Studying the Building Blocks of the Universe: the faint, low-mass galaxies A THESIS SUBMITTED TO THE FACULTY OF THE GRADUATE SCHOOL OF THE UNIVERSITY OF MINNESOTA BY Vihang Mehta IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF Doctor of Philosophy Advisor: Claudia Scarlata August, 2018 © Vihang Mehta 2018 ALL RIGHTS RESERVED Acknowledgements This achievement has only been made possible by a number of people helping and supporting me behind the scene. First and foremost, I have to thank my advisor, Claudia Scarlata, for all her support and advice through the past six years. Thank you for sticking with me quirky self through the ups and downs through the years. This would not have been possible without you believing in me and constantly pushing me to be the best I could. I have the highest respect for you as a researcher as well as a teacher and am honored to have you as my advisor and collaborator. The work presented here would not have been possible without the UVUDF, SPLASH, and WISPS programs and their respective PIs, Harry Teplitz, Peter Capak, and Matt Malkan. In addition to the UVUVDF, SPLASH, and WISP collaborations, I am indebted to Marc Rafelski, Iary Davidzon, Ivano Baronchelli, and James Colbert for all their help in getting me familiarized with the various programs as well as helping me with all the subtle issues that I encountered while working with the data. Not only did they welcome me into their collaborations and gave me an opportunity to do science, but they were also highly supportive of my work and provided ample guidance towards making it a success and for this, I am grateful. MIfA has been my home since I was part way through my undergrad and I am thankful for all the support the department has provided through the years. In particular, special thanks to Michael Rutkowski, Hugh Dickinson, and Dinesh Shenoy for their invaluable help in getting me acquainted with the nuances of the field and getting me kick-started on the basics. I also would like to thank my committee members, Evan Skillman, Larry Rudnick, Lucy Fortson, and Vuk Mandic for their time, expertise and guidance. Last but definitely not the least, the grad student body { without whom I would have lost my sanity through the years. I am eternally grateful to them for always being there to socially and mentally ground myself in reality in midst of the whirlwind that is grad school. I cannot put in words my gratitude towards my officemates, Micaela Bagley, Karlen i Shahinyan, and Melanie Beck for getting me through each day of grad school. Be it random silly questions about astronomy, coding, or day-to-day life, I have always been able to rely on you guys for aligning me in the right direction. I cannot thank you enough for all your support through the years. The research presented in this thesis was made possible by three major programs: the WFC3 Infrared Spectroscopic Parallel (WISP) survey, the UltraViolet Ultra Deep Field (UVUDF) program, and the Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH) program. Their respective acknowledgments are below. WISP: Support for HST Programs GO-11696, 12283, 12568, 12902 was provided by NASA through grants from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5- 26555. UVUDF : Support for HST Program GO-12534 was provided by NASA through grants from the Space Telescope Science Institute, which is operated by the Association of Uni- versities for Research in Astronomy, Inc., under NASA contract NAS5-26555. SPLASH : VM acknowledges the support from Jet Propulsion Laboratory under the grant award #RSA-1516084. VM also acknowledges support from the University of Min- nesota Doctoral Dissertation Fellowship 2016-17. Based in part on data collected at the Subaru Telescope and retrieved from the HSC data archive system, which is operated by Subaru Telescope and Astronomy Data Center at National Astronomical Observatory of Japan. Based in part on observations made with the Spitzer Space Telescope, which is oper- ated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. The Hyper Suprime-Cam (HSC) collaboration includes the astronomical communities of Japan and Taiwan, and Princeton University. The HSC instrumentation and software were developed by the National Astronomical Observatory of Japan (NAOJ), the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), the University of Tokyo, the High Energy Accelerator Research Organization (KEK), the Academia Sinica Institute for Astronomy and Astrophysics in Taiwan (ASIAA), and Princeton University. Funding was contributed by the FIRST program from Japanese Cabinet Office, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), the