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PX3A6 Galaxies and Cosmology

Lecturer: Matteo Brogi and Grant Kennedy
Weighting: 15 CATS

A galaxy is a system of stars, dust, stellar remnants and other bodies bound by gravity. Galaxies usually form groups, bound by their gravitational interaction, and these groups themselves tend to be part of even larger superclusters. We will see that we can put together quite simple explanations of what we observe in these complex systems.

Questions about the origin of the Universe, where it is going and how it may get there are the domain of cosmology. One of the questions addressed in the module is whether the Universe will continue to expand or ultimately contract. Relevant experimental data include those on the Cosmic Microwave Background radiation and the distribution of galaxies.


To illustrate how important physical principles, from different areas of physics, can be developed to yield a description of complex physical systems like galaxies. To present the credentials of the Universe as we know it (via experiment) and introduce the simplest models that can describe it. The module should stress the role of experimental data and emphasize cosmology as a physical science, which makes testable predictions that describe the observed Universe.


By the end of the module, students should be able to:

  • Describe the structure of our own Galaxy and how it fits into the ‘zoo’ of galaxies distributed through the Universe;
  • Explain the physical principles behind the observations used to study galaxies
  • Discuss the outstanding problems in the study of galaxies including the nature of galaxy cores and the roles of dark matter and dust
  • Recognise the importance of observations in constraining possible cosmological theories
  • Explain the evolution of model universes, and how this evolution depends on their energy density components
  • Discuss areas of cosmology where more work is needed to reconcile theory and observations


Galaxy classification; the Hubble Tuning Fork; elliptical and spiral galaxies; surface
brightness profiles. The Milky Way, its structure and properties; the role of stellar populations and the
interstellar medium.
Galaxy populations; luminosity functions, star formation vs AGN, radio galaxies and seyferts. Galaxy kinematics; Tully-Fisher relation; rotation curves; dark matter; virial mass.
The role and origin of dust and gas in galaxies; dust extinction laws; types of dusty galaxies. Introduction to galaxies at large scale: the Local Group and nearby clusters.

The history and foundations of modern cosmology: Olber’s Paradox, Hubble’s Law and the Cosmological Principle. Describing the evolution of the Universe: basics of space time and relativity, curvature, Friedmann equation, fluid and acceleration equations.
Model universes: describing the evolution when dominated by single component and multiple-components - the standard cosmological (benchmark) model.
Key properties of our Universe: tests of the standard cosmological model, evidence for dark matter; models for dark matter, origin of structure.
The early Universe: the Big Bang, connection to elementary particle physics and grand-unified field theories (GUTS), inflation, Big Bang nucleosynthesis, formation of the cosmic background radiation.

Commitment: 30 Lectures

Assessment: 2 hour examination.

Recommended Texts:
The following are useful, but not compulsory.

    S Philipps, The Structure and Evolution of Galaxies, Wiley, 2005
    B. Ryden: Introduction to Cosmology, Pearson 2013
    Michael Berry: Principles of cosmology and gravitation, IoP 1989
    A. Liddle: An Introduction to Modern Cosmology, Wiley, 2003