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The Properties of Massive Galaxies at Cosmic Noon: Evolutionary Copyright by Sydney Beth Sherman 2021 The Dissertation Committee for Sydney Beth Sherman Certifies that this is the approved version of the following Dissertation: The Properties of Massive Galaxies at Cosmic Noon: Evolutionary Pathways and Implications for Physical Models of Galaxy Growth Committee: Shardha Jogee, Supervisor Steven L. Finkelstein Caitlin Casey Volker Bromm Neal Evans Chris Conselice The Properties of Massive Galaxies at Cosmic Noon: Evolutionary Pathways and Implications for Physical Models of Galaxy Growth by Sydney Beth Sherman Dissertation Presented to the Faculty of the Graduate School of The University of Texas at Austin in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy The University of Texas at Austin May 2021 I have been lucky enough to be able to spend the last decade in my own little world studying galaxy evolution, of all things. This thesis is dedicated to all the people who made sure I didn’t make this journey alone. Acknowledgments I would like to start by thanking my PhD thesis committee and the faculty and staff of the UT Astronomy department. You have all prepared me for life after my PhD in more ways than you will ever know and for that I am extremely grateful for this experience. To the grad students - thanks for the hallway chats, Fridays at Crown, and spending too much time at cookies. Grad school would have been pretty boring without all of you. I’d also like to thank two women who don’t know me but have made a huge impact on my time in grad school. Angela Duckworth and Liz Wiseman, your books were there when I truly needed them and helped me immensely in getting to this finish line. Sometimes you just need to multiply yourself. There are a few hobbies that have really helped me through grad school. Thanks to The Pond Hockey Club and Ro Fitness for the really hard but really fun workouts. I’d be remiss if I didn’t give a huge thanks to my Dad for emailing me dozens of articles about sourdough bread baking until I gave in, wasted tons of flour pretending I was a microbiologist, and finally brought Boris the sourdough starter to life! I’ll always be a firm believer that freezers exist to be filled with homemade bread and chocolatey baked goods. Finally, thank you to my family for always encouraging me to do the things I’m interested in and stick with it. Mom and Dad, you froze your toes off and schlepped me around the country to play hockey, sent me to summer at camp so I could learn how to live away from home, helped me to travel the world, and encouraged me to take all the science, math, and programming classes that I was interested in (even if I could get an A in English with much less effort!). All of these things (and more!) helped me become the person I am today. I love you very much. v Abstract The Properties of Massive Galaxies at Cosmic Noon: Evolutionary Pathways and Implications for Physical Models of Galaxy Growth Sydney Beth Sherman, Ph.D. The University of Texas at Austin, 2021 Supervisor: Shardha Jogee The formation and evolution of massive galaxies in the first few billion years after the Big Bang remain important questions in extragalactic astronomy. Technological advancements allowing for multi-wavelength surveys that are both wide, covering large portions of the sky, and deep, pushing studies to higher redshifts, have opened the door for statistically significant studies of rare and important populations of galaxies at early times. Massive 11 galaxies (with stellar mass M? > 10 M ) provide an excellent testbed for theoretical models of galaxy evolution, however, because they have low number densities, large area surveys are required in order to locate uniformly-selected, statistically significant samples of these objects. In this thesis I detail the methods used to locate the largest samples to date of these massive galaxies, I investigate their number densities, quenched fractions, and specific star-formation rates, and I perform detailed comparisons of my empirical results with predictions from theoretical models. This work is a significant advancement as it mitigates uncertainties from Poisson statistics and cosmic variance, effects which have historically limited studies of the massive galaxy population at cosmic noon. Key results are summarized below. In Chapter 2 (Sherman et al. 2020a, MNRAS, 491, 3318) I present the high-mass end of the galaxy stellar mass function using a gri-selected sample of 5,352 star-forming galaxies 11 with M? > 10 M at cosmic noon, 1:5 < z < 3:5. This sample is uniformly selected across 17.2 deg2 (∼0.44 Gpc3 comoving volume from 1:5 < z < 3:5), mitigating the vi effects of cosmic variance and encompassing a wide range of environments. This area, a factor of 10 larger than previous studies, provides robust statistics at the high-mass end. Using multi-wavelength data in the Spitzer/HETDEX Exploratory Large Area (SHELA) footprint I find that the SHELA footprint star-forming galaxy stellar mass function is steeply declining at the high-mass end probing values as high as ∼10−4 Mpc−3/dex and as low as −8 −3 ∼5×10 Mpc /dex across a stellar mass range of log(M?