Japan Society for the Promotion of Science (JSPS), Japan Science and Technology Agency (JST), the Toray Science Foundation, NAOJ, Kavli IPMU, KEK, ASIAA, and Princeton University. ii This research makes use of software developed for the Large Synoptic Survey Telescope. We thank the LSST Project for making their code available as free software at http: //dm.lsst.org/. Based in part on observations obtained with MegaPrime and MegaCam, a joint project of CFHT and CEA/IRFU, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. This work is based in part on data products produced at Terapix available at the Canadian Astronomy Data Centre as part of the Canada-France-Hawaii Telescope Legacy Survey, a collaborative project of NRC and CNRS. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. iii Dedication I dedicate this thesis to my mother, Firuzi Mehta, who has been the cornerstone of my life. iv Abstract Faint, low-mass galaxies are the next frontier in extending our understanding of how our universe evolved into its present-day state that we observe. As the ever-advancing tech- nological prowess brings about the next generation of cutting-edge observational facilities, the limit down to which we can observe galaxies is constantly pushed to fainter fluxes and consequently, lower masses. With this new population of galaxies coming into focus, it also serves as a new set of subjects to test our models and theory of galaxy formation. While the current galaxy formation models have been widely successful at reproducing the general trends in observed properties of typical galaxies, they struggle to do so for galaxies in low 11 mass halos (MH . 10 M ). In simulations, the growth of the galaxies traces the growth of their parent dark matter halos too closely, which manifests as an over-prediction of low- mass galaxies compared to the observations. Feedback from star-formation and central black hole activity is necessary to decouple the evolution of the galaxies (made of baryonic material) from that of the dark matter halos. This is particularly critical for low-mass galaxies because of their shallow gravitational potential wells. The goal of this thesis is to understand the star-formation properties of faint, low-mass galaxies and to assemble statistically significant samples of these objects that can ultimately be used to perform more detailed follow-up studies and refine the galaxy formation models. Using deep UV imaging data obtained as part of the Hubble UltraViolet Ultra Deep Field (UVUDF) program, we measure the rest-UV luminosity functions for star-forming galaxies during the cosmic high-noon { the peak of cosmic star-formation rate at 1:5 < z < 3. With samples of galaxies extending ∼2 magnitudes deeper than other direct imaging studies, we definitively pin the faint-end slope for the rest-UV luminosity function at 1:5 < z < 3. We compare the star-formation properties of z ∼ 2 galaxies from these UV observations with results from Hα and UV+IR observations to find a lack of high SFR sources in the UV luminosity function. This can be explained by a population of dusty star-forming galaxies that are not properly accounted for by the generic relations used for dust corrections. We compute a volume-averaged UV-to-Hα ratio by abundance matching the rest-UV and Hα luminosity functions and find the observed ratio to deviate from the expectation for constant 9 star-formation history for low-mass galaxies (M? . 5 × 10 M ). We conclude that this could be due to a larger contribution from starbursting galaxies compared to the high-mass end. v We next focus on the low-mass, highly star-forming galaxies characterized by the pres- ence of strong (high EW) emission lines in their spectra and thought to be representative of the earliest galaxies in the universe. While abundant in the high redshift universe, these objects are rare at lower redshifts. In order to compile a statistically significant sam- ple of these, we use the Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH) dataset, which covers 2.4 deg2 on the Subaru-XMM Deep Field (SXDF) with deep opti- cal, near-infrared and mid-infrared imaging. We homogenize all available imaging data on to a common astrometric reference frame to generate multi-wavelength catalog containing ∼ 800; 000 objects with photometry in 28 bands, reliable photometric redshifts, and stellar population properties. Using this multi-wavelength catalog and applying a broadband selection technique to identify galaxies with strong emission lines, we identify samples of extreme emission line galaxies and Lyα-emitters over 0:06 < z < 0:7 and 2:4 < z < 3:8, respectively.