EMBEDDED CLUSTERS IN THE LARGE MAGELLANIC CLOUD By KRISTA ROMITA GROCHOLSKI A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2017 c 2017 Krista Romita Grocholski To- Aaron, Allegra, Mom, and Dad. All is possible with you at my side. Thank you. ACKNOWLEDGMENTS First, I would like to acknowledge the University of Florida Astronomy Department for providing me with the opportunity to complete my dissertation. I would like to thank Dr. Elizabeth Lada for taking me on as her graduate student, and for giving me the opportunity and freedom to become a confident, independent researcher. I would also like to thank Drs. Ata Sarajadini, Anthony Gonzalez, and Alessandro Forte for serving on my committee. I would like to give special thanks to Dr. Maria-Rosa Cioni; without your generous collaboration this dissertation project would not be possible. Drs. Margaret Meixner and Lynn Carlson deserve considerable credit for getting me started, not only in astronomy research, but in the wonderful field of star formation in the Large Magellanic Cloud. I will always be grateful for your support and friendship over the years. I would also like to acknowledge Dr. Igor Mikolic-Torreira for giving me the opportunity to apply my research skills beyond the realm of academia. Your guidance and enthusiastic support opened doors to me that changed the nature of my career. I cannot thank you enough. To my fellow UF Astronomy graduate students, the community you have created is something I am proud to have been a part of. You all were able to bring joy to even the most difficult times, and I cannot thank you enough for your friendship. In particular, I like to attempt to communicate the utmost appreciation and admiration for Deno, Tahlia, Amanda, and Rachel. Thank you, thank you thank you! I am a smarter, stronger, and decidedly more badass woman for having experienced the honor of your friendship. I would certainly have not made it through without each of you. I would also like to give special thanks to my fantastic office-mate, Kelsey, to whom I wish all of the happiness and success in the world, and Melissa, for her unwavering support, friendship, and outside-of-astronomy perspective over the past seven years. None of this would have been possible without the love and support of my exceptional family. Allegra, Mom, and Dad, you inspire me every day to be the best possible 4 version of myself. Throughout my life, I have always been able to count on you for encouragement, insight, wisdom, and laughter. Everything I am, and all I have achieved, are possible because of you. Finally, I would like to thank my husband Aaron. Your willingness to share your astronomy knowledge, particularly with DAOPHOT and IDL, made much of this dissertation possible. I am looking forward to us actually getting to live in the same state (!) and actually spending our lives together. It is impossible to express the extent of my gratitude and my love for you. 5 TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................4 LIST OF TABLES.....................................8 LIST OF FIGURES....................................9 ABSTRACT........................................ 12 CHAPTER 1 INTRODUCTION.................................. 14 2 IDENTIFICATION OF EMBEDDED CLUSTER CANDIDATES........ 20 2.1 Data....................................... 20 2.2 Embedded Cluster Survey Coverage...................... 21 2.3 Identifying Embedded Clusters in the Milky Way.............. 26 2.4 Identifying Clusters in the LMC........................ 28 2.5 Identifying Embedded Cluster Candidates in the LMC........... 30 2.5.1 Visual Identification of Embedded Cluster Candidates........ 31 2.5.2 Automated Cluster Detection Methods: Attempts and Results... 36 2.5.2.1 Density Mapping....................... 36 2.5.2.2 SExtractor.......................... 39 2.6 Artificial Cluster Tests............................. 62 2.7 Comparison to Other Surveys......................... 66 3 EMBEDDED CLUSTER PROPERTIES...................... 74 3.1 Sizes....................................... 74 3.2 Luminosities................................... 75 3.3 Masses...................................... 78 3.4 Accuracy..................................... 89 3.5 Completeness.................................. 101 4 ANALYSIS...................................... 116 4.1 Surface Densities................................ 116 4.2 Age Distributions................................ 120 4.3 The Embedded Cluster Mass Function.................... 126 4.4 Star Formation Rates and Efficiencies..................... 128 5 CONCLUSIONS................................... 145 REFERENCES....................................... 150 6 BIOGRAPHICAL SKETCH................................ 