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Deriving Dust Properties in Star Forming Clumps: a Look Across the Perseus Molecular Cloud with Herschel and SCUBA-2

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Deriving Dust Properties in Star Forming Clumps: a Look Across the Perseus Molecular Cloud with Herschel and SCUBA-2 Deriving Dust Properties in Star Forming Clumps: a Look Across the Perseus Molecular Cloud with Herschel and SCUBA-2 by Michael Chun-Yuan Chen B.Sc., University of British Columbia, 2012 A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE in the Department of Physics and Astronomy c Michael Chen, 2015 University of Victoria All rights reserved. This thesis may not be reproduced in whole or in part, by photocopying or other means, without the permission of the author. ii Deriving Dust Properties in Star Forming Clumps: a Look Across the Perseus Molecular Cloud with Herschel and SCUBA-2 by Michael Chun-Yuan Chen B.Sc., University of British Columbia, 2012 Supervisory Committee Dr. J. Di Francesco, Co-Supervisor (Physics and Astronomy) Dr. D. Johnstone, Co-Supervisor (Physics and Astronomy) Dr. J. Willis, Co-Supervisor (Physics and Astronomy) iii Supervisory Committee Dr. J. Di Francesco, Co-Supervisor (Physics and Astronomy) Dr. D. Johnstone, Co-Supervisor (Physics and Astronomy) Dr. J. Willis, Co-Supervisor (Physics and Astronomy) ABSTRACT Herschel and JCMT surveys of nearby star-forming regions have provided excellent images of cold dust emission across several wavelengths with unprecedented dynamic range and resolutions. Here we present spectral emissivity index and temperature maps of dust in the star-forming clumps of the Perseus molecular cloud determined from fitting SEDs to the combined Herschel and JCMT observations in the 160 mm, 250 mm, 350 mm, 500 mm, and 850 mm bands, employing the technique developed by Sadavoy et al. (2013). In NGC1333, the most complex and active star-forming clump in Perseus, we demonstrate that CO line contamination in the JCMT SCUBA- 2 850 mm band is typically insignificant. The derived spectral emissivity index, b, and dust temperature, Td, ranges between 0.8 - 3.0 and 7 - 50 K, respectively. Through- out Perseus, we see indications of heating from B stars and embedded protostars, and smooth b variations on the smaller scales. The distribution of b values seen in each clump differs from one clump to another, and is in general different from the diffuse ISM values (i.e., ∼ 2), suggesting that dust grain evolution is significant in star-forming clumps. We also found coincidences between low b regions and local temperature peaks as well as locations of outflows, which may provide hints to the origins of these low b value grains, and dust grain evolution in star-forming clumps in general. iv Contents Supervisory Committee ii Abstract iii Table of Contents iv List of Tables vii List of Figures viii Acknowledgements x Dedication xi 1 Introduction 1 1.1 Molecular Cloud Structure . 3 1.2 Perseus Molecular Cloud . 4 1.3 Tracing the Gas Structures . 5 1.4 Modified Blackbody Radiation and Dust Opacity . 6 1.5 Constraining Spectral Emissivity Index . 8 2 Observational Data 11 2.1 JCMT: SCUBA-2 Data . 11 2.2 JCMT: HARP Data . 13 2.3 JCMT: Removing CO Contamination . 14 2.4 Herschel: PACS and SPIRE Data . 16 2.5 Herschel: Filtering Data Spatially . 18 3 SED-fitting 19 4 Results: A Detailed Look at NGC1333 22 v 4.1 Overall Distributions of Td, b, and t300 . 22 4.2 Local Structures . 26 4.2.1 Local Structures: Temperature . 26 4.2.2 Local Structures: b ........................ 28 4.2.3 Local Structures: Optical Depth . 30 4.3 Column Density Estimation . 32 4.4 Relations between Td, b, and t300 .................... 34 5 Results: Perseus in General 39 5.1 Perseus Clumps: Temperature . 39 5.2 Perseus Clumps: b and τ300 ....................... 43 5.3 The b, Temperature, and Column Density Relations . 49 6 Discussion 52 6.1 Radiative Thermal Feedback . 52 6.2 Outflow Feedback . 55 6.3 Beta and Clump Evolution . 57 6.3.1 Beta Variation and its Relation to Temperature . 57 6.3.2 The Cause Behind b Variations . 60 6.3.3 Beta Variations Between Clumps . 64 7 Conclusion 68 A Uncertainties Associated with CO Contamination 72 A.1 CO Contamination Levels . 72 A.2 Effects of CO Contamination on the SED fittings: Towards Bright CO Sources . 77 A.3 Effects of CO Contamination on the SED fits: Towards Bright SCUBA- 2 Sources . 82 B Uncertainties associated with filtering Herschel Data 85 B.1 Uncertainties associated with flux scaling . 85 B.2 Uncertainties associated with the choice of mask . 88 B.2.1 The effects of filtering Herschel flux . 90 B.3 The effects of filtering on SED-derived parameters . 