ERC FUNDED PROJECTS

Galaxy formation is one of the most fascinating yet challenging fields of astrophysics. The desire to understand galaxy formation has led to the design of ever more sophisticated telescopes which show a bewildering variety of galaxies in the Universe. However, the degree to which an interpretation of this wealth of data can succeed depends critically on having accurate and realistic theoretical models of galaxy formation. While cosmological simulations of galaxy formation provide the most powerful technique for calculating the non-linear evolution of cosmic structures, the enormous dynamic range and poorly understood baryonic physics are main uncertainties of present simulations. This impacts on their predictive power and is the major obstacle to our understanding of observational data. The objective of this proposal is to drastically improve upon the current state-of-the-art by i) including more realistic physical processes, such as those occurring at the sphere of influence of a galaxy’s central black hole and ii) greatly extending spatial dynamical range with the aid of a novel technique I have developed. With this technique I want to address one of the major unsolved issues of galaxy formation: “How do galaxies and their central black holes coevolve?” Specifically, I want to focus on three crucial areas of galaxy formation: a) How and where the very first black holes form, what are their observational signatures, and when is the coevolution with host galaxies established? b) Is black hole heating solely responsible for the morphological transformation and quenching of massive galaxies, or are other processes important as well? c) What is the impact of supermassive black holes on galaxy clusters and can we calibrate baryonic physics in clusters to use them as high precision cosmological probes? The requested funding is for 50% of the PI’s time and three postdoctoral researchers to establish an independent research group at the KICC and IoA, Cambridge.

1 975 062 €

Start date: 2015-09-01, End date: 2020-08-31

This application proposes a programme of research directed at the outstanding puzzle of modern cosmology: the strangely small non-zero value of the vacuum density. This can be approached in three ways: (1) Evolution; (2) Revision of gravity; (3) Observer selection in the multiverse. The first two of these can be addressed by ongoing and future large galaxy surveys. Part of the research programme is directed at new ways of assuring robust measurements from these surveys of the main diagnostics of interest -- the effective equation of state of dark energy and the growth rate of density fluctuations. This will exploit and extend current work on systematics of galaxy properties as a function of large-scale environment in the cosmic web. But so far such tests show no deviation from standard gravity and a cosmological constant. This fact drives interest in a multiverse solution, in which different causally disconnected domains may be able to possess different effective cosmological constants. This research will concentrate on the astrophysically interesting question of how galaxy formation would be affected by different levels of vacuum energy. This previously been addressed only by oversimplified analytic arguments, and it is possible that the exponential sensitivity of galaxy formation efficiency to the vacuum density could be very different to the simple estimates. Current claims that the multiverse approach predicts the right level for the cosmological constant would then be disproved. In any case, there is much of interest to be learned regarding the robustness of current theories of galaxy formation by 'stress-testing' them outside the rather restricted parameter regimes normally considered. The result will be a deeper understanding of the assembly of cosmic structure in our universe, as well as indications of how it might have proceeded in other members of an ensemble.

2 191 778 €

Start date: 2015-10-01, End date: 2020-09-30

Wide field panoramic telescopes will become a major force in astronomy over the next decade. They will address a rich set of scientific problems, from ``killer asteroids'' to the cosmic dark energy. Pan-STARRS-1 (PS1), built by the University of Hawaii, is the first of this new generation of telescopes. European astronomers in Germany and the UK, including in the PI's host institute, make up a large fraction of the Science Consortium that, over the next 4 years, will exploit the data. This proposal is focused on the use of PS1 for cosmology. I propose a programme that combines state-of-the-art cosmological simulations and modelling with high-level analyses of the data. The goal is to test core assumptions of the standard cosmogonic model, LCDM, on scales and at epochs where it has not been tested before and where it can, in principle, be ruled out. At the same time, these tests will advance our understanding of the main constituents of our universe (dark matter and dark energy) and of the processes of galaxy formation and evolution. Two types of structure at opposite ends of the cosmological scale, the Milky Way and the large-scale distribution of galaxies at redshifts z<1.5, are ideally suited to this purpose. Studies of the Milky Way will test LCDM predictions for the hierarchical assembly of galaxies and the structure of their dark matter halos. Studies of the galaxy distribution will test LCDM predictions for the growth of structure and the connection between galaxies and dark matter. To link theory and data, I will construct mock catalogues using very large cosmological simulations and sophisticated modelling techniques. These catalogues will have a much broader applicability that just PS1 and I will make them publicly available using e-science techniques.

2 266 850 €

Start date: 2011-05-01, End date: 2017-04-30

I propose to measure the growth of non-linear structure in the dark universe to answer two fundamental questions in cosmology: Is the Cold Dark Matter structure formation theory compatible with the galaxy distribution on group scales? Is the accelerating expansion of the Universe caused by Dark Energy? This frontier research probes two key components of our standard cosmological model. This study is fundamental for understanding structure formation and galaxy evolution, leading to possible ground-breaking changes in our comprehension of gravitational physics. I will tackle this ambitious research plan by exploiting my extensive knowledge of galaxy survey analyses and propose to critically test our standard model by measuring three key properties: the shape and evolution of the Cold Dark Matter halo mass function; the efficiency of galaxy formation in Local Group sized systems; the evolution of the growth of structure. To achieve those decisive goals, I will build the DEGAS Team, an inter-disciplinary unit dedicated to solve photometric and spectroscopic survey systematics, to develop optimal clustering statistics for imaging surveys and to create a large variety of state-of-the-art mock Universes to interpret the statistical analyses. The techniques developed will be applied to two world-leading galaxy surveys: GAMA, a multi-wavelength redshift survey of which I am a founder and co-PI, and Pan-STARRS PS1, a unique 3/4-sky imaging survey. Using innovative clustering statistics accounting for individual photometric redshift distributions and statistically robust methods for halo mass function estimates, my DEGAS Team will provide the ultimate test for structure formation models, gain key insights on galaxy evolution and present novel constraints on the nature of gravity.

