Simulating Quasar Spectra from the Sloan Digital Sky Survey

Milaković, Dinko (2015) Simulating Quasar Spectra from the Sloan Digital Sky Survey. Diploma thesis, Faculty of Science > Department of Physics.

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Abstract

Quasars are the most distant astrophysical objects in the observable Universe that can be studied at high precision. The features seen in their spectra shed light onto the evolution of the Universe in the last 12 billion years. The quasar’s emission line properties and the absorption features created by intervening gas clouds, known as the Lyman a forest, contain a wealth of data useful in cosmological studies. They can be used to directly probe the distribution of baryonic and dark matter, to study baryonic acoustic oscillations, the expansion history of the Universe, locate anisotropies, constrain cosmological models, and many more. The purpose of this thesis is to generate a comprehensive set of simulated quasar spectra, providing an important tool for exploring a wide range of scientific topics derivable from observed quasar spectra. The main focus will be on Sloan Digital Sky Survey data, motivated by a project seeking to constrain any large-scale anisotropies in the Universe. The project uses quasar spectra from Data Release 10 to look for variations in the observed optical depth of neutral hydrogen across the sky, at any given redshift. This thesis will not discuss the actual spectral analysis performed to study the opacity of neutral hydrogen, but will focus on the necessity and production of mock data. Mock catalogues will allow us to identify and remove systematic errors, provide quantitative checks on other statistical methods used, and help to interpret scientific results. To produce the artificial quasar spectra with the observed properties of the Lyman a forest, I continued on previous work of John K. Webb and his program QSOSIM9. My new version of the program, QSOSIM10, generates the Lyman a forest under the assumption that the forest is represented fairly well by a set of discrete absorption lines. The program features an far more extensive set of the emission line features and new models of the column density and redshift distributions of neutral hydrogen, derived from high-resolution quasar spectra. The simulated spectra include physical effects seen in real spectra, such as the clustering of the intergalactic medium along the line-of-sight, the quasar proximity effect, and the heavy element transitions statistically, using known parameter distributions. The simulations employ the use of CLOUDY (a plasma simulation code) and CUBA (a radiative transfer code) calculations to derive heavy element column densities and model the cosmic ultraviolet background. The simulated spectra and the software developed in this thesis will also be suitable for other applications.

Item Type: Thesis (Diploma thesis)
Keywords: modern cosmology, Sloan Digital Sky Survey - SDSS, simulating QSO spectra, Doppler b-parameter
Supervisor: Smolčić, Vernesa
Date: 24 March 2015
Number of Pages: 92
Subjects: NATURAL SCIENCES > Physics > Astronomy and Astrophysics
Divisions: Faculty of Science > Department of Physics
Depositing User: Gordana Stubičan Ladešić
Date Deposited: 30 Apr 2015 12:59
Last Modified: 05 Sep 2016 15:37
URI: http://digre.pmf.unizg.hr/id/eprint/3925

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