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Investigation of the Intermediate and High End Initial Mass Function As Probed by Near-Infrared Selected Stellar Clusters Christine Trombley

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Investigation of the Intermediate and High End Initial Mass Function As Probed by Near-Infrared Selected Stellar Clusters Christine Trombley Rochester Institute of Technology RIT Scholar Works Theses Thesis/Dissertation Collections 3-1-2013 Investigation of the intermediate and high end initial mass function as probed by near-infrared selected stellar clusters Christine Trombley Follow this and additional works at: http://scholarworks.rit.edu/theses Recommended Citation Trombley, Christine, "Investigation of the intermediate and high end initial mass function as probed by near-infrared selected stellar clusters" (2013). Thesis. Rochester Institute of Technology. Accessed from This Dissertation is brought to you for free and open access by the Thesis/Dissertation Collections at RIT Scholar Works. It has been accepted for inclusion in Theses by an authorized administrator of RIT Scholar Works. For more information, please contact [email protected]. INVESTIGATION OF THE INTERMEDIATE AND HIGH END INITIAL MASS FUNCTION AS PROBED BY NEAR-INFRARED SELECTED STELLAR CLUSTERS By Christine M. Trombley A dissertation submitted in partial fulfillment of the requirements for the degree of Ph.D. in Astrophysical Sciences and Technology, in the College of Science, Rochester Institute of Technology March 2013 Approved by ________________________________________________________________ Prof. Andrew Robinson Date Director, Astrophysical Sciences and Technology i ASTROPHYSICAL SCIENCES AND TECHNOLOGY COLLEGE OF SCIENCE ROCHESTER INSTITUTE OF TECHNOLOGY ROCHESTER, NEW YORK CERTIFICATE OF APPROVAL Ph.D. DEGREE DISSERTATION The Ph.D. Degree Dissertation of Christine M. Trombley has been examined and approved by the dissertation committee as satisfactory for the dissertation requirement for the Ph.D. degree in Astrophysical Sciences and Technology. Dr. Donald F. Figer, Thesis Advisor i Dr. Karl Hirschman, Committee Chair Dr. Judith L. Pipher Dr. Michael Richmond Date ___________________________________ ii Abstract Young stellar clusters serve as powerful natural laboratories for studying the intermediate to high mass end of the initial mass function. The purpose of this dissertation is to measure the slope of the stellar initial mass function (IMF) over the intermediate to high mass range. Previous measurements are consistent with a “canonical” value over this mass regime, though the young massive star population in the Galactic Center may have a “top-heavy” distribution. In order to probe the IMF in stellar clusters that are preferentially more distant and more massive than the majority previously studied in the literature, the cluster sample is drawn from catalogs of infrared-selected candidates. Hubble Space Telescope near- infrared imaging is used to select the most promising candidates for young, massive stellar clusters. Follow-up near-infrared spectroscopy from two telescopes, covering the northern and southern latitudes, is used to identify the main sequence population and confirm a young age. The IMF is inferred from mass-magnitude relations using Geneva stellar evolutionary models. The slope at the intermediate to high mass range is measured for the completeness-corrected, background subtracted data. Deviations from the canonical IMF slope are discussed. No strong evidence in support of or against a stellar upper mass limit is found. The slope of the intermediate to high end slope of the IMF, as probed by the near-IR selected stellar clusters in this sample, is determined here to be Gamma (Γ)=-1.22, to within 0.31 dex, similar to the canonical value of -1.35. i Contents Abstract .......................................................................................................................................................... i Contents ........................................................................................................................................................ ii 1. Introduction ........................................................................................................................................... 1 1.1. The Initial Mass Function ............................................................................................................. 2 1.1.1. Variations .............................................................................................................................. 7 1.1.2. Stellar Evolution Models: Past and Present .......................................................................... 7 1.1.3. Method .................................................................................................................................. 8 1.1.4. Utilizing the IMF ................................................................................................................ 10 1.2. Upper Mass Cut Off .................................................................................................................... 11 1.3. Young Massive Clusters and Candidate Clusters ....................................................................... 14 2. Observations ....................................................................................................................................... 17 2.1. Sample of Cluster Candidates ..................................................................................................... 17 2.2. Spizter/IRAC Imaging: Reduction and Photometry ................................................................... 17 2.3. HST/NIC3 Imaging: Reduction and Photometry ........................................................................ 21 2.4. VLT/ISAAC Spectroscopy: Observations and Reduction .......................................................... 24 2.5. IRTF/SpeX Spectroscsopy: Observations and Reduction ........................................................... 25 2.6. Keck II/NIRC2 Imaging and Slitless Spectroscopy: Observations and Reduction .................... 28 2.6.1. Laser Guide Star Adaptive Optics Imaging ........................................................................ 28 2.6.2. Slitless Spectroscopy........................................................................................................... 32 2.7. Chandra/ACIS: Reduction .......................................................................................................... 37 2.8. VLT/MAD Imaging: Photometry in the core of R136 ................................................................ 37 3. Data Analysis ...................................................................................................................................... 43 3.1. Mercer 5 ...................................................................................................................................... 43 3.1.1. NIR Imaging ....................................................................................................................... 43 3.1.2. Slitless Spectroscopy........................................................................................................... 44 3.1.3. Metallicity ........................................................................................................................... 47 ii 3.1.4. Mass, Age, and Distance ..................................................................................................... 48 3.1.5. X-ray Source ....................................................................................................................... 51 3.1.6. Summary ............................................................................................................................. 52 3.2. Mercer 14 .................................................................................................................................... 52 3.2.1. Summary ............................................................................................................................. 54 3.3. Mercer 17 .................................................................................................................................... 54 3.3.1. Stellar Content .................................................................................................................... 55 3.3.2. Summary ............................................................................................................................. 58 3.4. Mercer 20 .................................................................................................................................... 58 3.4.1. Stellar Content .................................................................................................................... 58 3.4.2. Age, Reddening, Distance, Mass ........................................................................................ 65 3.4.3. Summary ............................................................................................................................. 66 3.5. Mercer 23 .................................................................................................................................... 66 3.5.1. Stellar Content .................................................................................................................... 67 3.5.2. Age, Reddening, Distance, Mass ........................................................................................ 73 3.5.3. Summary ............................................................................................................................. 73 3.6. Mercer 30 .................................................................................................................................... 73 3.6.1. Stellar Content ...................................................................................................................
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