#TITLE_ALTERNATIVE#

• Main Author: LINDA LARASATI (NIM : 103 10 021); Pembimbing : Dr. Hesti Retno Tri Wulandari, PRISCILLA
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/20406
• Institution: Institut Teknologi Bandung

This work builds directly from Mantz et al. (2014) as a partial reconstruction to study the properties of dark energy using NASA-Chandra’s X-ray observations of galaxy clusters. The main data set employed here consists of measured gas fractions (&#119891;&#119892;&#119886;&#119904;) from 40 X-ray luminous, massive, dynamically relaxed galaxy clusters spanning the redshift range 0.078 < z < 1.063. Because galaxy clusters are the most massive gravitationally bound structures in the universe, we can assume that their baryon fractions represent a good sample of the cosmic baryon fraction. Several simulations have indicated that the value of gas fraction, as a dominant contributor of baryonic matter in a cluster, tends to be redshift independent. This is also supported by X-ray observations. From this assumption, cosmological parameters constraints are determined using MCMC method via CosmoMC software for several cosmological models, especially for different dark energy models: (1) &#923;CDM, (2) constant- &#119908;, (3) evolving&#8722;&#119908;(z). <br /> <br /> The combination of gas fraction data set with several external data (e.g. CMB, SN Ia, and BAO) is used to produce a tighter constraint. Contribution of the gas fraction data gives about 11% reductions in uncertainty values. The constraint results of today's equation of state parameter (&#119908;0) are generally consistent with a value close to -1 (&#923;). However, the uncertainty range of those values still give possibilities for other dark energy models, such as phantom field or quintessence, to be considered. Meanwhile, the results from &#937;&#923; constraint generally conclude that around 70% of the universe constitutes of dark energy.