Ast 622: The Interstellar Medium

Spring 2008 Tue/Fri 3-4:30pm

The Interstellar Medium (ISM) is the gas and dust between the stars. Stars form from it, their winds and supernova enrich and replenish it. Temperatures in the ISM range from the very hot, $\gt 10^6$ K, to the very cold, $\lt 10$ K. Observed densities span an even wider dynamic range, from $\lt 10^{-3}$ to $\gt 10^6$ particles per cubic centimeter. Even the highest densities, however, are far more rarefied than the best vacuums currently attainable on Earth and thus the ISM allows us to explore physical processes in unique environments. This course will cover observations and theories of a wide range of ISM environments from pervasive diffuse, ionized gas to dense, molecular clouds. We will end with an overview of the circumstellar medium: protostellar and planetary disks.

Much of the class will be based around a new book, ``Physics and Chemistry of the Interstellar Medium'' by Sun Kwok (University Science Books). I will augment the material with additional notes and illustrative journal articles, linked below. Reading assignments will be given out from time to time (more in the second half of the semester) and I will call upon attendees at random to initiate discussions or elaborate on various points. Your participation in this regard will be a substantial part of your final grade.

The course will be graded through a combination of five approximately biweekly problem sets worth 10% each, in-class participation amounting to 25%, and a final oral exam worth 25%.

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• Chapter 1: The Interstellar Medium
  Additional material:
  • Multi-wavelength Milky Way, Trifid Nebula
  • Some useful units and constants
  • The Course of Science

• Chapter 2: Fundamental Concepts of Radiation
  

• Chapter 3: Measurements of Radiation
  Additional material:
  • Heterodyne detection
  • Fourier Transforms (from Condon & Ransom online course)
  • First fringes on the VLTI
  • Virtual Radio Interferometer
  • Examples of structure analysis in the visibility plane
  Assigned reading:
  • Thompson VLA summer school lecture (Read Section 1 only)

• Chapter 4: Photoionization and Recombination
  Additional material:
  • How ionized are HII regions?

• Chapter 5: Line Radiation from Atoms and Ions
  Additional material:
  • The three-level system
  • H$\alpha$, [OIII] and [SII] in the Rosette nebula
  • H$\alpha$, [OI] and [NII] in NGC6543
  • HI movie of the Galaxy (from Leiden/Argentine/Bonn survey)
  • The two-phase atomic ISM
  • 10GHz-10THz spectrum of a normal spiral (Braine & Hughes 1999)
  Assigned reading:
  • How the CNM/WNM ratio varies across the Galaxy

• Chapter 6: Continuum Radiation in the Gas Phase
  Additional material:
  • Rosette nebula at 20cm
  • The lifetime problem for ultra-compact HII regions
  • Synchrotron radiation
  • Galactic Center at 90cm
  • Super star clusters
  Assigned reading:
  • Supernebula in NGC5253: Free-free emission / Infrared recombination lines

• Chapter 7: Interstellar Molecules
  Additional material:
  • Characteristic energies of electronic, vibrational, and rotational transitions
  • SMA observations of the line forest in Orion KL (Beuther et al. 2005)
  • 4.7$\mu$m CO absorption lines in L1489 (Boogert et al. 2002)
  • Shocked H$_2$ and rotational CO in the HH211 outflow (Gueth & Guilloteau 1999)

• Chapter 8: Vibrational Spectroscopy of Polyatomic Molecules
  (Not covered)

• Chapter 9: Molecular Excitation and Abundance Determination
  Additional material:
  • The CO-H2 conversion factor
  • Deriving column densities from line integrated intensities
  • Orion CO 3-2 channel maps (from JCMT/HARP press release)
  • CO and $^{13}$CO maps of Taurus (Goldsmith et al. 2008)
  • D/H ratios in the ISM and solar system (Messenger 2000)
  Assigned reading:
  • Non-LTE radiative transfer (Section 2)

• Chapter 10: Interstellar Grains: Physical Processes
  Additional material:
  • N(HI) vs E(B-V) (Jenkins & Savage 1974)
  • X-rays compared to NIR in Orion (from COUP)
  • Interstellar polarization map of the Galaxy (Mathewson & Ford 1970)
  • Measuring the dust emissivity at 1.2mm
  • Scattered light image of a debris disk
  • Measuring the size of Eris
  Assigned reading:
  • Jewitt dust tutorial

• Chapter 11: The Chemical Composition of Interstellar and Circumstellar Grains
  Additional material:
  • Hale Bopp stars HD100546 and HD69830 (press release)
  • Crystalline silicate in brown dwarf disks (Apai et al. 2005)
  • Crystalline water ice on Quaoar
  • Extragalactic silicate emission (Sturm et al. 2005)
  Assigned reading:
  • Grain growth in Herbig Ae/Be disks

• Chapter 12: Carbonaceous Grains
  (Not covered)

• Chapter 13: The Origin of Interstellar Dust
  Additional material:
  • Expanding CO bubble around TT Cygni (Olofsson et al. 2000)
  • Heavy molecules in the carbon star IRC10216 (Lucas & Guelin 1999)
  • Silicate Stardust in Meteorites
  Assigned reading:
  • Type II SN as a significant source of dust? (Rebuttal) (The final answer?)

• Chapter 14: Chemical Reactions in the ISM
  Additional material:
  • CO, H$_2$, and PAH emission in the Orion bar PDR (Tielens et al. 1993)
  • Molecular depletion in a starless core (Tafalla et al. 2002)
  • Ice evaporation in hot cores (van der Tak et al. 2000)
  Assigned reading:
  • van Dishoeck & Blake Review

• Chapter 15: Gas Dynamics, Gravitational Collapse, and Stellar Winds
  Assigned reading:
  • Barnard 68 as a Bonnor-Ebert sphere

• Chapter 16: Interaction between Stars and the ISM
  Additional material:
  • The Hot Ionized Medium

• Chapter 17: Beyond the Galaxy
  Additional material:
  • Lyman alpha forest at low and high redshifts
  • The epoch of reionization (Fan et al. 2006)
  • The IGM in the Hydra cluster (McNamara et al. 2000)
  • SFE-dense gas relation in starbursts (Gao & Solomon 2004)
  • Redshifted SED of starburst galaxy (Melchior et al. 2001)
  • Deep fields at optical and mm wavelengths
  • Carilli Aspen lecture
  Assigned reading:
  • The Warm-Hot Intergalactic Medium
  • Star formation along the Hubble sequence

• Beyond the book: The Circumstellar Medium
  A major area of current research at the IfA and elsewhere is the study of circumstellar disks. They funnel material onto a a protostar and are the site of planet formation. We can use a lot of what we have learned about the ISM to help understand the circumstellar medium. I will spend the last part of the course discussing the theory and observations of protostellar and planetary debris disks.
  Assigned reading:
  • A disk primer
  • Disk SED theory

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