AST 403: Galaxies and Intergalactic Medium

3 credits | Prerequisites: AST 301

Course rationale

This is an elective course designed for students majoring in physics, mathematics, engineering or computer science. Students can take it as part of a minor or specialization in astronomy and astrophysics or as a free elective. The course intends to give an overview of the structure, formation and evolution of galaxies and their observations at different wavelengths. It introduces galaxies within the broader context of intergalactic medium and demonstrates the efficacy of physical laws in describing the largest bound structures of the universe.

Course content

Milky Way: galaxies in an expanding universe, mapping our Milky Way, solar neighborhood, stars in the Galaxy, galactic rotation, meteorology of the interstellar gas. The orbits of stars: weighing the Galaxy, two-body relaxation, close and weak encounters, orbits of disk stars, epicycles, the collisionless Boltzmann equation. The Local group: satellites of the milky way, the Magellanic clouds, standard candles, dwarf spheroidal galaxies, tidal limit, Andromeda galaxy, formation of the local group, formation of milky way, dwarf elliptical and spheroidals, future of the local group, galaxy groups as homes of disk galaxies. Spiral and S0 galaxies: detecting diffuse emission, surface photometry of disk galaxies, observing galactic gas, cool gas in the disk, rotation curve of galaxies, dark matter, Tully-Fisher relation, sequence of disk galaxies, spiral arms and galactic bars, theories of spiral structure formation, bulges and centers of disk galaxies. Elliptical galaxies: photometry, shape of elliptical galaxies; twisty, disky and boxy shapes; stellar velocities, Faber-Jackson relation, fundamental plane, rotation, stellar orbits, stellar populations and gas, dark matter and black holes. Galaxy clusters: clusters as homes of S0 and elliptical galaxies, hot intergalactic gas in clusters, intra-cluster medium (ICM), galaxy evolution in clusters, intergalactic dark matter, x-ray emission from ICM, radio emitting regions of ICM. Active galaxies: active galactic nuclei, Seyfert galaxies, radio galaxies, synchrotron emission from radio galaxies, quasars, fast jets from active nuclei, metals in intergalactic gas, Lyman-α forest, the first galaxies of cosmic dawn, star formation history of the universe. Gravitational collapse and galaxy formation: spherical collapse models, collisionless dynamics, Jeans theorem, spherical equilibrium models, collisionless relaxation, gravitational collapse of the cosmic density field, formation and structure of dark matter halos, formation and evolution of gaseous halos. Star formation in galaxies: giant molecular clouds, cloud formation, magnetic fields, supersonic turbulence, formation of individual stars, empirical star formation laws, initial mass function. Chemical evolution of galaxies: overview of stellar evolution, stellar chemical production, the closed-box model, abundance ratios, stellar energetic feedback, chemical evolution of disk galaxies. Transformation of galaxies: formation of disk galaxies, origin of disk galaxy scaling relations, disk instabilities, high-speed encounters of galaxies, tidal stripping, dynamical friction, galaxy merging, harassment and cannibalism. Intergalactic medium: ionization state of the intergalactic medium (IGM), ionizing sources, evolution of IGM, properties of absorption lines, Lyman-α forest, Lyman-limit systems.

Course objectives

  1. Describe the properties of the Milky Way and use it to understand the general properties of disk galaxies.
  2. Differentiate between disk and elliptical galaxies.
  3. Introduce the Local Group and locate our Galaxy within this group.
  4. Comprehend the formation and evolution of clusters of galaxies and the evolution of galaxies within clusters.
  5. Understand the intergalactic medium and intracluster medium as a source of astronomical information.
  6. Explain the formation of galaxies using spherical collapse and equilibrium models.
  7. Comprehend the role of galaxy observations in understanding the universe we inhabit.


  1. L. S. Sparke & J. S. Gallagher, III, Galaxies in the Universe: An Introduction, Cambridge University Press, 2007.
  2. H. Mo, F. van den Bosch & S. White, Galaxy Formation and Evolution, Cambridge University Press, 2010.
  3. Peter Schneider, Extragalactic Astronomy and Cosmology: An Introduction, Springer, 2006.