Archivi tag: large scale structure

Simulating the first realistic cosmic web

Un gruppo di ricercatori guidati da Mark Vogelsberger dell’Harvard-Smithsonian Center for Astrophysics, in collaborazione con l’Heidelberg Institute for Theoretical Studies in Germania, hanno realizzato la prima mappa virtuale, alquanto realistica, dell’Universo utilizzando una simulazione numerica denominata “Illustris“. Il modello ha permesso di ricreare uno spazio cubico di lato pari a 350 milioni di anni-luce in un intervallo di tempo di circa 13 miliardi di anni e con una  risoluzione senza precedenti.

Continua a leggere Simulating the first realistic cosmic web

BOSS quasars yield a precise determination of cosmic expansion

An artist’s conception of how BOSS uses quasars to measure the distant universe. Light from distant quasars is partly absorbed by intervening gas, which is imprinted with a subtle ring-like pattern of known physical scale. Astronomers have now measured this scale with an accuracy of two percent, precisely measuring how fast the universe was expanding when it was just 3 billion years old. (Illustration by Zosia Rostomian, Lawrence Berkeley National Laboratory, and Andreu Font-Ribera, BOSS Lyman-alpha team, Berkeley Lab.)
La survey del cielo denominata Baryon Oscillation Spectroscopic Survey (BOSS), che rappresenta la parte più grande della terza survey Sloan Digital Sky Survey (SDSS-III), ha osservato i quasar distanti per realizzare una mappatura delle variazioni di densità del gas intergalattico a redshift elevati permettendo così di tracciare la struttura dell’Universo primordiale. BOSS ci fornisce da un lato una carta temporale della storia evolutiva dell’Universo al fine di avere maggiori indizi sulla natura dell’energia scura e dall’altro ci permette di realizzare nuove misure della struttura su larga scala, le più precise mai ottenute sull’espansione cosmica sin dall’epoca in cui si sono formate le prime galassie.

Continua a leggere BOSS quasars yield a precise determination of cosmic expansion

Cosmological Quests for the Next Decade

The inaugural cosmology conference in April 2014 will celebrate 40th anniversary of KASI. The workshop will cover recent progresses in observational and theoretical cosmology including the galaxies and large-scale structures, peculiar velocities, cosmic microwave background radiation, type Ia supernovae and gravitational lensing on the observational side, and the early universe, inflation, dark energy, dark matter, non-Gaussianity and numerical simulation in the theoretical side. Through close assessment of the present data and our current understanding we will be able to make plans for opening future windows in studying and describing our universe.

Tracing the cosmic Web

Large galaxy redshift surveys have revealed that the Universe has a striking weblike structure. On these scales, galaxies and matter in the universe are arranged in a complex network of dense compact clusters, elongated filaments, two-dimensional sheets, and huge near-empty voids. The Cosmic Web is one of the most intriguing and striking patterns found in nature, rendering its analysis and characterization far from trivial. The absence of an objective and quantitative procedure for identifying and isolating clusters, filaments and voids in the cosmic matter distribution has been a major obstacle in investigating the structure and dynamics of the Cosmic Web. The overwhelming complexity of the individual structures and their connectivity, the huge range of densities and the intrinsic multiscale nature prevent the use of simple tools that may be sufficient in less demanding problems. One aspect that the workshop will focus on strongly is the analysis and identification of the Cosmic Web and its various components. Progress on the study of the weblike geometry of the Megaparsec  and sub-Megaparsec matter distribution and of the relation between the large scale weblike environment and the galaxies populating its constituents has been hampered by the absence of a well-defined, commonly accepted language for quantifying its structure and topology. Quantities as basic and general as the mass and volume content of clusters, filaments, walls and voids are still not firmly established or defined.  Since there is not yet a common framework to objectively define filaments and walls, the comparison of results of different studies concerning properties of the filamentary network — such as their internal structure and dynamics, evolution in time, and connectivity properties — is usually rendered cumbersome and/or difficult. Over the years, a variety of heuristic measures were forwarded to analyze specific aspects of the spatial patterns in the large scale Universe. In recent years we have seen the development of more solid and well-defined machineries for the description, characterization and quantitative analysis of the intricate and complex spatial patterns of the Cosmic Web. They address the full range of weblike features simultaneously, instead of focusing just on voids, or filaments in their own right.  For a successful identification and characterization of the Cosmic Web we also need sophisticated reconstructions of the cosmic density field on the basis of the observed galaxy distribution.