1 256 696 €

Start date: 2011-01-01, End date: 2016-12-31

Several hundred million years after the Universe was born the first stellar systems began to shine. Energetic photons from early hot stars, free from enrichment by heavy elements, reionised the hydrogen in deep space. Ambitious observational facilities will directly chart this final frontier in cosmic history and any insight we can obtain now will be invaluable in future planning. Key questions include: what is the duration of this reionisation period; was this `cosmic dawn’ a brief or extended process; and what physical processes governed the subsequent evolution of these early galaxies? This proposal aims to trace the history and physics of cosmic reionisation by fully characterising the star-forming galaxy population during and towards the end of the reionisation era. The proposed program has three complementary themes. (i) Tracing the duration of the reionisation process by analysing diagnostic nebular emission lines in the spectra of early galaxies using radiative transfer calculations; the proposed measures can be usefully compared with independent signatures of cold gas during similar epochs determined by the European LOFAR interferometer. (ii) Determining whether star-forming galaxies are the sole agent of reionisation by addressing key uncertainties relating to the number of ionising photons they produce and the fraction that escape; this requires detailed spectroscopy of gravitationally-lensed examples. (iii) Inferring the abundance of the earliest galaxies whose direct detection is beyond reach of current facilities. Stellar masses and ages of galaxies seen at later times will be used to plan surveys in time for the upcoming launch of the James Webb Space Telescope. This research program is observationally challenging but I have demonstrated the relevant techniques are practical through pilot programmes undertaken in California. I am proposing to relocate to University College London and establish a new research effort in Europe to achieve these goals.

2 458 405 €

Start date: 2015-10-01, End date: 2021-09-30

Much of the foundational evidence for our current model of cosmology, describing the origins and evolution of the Universe, has come from observations of the Cosmic Microwave Background (CMB). This is relic light that has been travelling for almost 14 billion years since the Big Bang, carrying a picture of the Universe in its infancy. So far it has told us what the Universe is made of today, as well as its average density and its age. We find that it is only 5% normal matter, with the remainder composed of unknown components: 72% Dark Energy and 23% Dark Matter. We do not yet know their nature. We have also seen signatures that support the idea that structure in the Universe was seeded by tiny ripples in the otherwise smooth space, created during a rapid expansion of the Universe in the first trillionth of a second, called inflation'. In Oxford I now propose to target additional information encoded in the CMB, by looking at measurements with higher resolution and sensitivity than ever before. The main goals of this proposal are to uncover convincing evidence for the inflationary scenario, and to better determine the nature of the Dark Energy component, particularly at early cosmic times. My team will be using data from the Atacama Cosmology Telescope, a 6m telescope in Chile, and from ESA's Planck Satellite mission, which is observing the CMB over the whole sky and launched in 2009. We will have to deal with contamination both from our own Galaxy and from many other distant galaxies in order to convincingly extract the underlying signals from the high energy Universe.

1 500 000 €

Start date: 2011-01-01, End date: 2016-06-30

The gas and dust discs around young stars are thought to be the birthplace of planetary systems and are a key area to study if further progress is to be made on understanding the history of our solar system and our own origins. Once planets have formed in these discs, they dynamically sculpt their environment, for instance by opening tidally-cleared gaps or triggering spiral arms and disc warps. The late stages of this process are likely observed in the “transitional” discs, where regions spanning tens of astronomical units (AU) have been cleared. The aim of this project is to image the planet formation signatures both during the transitional disc and the earlier T Tauri or Herbig Ae/Be stars phase, where the protoplanetary bodies are just starting to carve gaps in the optically thick disc. For this purpose, we will employ the latest generation of near-infrared, mid-infrared, and sub-millimeter interferometric instruments that will allow us to trace a wide range of stellocentric radii, disc scale heights, and dust opacities. We will make use of recent revolutionary advancements in infrared detector technology and equip the CHARA/MIRC 6-telescope beam combiner with a low-read noise camera that will significantly increase the sensitivity of this instrument and enable us to image protoplanetary discs with 2.5 times higher resolution and much higher efficiency than ever before. These quick-look imaging capabilities will enable us to trace time-variable structures in the inner few AU and to investigate their relation to the commonly observed photometric and spectroscopic variability. Our interferometric observations in spectral lines aim to detect the accretion signatures of the young protoplanets themselves. Employing sophisticated radiation hydrodynamics simulations we will achieve an unprecedented global view on protoplanetary disc structure and obtain fundamentally new constraints on theoretical models of planet formation, planet-disc interaction, and disc evolution.

1 648 265 €

Start date: 2015-07-01, End date: 2020-06-30