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Modeling the Constituents of the Early Universe

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Modeling the Constituents of the Early Universe Modeling the Constituents of the Early Universe The Harvard community has made this article openly available. Please share how this access benefits you. Your story matters Citable link http://nrs.harvard.edu/urn-3:HUL.InstRepos:40046472 Terms of Use This article was downloaded from Harvard University’s DASH repository, and is made available under the terms and conditions applicable to Other Posted Material, as set forth at http:// nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of- use#LAA Modeling the Constituents of the Early Universe A dissertation presented by Natalie Mashian to The Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the subject of Physics Harvard University Cambridge, Massachusetts May 2017 c 2017 | Natalie Mashian All rights reserved. Dissertation Advisor: Professor Abraham Loeb Natalie Mashian Modeling the Constituents of the Early Universe Abstract Understanding how baryons assembled into the first stars and galaxies given the underlying dark matter distribution in the early Universe remains one of the key challenges in the field of cosmology. Given the great distances and extreme faintness of the oldest celestial objects, direct observation of the high redshift Universe remains difficult. Due to the biased, small number statistics, various other avenues have been sought out and paved to construct a coherent picture of the large-scale structure of the Universe at these early times. This thesis explores several of these avenues in a series of studies aimed at characterizing the first galaxies and the star-forming molecular gas that drives their evolution in the early Universe. We model the effects of strong gravitational lensing and find that by magnifying sources that would otherwise be too faint to detect and lifting them over the instrumental detection threshold, lensing allows us to probe the luminosity function (LF) below current survey limits and constrain the low-luminosity cut-off of the Schechter LF. Using the most recent dust estimates and z ∼ 4-8 LF measurements, we then model the LF evolution at higher redshifts by employing abundance matching techniques and derive the redshift evolution of the star formation rate density along with the associated cosmic reionization history. To model the molecular interstellar medium (ISM), we employ the large velocity gradient (LVG) method, a radiative transfer technique used to quantitatively analyze iii CO spectral line energy distributions (SLEDs). In particular, we probe the average state of the molecular gas in HDF 850.1, a z ∼ 5.2 submillimetre source, as well as a series of local starburst, Seyfert, and ultraluminous infrared galaxies. We identify characteristic properties of the local and high-redshift ISM, including the kinetic temperature, gas density, and column density in each case, and derive the gas masses of the various CO-emitting sources along with the corresponding CO-to-H2 conversion factors. Furthermore, we develop a theoretical framework to estimate the intensity mapping signal and power spectrum of any CO rotational line emitted at high redshifts, particularly during the epoch of reionization. By linking the characteristic properties of emitting molecular clouds to the global properties of the host halos, we model the spatially averaged brightness temperature of all the CO transitions and find the predicted signals to be within reach of existing instruments. We further apply our formalism to compute the cumulative CO emission from star-forming galaxies throughout cosmic time. Lastly, we explore the emergence of planetary systems around carbon-enhanced metal-poor (CEMP) stars, possible relics of the early Universe residing in the halo of our galaxy. We determine the maximum distance from the host CEMP star at which carbon-rich planetesimal formation is possible and characterize the potential planetary transits across these chemically anomalous stars. We conclude by exploring the possibility of probing the stellar