92 C Uncertainties Associated with Dust Opacity 94 vi Bibliography 97 vii List of Tables Table 2.1 Details of the observed PONG regions . 12 Table 3.1 JCMT GBS Target Coordinates in Perseus . 21 viii List of Figures Figure 1.1 Sample Herschel SEDs . 9 Figure 2.1 SCUBA-2 850 mm and HARP CO maps of NGC 1333 . 13 Figure 2.2 Herschel 160 mm and 500 mm maps of NGC 1333 . 17 Figure 4.1 Histograms of Td, b, and τ300 in NGC 1333 . 23 Figure 4.2 NGC 1333 Td map . 25 Figure 4.3 NGC 1333 b map . 29 Figure 4.4 NGC 1333 τ300 map . 31 Figure 4.5 NGC 1333 column density maps . 33 Figure 4.6 Scatter plot of b v.s. Td in NGC 1333 . 35 2 Figure 4.7 Reduced χ distribution in b-Td space . 36 Figure 4.8 Scatter plot of derived b v.s. τ300 in NGC 1333 . 38 Figure 5.1 Histograms of Td in Perseus clumps. 40 Figure 5.2 Maps of Td in the B1 and B5 clumps . 41 Figure 5.2 Maps of Td in the IC348, L1448, and L1455 clumps . 42 Figure 5.3 Histograms of b for Perseus clumps. 44 Figure 5.4 Maps of b in the B1 and B5 clumps . 45 Figure 5.4 Maps of b in the IC 348, L1448, and L1455 clumps . 46 Figure 5.5 Maps of τ300 in the B1 and B5 clumps . 47 Figure 5.5 Maps of τ300 in the IC 348, L1448, and L1455 clumps . 48 Figure 5.6 Scatter plots of b vs. Td for each Perseus clumps . 50 Figure 5.7 Scatter plots of b vs. column density for each Perseus clump . 51 Figure 6.1 Detailed τ300 maps of NGC 1333 and L1448 . 56 Figure 6.2 The behavior of g01(Td)...................... 59 Figure 6.3 The map of α in NGC 1333 . 61 Figure 6.4 b as function of maximum grain size . 63 Figure 6.5 Bar graph of b categories . 66 ix Figure A.1 SCUBA-2 map of NGC 1333 overlaid with filtered CO . 74 Figure A.2 Histogram of percentage CO contribution . 75 Figure A.3 Scatter plot of CO vs 850 mm flux . 76 Figure A.4 The influence of different CO removal methods on SED fits . 78 Figure A.5 Temperature difference v.s. CO fraction in bright CO regions . 80 Figure A.6 Temperature difference v.s. filtered fluxes . 81 Figure A.7 Temperature difference v.s. CO fraction in bright 850 mm regions 83 Figure B.1 Flux difference due to choice of filtering scaling factor . 86 Figure B.2 Td and τ300 difference due to choice of filtering scaling factor . 87 Figure B.3 Flux difference due to choice of mask used for filtering . 89 Figure B.4 Maps of the retained and removed Herschel flux after filtering . 90 Figure B.5 Comparison between fractional filtered-out Herschel emission . 91 Figure B.6 Effects of Herschel filtering on SED fits . 93 Figure C.1 OH5 model of dust opacity as a function of wavelength . 95 x ACKNOWLEDGEMENTS I would like to thank my supervisors, James Di Francesco and Doug Johnstone, for taking me in as a student and providing me with such an exciting opportunity to do research in astronomy. I appreciate the insights and advice that they have given me, as well as their tremendous support when I struggled with my thesis writing. I would also like to extend this gratitude to my scientific collaborators, particularly the JCMT GBS team members, who have provided me with many help and insights on my project. To my fellow graduate students, for being incredible friends who have made grad- uate school a very delightful place to be. I will not forget all those stimulating discussions and cookie snatching. A special thanks to Steve Mairs for being such a close and supportive friend, who has been poking star formation with a stick with me since we were undergrads. And of course, many thanks to my supportive, loving family, who I love very much. xi DEDICATION To my loving parents, who have always been incredibly supportive of me in my pursue for science. And to my grandma, who was excited that I got into graduate school for studying astronomy/astrophysics but did not have the chance to see me finish. Chapter 1 Introduction Stars are one of the most important constituents of galaxies, and consequently the Universe. They are the main source of optical light in galaxies and the main driver of chemical evolution in the Universe, converting hydrogen and helium into heavier elements such as silicon and iron, the main components of terrestrial planets, and carbon, the fundamental building block of life as we know it. To begin this process of chemical evolution, stars have to be condensed out of large bodies of gas that aggregated with the formation of galaxies. Only towards the end of stellar existence can the heavier elements produced deep inside the stars, along with the unprocessed gas, be returned into interstellar space through powerful stellar winds or supernovae before new generations of stars are formed out of the newly enriched interstellar gas.
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