INVESTIGATING [X/FE], IMF AND COMPOSITENESS IN INTEGRATED MODELS By BAITIAN TANG A dissertation submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY WASHINGTON STATE UNIVERSITY Department of Physics and Astronomy MAY 2015 c Copyright by BAITIAN TANG, 2015 All Rights Reserved c Copyright by BAITIAN TANG, 2015 All Rights Reserved To the Faculty of Washington State University: The members of the Committee appointed to examine the dissertation of BAITIAN TANG find it satisfactory and recommend that it be accepted. Guy Worthey Ph.D., Chair Sukanta Bose, Ph.D. Matthew Duez, Ph.D. ii ACKNOWLEDGEMENT First and foremost I offer my sincerest gratitude to my advisor, Dr. Guy Worthey, who supported my study and research with motivation, enthusiasm, and immense knowledge. There were times when research funding was scarce, but his optimism, diligence and patience taught me the true meanings of research. Dr. Worthey gave me lots of free space in pursuing the research that interested me, and backed me up with his astrophysical proficiency. I would also like to thank the rest of my committee members: Dr. Sukanta Bose, and Dr. Matthew Duez for their encouragements and comments. Their courses, general relativity and astrophysical fluids, have expanded my eyesight to a much broader horizon. My sincere thanks also go to Dr. Qiusheng Gu and Dr. Zhaohui Shang, who supported my job applications and gave many insightful suggestions. During my Ph.D. study, I have been blessed with a friendly and cheerful group of fellow students. We enjoyed the great life and culture of the northwest. My friends and colleagues in China also responded to my daily or research questions with great welcome. The Department of Physics and Astronomy has provided the support I have needed to finish the courses and complete my dissertation. NASA and the College of Arts and Sciences have funded my studies. Last, but not the least, I would like to thank my parents for giving birth to me and supporting me spiritually throughout my life. iii INVESTIGATING [X/FE], IMF AND COMPOSITENESS IN INTEGRATED MODELS Abstract by Baitian Tang, Ph.D. Washington State University May 2015 Chair: Guy Worthey This dissertation explores several existing challenges of evolutionary stellar population synthesis models in integrated light: age-metallicity degeneracy, initial mass function (IMF), elemental abundances, and compositeness. First, we search for age-sensitive and metal- sensitive colors in three photometric systems. We also add to the discussion of optical to near-infrared Johnson-Cousins broad band colors, finding a great decrease in age sensitivity when updated isochrones are used. Then we investigate the element abundances and com- positeness of our models, in which we assume a single-peak abundance distribution and the same elemental abundance trends as the Milky Way bulge stars. Varying the width of the abundance distribution function reveals novel “red lean” and “red spread” effects. Next, we study three effects that co-determine the dwarf/giant ratio: the IMF slope, the IMF low mass cut-off (LMCO), and AGB star contributions. This degeneracy can be lifted for old, metal-rich stellar populations, although at an observationally challenging level ( 0.02 mag). ≈ Finally, we select and reduce more than 200 z 0.4 red galaxy spectra from the DEEP2 ∼ sky survey, and measure the Lick-style spectral indices from the composite spectra. Multiple iv optical IMF-sensitive indices suggest a shallower IMF that qualitatively agrees with current literature. v TABLE OF CONTENTS ACKNOWLEDGEMENT ............................... iii ABSTRACT ....................................... iv TABLE OF CONTENTS ............................... vi LIST OF TABLES .................................... ix LIST OF FIGURES ................................... x CHAPTER 1 INTRODUCTION TO STELLAR POPULATION SYNTHESIS ..... 1 2 ON DISTINGUISHING AGE FROM METALLICITY WITH PHOTO- METRIC DATA ................................... 12 2.1 Introduction.................................... 12 2.2 Analysis ...................................... 14 2.2.1 DDO,BATC&Str¨omgren . .. .. 14 2.2.2 Element Sensitivity . 21 2.2.3 (B V ) vs. (V K)Plots ....................... 22 − − 2.3 Discussion..................................... 26 2.3.1 Str¨omgren System: Empirical Leverage? . 26 2.3.2 ModelGridDifferences.......................... 27 vi 2.4 Summary ..................................... 30 3 COMPOSITE STELLAR POPULATIONS AND ELEMENT BY ELE- MENT ABUNDANCES IN THE MILKY WAY BULGE AND ELLIP- TICAL GALAXIES ................................. 32 3.1 Introduction.................................... 32 3.2 Composite Stellar Populations with Metallicity-dependent Chemical Compo- sition........................................ 