ERC FUNDED PROJECTS

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

Einstein’s theory of General Relativity (GR) is tested accurately within the local universe i.e., the solar system, but this leaves open the possibility that it is not a good description at the largest scales in the Universe. The standard model of cosmology assumes GR as a theory to describe gravity on all scales. In 1998, astronomers made a surprising discovery that the expansion of the Universe is accelerating, not slowing down. This late-time acceleration of the Universe has become the most challenging problem in theoretical physics. Within the framework of GR, the acceleration would originate from an unknown “dark energy.” Alternatively, it could be that there is no dark energy and GR itself is in error on cosmological scales. The standard model of cosmology is based on a huge extrapolation of our limited knowledge of gravity. This discovery of the late time acceleration of the Universe may require us to revise the theory of gravity and the standard model of cosmology based on GR. The main objective of my project is to develop cosmological tests of gravity and seek solutions to the origin of the observed accelerated expansion of the Universe by challenging conventional GR. Upcoming surveys will make cosmological tests of gravity a reality in the next five years. There are remaining issues in developing theoretical frameworks for probing gravitational physics on cosmological scales. We construct modified gravity theories as an alternative to dark energy and analyse “screening mechanisms” to restore GR on scales where it is well tested. We then develop better theoretical frameworks to perform cosmological tests of gravity that include non-linear scales by exploiting our theoretical knowledge of the models and our state-of-the-art simulations. This grant will exploit and develop the world-leading position of the group initiated by Kazuya Koyama at the University of Portsmouth funded by the ERC starting grant (2008-2013).

1 701 133 €

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

"Modern astrophysics has pushed the observational frontier to a time a billion years after the Big Bang. Lying beyond this frontier is the period when the first stars and galaxies formed, whose light heated and ionized the Universe in the process known as reionization. Understanding this ""epoch of reionization"" would fill in a key missing period in our picture of the history of the Universe. Existing observational techniques have scratched the surface, but new observational techniques are required to truly understand this early period of galaxy formation. My work will lay the theoretical foundations for three novel probes of this period - 21 cm tomography, the 21 cm global signal, and line intensity mapping - that would enable three dimensional maps of the epoch of reionization. If realized through challenging radio-frequency observations, these techniques would transform our understanding of the first galaxies. Through this ERC starting grant, I will build the theoretical framework needed to predict and interpret observations of line emission from gas in and surrounding the first generation of galaxies. My team will aim to develop models of the interplay between radiation from the first galaxies and the heating, ionization, and illumination of hydrogen gas that lies in the space between galaxies. At the same time, we will build models of the formation and properties of the atomic and molecular gas that fills the space inside galaxies. By combining probes of this ""inner"" and ""outer"" space a complete nature of galaxy formation during the first billion years might be achieved. Analysis of sky averaged 21 cm observations will complement this with a broad overview of galaxies back to a few hundred million years after the big bang. This work will provide a clear theoretical road map to guide the design of next generation radio telescopes, such as the Square Kilometer Array, to achieve this ambitious goal."

1 495 220 €

Start date: 2015-04-01, End date: 2020-03-31

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