Galaxies hold a fossil record of their own formation, and astronomers at the University of Nottingham are decoding that record by studying both nearby galaxies in exquisite detail and distant ones seen as they were billions of years ago. This work addresses a fundamental gap in our understanding: how did galaxies—the vast collections of stars, gas, dust, and dark matter that fill the Universe—actually come into existence? By using spectroscopy to measure the motions of stars, researchers can map the distribution of invisible dark matter that dominates a galaxy’s mass. By studying starlight at different wavelengths, they can reconstruct when and where stars formed. And by observing galaxies at far-infrared wavelengths, they can see through the obscuring dust that hides much of a galaxy’s structure. This is fundamental science with no immediate practical application. But similar curiosity-driven research into the nature of galaxies has, in the past, led to unexpected breakthroughs—for example, the discovery of dark matter itself, which now shapes our understanding of cosmology and particle physics. A deeper grasp of how galaxies assemble could one day inform everything from how we model complex gravitational systems to how we interpret data from next-generation telescopes.
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The Astronomy Group in the School of Physics & Astronomy at the University of Nottingham specializes in studying the formation and evolution of galaxies. These gravitationally-bound collections of stars, gas, dust and dark matter are some of the most beautiful objects in the Universe, and a major theme in modern astronomy involves trying to understand how they came into existence. One of the tools that we use to try and answer this question involves studying nearby galaxies. Their relative closeness means that we can examine them in great detail, to search for archaeological clues as to how they were made. Galaxies have very long 'memories,' so information imprinted when they formed is likely to have left traces even today. One particularly useful tool in this regard involves using spectroscopy to study the motions of stars in galaxies. Not only are the stars' motions an important part of any complete description of a galaxy, but also since these motions are dictated by the gravitational pull of all the mass of the system, we can use the orbital motions to learn about the distribution of the dark matter that usually dominates galaxies' masses. Spectroscopy also allows us to study the kinds of stars that make up different parts of a galaxy, from which we can infer when and where stars formed within these systems. One complicating factor arises from the 'dust' that permeates many galaxies, obscuring our view. By studying galaxies at far-infrared wavelengths, we can see the emission from this cool material, telling us where it is to be found and how it relates to the other components that make up galaxies. We are therefore engaged in a range of programmes to study the properties of nearby galaxies based both on the spatial distribution of their emission at all wavelengths to learn about their visible components and on the detailed properties of their spectra from which we infer their star formation histories, dynamics and dark matter properties. A second powerful tool involves studying galaxies at large distances from us. Due to the finite speed of light, such observations allow us to see galaxies as they were in the past, and by pushing this technique to ever greater distances we can now directly study galaxies through 90% of the age of the Universe. One of the challenges of this approach is that distant galaxies appear small and faint, but ever larger telescopes and new instrumentation mean that many of the techniques described above for studying nearby galaxies can now be applied to studying these distant systems. Another issue is that many of these distant galaxies are quite rare, so it is only by undertaking the kind of large systematic searches that we are engaged in that we can quantify their properties. One final complication is that the light from distant galaxies appears redshifted, so, for example, the far-infrared emission from dust is observed in the sub-millimetre part of the spectrum. We therefore have to employ a range of different observations to study the same phenomena in galaxies at different distances. Finally, we are involved in studying the environment in which different types of galaxies are located. The properties of galaxies are found to vary dramatically depending on such factors as the number of neighbours around them, but the details of how these differences occur remain to be quantified. Again, we are exploiting a range of techniques involving large surveys to study the distribution of galaxies on the largest scales, and detailed studies of smaller representative slices of the Universe to understand the processes that dictate galaxy type. The tools we use involve observations all across the spectrum to study both the galaxies and their environment, and full high-performance computer simulations that seek to reproduce the properties of the Universe all the way from the large-scale environment down to the formation of individual galaxies.
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