Diffuse Matter in the Universe

361 Pages·2001·2.196 MB·English

by  Dopita M.A., Sutherland R.S.

Michael A. Dopita & Ralph S. Sutherland
Diffuse Matter in the Universe,
Subtitle, Edition
SPIN Springer’s internal project number, if known
Physics – Monograph
(Editorial W. Beiglbo¨ck)
January 9, 2001
Springer-Verlag
Berlin Heidelberg NewYork
London Paris Tokyo
HongKong Barcelona
Budapest
‘...Light is a confused aggregate of Rays indued with all
sorts of Colours, as they are promiscuously darted
from the various parts of luminous bodies. A natu-
ralist would scarce expect to see ye science of those
colours become mathematicall, and yet I dare affirm
that there is as much certainty in it as in any other
part of Opticks.’
Sir Isaac Newton, in a letter to the Royal Society, 1672

Preface
Here come the golden words
place(s), Firstname Surname
month year Firstname Surname

Contents
1. What is Diffuse Matter?.................................. 1
1.1 Phases ................................................ 5
1.2 Observability .......................................... 7
2. Line Emission Processes .................................. 11
2.1 Atomic Spectra ........................................ 11
2.1.1 Resonance Lines ................................. 11
2.1.2 Pure Recombination Lines......................... 14
2.1.3 The Spectroscopic Notation........................ 18
2.1.4 Intercombination and Forbidden Lines .............. 22
2.2 Molecular Spectra ...................................... 23
2.2.1 Rotating Diatomic Molecules ...................... 24
2.2.2 Rotational Wavefunction Symmetry ................ 26
2.2.3 Rotating Diatomic Molecules with Identical nuclei .... 29
3. Collisional Excitation ..................................... 33
3.1 Collisional Excitation by Electron Impact ................. 34
3.1.1 Limiting Cases................................... 37
3.2 The Three–Level Atom.................................. 38
3.2.1 Low Density Limit; E ∼E ..................... 39
12 23
3.2.2 Ions in which E (cid:2)E .......................... 41
23 12
3.2.3 Infrared Line Diagnostics.......................... 45
3.3 The General Multi–Level Atom .......................... 45
4. Line Transfer Effects...................................... 49
4.1 Resonance Line Transfer ................................ 49
4.1.1 Resonance Line Absorption by Heavy Elements ...... 50
4.1.2 Absorption Line Studies of the ISM................. 52
4.1.3 Line Transfer in Emission Resonance Lines .......... 56
4.1.4 Line Transfer in the Lyman Series .................. 60
4.2 Fluorescent Processes ................................... 62
4.2.1 The Bowen Mechanism............................ 62
4.2.2 Oi Fluorescence with Lyβ. ........................ 63
4.2.3 H Fluorescence with Lyα ......................... 63
2
X Contents
4.2.4 Raman Scattering Fluorescence .................... 63
4.3 Astrophysical Masers ................................... 65
4.3.1 Theory.......................................... 65
4.3.2 Observations of Galactic Masers.................... 69
4.3.3 Observations of Extragalactic Masers ............... 72
5. Collisional Ionisation Equilibrium......................... 77
5.1 Collisional Ionisation.................................... 77
5.1.1 The Case of Hydrogen ............................ 80
5.2 Recombination ......................................... 81
5.2.1 Radiative Recombination Rates .................... 83
5.2.2 Di–electronic Recombination Rates ................. 84
5.3 Photoionisation ........................................ 85
5.3.1 From Outer Shells................................ 85
5.3.2 From Inner Shells ................................ 86
5.3.3 The Milne Relation............................... 87
5.3.4 Photoionisation Cross–sections ..................... 88
5.4 Charge–Exchange ...................................... 91
5.5 Coronal Equilibrium .................................... 94
5.5.1 The Case of a Pure Hydrogen Plasma............... 95
5.5.2 Ionisation Equilibrium of Heavy Elements ........... 96
6. Continuum & Recombination Line Processes ............. 99
6.1 Free–Free Continuum Emission........................... 99
6.1.1 free–free Gaunt factors............................ 101
6.2 The Free–Bound Continuum ............................. 104
6.3 The Two–Photon Process ............................... 107
6.4 Recombination Line Emission ............................ 109
6.4.1 Recombination Line Spectra ....................... 109
6.4.2 The Radio Recombination Lines.................... 111
7. Cooling Plasmas.......................................... 115
7.1 The Cooling Function................................... 115
7.2 Conditions for Non-Equilibrium Cooling................... 118
7.3 Heat Transport ........................................ 121
7.3.1 Electron Conduction.............................. 122
7.3.2 Boundary Layer Mixing ........................... 124
7.4 Cold Clouds in Hot Gas ................................. 125
7.5 Thermal Instabilities.................................... 127
7.5.1 In a Stationary Medium........................... 128
7.5.2 In an Expanding Medium ......................... 130
7.6 Hot Galactic Coronae ................................... 131
7.6.1 Early-Type Galaxies .............................. 131
7.6.2 Clusters of Galaxies .............................. 134
7.6.3 Disk Galaxies .................................... 137
Contents XI
8. Interstellar Shocks........................................ 145
8.1 Why Do Shocks Exist?.................................. 145
8.2 J-Shocks .............................................. 149
8.2.1 The Rankine-Hugoniot Jump Conditions ............ 151
8.2.2 Radiationless Shocks.............................. 152