During the course of the workshop, we will discuss and assess the different identification and reconstruction techniques, and contrast them with an aim towards developing a consensus among experts in the field. Amongst the specific issues that will be addressed are the following ones:

  • to increase our understanding of dynamics and evolution of the Cosmic Web, and the relation between the dark matter, gaseous
  • and galaxy distribution.
  • to obtain a handle on the way in which the web environment affects the formation and evolution of galaxies.
  • to obtain a representative census of the various methods to dissect the Cosmic Web and to identify its various components.
  • to assess and explore the fundamental differences between the different web analysis techniques.
  • to adapt techniques used for idealized theoretical and numerical circumstances to a range of observational data and surveys. Compare
  • the performance of the instruments for analysis of computer simulations with those used for the analysis of observational data and surveys.
  • to provide participants (before the meeting) with a z = 0 simulation snapshot and to compile comparative analyses of the simulation during the workshop. This comparison is intended to be published in a peer-reviewed journal.

Anisotropic Universe: from microwaves to ultrahigh energies

The study of anisotropies connects and unravels fundamental issues in various fields of astrophysics and cosmology. With the recent experimental progress, it is now possible to analyze, understand, and cross-correlate the anisotropic skies observed by Planck, 2MASS Redshift Survey, ChandraFermi, AMS-2, HAWC, IceCube, and Auger, – to cite but a few major instruments that scrutinize the Universe from microwaves to ultrahigh energies, in photons, cosmic rays, and neutrinos. Anisotropic features can reveal key information on the structure and the nature of the components of the Universe, and provide hints on the origin of high energy emission.

Instead of focusing on one particular field, we are planning for an interdisciplinary workshop on anisotropies and fluctuations in astrophysics and cosmology. Gathering researchers from various backgrounds, we aim at putting together our tools and our knowledge on anisotropies and fluctuations. Various methods and theories have been developed in parallel but their use has often been restricted to one particular area.

In particular, during the meeting we will be sharing our experience on

1) theoretical predictions of anisotropy signatures, for given configurations of source populations and of the whole Universe,
2) anisotropy analysis and measurement techniques,
3) cross-correlation of data from various wavelengths and messengers, fluctuations in time.

Theoretical Challenges in Large Scale Structure

In the last ten years, a wealth of observational data has revolutionized cosmology, allowing to pin down the cosmological parameters with an amazing precision. In the currently favored cosmological model, the wide range of cosmological structures we observe today formed from the nonlinear evolution of tiny fluctuations which were imprinted during an inflationary phase in the early Universe. While cosmology has already offered a number of outstanding achievements, such as the detection of primeval fluctuations in the cosmic microwave background (CMB) and the discovery of dark energy, a number of key questions remain unanswered, including:

  • What is the nature of dark energy?
  • Is it Einstein’s cosmological constant, a different substance with unusual equation of state, or perhaps a signature of a breakdown of Einstein’s General Relativity on cosmological scales?
  • Are the initial conditions in the Universe compatible with the theory of inflation, or do they require an alternative description?
  • Are there primordial non-Gaussianities that would invalidate the simplest models of inflation?
  • What is the mass of neutrinos?
  • Are the masses of neutrino families degenerate?
  • Are there more that 3 neutrino families?

Cosmological observations of the CMB have played a leading role in recent years, a process that will culminate with the Planck resuts to be announced in March 2013. However, the future of observational cosmology is likely to be dominated by the large scale structure (LSS) of the Universe, which encodes information on the clustering of dark matter as a function of time and scale and, therefore, is sensitive to physical quantities such as the neutrino mass or the dark energy equation of state. There are currently two major approaches to the LSS: the first consists in measuring galaxy positions and relating these to the underlying dark matter clustering. This method, called galaxy clustering, has good signal, but the theoretical modeling suffers from uncertainties arising from our lack of understanding of galaxy bias. The second consists in measuring the weak gravitational lensing induced by the dark matter through the distortion of distant galaxy images. This technique, called weak lensing, furnishes a more direct probe of the dark matter distribution. However, it suffers from a lower overall signal and from various observational systematics.

