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An Observational Study of Dense Gas in the Ophiuchus Molecular Cloud

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An Observational Study of Dense Gas in the Ophiuchus Molecular Cloud The Initial Conditions of Clustered Star Formation: An Observational Study of Dense Gas in the Ophiuchus Molecular Cloud by Rachel Katherine Friesen B.Sc.H, Queen’s University, 2002 M.Sc., University of Victoria, 2005 A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY in the Department of Physics and Astronomy c Rachel Katherine Friesen, 2009 University of Victoria All rights reserved. This dissertation may not be reproduced in whole or in part, by photocopying or other means, without the permission of the author. ii The Initial Conditions of Clustered Star Formation: An Observational Study of Dense Gas in the Ophiuchus Molecular Cloud by Rachel Katherine Friesen B.Sc.H, Queen’s University, 2002 M.Sc., University of Victoria, 2005 Supervisory Committee Dr. J. Di Francesco, Co-Supervisor (Herzberg Institute of Astrophysics) Dr. C. J. Pritchet, Co-Supervisor (Department of Physics and Astronomy) Dr. K. A. Venn, Departmental Member (Department of Physics and Astronomy) Dr. R. G. Hicks, Outside Member (Department of Chemistry) iii Supervisory Committee Dr. J. Di Francesco, Co-Supervisor (Herzberg Institute of Astrophysics) Dr. C. J. Pritchet, Co-Supervisor (Department of Physics and Astronomy) Dr. K. A. Venn, Departmental Member (Department of Physics and Astronomy) Dr. R. G. Hicks, Outside Member (Department of Chemistry) ABSTRACT In this dissertation I present a detailed survey of molecular line emission (including + + + NH3, C2S, HC5N, N2H , N2D and H2D ) towards clustered star forming Cores in the nearby Ophiuchus molecular cloud, with the aim of characterizing the distribution and kinematics of the dense gas within a clustered star forming environment and compare these results with those found in more isolated star forming regions. I show that the dense Oph Cores present characteristics of both isolated and clustered star forming regions in several key parameters, including Core kinematics, temperatures + and chemistry. At the higher gas densities where the N2H emission is excited, I show that the presence of an embedded protostar is correlated with increased gas + motions. I additionally present evidence of N2H depletion from the gas phase, + suggesting that in higher density, clustered environments N2H may not accurately trace the physical conditions of the densest core gas. I present the distribution of + + H2D and N2D across the Oph B Core, and show the distribution is not simple or easily explained by chemical models of evolving, isolated cores. Finally, I summarize the results of this dissertation, the questions it raises concerning the exploration of how stars form in clusters, and discuss how these questions may be answered through upcoming observational surveys and by new telescope facilities. iv Contents Supervisory Committee ii Abstract iii Table of Contents iv List of Tables vii List of Figures ix Acknowledgements xiii Dedication xiv 1 The Formation of Stars in Clusters 1 1.1 Molecular Clouds, Cores and Clumps . 2 1.2 Tracing Physical Conditions . 4 1.2.1 Thermal continuum emission from cold dust . 4 1.2.2 Molecules ............................. 8 1.2.3 The Ophiuchus Molecular Cloud . 15 1.3 Characterizing Cluster-Forming Cores Through Multi-Molecular Ob- servations ................................. 21 1.3.1 ChapterSummaries. 21 2 NH3 Observations of Dense Cores in Ophiuchus 25 2.1 Introduction................................ 25 2.2 ObservationsandDataReduction . 27 2.2.1 GreenBankTelescope . 29 2.2.2 Australia Telescope Compact Array . 30 2.2.3 VeryLargeArray ......................... 32 v 2.2.4 Combining Single Dish and Interferometer Data Sets . ... 33 2.3 Results................................... 35 2.3.1 Comparison with submillimeter dust continuum emission... 35 2.3.2 Single Dish C2S and HC5NDetections ............. 42 2.4 NH3 LineAnalysis ............................ 45 2.4.1 NH3 HyperfineStructureFitting . 45 2.4.2 LineCentroidsandWidths. 49 2.4.3 Kinetic Temperatures and Non-Thermal Line widths . .. 55 2.4.4 Column Density and Fractional Abundance . 58 2.4.5 H2 Density............................. 63 2.5 Discussion................................. 63 2.5.1 Discussion of small-scale features . 63 2.5.2 DiscussionoftheCores. 67 2.5.3 Implications for Clustered Star Formation . .. 74 2.6 Summary ................................. 74 + 3 N2H Observations of the Cluster-Forming Ophiuchus B Core 79 3.1 Introduction................................ 79 3.2 ObservationsandDataReduction . 82 3.2.1 Nobeyama45mRadioTelescope . 82 3.2.2 BIMA ............................... 83 3.2.3 ATCA ............................... 83 3.3 Results................................... 