The Physics of the Interstellar Medium:Course
Outline
Important notes on using this page: The links numbered 1-9 below will take you lower on this
page, to the beginning of that section of the course. Within each section,
a number of "Parts" are linked. The parts are listed in the order
they are covered on the syllabus, which approximates the order they were
covered in class. The link to each Part will take you to a group of jpg
files of handwritten notes ("version 1996" for now). To go to
the previous or next Part, just hit the "Back" button and then
select the Part before or after the one you're at. The notes are arranged
this way in order to be useful both to those who are taking this class,
and to others, outside the class. Eventually, the hyperlinks will be more
refined. Please surf a bit for now! Thanks. AG
1. Introduction: Defining Features of "a" galactic
ISM
2. Kinetic Equilibrium & Radiative Processes: Overview
3. The ISM of the Milky Way
4. Interaction of Photons with the ISM
5. Star Formation in Molecular Clouds
6. Interaction of Stellar Winds with the ISM
7. The ISM in External Galaxies at z~0
8. The Intergalactic Medium
9. The "ISM" at z>>0
- Introduction:
(Part
1, Part
2 (+pictures),
Part
3, Part
4) Defining Features of "a" galactic ISM (special pictorial
web page click here)
- Earliest Observations
- The "Modern" View & How we Got It
- Composition
- Gas, Dust, Electrons, Cosmic Rays, Photons
- Extent
- Scale Height & Radial Distribution
- Interstellar "Clouds"
- Extragalactic Perspective
- Comparison with Stellar Distribution
Temperature Structure
The "Hot," "Cold," and "Warm" ISM
Ionization State
Interactions with of ISM & Stars
example: Strömgren Sphere Analysis
Influence of Cosmic Rays
Density Structure
Measures of Column Density and Volume Density
Hierarchy of Interstellar "Clouds"
Velocity Structure
Galactic Scales
Within Individual "Clouds"
Magnetic Field Structure
Flux-freezing & Ambipolar Diffusion
Measurement Techniques
Confinement of Cosmic Rays & "Support" of Clouds
Time Scales & Stability
Virial Equilibrium
Instabilities (e.g. Jeans)
Nature of the ISM: Above "Variables" Inseparable
Kinetic Equilibrium & Radiative Processes:
Overview (Part
1, Part
2)
- Thermodynamic Equilibrium
- Partition Function
- Kinetic, Excitation, Color, Antenna, Bolometric, and Other "Temperatures"
Non-equilibrium Distributions
Excitation Processes
Collisional
Recombination
Non-LTE (Pumping)
Radiative Processes
Radiative Transfer Definitions
Emission & Absorption Coefficients
Continuum Emission
Thermal
Bremsstrahlung & Synchrotron
Scattering Processes
The Influence of Shocks
In SNe, Star-forming Regions, and in Accretion Disks (more below)
What combination of the above will be observed where?
Depends on l.o.s. Temperature, Density, Abundance, and Velocity Distribution
The ISM of the Milky Way (Part
1, Part
2, Part
3, Part
4, Part
5)
- Introduction: The Multi-Phase Paradigm
- Basic Assumptions
- Pressure, Mass, and Energy Balance
- Time Dependence
The "Cold" ISM
History and Definitions
"Out the window"
Permitted and Forbidden Transitions
Critical Density
Atomic Gas (H I; special
web page)
Origin of the 21-cm Line: Flipping a Spin
21-cm line Surveys
Collisional Excitation
Optical Depth Considerations
High-Velocity and High-Latitude Clouds
Detection
Origin & Evolution
Molecular Gas
The Difficulty in Directly Observing H2
Role of "Trace" Species"
Molecular Line Mapping
Masers (more in AGN discussion)
Dust
What is dust?
Cause of interstellar extinction
Range of Sizes from "Big Molecules" to Planetesimals
Measured/Measurable Properties
Optical Efficiency Factors
Cross-sections for emission, absorption & scattering
Albedo
Extinction as a function of l
Total-to-Selective Extinction
Spectral "features"
Thermal Emission as a function of l
Is the blackbody approximation adequate?
Are grains fractal?
Polarization as a function
of l
Polarization due to Scattering
Polarization due to Aligned Grains
Using Polarization to Map B
Polarization of Background Starlight
Polarization of Thermal Emission
Molecules & Dust Together
Formation of Molecules
on Dust
in the Gas Phase
Destruction of Molecules
by cosmic rays
by photons
by electrons & collisions
Heating & Cooling
Atomic & Molecular Coolants
Dust Heating & Cooling
The "Hot" ISM
The Warm Neutral Medium: Broad H I lines
The Warm Ionized Medium: Absorption Line Observations
Radio Continuum Emission & Pulsars as Probes
Distinguishing Bremsstrahlung from Synchrotron from Thermal Emission
Polarization of Synchrotron Emission
Rotation and Dispersion Measure
Faraday Rotation
RM/DM of Pulsars as a Probe of B
X-rays as a "Probe" of the ISM
X-ray "Shadows" of Molecular Clouds
Calibration of the CO/H2
ratio (a.k.a. the "X-factor")
How Appropriate are Multi-Phase Models?