35 3.2.1 Abundance Distribution Functions (ADFs) . 38 3.2.2 Milky Way Bulge Chemical Composition . 42 3.2.3 300 km s−1 Elliptical Galaxy Chemical Composition . 46 3.3 Results....................................... 47 3.4 Discussion..................................... 52 3.4.1 Varying the Widths of the ADFs: Red Lean and Red Spread . 52 3.4.2 Comparing Chemical Compositions of the Milky Way Bulge and El- liptical Galaxies . 56 3.4.3 Recovering Abundances with Simple Stellar Population Models . 59 3.4.4 Detectability of ADF Width . 61 3.5 Summary ..................................... 63 4 ON DISENTANGLING INITIAL MASS FUNCTION DEGENERACIES IN INTEGRATED LIGHT ............................ 65 4.1 Introduction.................................... 65 4.2 IMFslope,LMCO,andAGB .......................... 68 4.2.1 Modeldescription............................. 68 4.2.2 An Old, Metal-rich Population . 70 4.2.3 A Young, Metal-rich Population . 71 vii 4.2.4 Colors and Indices Broken into Evolutionary Phases . 72 4.3 ADF-IMFcoupling ................................ 79 4.4 Discussion..................................... 83 4.4.1 SwappingModels ............................. 83 4.4.2 Feasibility of Breaking the Degeneracy . 85 4.4.3 A Combination of Multiple Effects . 88 4.4.4 Recovering [X/Fe], IMF slope, LMCO, and AGB Percentage . 90 4.5 Summary ..................................... 93 5 INITIAL MASS FUNCTION OF RED GALAXIES AROUND z = 0.4: A SPECTROSCOPIC APPROACH ....................... 94 5.1 Introduction.................................... 94 5.2 SpectralReduction ................................ 98 5.2.1 SampleSelection ............................. 98 5.2.2 Composite Spectra and Index Measurements . 101 5.3 Non-universalIMF ................................ 103 5.3.1 ModelsandLocalObservables . 103 5.3.2 Comparison ................................ 105 5.4 Discussion..................................... 107 5.4.1 PossibleIMFDegeneracies . 107 5.4.2 IMF in High-redshift Galaxies . 108 5.4.3 TheWaystoImprove........................... 109 5.5 Summary ..................................... 109 BIBLIOGRAPHY .................................... 111 viii List of Tables 2.1 Metallicity Sensitivities at 8 Gyr, Z⊙ ...................... 15 2.2 Index Changes at 8 Gyr, Z⊙ ........................... 21 3.1 Mean [M/H] for Composite Populations Peaking at [M/H] = 0 . 53 3.2 Recovery of Population Parameters Under an SSP Hypothesis . ...... 60 4.1 Colors and Indices of Each Phase for the Old Population . ... 75 5.1 Optical IMF-sensitive Indices . 98 ix List of Figures 2.1 DDOC(35-48)vs.C(41-42)plot . 16 2.2 BATC5795-6075vs. 6075-6660plot. .. 17 2.3 Str¨omgren [c1] vs. [m1]plotofW94models................... 19 2.4 Str¨omgren [c1] vs. [m1]plotofB09models ................... 20 2.5 (B V ) vs. (V K)plotofB94models.................... 24 − − 2.6 (B V ) vs. (V K)plotofB09models.................... 25 − − 2.7 Str¨omgren plot with star forming galaxies . .. 28 2.8 (B R) vs. (R K)plotofB94andB09models . 31 − − 3.1 FouranalyticalADFs............................... 39 3.2 ObservedADFsvs. normal-widthADF. 40 3.3 MilkyWayBulgeADFs ............................. 41 3.4 Abundance trends in the Milky Way bulge . 44 3.5 Integrated light index diagrams . 49 3.6 Narrow,normalandwidewidthADFs . 55 3.7 DetectabilityofADFwidth ........................... 62 4.1 Color-color and index-index plots for old, metal-rich population . ..... 69 4.2 Color-color and index-index plots for young, metal-rich population...... 71 4.3 Number of stars, luminosities, and colors vs. evolutionary points ....... 73 4.4 Vectors presenting star number increment in different phases. ......... 74 4.5 Spectraandspectralratiosofeachphase.. ...... 78 x 4.6 IMFslopedriftsofeachphaseatoldage . 80 4.7 IMFslopedriftsofeachphaseatyoungage . .. 81 4.8 CSPs with IMF [M/H]dependence....................... 84 − 4.9 Color-color and index-index plots at old age using FSPS models . ... 86 4.10 Color-color and index-index plots at young age using FSPS models ..... 87 4.11 Symposium of multiple effects . 89 4.12 Recoveringparameters . 92 5.1 Galaxy color magnitude diagram . 100 5.2 Spectrabeforeandafterstacking. .... 102 5.3 Comparingobservablesandmodels . 106 xi CHAPTER 1 INTRODUCTION TO STELLAR POPULATION SYNTHESIS Galaxies, the building blocks of our mysterious Universe, have attracted increasing attention since the great debate by Harlow Shapley and Heber Curtis in 1920. Early workers, such as Edwin Hubble1, revealed that hundreds of thousands of galaxies wander outside the Milky Way galaxy. By studying the resolved stars in the central region of the Andromeda galaxy and its two companion galaxies, Baade (1944) proposed two distinct stellar populations: Population I stars are young and