxy clustering signatures with dark matter simulations allows one to model and understand the clustering of galaxies and their formation and evolution within their parent dark matter halos. Clustering measurements can determine the parent dark matter halo mass of a given galaxy population, connect observed galaxy populations at different epochs, and constrain cosmological parameters and galaxy evolution models. This chapter describes the methods used to measure the two-point correlation function in both redshift and real space, presents the current results of how the clustering amplitude depends on various galaxy properties, and discusses quantitative measurements of the structures of voids and filaments. The interpretation of these results with current theoretical models is also presented.

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Blobrana


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Title: The cosmic web and the orientation of angular momenta
Authors: Noam I. Libeskind, Yehuda Hoffman, Alexander Knebe, Matthias Steinmetz, Stefan Gottlöber, Ofer Metuki, Gustavo Yepes

We use a 64h^{-1}Mpc dark matter (DM) only cosmological simulation to examine the large scale orientation of haloes and substructures with respect the cosmic web. A web classification scheme based on the velocity shear tensor is used to assign to each halo in the simulation a web type: knot, filament, sheet or void. Using ~10^6 haloes that span ~3 orders of magnitude in mass the orientation of the halo's spin and the orbital angular momentum of subhaloes with respect to the eigenvectors of the shear tensor is examined. We find that the orbital angular momentum of subhaloes tends to align with the intermediate eigenvector of the velocity shear tensor for all haloes in knots, filaments and sheets. This result indicates that the kinematics of substructures located deep within the virialised regions of a halo is determined by its infall which in turn is determined by the large scale velocity shear, a surprising result given the virilaised nature of haloes. The non-random nature of subhalo accretion is thus imprinted on the angular momentum measured at z = 0. We also find that haloes' spin axis is aligned with the third eigenvector of the velocity shear tensor in filaments and sheets: the halo spin axis points along filaments and lies in the plane of cosmic sheets.

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Blobrana


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Posts: 131433
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Axis of evil
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Universal Alignment

The universe has no center and no edge, no special regions tucked in among the galaxies and light. No matter where you look, it's the same - or so physicists thought. This cosmological principle - one of the foundations of the modern understanding of the universe - has come into question recently as astronomers find evidence, subtle but growing, of a special direction in space.
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Blobrana


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Universe Spin
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Title: Detection of a Dipole in the Handedness of Spiral Galaxies with Redshifts z ~ 0.04
Authors: Michael J. Longo

A preference for spiral galaxies in one sector of the sky to be left-handed or right-handed spirals would indicate a parity violating asymmetry in the overall universe and a preferred axis. This study uses 15158 spiral galaxies with redshifts <0.085 from the Sloan Digital Sky Survey. An unbinned analysis for a dipole component that made no prior assumptions for the dipole axis gives a dipole asymmetry of -0.0408±0.011 with a probability of occurring by chance of 7.9 x 10-4. A similar asymmetry is seen in the Southern Galaxy spin catalogue of Iye and Sugai. The axis of the dipole asymmetry lies at approx. (l, b) =(52°, 68.5°), roughly along that of our Galaxy and close to alignments observed in the WMAP cosmic microwave background distributions. The observed spin correlation extends out to separations ~210 Mpc/h, while spirals with separations < 20 Mpc/h have smaller spin correlations.

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Original spin: Was the universe born whirling?

A big bang that was also a big spin could explain a surprising alignment of galaxies - not to mention the origin of matter itself.
That is what physicist Michael Longo at the University of Michigan in Ann Arbor thinks he has found. If so, a wholesale review of our assumptions about the cosmos would be on the cards--and perhaps a solution to one of its biggest mysteries, the puzzling fact of matter's existence. As an anonymous peer-reviewer of Longo's most recent paper wrote: "Such claim, if proven true, would have a profound impact on cosmology and would very likely result in a Nobel prize."

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