Interaction of Photons with the ISM (Part
1, Part
2)
- H II Regions & Photon-Dominated Regions
- Strömgren Spheres
- "Clumpy" H II Regions
- Radio Recombination Lines
- General Shock Physics (Basic Equations, More Later)
- Compact and Ultra-Compact H II Regions
- Cometary H II Regions & Bow shock models
Champagne-flow models
Heating and Cooling in H II Regions
Ionization Fraction & Chemical Balance in PDRs
Measurements & Theories
Effects on Ion-Neutral Coupling
The Effect of High-Energy Photons on Molecular Clouds (e.g. in AGNe)
Star Formation in Molecular Clouds (Part 1,
Part
2)
- Giant Molecular Clouds, Dark Clouds, Cloud Cores & the "Modern"
Star Formation Paradigm
- Cloud Support & Dynamics
- "Larsons Laws" & Virial Equilibrium
- Role of Magnetic Fields (Part I)
Pressure Confinement
Self-similar Structure
Rotation
The Role of Magnetic Fields in Star-Forming Regions (Part II)
What matters: Static Fields, Turbulence and/or Waves?
Measurements of Field Strength
Measurements of Field Structure
MHD Simulations
Disks
Radiated Spectrum & Dependence on Viewing Angle
The Role of Scattered Light
Fragmentation & Instabilities
Planet Formation
Infall & Outflow
Expectations & Observations of Inflow
What Determines the Initial Mass Function of Stars?
Agglomeration Theories
Fragmentation Scenarios
"Fractal" Scenarios & Speculation
Interaction of Stellar Winds with the ISM (Part
1)
- Winds from Young Stars
- Observed Properties of Outflows (on ~pc scales)
- Comparison of Outflow Mechanical Luminosity & Protostars
Luminosity
- Aspect Ratio
- "Hubble Flow"
Observed Properties of Jets (on ~0.1 pc scales)
Emission from Herbig-Haro Objects and "Shocked" H2
Continuum and Line Radiation Produced in Shocks
Temperature, Ionization & Velocity Structure of Jets
Energy dissipated
Collimation Mechanism
The "X-wind Model"
Other proposals
Origin of the Relevant B-field: Stellar or Interstellar?
Jet-driven Outflows
(M)HD Simulations of Jets & Outflows
FU Orionis Activity & Episodic Jets: Magnetic Variability?
Mass Loss from Main Sequence & Evolved Stars
Production of Dust
Variety
Subsequent Processing to Produce Observed I-S Dust
Planetary Nebulae
Supernova Remnants
Observations
Multi-Wavelength Radiation
Optical Line & Continuum Emission
Synchrotron Radiation
Shock Physics & Chemistry
Time Evolution: Phases in the Expansion
Energy Deposited into ISM
Simulations
The
ISM in External Galaxies at z~0
- Variations with the Realm of "Normal" Galaxies
- Density Structure
- Velocity Structure & Rotation Curves
- X-ray
emission
...more
- Origin of High-velocity Clouds
Metallicity Variations
Magnetic Field Structure
"Active" and "Starburst" Galaxies
The Cause(s) of Starbursts
Jets and Disks in AGNe
The
Intergalactic Medium
- Observations:
Present & Future
- Lyman-
a clouds,
Lyman Limit systems and the Lyman Forest
- Metal-line systems
Relationship of the ISM & IGM
Coronal Gas?
Intracluster Gas in Galaxy Clusters/Cooling
Flows
The
"ISM" at z>>0
- Observations
- Highly
Redshifted CO
- Future Prospects: Other lines, other techniques
Cosmological Predictions
Lower Metallicity?
Origin of the Intergalactic & Interstellar Magnetic Fields
Observational Feasibility Estimates
Polarization of the Microwave Background
Other: Dielectronic
recombination; diffuse
interstellar bands;
polarization of the CMB.
Notes:
Specific "historical" lectures
are not included in this outline. Instead, I will incorporate an historical
perspective into topical lectures, whenever it is appropriate. For example,
in presenting what appear to be "simple models" like the Strömgren
sphere or Jeans collapse, I will discuss the observations Strömgren
or Jeans would have had available at the time they made their models.
Similarly, specific "observational
technique" lectures are not included. Techniques will be discussed
in context.