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Two component baryonic-dark matter structure formation in top-hat model
, Article New Astronomy ; Volume 14, Issue 4 , 2009 , Pages 398-405 ; 13841076 (ISSN) ; Rahvar, S ; Mohamad Zadeh Jassur, D ; Sharif University of Technology
2009
Abstract
In this work we extend simple top-hat model of structure formation to the two component system made of baryonic and dark matter. We use Harrison-Zeldovich spectrum as the initial condition for the structures and calculate their evolution up to the present time. While we do not take into account some complications during the structure formation, such as the merging of galaxies, however this formalism can give us a qualitative picture from the formation of structures. We show that in this model small scale structures evolve faster than the larger ones and it predicts a down-top scenario for the structure formation. The trend of power spectrum in this model is compatible with the observations...
Spherical collapse in modified newtonian dynamics
, Article Astrophysical Journal ; Volume 694, Issue 2 , 2009 , Pages 1220-1227 ; 0004637X (ISSN) ; Rahvar, S ; Haghi, H ; Sharif University of Technology
Abstract
Modeling the structure formation in the universe, we extend the spherical-collapse model in the context of modified Newtonian dynamics (MOND) starting with the linear Newtonian structure formation followed by the MONDian evolution. In MOND, the formation of structures speeds up without a need for dark matter. Starting with the top-hat overdense distribution of the matter, the structures virialize with a power-law profile of the distribution of matter. We show that the virialization process takes place gradually from the center of the structure to the outer layers. In this scenario, the smaller structures enter the MONDian regime earlier and evolve faster, hence they are older than larger...
The Study of Fossil Galaxy Groups by Excursion Set Theory of Nonlinear Structure Formation
, M.Sc. Thesis Sharif University of Technology ; Baghram, Shant (Supervisor) ; Rahvar, Sohrab ($item.subfieldsMap.e)
Abstract
In the standard cold dark matter (CDM) family of cosmological models,the cosmological structures form hierarchically with the assumption of cold dark matter existence. The structure formation in the current CDM paradigm is capable of estimating the distribution function of the structures. It gives us a correct view from our observations of galaxies and structures. One of the successful methods to explain the statistics of cosmlogoical structures and their formation time is Excursion Set Theory. The excursion set theory considers the density field for each point in the universe smoothed with a spatial window function using the physics of random processes. The statistics of the structures can...
Structure Formation and Galactic Dynamics in Modified Gravity (MOG)
, Ph.D. Dissertation Sharif University of Technology ; Rahvar, Sohrab (Supervisor) ; Mohammad Movahed, Sadegh (Co-Advisor)
Abstract
The standard model of Cosmology (SM), based on Einstein’s theory of general relativity (GR), is the best model in describing the cosmic-scale observations. In galactic scales, however, galactic dynamics show a discrepancy between the observed luminous mass and the predicted value from the theory. Two approaches are suggested to eliminate this inconsistency: assuming the existence of dark matter within the context of GR, or modifying the theory of gravity in galactic scales, like MOND or MOG. In this thesis, we study the spherical collapse and the formation of shell galaxies in MOG, in comparison with SM. We introduce the action and the field equations of MOG and the equation of motion of a...
Formation of Supermassive Black Holes in the Center of Galaxies by Primordial Black Holes
, M.Sc. Thesis Sharif University of Technology ; Rahvar, Sohrab (Supervisor)
Abstract
One of the most important topics of interest to cosmologists and astrophysicists is the origin of supermassive black holes that form the center of most galaxies.In this research, we will introduce a mechanism for the growth of primordial black holes at the early universe, and we will argue that by this mechanism, with the assumptions that will be given in the relevant section, black holes of the order of 〖10〗^6 M_⊙ can be formed.Then assuming that there are supermassive black holes at the center of most galaxies, by calculating the number density of galaxies in comoving coordinate We will set the number density of galaxies in comoving coordinate and the number density of grown primordial...