156 7 LIST OF TABLES Table page 2-1 Parameter Values Used in Initial SExtractor Tests................. 42 2-2 Properties of Artificial Clusters for SExtractor Tests............... 47 2-3 Properties of Artificial Clusters for SExtractor Tests II.............. 57 2-4 Parameter Values Used in Final SExtractor Tests................. 58 2-5 Properties of the Artificial Clusters and Their Completeness........... 73 3-1 Cluster Mass Model Grid Input Assumptions................... 82 3-2 Properties of Artificial Clusters for Accuracy Tests................ 91 3-3 Properties of Embedded Cluster Candidates.................... 109 4-1 Surface Densities of the LMC VMC Tiles...................... 119 4-2 Star Formation Rates per unit area for the LMC VMC Tiles........... 129 4-3 Star Formation Efficiencies for the LMC VMC Tiles................ 134 4-4 Properties of Molecular Clouds Containing Embedded Clusters.......... 140 8 LIST OF FIGURES Figure page 1-1 A recreation of the mass versus age plot of LMC clusters from Baumgardt et al. (2013).......................................... 19 2-1 A 3-color image of the LMC, outlining the coverage of our survey........ 22 2-2 Ks band images of the VMC tiles included in the embedded cluster survey... 23 2-3 Ks band images of the VMC tiles included in the embedded cluster survey cont. 24 2-4 A Spitzer SAGE 8 µm image of the LMC, outlining the locations of the completed VMC tiles....................................... 25 2-5 Age histogram of LMC clusters from Baumgardt et al.(2013).......... 32 2-6 Illustration of how Milky Way embedded clusters would appear in the VMC images, part 1..................................... 33 2-7 Illustration of how Milky Way embedded clusters would appear in the VMC images, part 2..................................... 34 2-8 Illustration of how Milky Way embedded clusters would appear in the VMC images, part 3..................................... 35 2-9 The locations of VMC PSF stars in the N159 region of the VMC 6 6 tile.... 38 2-10 Two subregions of the VMC 6 6 tile that were used for cluster identification tests 40 2-11 Histograms of the PSF photometry for four of the VMC tiles........... 46 2-12 Histograms of the SExtractor photometry outputs................. 49 2-13 Histograms of the SExtractor photometry outputs cont.............. 50 2-14 Histograms of the SExtractor photometry outputs cont............... 51 2-15 Histograms of the SExtractor photometry outputs cont............... 52 2-16 Scatter plots of the SExtractor photometry outputs................ 54 2-17 Scatter plots of the SExtractor photometry outputs cont.............. 55 2-18 Scatter plots of the SExtractor photometry outputs cont.............. 56 2-19 A subregions of the VMC 6 6 tile that illustrate the differences in our detection methods......................................... 57 2-20 Illustration of how the best automated cluster ID method works in the 30 Doradus region.......................................... 59 9 2-21 Illustration of the effectiveness of the best automated cluster ID method in relation to artificial cluster mass................................ 60 2-22 Completeness maps for the artificial cluster tests.................. 63 2-23 Completeness curves from the artificial cluster tests................ 65 2-24 Images of a embedded cluster candidate in Hα and Spitzer bands......... 68 2-25 Images of a embedded cluster candidate in Hα and Spitzer bands......... 69 2-26 A VMC Ks band image of the N159W region of the LMC............. 70 2-27 Image showing the extent of the Hubble Tarantula Treasury Project coverage.. 71 3-1 The size distribution of the LMC embedded cluster candidates.......... 76 3-2 The luminosity function of the LMC embedded cluster candidates........ 77 3-3 Effect of Age Assumption on the Mass-Luminosity relations for the Mass Model Grid.......................................... 83 3-4 Effect of Metallicity Assumption on the Mass-Luminosity relations for the Mass Model Grid...................................... 84 3-5 Effect of IMF Assumption on the Mass-Luminosity relations for the Mass Model Grid.......................................... 85 3-6 Effect of Maximum Stellar Mass Assumption on the Mass-Luminosity relations for the Mass Model Grid............................... 86 3-7 The Embedded Cluster Mass Function....................... 88 3-8 The Effects of Assumptions on the Embedded Cluster Mass Function...... 90 3-9 Comparing Measured Radii to Input Core Radii of artificial clusters....... 92 3-10 Comparing Measured Radii to Core Radii of artificial clusters separated out by cluster mass...................................... 94 3-11 Comparing Measured Luminosities to Input Luminosities............