/M ) ∼ 11 - 12. I compare the empirical star-forming galaxy stellar mass function at the high mass end to three types of numerical models: hydrodynamical models from IllustrisTNG, abundance matching from the UniverseMachine, and three different semi-analytic models (SAMs; SAG, SAGE, GALACTICUS). At redshifts 1:5 < z < 3:5 I find that results from IllustrisTNG and abundance matching models agree within a factor of ∼2 to 10, however the three SAMs strongly underestimate (up to a factor of 1,000) the number density of massive galaxies. I discuss the implications of these results for our understanding of galaxy evolution. In Chapter 3 (Sherman et al. 2020b, MNRAS, 499, 4239) I explore the buildup of 11 quiescent galaxies using a Ks-selected sample of 28,469 massive (M? ≥ 10 M ) galaxies at redshifts 1:5 < z < 3:0, drawn from a 17.5 deg2 area (0.33 Gpc3 comoving volume at these redshifts). This allows for a robust study of the quiescent fraction as a function of mass at 1:5 < z < 3:0 with a sample ∼40 times larger at log(M?/M )≥ 11:5 than previous studies. I derive the quiescent fraction using three methods: specific star-formation rate, distance from the main sequence, and UVJ color-color selection. All three methods give similar values at 1:5 < z < 2:0, however the results differ by up to a factor of two at 2:0 < z < 3:0. At redshifts 1:5 < z < 3:0 the quiescent fraction increases as a function of stellar mass. By 11 z = 2, only 3.3 Gyr after the Big Bang, the universe has quenched ∼25% of M? = 10 M 12 galaxies and ∼45% of M? = 10 M galaxies. I discuss physical mechanisms across a range of epochs and environments that could explain these results. I compare these results with predictions from hydrodynamical simulations SIMBA and IllustrisTNG and semi-analytic models (SAMs) SAG, SAGE, and Galacticus. The quiescent fraction from IllustrisTNG is higher than our empirical result by a factor of 2 − 5, while those from SIMBA and the three SAMs are lower by a factor of 1:5 − 10 at 1:5 < z < 3:0. In Chapter 4 (Sherman et al. 2021) I present the main sequence for all galaxies and star- 11 forming galaxies for a sample of 28,469 massive (M? ≥ 10 M ) galaxies at cosmic noon (1:5 < z < 3:0), uniformly selected from a 17.5 deg2 area (0.33 Gpc3 comoving volume at these redshifts). This large sample allows for a novel approach to investigating the vii galaxy main sequence that has not been accessible to previous studies. I measure the main sequence in small mass bins in the SFR-M? plane without assuming a functional form for the main sequence. With a large sample of galaxies in each mass bin, I isolate star-forming galaxies by locating the transition between the star-forming and green valley populations in the SFR-M? plane. This approach eliminates the need for arbitrarily defined fixed cutoffs when isolating the star-forming galaxy population, which often biases measurements of the scatter around the star-forming galaxy main sequence. I find that the main sequence for all galaxies becomes increasingly flat towards present day at the high-mass end, while the star-forming galaxy main sequence does not. I attribute this difference to the increasing fraction of the collective green valley and quiescent galaxy population from z = 3:0 to z = 1:5. Additionally, I measure the total scatter around the star-forming galaxy main sequence and find that it is ∼ 0:5 − 1:0 dex with little evolution as a function of mass or redshift. I discuss the implications that these results have for pinpointing the physical processes driving massive galaxy evolution. This thesis concludes (Chapter 5) with a discussion of the key results presented in Chapters 2, 3, and 4 and their impact on the understanding of massive galaxy evolution. I also discuss the future of extragalactic studies of massive galaxies and how this work can contribute to those studies. viii Table of Contents List of Tables........................................................................................................ xii List of Figures ...................................................................................................... xiii Chapter 1 Introduction....................................................................................... 1 1.1 Massive Galaxy Evolution ........................................................................ 1 1.2 Practicalities of Studying Massive Galaxies................................................ 2 1.3 Properties of Massive Galaxies at z > 1 ....................................................
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