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The Impact of Giant Stellar Outflows on Molecular Clouds

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The Impact of Giant Stellar Outflows on Molecular Clouds The Impact of Giant Stellar Outflows on Molecular Clouds A thesis presented by H´ector G. Arce Nazario to The Department of Astronomy in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the subject of Astronomy Harvard University Cambridge, Massachusetts October, 2001 c 2001, by H´ector G. Arce Nazario All Rights Reserved ABSTRACT Thesis Advisor: Alyssa A. Goodman Thesis by: H´ector G. Arce Nazario We use new millimeter wavelength observations to reveal the important effects that giant (parsec-scale) outflows from young stars have on their surroundings. We find that giant outflows have the potential to disrupt their host cloud, and/or drive turbulence there. In addition, our study confirms that episodicity and a time-varying ejection axis are common characteristics of giant outflows. We carried out our study by mapping, in great detail, the surrounding molecular gas and parent cloud of two giant Herbig-Haro (HH) flows; HH 300 and HH 315. Our study shows that these giant HH flows have been able to entrain large amounts of molecular gas, as the molecular outflows they have produced have masses of 4 to 7 M |which is approximately 5 to 10% of the total quiescent gas mass in their parent clouds. These outflows have injected substantial amounts of −1 momentum and kinetic energy on their parent cloud, in the order of 10 M km s and 1044 erg, respectively. We find that both molecular outflows have energies comparable to their parent clouds' turbulent and gravitationally binding energies. In addition, these outflows have been able to redistribute large amounts of their surrounding medium-density (n ∼ 103 cm−3) gas, thereby sculpting their parent cloud and affecting its density and velocity distribution at distances as large as 1 to 1.5 pc from the outflow source. Our study, in combination with other outflow studies, indicate that a single giant molecular outflow in a molecular cloud of less than about 80 M has the potential to seriously disrupt its parent cloud. We, therefore, conclude that the cumulative action of many giant outflows will certainly have a profound effect on their cloud's evolution and fate. Our detail study of the outflow morphology, velocity structure, and momentum distribution |among other properties of both outflows| lead us to suggest that they are predominantly formed by bow-shock prompt entrainment, from an episodic wind with a time-varying axis. Close to the outflow source of HH 315, though, the coexistence of a jet-like wind and a wide-angle wind explains better the observed outflow properties. iii iv Contents Abstract . iii List of Figures . ix List of Tables . xiii Acknowledgments . xv 1 Introduction 1 1.1 A brief introduction to star formation . 1 1.2 The outflow stage . 6 1.2.1 Herbig-Haro flows . 6 1.2.2 Molecular Outflows . 9 1.3 Outflow-Cloud interaction . 11 1.3.1 Outflow-cloud interaction in the immediate vicinity of the out- flow source . 12 1.3.2 Outflow-cloud interaction at parsec scales . 21 1.4 What drives molecular outflows? . 22 1.5 Brief discussion of shocks . 30 1.5.1 Properties of shocks . 30 1.5.2 Shocks with Magnetic Fields . 34 1.5.3 Bow shocks in collimated winds from young stellar objects . 35 1.6 Why this Thesis? . 36 1.7 Thesis Plan . 39 v 2 The Episodic, Precessing Giant Molecular Outflow from IRAS 04239+2436 (HH 300) 43 2.1 Introduction . 44 2.2 Observations . 47 2.2.1 12CO(2{1) Data . 47 2.2.2 12CO(1{0), 13CO(1{0), and C18O(1{0) Data . 50 2.3 Results . 51 2.3.1 13CO(1{0) Maps . 52 2.3.2 12CO Maps . 55 2.3.3 Outflow Physical Properties . 59 2.4 Discussion . 68 2.4.1 Mass and Energetics . 68 2.4.2 Mass-Velocity Relation . 71 2.4.3 The episodic and precessing nature of the flow . 76 2.4.4 Effects on the cloud . 81 2.4.5 The structure of B18w . 85 2.4.6 The cumulative effect of outflows . 87 2.5 Conclusion . 87 3 The Mass-Velocity and Position-Velocity Relations in Episodic Out- flows 91 3.1 Introduction . 