85 3.3.1 SingleDishData ......................... 85 3.3.2 ATCAData............................ 90 + 3.4 N2H LineAnalysis ........................... 95 3.4.1 SingleDishResults . .. .. 98 3.4.2 InterferometerResults . 110 3.5 Discussion ................................. 112 3.5.1 Generaltrends .......................... 112 3.5.2 Small-ScaleFeatures . 116 + 3.5.3 Comparison of N2H and NH3 emission in Oph B . 120 + 3.5.4 Are N2H and NH3 tracing the Oph B Core interior? . 129 3.6 Summary ................................. 130 vi 4 The Deuterium Fractionation of the Ophiuchus B2 Core 133 4.1 Introduction................................ 133 4.2 Observations................................ 136 + 4.2.1 N2D atIRAM.......................... 136 + + 4.2.2 H2D and N2H attheJCMT ................. 137 4.3 Results................................... 138 4.4 Analysis .................................. 141 + + 4.4.1 N2H and N2D multi-component line fitting . 141 + 4.4.2 H2D Gaussianlinefitting. 146 4.4.3 Centroid velocity and line widths . 146 4.4.4 Opacityandexcitationtemperature . 149 4.4.5 Column density and fractional abundance . 149 + + + 4.4.6 Using H2D , N2H and N2D to determine TK ........ 156 4.5 Discussion ................................. 160 4.5.1 Linewidthsanddensity . 160 4.5.2 Trends in the deuterium fractionation . 163 4.5.3 What is affecting the deuterium fractionation in Oph B2?. 167 4.6 Summary ................................. 170 5 Conclusions 173 5.1 Surprises and implications for future research . ...... 173 5.2 Future initiatives in star formation studies . ...... 176 5.2.1 Largescalemapping . 176 5.2.2 Astronomical facilities and upgrades . 177 A Determining Physical Parameters from HFS Line Fitting Results 179 A.1 KineticTemperature . .. .. 179 A.2 ColumnDensity.............................. 180 A.3 Consequences of 0.3 km s−1 Velocity Resolution . 183 A.4 Linewidths ................................ 183 A.5 Opacity .................................. 185 A.6 KineticTemperature . .. .. 186 + B Calculating N2H column density 187 Bibliography 189 vii List of Tables Table 1.1 Physical parameters of dense Cores in Ophiuchus . ...... 19 Table 2.1 Rest frequencies of all observed spectral lines . ........ 27 Table2.2 GBTObservationDetailsbyRegion . 30 Table 2.3 ATCA and VLA Observation Details by Region . .. 32 Table 2.4 NH3 (1,1) clumpfind peaks and parameters . 38 Table 2.5 GBT C2S 21 10 and HC5N 9 8PeakParameters . 42 − − Table 2.6 NH3 (1,1) Line Characteristics in Combined Data . 48 Table 2.7 Physical Properties of Filaments Derived From Fitted Parameters 59 Table 2.8 Derived Parameters at NH3 (1,1)PeakLocations . 77 Table 2.8 Derived Parameters at NH3 (1,1)PeakLocations . 78 Table3.1 ATCATargetsinOphB2 . 84 + Table 3.2 N2H 1-0 clumpfind peaksandparametersinOphB . 88 + Table 3.3 N2H 1-0 Line Characteristics in Oph B1, B2 and B3 . 100 + Table 3.4 Derived Parameters at N2H 1-0PeakLocations . 101 + Table 3.4 Derived Parameters at N2H 1-0PeakLocations . 102 Table 3.5 Derived Parameters for 850 µm clumps and Class I protostars . 103 Table 3.6 Derived Column Densities, Fractional Abundances and Non-thermal LineWidthsinOphB1,B2andB3 . 109 + Table 3.7 Mean Derived Physical Parameters for N2H clumps, 850 µm clumpsandClassIprotostars . 118 Table 4.1 Observed Species, Transitions and Frequencies . ........ 136 + Table 4.2 N2H 4-3 hyperfine components, velocities and LTE line strengths 143 + Table 4.2 N2H 4-3 hyperfine components, velocities and LTE line strengths 144 + Table 4.3 Impact of Tex on τ, Qrot and N(ortho-H2D ) .......... 154 viii + + + Table 4.4 Mean NH3, N2H , N2D and H2D vLSR and ∆v inOphB2 . 162 ix List of Figures Figure 1.1 A comparison of submillimetre continuum emission from dense cores in clustered and isolated regions . 7 + Figure 1.2 Comparison of molecular line emission from NH3, N2H , CO and CS with millimetre continuum emission in the starless L1498 and L1517Bcores ............................ 10 Figure 1.3 Proposed chemical differentiation of an evolved, isolated starless core ................................. 13 Figure 1.4 Locations of nearby molecular clouds overlaid on an IRAS galaxy image ................................ 16 Figure 1.5 Visual extinction towards the Ophiuchus molecularcloud. 17 Figure 1.6 Spitzer Space Telescope IRAC and MIPS image of the Lynds 1688 region of the Ophiuchus molecular cloud. 19 Figure 1.7 Central L1688 region in 850 µm continuum emission . 20 Figure 2.1 850 µm continuum emission in the central Ophiuchus molecular cloud, originally mapped at the JCMT . 28 Figure 2.2 Integrated NH3 (1,1) intensity towards the Oph B Core (includ- ing B1, B2, and B3) obtained with the GBT, ATCA and VLA telescopes.............................. 36 Figure 2.3 Integrated NH3 (1,1) intensity towards the Oph C Core obtained with the GBT, ATCA and VLA telescopes . 40 Figure 2.4
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