8.2.3 Isothermal Shocks ................................ 154
8.3 The Drivers of Interstellar Shocks ........................ 156
8.3.1 Supernova Explosions............................. 156
8.3.2 Stellar Wind Bubbles ............................. 160
8.3.3 Galactic Jet-Driven Bubbles ....................... 162
8.4 The Radiative Properties of J-shocks...................... 164
8.4.1 Radiation Properties of Shock Fronts ............... 164
8.4.2 The Structure of Radiative J-Shocks ................ 168
8.4.3 Spectra of Old Supernova Remnants ................ 171
8.4.4 Spectra of Herbig-Haro Objects .................... 173
8.5 C-Shocks .............................................. 176
8.5.1 The Structure & Spectrum of C-Shocks ............. 177
9. The Theory of Photoionised Regions...................... 185
9.1 Photoionisation of Hydrogen Hii Regions.................. 186
9.1.1 Equilibrium Ionisation & Ionisation Parameters ...... 186
9.1.2 The Diffuse Field: Case A & Case B................. 190
9.1.3 Ionisation Fronts ................................. 191
9.1.4 Jump Conditions in Ionisation Fronts ............... 193
9.1.5 Photoionisation of Neutral Condensations ........... 196
9.2 Hii Regions with Heavy Elements ........................ 199
9.2.1 Ionisation Structure of Hydrogen & Helium Nebulae... 199
9.2.2 Nebular Structure with Heavy Elements............. 203
9.2.3 Nebular Equilibrium Temperature .................. 204
9.3 Photoionisation by X-ray Sources......................... 207
9.4 Radio Continuum of Hii Regions ......................... 209
10. Parameters of Photoionised Regions ...................... 215
10.1 Nebular Parameters .................................... 215
10.1.1 Nebular Temperature ............................. 215
10.1.2 Ionised Masses & Densities ........................ 219
10.2 Ionising Source Parameters .............................. 221
10.2.1 UV Flux Distribution............................. 221
10.2.2 Stellar Atmospheric Modelling ..................... 221
10.2.3 Zanstra Temperatures............................. 223
10.2.4 Energy Balance (Stoy) Temperatures ............... 225
10.3 Photoionisation Modelling ............................... 226
10.3.1 Ionisation Correction Factors ...................... 228
10.3.2 Self-Consistent Photoionisation Modelling ........... 229
10.4 Abundances ........................................... 231
XII Contents
10.4.1 Galactic Abundance Gradients from Hii Regions ..... 231
10.4.2 Abundances in Planetary Nebulae (PNe) ............ 234
10.4.3 Nova Shells...................................... 237
11. Photoionising Shocks ..................................... 243
11.1 Radiative Properties of Fast Shocks....................... 244
11.1.1 Production of Photoionised Shock Precursors ........ 244
11.1.2 The Structure of Radiative Fast Shocks ............. 246
11.1.3 Narrow Line Regions in Active Galaxies............. 248
11.2 The Oxygen-Rich Supernova Remnants ................... 250
12. Interstellar Dust.......................................... 255
12.1 Stardust Formation..................................... 256
12.1.1 Grain Condensation in Oxygen-Rich Atmospheres .... 258
12.1.2 Grain Condensation in Carbon-Rich Atmospheres .... 260
12.2 Optical Properties of Dust............................... 261
12.2.1 Extinction : Definitions ........................... 261
12.2.2 Optical Efficiency Factors ......................... 265
12.2.3 Polarisation by Dust.............................. 267
12.3 Grain Photoheating..................................... 269
12.3.1 Quantum Heating ................................ 270
12.4 Grain Charging ........................................ 271
12.5 The Life Cycle of Grains ................................ 273
12.5.1 Thermal Sputtering of Grains...................... 274
12.5.2 Grain-Grain Collisions ............................ 275
12.6 Spectral Signatures of Grain Materials .................... 277
12.6.1 Constraints from the Spectral Energy Distribution.... 277
12.6.2 Silicates......................................... 278
12.6.3 Icy Grain Mantles ................................ 278
12.6.4 Polycyclic Aromatic Hydrocarbons (PAHs) .......... 279
12.6.5 The Diffuse Interstellar Bands (DIBs). .............. 280
13. Introduction to Astrochemistry........................... 283
13.1 Molecular Formation and Destruction ..................... 283
13.1.1 Neutral Gas-Phase Reactions ...................... 283
13.1.2 Ion-Molecule Chemistry ........................... 284
13.1.3 Dust-Grain Moderated Chemistry .................. 285
13.1.4 Molecular Destruction Processes.................... 287
13.2 Chemistry of Particular Regions.......................... 289
13.2.1 Cold Molecular Clouds............................ 289
13.2.2 Photodissociation Regions ......................... 291
13.2.3 Shock Chemistry ................................. 295
13.2.4 Hot Molecular Cores.............................. 297
Contents XIII
14. Thermal Phases of Diffuse Matter ........................ 299
14.1 Phase Stability......................................... 301
14.2 Thermal Phases of Galactic Interstellar Gas ............... 303
14.2.1 Giant Molecular Clouds ........................... 303
14.2.2 The Atomic ISM ................................. 305
14.2.3 The Warm Ionised Phases ......................... 307
14.2.4 The Hot Ionised Component ....................... 309
14.3 Feedback & Mass Exchange.............................. 310
14.3.1 Shells, Supershells & Interstellar Froth .............. 310
14.3.2 Self-Propagating Star Formation ................... 313
14.3.3 Self-Regulated Star Formation ..................... 315
14.3.4 Mass Exchange .................................. 318
14.3.5 Dust Evolution in a Multi-Phase Medium ........... 319