92 3.2 Mass-Velocity Relation . 93 3.2.1 Observing the M − v Relation . 93 3.2.2 Modeling the M − v Relation . 94 3.2.3 The M − v Relation in Episodic Outflows . 95 3.3 Position-Velocity Relation . 98 3.3.1 Observing p(v) . 98 vi 3.3.2 Modeling p(v) . 98 3.3.3 The p(v) in Episodic Outflows . 100 3.4 Discussion and Conclusions . 101 3.4.1 Reconstructing History . 101 3.4.2 The need for new models . 101 4 The Great PV Ceph Outflow: A Case Study in Outflow-Cloud Interaction 103 4.1 Introduction . 104 4.2 Observations . 109 4.2.1 12CO(2{1) Data . 109 4.2.2 12CO(1{0), 13CO(1{0), and C18O(1{0) Data . 111 4.3 Results . 112 4.3.1 12CO(2{1) Maps . 112 4.3.2 13CO(1{0) Maps . 117 4.3.3 Dissecting the PV Ceph cloud . 120 4.3.4 The flow in context with its parent cloud's structure . 125 4.3.5 Outflow Mass . 126 4.4 Discussion . 132 4.4.1 Mass and Energetics of the Outflow . 132 4.4.2 The effects of the outflow on the ambient gas . 136 4.5 Summary and Conclusion . 147 5 Molecular bow shocks, jets and wide-angle winds: a high resolution study of the entrainment mechanism of the PV Ceph Outflow 151 5.1 Introduction . 152 5.2 Observations . 155 5.3 Results . 158 vii 5.3.1 The region surrounding HH 315B and HH 315C (hh315b+c) . 158 5.3.2 The region surrounding HH 215 and PV Ceph (hh215) . 167 5.3.3 The region surrounding HH 315E . 175 5.4 Analysis and Discussion . 176 5.4.1 Temperature distribution . 176 5.4.2 Kinematics and momentum distribution . 182 5.4.3 Bow shocks, jets, and wide-angle winds . 192 5.4.4 Episodicity and axis wandering of the HH 315 flow . 199 5.5 Summary . 204 6 A Quantitative Comparison 207 6.1 Outflow-cloud interaction . 208 6.1.1 Disruption of a cloud by a giant outflow . 208 6.1.2 Many outflows in one cloud . 218 6.1.3 Recipe for destruction . 223 6.1.4 Concluding Remarks . 224 6.2 Driving mechanism . 226 6.3 Episodicity . 231 6.4 Wandering outflow axis . 234 7 Summary and Future Work 239 7.1 Summary . 239 7.2 Future Work . 243 A Estimating Excitation Temperature Using CO Line Ratios 247 Bibliography 251 viii List of Figures 1.1 Taurus molecular cloud complex observed at three different molecular spectral lines . 3 1.2 Schematic picture of a star-forming region . 5 1.3 Image of the inner region of the HH 111 jet . 7 1.4 Map of the L1551-IRS5 molecular outflow . 10 1.5 L1228: example of core disruption by an outflow through kinematical evidence . 13 1.6 L43: example of an outflow-created core cavity revealed by the pres- ence of a reflection nebula . 14 1.7 HH 56/57 region: example of a core cavity created by an outflow, revealed as a region of lower extinction in a dark cloud . 16 1.8 Mon R2: example of an outflow-created cavity revealed through molec- ular line observations . 17 1.9 NGC 1333: example of a region where outflow-created cavities are observed in millimeter continuum emission . 18 1.10 Velocity maps of the L1228 bipolar 13CO(1{0) outflow . 20 1.11 Schematic illustration of the wide-angle wind, jet bow shock, and turbulent jet entrainment models. 24 1.12 RNO 43: Example of a bow-shock entrained molecular outflow, in- ferred from the outflow kinematics and morphology . 28 1.13 L1157: Example of a bow-shock entrained molecular outflow, inferred from the outflow chemistry and morphology . 29 1.14 Schematics of a plane-parallel shock . 31 ix 1.15 Schematic illustration of the behavior of shocked gas . 32 1.16 Schematic illustration a bow shock . 35 1.17 Cartoon figure of the on-the-fly mapping technique . 38 1.18 Schematic representation of thesis observations . 40 2.1 13CO(1{0) integrated intensity map of the B18 cloud . 46 2.2 Average spectra of mapped region in B18w . 49 2.3 13CO(1{0) velocity maps of the B18w region . 53 2.4 Velocity maps of the 12CO(2{1) HH 300 molecular outflow . 56 2.5 Velocity maps of the 12CO(1{0) HH 300 molecular outflow . 57 2.6 12CO(1{0) integrated intensity map of HH 300 overlaid on optical image of the region . 57 2.7 Velocity-dependent opacity correction of 12CO(1{0) line in the HH 300 molecular outflow . 63 2.8 Momentum map of the HH 300 molecular outflow . ..
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