The question of whether these methods can achieve their promise depends on whether the aforementioned theoretical and observational uncertainties can be resolved. This is the subject of the proposed conference. One of the main conference topics is on theoretical aspects, because a lack of progress in this area could seriously hinder the promised achievements of the future surveys. There are many theoretical aspects that need to be understood better if the connection between fundamental physics and LSS observables is to be fully exploited. Among the open theoretical questions are understanding the nonlinear clustering of dark matter and the bias of tracers such as galaxies or Ly-alpha absorption lines, quantifying the effects of baryons and feedback from galaxy formation on the weak lensing observables, modeling the signature of redshift space distortions, assessing the information content of high order correlations (mostly bispectrum and trispectrum) of galaxy clustering and weak lensing observables.

Another focus will be on new methods that have been developed in recent years. Among them are primordial non-Gaussianity in the 2-point and higher order correlations of biased tracers as a probe of inflation, methodologies that can reduce the impact of traditional limitations (such as sampling variance or shot noise), the use of reconstruction techniques to increase the information on cosmological parameters or the combination of several LSS techniques (e.g. weak lensing, galaxy clustering, cluster counts) to improve constraints. With a suitable application of these methods, the future surveys may be able to extend their initially planned objectives and have a far greater impact than originally expected.

The third broad topic of the conference will be on the challenges and limitations imposed by the data. Galaxy clustering data is contaminated by the presence of stars, variable selection functions etc., while weak lensing measurements are contaminated by distortions of the point spread function, systematics in the extraction of galaxy ellipticities, uncertainties in the determination of photometric redshifts etc. All these sources of systematic errors may impact the desired sensitivity of the survey and, therefore, must be understood thoroughly.

More info: LSS13

Galaxies within the Cosmic Web

The Kavli Institute for Cosmological Physics (KICP) at the University of Chicago will host “Galaxies within the Cosmic Web” workshop on June 17-21, 2013. The workshop will be held in the lecture hall 120 in the Kersten Physics Teaching Center (KPTC) on the University of Chicago campus. During the last thirty years, studies of structure formation have played a key role in establishing the Cold Dark Matter (CDM) paradigm of structure formation in an expanding universe. In the CDM model the initial Gaussian density perturbations are shaped by gravity into a cosmic web of voids and filaments, at the intersection of which galaxies and galaxy clusters are mainly thought to form. Although the model has been a tremendous success in explaining the observed large-scale structure of the universe, many key aspects of how galaxies form and evolve within this cosmic web of dark matter and diffuse gas are still not understood. The gaps in our understanding not only hamper interpretation of the wealth of observational data on galaxy evolution, but also represent a major systematic uncertainty for cosmological probes of the accelerated expansion of the universe, the nature of gravity, and forecasts and interpretation of direct and indirect dark matter searches. This workshop will assemble both observers and theorists (target size ~60-80 people) who work on all key aspects of galaxy formation to assess recent progress and, most importantly, to germinate new ideas for how to improve our understanding of galaxy formation, the relation between the baryonic mass of galaxies and their parent halos, the effects of galaxy assembly and associated feedback on the spatial distribution of dark matter, and the interpretation of galaxy clustering and bias from large surveys to constrain the evolution of dark energy. The focus of the meeting will be on the most rapidly developing and interesting topics of research, and the format will include ample time for discussion and unstructured interaction.

Cosmology, Large Scale Structure and First Objects

Cosmology, Large Scale Structure and First Objects – This USP Conference shall cover the key issues of Cosmology, from particle physics, fundamental gravitation, cosmic background radiation, dark matter and dark energy, large-scale structure, simulations of the formation of structure in the Universe, as well as comparisons to observations.  Continua a leggere Cosmology, Large Scale Structure and First Objects

The TAIPAN Survey: Toward the Next Generation of Spectroscopic All-Sky Surveys

The TAIPAN Survey: Toward the Next Generation of Spectroscopic All-Sky Surveys – The workshop is designed to bring together experts and researchers to discuss the science prospects and goals of the proposed TAIPAN survey.  Continua a leggere The TAIPAN Survey: Toward the Next Generation of Spectroscopic All-Sky Surveys