Galactic massive star forming regions near and far [Elektronische Ressource] : a (sub)millimeter study of the Orion Molecular Cloud 1 and W49A / Tzu-Cheng Peng

Peng Li, Tzu-Cheng

Sujets

• Astronomie

Informations

• Publié par: rheinische_friedrich-wilhelms-universitat_bonn
• Publié le: 01 janvier 2010
• Nombre de lectures: 56
• Langue: English
• Poids de l'ouvrage: 18 Mo

Extrait

Galactic massive star forming regions near and far: a (sub)millimeter
study of the Orion Molecular Cloud 1 and W49A
Dissertation
zur
Erlangung des Doktorgrades (Dr. rer. nat.)
der
Mathematisch-Naturwissenschaftlichen Fakulta¨t
der
Rheinischen Friedrich-Wilhelms-Universita¨t Bonn
vorgelegt von
Peng, Tzu-Cheng
aus
Taiwan
Bonn (Mai, 2010)AngefertigtmitGenehmigungderMathematisch-NaturwissenschaftlichenFakult¨atder
Rheinischen Friedrich-Wilhelms-Universit¨at Bonn
Diese Dissertation ist auf dem Hochschulschriftenserver der ULB Bonn
http://hss.ulb.uni-bonn.de/diss online
elektronish publiziert. Das Erscheinungsjahr ist 2010.
1. Referent: Prof. Dr. K. M. Menten
2. Referent: Prof. Dr. P. Kroupa
Tag der Promotion : 03.09.2010
iiAbstract
Massive stars play an important role in shaping the structure of galaxies due to the
large energy output during their lifetime. However, because of the short evolutionary
time scales, the large extinction toward their birth places, and the large distance
of massive stars, our understanding of their formation is still sketchy. Hence, the
observations oftwo well-known massive star formingregions in our Galaxy (W49Aat
11.4 kpc and Orion Molecular Cloud 1 at 414 pc) were carried out using the IRAM
30 m and APEX telescopes, including large-scale mappings of various molecular line
+emission, such as CO isotopologues, HCN, HCO , and SiO. The results of W49A
show thatits starburst was triggered by expanding shells, causing fragmentationthat
lead to the formation of massive stars. The cause of the shell expansion is not clear,
but likely due to the stellar feedbacks from a first generation of young massive stars
by strong stellar winds and ultraviolet radiation, or the interaction between stars in
a cluster, which is possibly related to the large-scale gas ejections found in the W49
50complexwithatotalkineticenergyoffewtimes10 erg. ApartfromW49A,thestudy
in Orion Molecular Cloud 1 reveals a more detailed picture of young massive stars
strongly interacting with their local environment. The highly excited CO emission
in Orion Molecular Cloud 1 shows two main components: one is the north-south
dense ridge where two active star-forming regions (Orion BN/KL and Orion South)
are located, and the other one consists of photon-dominated regions (e.g., the Orion
Bar and Orion East) spread over the whole area, where gas and dust are heated by
ultraviolet photons from the Trapezium cluster. In addition, several outflows are
detected in the higher-J transitions of CO, which indicates the important role of
shock heating associated with star-forming activities.
iiiTo My Parents
vAcknowledgements
I have benefited from the inputs and discussion from my colleagues and friends over
my study in the Max Planck Institute forRadioastronomy in Bonn. I wish to express
my gratitude to Friedrich Wyrowski for his patient supervision and some of his ideas
in this thesis. I also thank Professor Karl Mention for his support during my study. I
want to thank Floris van der Tak for the help in the radiative transfer modeling and
the discussion in W49A. I also want tothank Malcolm Walmsley for his many helpful
comments in W49A and the Orion Bar. I would like to thank Luis Zapata for the
discussion and inspiration in the study of Orion BN/KL and South. I wish to thank
Berengere Parise, Edwige Chapillon, and Peter Schilke for the useful discussion in
Orion Bar and the PDR modeling. I want to thank Endrik Kru¨gel for the discussion
in the dust mass calculation. I want to thank Kazi Rygl for her help to improve my
manuscript. I am also grateful to the International Max Planck Institute Research
School for Astronomy and Astrophysics at the Universities of Bonn and Cologne for
its support. In the end, Iwish tothank my parents in Taiwan and some ofmy friends
in Bonn: Ko-Po Yin, Cho-Chung Huang, Li-Rung Huang, and Oliver Nitchke, for
their kindly support and company.
viiContents
Abstract iii
Acknowledgements vii
List of Tables xi
1 Introduction 1
1.1 Massive Star Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.1 Massive star formation in external galaxies . . . . . . . . . . . . . . . . . . . 2
1.1.2 Star Formation Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Molecular and Dust Emission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3 Thesis Motivation & Sources Selection . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.3.1 W49A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.3.2 Orion Molecular Cloud 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.3.3 Thesis overview and publication plan . . . . . . . . . . . . . . . . . . . . . . . 11
I Galactic Starburst Template W49A 15
2 Observations toward W49A 17
2.1 IRAM 30 m Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.2 APEX Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3 W49A Results 21
3.1 Molecular line emission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.2 Dust continuum emission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
4 RADEX Modeling of W49A 79
4.1 Estimations of the temperature and the density . . . . . . . . . . . . . . . . . . . . . 79
4.2 RADEX Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
13 184.2.1 CO and C O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
+4.2.2 The abundance ratios among HCN, HCO , and HNC . . . . . . . . . . . . . 83
4.2.3 H density and kinetic temperature distribution. . . . . . . . . . . . . . . . . 902
5 W49A Discussion 97
5.1 Expanding shells in W49A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
5.1.1 Molecular spectra toward the shell expansion center . . . . . . . . . . . . . . 100
5.1.2 Mid-infrared emission of the shells . . . . . . . . . . . . . . . . . . . . . . . . 103
5.1.3 The driving mechanism of the expanding shells . . . . . . . . . . . . . . . . . 108
5.1.4 Fragmentation of the shell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
5.2 Large-scale gas ejections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
5.3 UC H II regions in W49A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
+5.4 The HCO /HCN and HNC/HCN ratios . . . . . . . . . . . . . . . . . . . . . . . . . 118
5.5 X-ray emission and shock tracers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
6 W49A Conclusions 133
ixII Large-Scale Mappings of highly excited CO in Orion Molecular
Cloud 1 135
7 Observations toward OMC-1 137
7.1 APEX Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
8 OMC-1 Results 139
8.1 Large-scale characteristics of OMC-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
8.1.1 Velocity Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
8.1.2 Line Ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
8.2 Orion BN/KL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
8.3 Orion South . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
8.4 Orion Bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
8.5 Orion East . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
9 RADEX Modeling of OMC-1 193
9.1 The excitation temperature and the density estimation . . . . . . . . . . . . . . . . . 193
9.2 RADEX modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
10 OMC-1 Discussion 199
10.1 Orion BN/KL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
10.2 Orion South . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
10.3 Orion Bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
10.4 Orion East . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
11 OMC-1 Conclusions 223
12 Summary 225
Bibliography 227
A Position-velocity diagrams of the shells in W49A 235
B 247
B.1 Column Density Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
B.2 Dust Mass Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250
C The RADEX modeling results of W49A 251
D Spitzer color-color images of W49A 261
E The Meudon/RADEX results of the Orion Bar 265
x