«by Shailendra Kumar Vikas Bachelor of Technology, Indian Institute of Technology, Kharagpur, 2001 Master of Science, University of Pittsburgh, 2007 ...»
QUASARS, CARBON, AND SUPERNOVAE:
EXPLORING THE DISTRIBUTION OF ELEMENTS
IN AN EXPANDING UNIVERSE
Shailendra Kumar Vikas
Bachelor of Technology, Indian Institute of Technology, Kharagpur,
Master of Science, University of Pittsburgh, 2007
Submitted to the Graduate Faculty of
the Department of Physics and Astronomy in partial fulﬁllment
of the requirements for the degree of Doctor of Philosophy University of Pittsburgh 2013
UNIVERSITY OF PITTSBURGH
DEPARTMENT OF PHYSICS AND ASTRONOMYThis dissertation was presented by Shailendra Kumar Vikas It was defended on Aug 10, 2012 and approved by W. Michael Wood-Vasey Jeﬀery Newman Andrew R. Zentner Vittorio Paolone Rupert Croft Dissertation Director: W. Michael Wood-Vasey ii Copyright c by Shailendra Kumar Vikas 2013 iii
QUASARS, CARBON, AND SUPERNOVAE: EXPLORING THE
DISTRIBUTION OF ELEMENTS IN AN EXPANDING UNIVERSEShailendra Kumar Vikas, PhD University of Pittsburgh, 2013 This thesis consists of three diﬀerent studies with a common goal of understanding the constituents and structures of the universe.
The current understanding of galaxy formation is not complete. Cold and hot ﬂows in galaxies play a role in the evolution and transportation of elements within halos. Ionized carbon clouds are often observed in the spectra of back-lighting quasars. I study the clus- tering properties of the triply ionized carbon clouds from SDSS-III data to determine the minimum mass of the host halo in which galaxy formation processes produce such clouds.
Apart from enabling better understanding of these clouds, this result will help constrain galaxy formation theory and the associated feedback processes.
Standard cosmological theory produces an excess of baryonic structure compared to the observed one. Energetic quasars are often envisaged as the process which injects kinetic energy into the structures and halts the structure formation. I study the outﬂow in SDSS- III quasars through the observed velocities of the triply ionized carbon clouds detected in their spectra. Using more accurate modeling of the abundance of carbon clouds, I make robust conclusions about properties of outﬂow systems. Understanding the velocities of such outﬂow helps constrain the amount of energy injected in the feedback process of quasars and helps in explaining the observed baryonic structure of the Universe.
Supernovae Ia enable us to measure distances at diﬀerent redshifts. Distances enable us to infer the expansion history of the Universe and measure the current accelerated expansion.
The equation-of-state parameter, w, of the dark energy responsible for this acceleration, can iv be determined from the expansion history. I estimate w using data from ESSENCE and other current supernova surveys and measure the eﬀect of the important systematic uncertainties that are expected to have the largest contribution to the uncertainty in our understanding of dark energy.
I would ﬁrst like to thank my adviser, Michael Wood-Vasey for the support and guidance.
He took me as his student at a challenging time for me when me and my wife had just been blessed with daughter. He gave me independence to carry my research and understood my weak and strong points. His help, throughout my time as his student, goes beyond the responsibilities of an adviser.
I would also like to thank my wife, Laxmi, and daughter, Sana, for their love, support and motivation to complete my studies. I would not be able to manage in the hectic times of thesis writing and job search.
I thank Brian Cherinka for his help by proof reading my thesis in detail. His help has signiﬁcantly improved the quality of this thesis.
I thank my colleges Benjamin Brown, Brian Cherinks, Andrew Hearin, Chengdong Li, Daniel Matthews, Mei-yu Wang, Anja Weyant, Sui Chi Woo for discussion which help me enrich and broaden my knowlege.
I have made use of the Python programming language along with the very useful Python packages “matplotlib,” “numpy,” “scipy,” “pyminuit.” Computations for this thesis made use of the Odyssey cluster supported by the FAS Sciences Division Research Computing Group at Harvard University.
