Properties of the earliest galaxies

Lead Research Organisation: University of Bristol
Department Name: Physics


The gross cosmological parameters of the Universe that describe how fast it expands and how its expansion changes with time are thought to be known to a fair degree of accuracy. However, we do not have a deep understanding of the material of the Universe - the dark matter and dark energy that dominate over the ordinary ('baryonic') matter that is the familiar stuff of every-day life. We also don't understand the processes that cause this baryonic matter to form into structures such as planets, stars, galaxies, and clusters of galaxies. The purpose of the research to be funded by this grant is to gain some understanding of the largest-scale phenomena that affect the formation of structure by looking at the formation and evolution of galaxies and clusters of galaxies, and the internal substructure that they contain. Clusters of galaxies are often studied by their X-ray emission, which comes from hot gas held by the gravity field of their huge masses. At Bristol we also look at the gas in another way, by the 'shadow' that it casts against the microwave background radiation, which is a universal radiation field that was created soon after the Big Bang. Comparing the results from these ways of finding clusters tells us a lot more about the gas, and so about the mass holding the gas, than either technique alone. This trick is useful for discovering how much mass in the cluster is made up by dark matter and how much is baryonic matter, and whether these components of the mass of the cluster are distributed differently. Such a difference in distribution can occur in the cluster formation process, as it settles into a steady state, or later as the gas radiates energy away. We can also use the clusters that we find to study the expansion of the Universe itself, to find out more about the mysterious dark energy. There is a problem caused by the energy radiated by clusters - as the gas cools, it should drop inwards. But we see too little central gas - something is regulating the infall. It is thought that a major influence on the gas, and perhaps a source of all the energy needed to stop the infall, is the outflow of material from active galaxies, particularly radio galaxies, in the centres of the clusters. Active galaxies are galaxies where there seems to be a very massive black hole at their cores. These black holes themselves have the mass of a small galaxy, and are capable, somehow, of producing flows of gas at close to the speed of light away from themselves. This is a bit strange, since we normally think of black holes as being places where everything falls inwards, and the physics of how the outflows work, and how much energy they produce, is largely unknown. We need to measure that energy, and understand the physics of the process, in order to understand how black holes affect the clusters and galaxies in which they are located, and we will do much work on the radio, X-ray, infra-red properties of galaxy cores, and some theory, to try to understand what is going on. We expect to find out a lot about the black holes themselves, too. The most obvious feature of clusters of galaxies is the galaxies themselves, and we are also interested in knowing how galaxies form and change with time, why there are different types of galaxy, and how the galaxies affect the Universe as a whole. We have found that the stars in the earliest galaxies emit enough radiation to cause the entire Universe to change from being cold to being very hot, so that gas in the Universe changes from being neutral atoms to being a plasma, at a temperature like that of a star. How this happens, and what those first galaxies look like, is a focus of our research. We also want to know what happened to these early galaxies as they collided with one another, as their stars aged (and perhaps exploded), and as their central black holes kept pumping out energy, so we look also at nearby galaxies to study changes over the history of the Universe.


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Davies L (2010) Limits on the molecular gas content of z~ 5 LBGs The molecular gas content of z ~5 LBGs in Monthly Notices of the Royal Astronomical Society: Letters

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Douglas L (2010) Spectroscopy of z~ 5 Lyman break galaxies in the ESO Remote Galaxy Survey Spectroscopy of z ~ 5 Galaxies in Monthly Notices of the Royal Astronomical Society

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Douglas L (2009) Photometric selection of z ??? 5 Lyman break galaxies in the ESO Remote Galaxy Survey in Monthly Notices of the Royal Astronomical Society

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Stanway E (2008) A limit on the number density of bright z â?? 7 galaxies in Monthly Notices of the Royal Astronomical Society

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Description This work focussed on the identification and study of the properties of galaxies seen in the universe when it was only 1-2 billion years old. They were identified from their strong ultra-violet emission, which arises from the ongoing formation of hot massive and young stars within those galaxies. They are of extreme interest because they represent the first observational stages of galaxy evolution that we can currently study in any detail.

A large sample of these sources was identified and their reality confirmed though imaging and spectroscopy via an ESO large programme ( a large amount of telescope time assigned to the project on Europe's largest telescopes). The statistics of their distribution from field-to-field was studied, identifying two regions that appeared to be significantly clustered - likely precursors of the clusters of galaxies observed in today's universe, and therefore key targets for follow-up study.

Further observations of the densest fields were used to explore a key poorly-understood aspect of these galaxies. They were selected for their apparent ongoing star formation, but it was possible that significantly more star formation, both within the galaxies and in their general surroundings could have been hidden by dusty clouds surrounding the forming stars, and absorbing all of their emission. By looking for any of this emission re-radiated in the infra-red, we showed that neither the galaxies nor their environments contained large amounts of dust or molecular gas that would indicated a large amount of hidden star formation.
Exploitation Route These results have been built on both by us and by other researches in further elucidating how galaxies and structures evolved in the young universe.

Similarly the results will be of use to educators who wish to inform students and the public of our current understanding of how galaxies and massive structures within the universe evolve.
Sectors Education,Culture, Heritage, Museums and Collections

Description The work carried out during the period of this award is impacting and influencing the further study of the young universe by researchers including ourselves through triggering further observation and analysis of galaxies and structures in the young universe. The understanding developed by this work, and the new issues raised helps form the context for and motivates UK involvement in new and future projects such as LSST, EELT, SKA. The larger picture of galaxy and structure evolution, of which this forms a part, will be used to educate new generations of students, and enthuse the public, and should contribute to maintaining the profile of the STEM subjects.
First Year Of Impact 2008
Sector Education,Culture, Heritage, Museums and Collections
Impact Types Cultural

Description STFC standard grant (astronomy)
Amount £480,119 (GBP)
Organisation Science and Technologies Facilities Council (STFC) 
Sector Public
Country United Kingdom
Start 03/2011 
End 03/2012
Description Press releases & follow-up press interviews 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Newspaper & web reports, radio & TV reports and interviews

Media reports were widely noted from anecdotal feedback, clearly enthuses public wrt basic science
Year(s) Of Engagement Activity 2009,2010