Galaxies & Cosmology

Part 1

There are four chapters in Part 1 of Galaxies and Cosmology:

Chapter One - The Milky Way - Our Galaxy.

At this point in the course you will start to consider the Universe on larger scales than individual stars or star clusters. The study of galaxies begins by considering the galaxy in which we live - the Milky Way Galaxy (image of the Milky Way shown at top left of this page, courtesy of NASA).

Comments:

• Describe the main structural components of the Galaxy (disc, bulge and halo).
• Describe the constituents of the Galaxy (dark matter, different populations of stars, gas and dust).
• Describe the observational techniques that are used to map the structure of the Galaxy.
• Explain the principle by which the mass of the Galaxy could be measured by using rotation curve measurements, and recognize the difficulties in applying this technique in practice.
• Describe the evidence supporting the idea that the central regions of the Galaxy contain a massive black hole.
• Explain the effects of cosmic recycling and galactic mergers on the evolution of the Galaxy.

Chapter Two - Normal Galaxies.

This chapter considers galaxies external to our own Milky Way. The starting point for this is to consider how galaxies are classified according to their morphological characteristics. The chapter then considers how the physical properties of galaxies are measured, before introducing the very important topic of the determination of distances to galaxies. The final section of the chapter provides an introduction to one of the most exciting areas of modern astronomy, namely the study of the origin and evolution of galaxies.

Comments:

The learning outcomes are given as:

• Classify galaxies according to the modified Hubble scheme described in this chapter.
• Compare and contrast the physical properties of the various Hubble classes.
• Describe the main sources of emission from normal galaxies at optical, far-infrared and X-ray wavelengths.
• Understand the significance of surface brightness and isophotes in assessing galactic luminosities and sizes.
• Describe techniques that are used to determine the masses of galaxies, and comment on the results of applying these techniques.
• List the major methods used to measure astronomical distances of objects that lie beyond the Milky Way, and describe and use some of those methods in detail.
• Write down Hubble's law and comment on the problems associated with the determination of the Hubble constant.
• Describe the different scenarios that have been proposed to account for galaxy formation.

Chapter Three - Active Galaxies.

Active galaxies come in a variety of types: quasars, radio galaxies, Seyfert galaxies and blazars. All of these types of galaxy are characterized by spectral peculiarities. This chapter starts by comparing the spectral characteristics of active galaxies with those of normal galaxies and by introducing the concept of the spectral energy distribution - which provides a useful way of showing the broadband spectrum of a galaxy. The observed characteristics of the different types of active galaxy are then reviewed. The chapter then considers the arguments that support the notion that all such galaxies harbour an accreting supermassive black hole, and examines the 'unified' models for active galaxies. The chapter ends by considering some of the outstanding questions in active galaxy research.

Comments:

The learning outcomes are:

• Explain how and why the optical spectrum of an active or starburst galaxy differs from that of a normal galaxy.
• Explain how and why the broadband spectrum of an active or starburst galaxy differs from that of a normal galaxy.
• Describe briefly the observed features of starburst galaxies and the four main classes of active galaxies (quasars, radio galaxies, Seyfert galaxies and blazars).
• Understand the evidence that indicates the presence of a compact active galactic nucleus (AGN) in active galaxies.
• Explain why an AGN should emit broad lines, narrow forbidden lines and continuous radiation.
• Give an account of an accreting massive black hole as the engine of the AGN and relate its luminosity to the mass accretion rate.
• Outline some of the outstanding problems relating to the evolution of active galaxies.

Chapter Four - The Spatial Distribution of Galaxies.

This chapter considers the way in which galaxies are distributed in space. The approach taken is to start by considering our local neighbourhood, and it is found that the Milky Way exists within a loose collection of thirty or so galaxies that is called the Local Group. Looking beyond the Local Group, the chapter moves on to consider clusters of galaxies. These are systems that may contain more than a thousand galaxies in a volume that is only a few megaparsecs across. The chapter discusses three different methods that are used to determine the masses of clusters of galaxies, and you will see that all such methods point to the existence of vast quantities of dark matter within these systems. Moving on to larger scales, the chapter then discusses how the distribution of galaxies on the largest scales is currently being measured by means of redshift surveys. Although the focus of the chapter is on the spatial distribution of galaxies, there is also discussion of techniques that are used to map the large-scale distribution of cool intergalactic gas and of dark matter. The chapter concludes by returning to the distribution of galaxies, and gives an outline of a technique that can be used to characterize the structure in the Universe - a process that is vital in testing theories of the formation of large-scale structure against observation.

Comments:

Learning outcomes are:

• Describe the hierarchy of structure that is observed in the Universe from the scale of individual galaxies up to the scale at which the Universe starts to appear uniform.
• Discuss the different approaches that have been adopted to survey the distribution of galaxies in the Universe around us.
• Describe the typical physical properties of groups and clusters of galaxies.
• Describe techniques used to determine the masses of clusters of galaxies, and comment on the results of applying these techniques.
• Describe how the distribution of neutral gas in the intergalactic medium can be studied by the analysis of the spectra of distant quasars.
• Discuss how the distribution of dark matter can be inferred from measurement of gravitational lensing effects.
• Understand why it is useful to be able to characterize the large-scale distribution of galaxies using techniques such as the counts-in-cells method.