black hole population using astrometric observations provided by missions such as Gaia. We predict that nearly 3×105 astrometric binaries hosting black holes should be discovered during Gaia's five year mission. The invisible companions of astrometrically observed metal-poor, low-mass stars may be stellar remnants from the dawn of the Universe, offering to shed light on iv the formation of the first stellar black holes in the early stages of galaxy assembly. v Contents Abstract iii Acknowledgments xii Dedication xiii 1 Introduction 1 1.1 Early Galaxies . .2 1.1.1 Theoretical Perspective . .2 1.1.2 High-Redshift Observations . .5 1.1.3 Stellar Archaeology . .7 1.2 Cool Molecular Gas . .9 1.2.1 Tracing the Molecular ISM . 10 1.2.2 Modeling CO Excitation . 12 1.2.3 Observational Studies . 14 I High Redshift Galaxies 17 2 Constraining the Minimum Luminosity of High Redshift Galaxies through Gravitational Lensing 18 2.1 Abstract . 19 2.2 Introduction . 20 vi CONTENTS 2.3 The Lensing Model . 24 2.4 Results . 32 2.5 Discussion . 43 2.6 Acknowledgements . 44 3 An Empirical Model for the Galaxy Luminosity and Star Formation Rate Function at High Redshift 45 3.1 Abstract . 45 3.2 Introduction . 46 3.3 The Formalism . 50 3.3.1 The Observed Star-Formation Rate Functions . 50 3.3.2 Method to derive the average SF R − Mh relation . 53 3.3.3 Modeling the SFR Functions . 55 3.4 Results . 56 3.4.1 The Constant SF R − Mh Relation . 56 3.4.2 The Modeled SFR Functions at z = 4 − 8 .............. 59 3.4.3 A Prediction for the UV LF at z = 9 − 10 . 61 3.4.4 Extrapolation to z ∼ 20 and Predictions for JWST . 63 3.4.5 Contribution of Galaxies to Cosmic Reionization . 67 3.5 Summary . 71 3.6 Acknowledgements . 73 II The Molecular Interstellar Medium 74 4 The Ratio of CO to Total Gas Mass in High-Redshift Galaxies 75 4.1 Abstract . 75 4.2 Introduction . 76 4.3 Large Velocity Gradient Model . 79 vii CONTENTS 4.4 Analysis of HDF 850.1 . 83 4.4.1 Properties of the Galaxy . 83 4.4.2 Separate CO, C+ Virialized Regions . 86 4.4.3 Separate CO, C+ Unvirialized Regions . 89 4.4.4 Optically thin [CII]........................... 90 4.4.5 Uniformly Mixed CO, C+ Virialized Region . 92 4.4.6 Uniformly Mixed CO, C+ Unvirialized Region . 95 4.5 Cosmological Constraints . 95 4.6 Summary . 100 4.7 Acknowledgements . 101 5 High-J CO Sleds in Nearby Infrared Bright Galaxies Observed by Her- schel/PACS 103 5.1 Abstract . 104 5.2 Introduction . 105 5.3 Target Selection, Observations, and Data Reduction . 107 5.4 Excitation Analysis . 118 5.4.1 CO SLEDs and Line Ratios . 118 5.4.2 LVG Radiative Transfer Model . 122 5.4.3 Fitting Procedure . 125 5.5 LVG Results & Discussion . 127 5.5.1 NGC 253 . 135 5.5.2 M 83 . 140 5.5.3 M 82 . 141 5.5.4 NGC 4945 & Circinus . 142 5.5.5 NGC 1068 . 144 5.5.6 NGC 4418 . 145 viii CONTENTS 5.5.7 IC 694 & NGC 3690 . 145 5.5.8 Arp 220 . 146 5.5.9 NGC 6240 . 147 5.5.10 Mrk 231 . 148 5.6 Summary . 149 5.7 Acknowledgements . 152 6 Predicting the Intensity Mapping Signal for multi-J CO lines 154 6.1 Abstract . 154 6.2 Introduction . 155 6.3 Modeling the CO Emission . 159 6.3.1 CO Brightness Temperature . 159 6.3.2 The Star Formation Model . 162 6.3.3 Theoretical Models for LVG Parameters . 164 6.3.3.1 Gas Kinetic Temperature . 165 6.3.3.2 Cloud volume density . 166 6.3.3.3 Velocity Gradient . 172 6.3.3.4 CO-to-H2 Abundance Ratio . 172 6.3.3.5 CO Column Density, including photodissociation . 172 6.3.4 Model CO SLEDs . 176 6.4 Results . 179 6.4.1 Predicted CO Fluxes and Spatially Averaged CO Brightness Tem- perature . 179 6.4.2 CO Power Spectrum . 186 6.5 Discussion . 190 6.6 Acknowledgements . 195 7 Spectral Distortion of the CMB by the Cumulative CO Emission from ix CONTENTS Galaxies throughout Cosmic History 196 7.1 Abstract . 196 7.2 Introduction . 197 7.3 The Formalism . 201 7.4 Results . 204 7.5 Discussion . 209 7.6 Acknowledgements . 211 III Early Planetary Systems 212 8 CEMP Stars: Possible Hosts to Carbon Planets in the Early Universe 213 8.1 Abstract . 213 8.2 Introduction . 214 8.3 Star-forming Environment of CEMP Stars . 217 8.4 Orbital Radii of Potential Carbon Planets . ..
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