Chapter 4 could not have been possible without the help and guidance from Gautham Narayan and Richard Kessler. Supernova analysis software, SNANA, created by Richard Kessler was instrumental for the analysis done in the chapter. I was highly beneﬁted by the many analysis code created by Gautham Narayan and Michael Wood-vasey.
Chapter 2 & 3 uses the absorber ﬁnding software provided by Britt Lundgren. The absorbers catalog has been instrumental for the study done in these chapters. The code to xii calculate the completeness map of the survey was provided by Adam Meyers, which was crucial for the study in Chapter 2. The study also beneﬁted greatly by useful suggestions and discussion from Jeﬀrey A. Newman, Sandhya Rao and Andrew R. Zentner. The code to calculate the dark matter correlation function provided by Andrew R. Zentner was helpful in study. The data for these studies was provided by SDSS-III.
Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Oﬃce of Science. The SDSS-III web site is http://www.sdss3.org/.
SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration including the University of Arizona, the Brazilian Participation Group, Brookhaven National Laboratory, University of Cambridge, Carnegie Mellon University, University of Florida, the French Participation Group, the German Participation Group, Harvard University, the Instituto de Astroﬁsica de Canarias, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins University, Lawrence Berkeley National Laboratory, Max Planck Institute for Astrophysics, Max Planck Institute for Extraterrestrial Physics, New Mexico State University, New York University, Ohio State University, Pennsylvania State University, University of Portsmouth, Princeton University, the Spanish Participation Group, University of Tokyo, University of Utah, Vanderbilt University, University of Virginia, University of Washington, and Yale University.
xiii 1.0 INTRODUCTION
This dissertation explains the background and details of my contribution to improve the understanding of the Universe and its constituent. I study constituents diﬀerent epochs of the Universe, encompassing the distribution of elements during the epoch when galaxies were very actively evolving and forming stars to the acceleration of the expansion of universe at recent epochs.
The ﬁrst chapter provides a brief introduction to our current understanding of the universe and the relevance of my thesis towards improving that understanding. It explains the current standard cosmology, also known as ΛCDM cosmology, which explains various important epochs of the evolution of the universe. The diﬀerent projects of my thesis are presented in each of the chapter. In Chapter 2, I measure the special clustering strength of carbon clouds with respect to quasars to determine the host halo mass of these absorbers.
In Chapter 3, I present the most detailed measurements and analysis to date of the carbon clouds from the outﬂow of quasars. In Chapter 4, I measure properties of dark energy using Supernovae Ia and estimate the systematic error due to the largest expected contributors.
In the Appendix, I describe the enhancement to a pipeline used to detect absorption lines in quasar spectra. The enhanced absorber pipeline is used in the work described in Chapter 2 and Chapter 3.
In the standard picture of ΛCDM cosmology, the universe is made of three main constituents: 1. Matter; 2. Radiation; and 3. Dark Energy. The “Matter” component can be further divided as “dark matter”, which only interacts gravitationally, and ordinary matter (baryons). Fig. 1.1 shows the contributions of diﬀerent components. The contributions of dark energy, dark matter, and baryons are approximately 74%, 22%, and 4% respectively, of the total energy density at the present epoch, while the contribution of radiation is negligible (Komatsu et al. 2011; Larson et al. 2011; Jarosik et al. 2011). The dark matter is approximately ﬁve times more abundant than the ordinary matter and therefore plays a central role in the formation of structures, while the ordinary material largely traces the gravitational potential deﬁned by the dark matter. Standard cosmology also assumes that Einstein’s theory of General Relativity, which has been tested quite accurately at various scales, is the guiding principle for the universe. The density of each components evolves at a diﬀerent rates; because of this, at various times during the evolution of the universe, diﬀerent components played the dominant role. The geometry of the universe has been measured to be very close to being ﬂat with a high degree of accuracy (Komatsu et al. 2011; Larson et al.
2011; Jarosik et al. 2011). As such, I assume it to be ﬂat throughout this dissertation.
Figure 1.1 The constituents of the universe at the present epoch.
