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Cosmic Web and the Role of Environment on the Clustering of Cosmic Structures

Ghodsi, Laya | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53241 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Baghram, Shant
  7. Abstract:
  8. The standard model of Cosmology (ΛCDM, based on the cosmological constant and cold dark matter) is the simplest model that many of its predictions match with observations. Large scale observations are one of the most important observational data in Cosmology. This type of observation reveals that the cosmos have a web-like structure at large scales called "Cosmic web". This web consists of dense regions full of galaxies (Knot), long filamentary structures (Filament), flat sheets (Sheet), and low-density vast regions (Void). The cosmic web is the most prominent representative of the distribution of galaxies and dark matter in large scales and studying it can provide cosmologists with valuable information about the formation and evolution process of cosmic structures. The central idea of this project lies in the intersection of the concepts of the cosmic web and cosmological standard rulers. Cosmological standard rulers are important not only because their distances can be determined directly, but also because they can serve as distance indicators to calibrate the relation between distance and redshift. The length of large filaments can be an option for the standard ruler because the general skeleton of the cosmic web has been almost unchanged in late times (z<1). But, the length of filaments is not a well-defined variable and it extremely depends on the used filament-finder method. So, in this project, we aim to find an alternative variable similar to the length of filaments that can be used as a standard ruler.In the first section of this project, we investigate a variable called "Distance to the nearest neighbor" for galaxy groups as a potential alternative for the length of filaments to be used as a standard ruler. To do this, we study the data of galaxy groups from the Tempel observational catalogs (SDSS survey) using two measures: distance to the nearest neighbor and J function. As a result, we find out that the mean distance to the nearest neighbor and the clustering that is shown in J function are independent of redshift up to z=0.2. The mean distance to the nearest neighbor is bigger for the more massive and luminous groups, while the clustering that is shown in J function is smaller for these groups.Usually, cosmologists explore the cosmic web from two different points of view; one can consider the components of the cosmic web as independent structures or the host environments of galaxy groups and dark matter halos. In the second point of view, which is emphasized in this project, some of the important features of galaxy groups and dark matter halos strongly depend on their host environment. In the second section of this project, we investigate the dependence of the clustering of dark matter halos in simulations on the cosmic web components as their host environment. To do this, we study the data from four different filament-finder methods (CLASSIC, V-web, T-web, and ORIGAMI) on one N-body simulation using three clustering measures: two-point correlation function, distance to the nearest neighbor, and J function. As a result, we realize that in all filament-finder methods, except T-web, the most clustered cosmic web components are knots, filament, sheets, and voids in decreasing order
  9. Keywords:
  10. Cosmic Web ; Correlation Functions ; Clustering ; Standard Ruler ; J-Factor ; Distance to the Nearest Neighbor ; Environmental Dependence

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