University of Groningen Molecular line tracers of high-mass star forming regions Nagy, Zsofia IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document Version Publisher's PDF, also known as Version of record Publication date: 2013 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Nagy, Z. (2013). Molecular line tracers of high-mass star forming regions. s.n. Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons). The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license. 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G.A. Fuller Prof. dr. M. Gerin Prof. dr. I. Kamp ISBN 978-90-367-6378-3 ISBN 978-90-367-6379-0 (electronic version) Front cover - Background: 13CO 3-2 integrated intensity map of the Orion Bar and Ridge region observed with the James Clerk Maxwell Telescope (JCMT). The data are from the JCMT archive (http://www1.cadc-ccda.hia -iha.nrc-cnrc.gc.ca/jcmt). The CH+ J=1-0 spectra observed with Her- schel/HIFI analysed in this thesis are overlaid toward the observed positions (CO+ peak of the Orion Bar and Orion S). Back cover - Background: Image of the Orion Nebula made with the NASA/ESA Hubble Space Telescope. Credit: Image Data - Hubble Legacy Archive (http://hla.stsci.edu), Processing - Robert Gendler. The molecules in the foreground are from the website of Wikimedia Commons (https://commons.wikimedia.org/wiki). The molecules (from top to bot- tom): CH3OH, SO2, and H2CO. The foreground pictures apart from the molecules are based on photos by the author. Contents 1 Introduction 1 1.1 Star formation and the interstellar medium ............ 1 1.1.1 Phases of the interstellar medium .............. 2 1.1.2 Star formation ........................ 4 1.1.3 High-mass star-formation .................. 5 1.2 Interpretation of molecular line observations ............ 12 1.2.1 Radiative transfer models .................. 12 1.2.2 Chemical models ....................... 15 1.3 Summary of the thesis ........................ 18 2 Physical and chemical differentiation of W49A 23 2.1 Introduction .............................. 25 2.2 Observations and data reduction .................. 26 2.3 Results ................................. 26 2.3.1 Line identification ...................... 26 2.3.2 The detected species ..................... 31 2.3.3 Line profiles and velocity structure ............. 37 2.3.4 Excitation and column densities .............. 38 2.4 Discussion ............................... 47 2.4.1 The importance of UV irradiation ............. 47 2.4.2 Comparison to regions with shock chemistry ....... 49 2.4.3 Comparison to starburst galaxies and AGNs ........ 51 2.5 Summary ............................... 54 2.6 Appendix: The detected lines toward the center of W49A .... 54 3 Extended warm and dense gas towards W49A 73 3.1 Introduction .............................. 75 3.2 Observations and Data reduction .................. 76 3.3 Results ................................. 77 3.3.1 Line selection ......................... 77 3.3.2 Excitation conditions ..................... 80 3.3.3 Kinetic temperature estimates ............... 82 3.3.4 Volume- and column density estimates ........... 84 3.4 Discussion ............................... 87 3.4.1 Possible heating sources ................... 89 3.4.2 Comparison to the cooling rate ............... 91 3.4.3 Comparison to other warm and dense regions ....... 92 3.5 Summary and conclusions ...................... 95 3.6 Appendix - Radex line ratio plots .................. 96 4 The chemistry of ions in the Orion Bar I. - CH+, SH+ and CF+ 99 4.1 Introduction ..............................101 4.2 Observations and Data reduction ..................102 4.3 Results .................................104 4.3.1 The detected CH+, SH+, and CF+ transitions ...... 104 4.3.2 Physical conditions traced by CH+ and SH+ ....... 105 + + 4.4 The formation of CH and SH via H2 vibrational excitation . 112 4.4.1 Estimate based on an analytic approximation ....... 112 4.4.2 CH+ formation ........................114 4.4.3 SH+ formation ........................115 4.5 The destruction of CH+ and SH+ ..................117 4.6 Discussion ...............................120 4.6.1 The formation of CH+ and SH+ ..............120 4.6.2 CH+ and SH+ as tracers of the warm PDR surface . 121 4.6.3 An extension of the ‘CF+ ladder’ in the Orion Bar . 123 4.7 Conclusions and outlook .......................123 5 Spatially extended OH+ emission in Orion 125 5.1 Introduction ..............................127 5.2 Observations .............................128 5.3 Results .................................129 5.3.1 Line profiles ..........................129 5.3.2 Spatial distribution ......................132 5.3.3 Column densities .......................133 5.4 PDR models .............................134 5.5 Excitation of OH+ ..........................138 5.5.1 Inelastic collision rates for the OH+– e− system ...... 138 5.5.2 Collisional and radiative excitation .............140 5.5.3 Effect of reactive collisions ..................141 vii 5.6 Discussion ...............................142 5.6.1 Changing the ionization rate ................142 5.6.2 Possible ion sources .....................142 5.6.3 Radiative pumping ......................143 5.6.4 Comparison with extragalactic systems .......... 144 5.7 Conclusions ..............................144 6 The UV-illuminated surface of Orion S 147 6.1 Introduction ..............................149 6.2 Observations and data reduction ..................150 6.3 Results .................................152 6.3.1 Line profiles ..........................152 6.3.2 Column densities .......................153 6.3.3 Chemistry driven by vibrationally excited H2 ....... 158 6.4 Discussion ...............................161 6.4.1 Comparison to the Orion Bar ................162 6.4.2 Reactive ions as PDR chemistry diagnostics ........ 166 6.5 Summary and future plans ......................168 7 Summary 171 8 Nederlandse samenvatting 181 9 Magyar ¨osszefoglal´o 191 viii 1 Introduction 1.1 Star formation and the interstellar medium The interstellar medium (ISM) is a key component of a galaxy as it is the place of birth of future generations of stars. The ISM itself is dependent on earlier generations of stars that influence its chemical composition and physical structure over the life-time of galaxies (see reviews by Draine 2011, Tielens 2005). Star-formation occurs in molecular clouds consisting of atoms, molecules, ions, and dust. Its structure and chemical composition is affected by previous populations of stars through supernova explosions, outflows, stellar winds, and irradiation. Star-formation in molecular clouds can occur in isolation (typically low-mass stars, M . 8 M⊙) or in clusters (typically high-mass stars, M & 8 M⊙). The type of star-formation set in a cloud is dependent on its physical parameters (e.g. Kennicutt & Evans 2012, and references therein). Dark molecular clouds are ideal sites for the formation of low-mass stars. These clouds range from globules with sizes of a few pc up to dark clouds or cloud complexes with sizes of &10 pc. The formation of massive stars typically occurs in the densest parts of 40 pc size Giant Molecular Clouds (GMCs). These star-forming sites and their∼ properties are the subject of the current thesis. The young massive stars formed in GMCs largely affect their physical and chemical structure through their radiation and mechanical feedback (such as outflows or stellar winds). We focus on these feedback effects in this thesis, based on molecular line surveys. In this chapter we give a general overview of the interstellar medium (Section 1.1.1) and star-formation (Sect. 1.1.2), focusing on the formation of high-mass stars (Sect. 1.1.3). We discuss the structure of high-mass star forming regions with two examples that are analysed in the thesis. We discuss commonly used tools for the interpretation of molecular line observations, such as radiative 2 1. Introduction transfer and chemical models (Sect. 1.2). We give a summary of the most important results of the thesis in Section 1.3. 1.1.1 Phases of the interstellar medium The gas in the ISM has different phases including ionized, neutral