The dark energy, dark matter and baryons are approximately 74%, 22% and 4% of the total energy density. The radiation is negligible at the present epoch.
The universe is believed to have been in a very hot and dense state at the earliest fraction of a second. The natural forces were uniﬁed. As the universe expanded, it cooled and 2 the natural forces started to separate. This expansion was most dramatic during a period of “inﬂation”, during which it increased about 1050 times in scale (see Fig. 1.2). As the cooling process continued, the quarks and photons remained in thermal equilibrium. When the universe cooled suﬃciently, the quarks combined to form stable protons and neutrons.
As the cooling continued, the neutrons and protons interacted and started to fuse together to make nuclei of elements heavier than hydrogen, a process called “nucleosynthesis”. The era of nucleosynthesis created nuclei of helium and a very small amount of lithium and beryllium. These nuclei and free electrons continued to interact with photons because they are electrically charged and thus easily interact with photons. The large cross-sections of nuclei and free electrons inhibited free streaming of photons and made the universe opaque.
The temperature eventually cooled enough (T∼3000 K) for the electrons to combine with nuclei to make neutral atoms. These atoms, being neutral, did not strongly interact with photons (peak λ ∼ 1µm), allowing photons to stream freely afterwards. We observe these photons today as the Cosmic Microwave Background (CMB). This epoch is known as the “recombination” era (Fig. 1.2, Marked as “Afterglow Light Pattern”).
1.2 STRUCTURE FORMATION
The universe continued to expand and cool after recombination. The matter component of the universe at this point consisted of dark matter and atoms of hydrogen, helium, and traces of lithium. Due to the expansion of the universe, the CMB photons were redshifted out of the optical range. No stars or other bodies had yet formed; there was nothing hot enough to generate optical photons. Due to the lack of optical photons, this era is also known as the dark ages. The dark matter formed large scale structure by gravitating to initial regions of small overdensities. Subsequently, these overdensities grew bigger and gas clouds of hydrogen and helium fell into them. The gas clouds continued to cool through radiation and form more dense clouds. The gravitation instability in these clouds caused the gas to collapse and form the ﬁrst generation of stars, also known as population III stars (see Fig. 1.2; Bromm et al. 2009; Chiappini et al. 2011). The ﬁrst stars were much more massive 3 than stars found today. Massive stars are both short lived and very bright. Such extreme brightness caused the ionization of regions surrounding the stars, and the universe became ionized again. This epoch is also called the era of reionization (Wyithe and Loeb 2003;
Bromm et al. 2009; Robertson et al. 2010).
Figure 1.2 Evolution of the universe over 13.
7 billion years. Important epoch of inﬂation, recombination, dark ages, and ﬁrst star formation are shown. Credit: NASA / WMAP Science Team Small inhomogeneities in the early universe started to grow after recombination. Dark matter gravitated towards overdensities. Fig. 1.3 shows the simulated structure of universe at large scale. The plots, from top left to bottom right, are snapshots of the universe at redshift z=18.3, 5.7, 1.4 and 0.0 from a numerical simulation called the Millennium Simulation (Springel et al. 2005). As can be seen from these plots, the structures are more evolved and show ﬁlamentary structure at smaller redshift. Fig. 1.4 shows the observed structure 4 of our local universe, where each point denotes a real galaxy. The ﬁlamentary structure, as predicted by the simulation, is evident in the observed data, leading to the conclusion that ordinary matter follows the dark matter potential.
Figure 1.3 Computer simulation of large-scale structure of universe from the Millennium Simulation.
From top left to bottom right the structure at redshift z= 18.3, 5.7, 1.4 and
0.0 respectively. The bar in each ﬁgure shows the scale of 125 Mpc/h. (Springel et al. 2005, http://www.mpa-garching.mpg.de/galform/virgo/millennium) The structures continued to evolve, enhancing inhomogeneity. Baryons condensed in these overdensities and began to form more complex object than stars (e.g., proto-galaxies, quasars, galaxies, galaxy clusters etc.). Quasars are known to have existed as early as redshift 7.085, which is only 0.77 billion years after the Big Bang (Mortlock et al. 2011).