Astrophysics ResearchThe research interests of the group run from X-ray to radio wavebands, and cover planetary, galactic, extragalactic, and cosmological subjects.
Planet Formation and Collisional EvolutionPlanet formation is common, with a Jupiter-mass planet in close orbit around at least 5% of all main sequence stars. The systems that are observed are surprisingly diverse and very different from our solar system. Observations cannot trace the full history of planet formation, but do provide snapshots of either early protoplanetary disks, or the late stages after planetary systems or debris disks have formed. As a result, we cannot observationally connect the early and late stages of planet formation, and it is not known how such a diversity of extrasolar systems arises, or what determines the type of solar system that develops. One solution is to build a numerical model that can evolve a broad range of protoplanetary disks through to final planetary systems or debris disks. Such a complete model of planet formation has eluded the astrophysics community because of numerical limitations and incomplete/unknown physics.
We are currently developing a state of the art numerical method that will include the most realistic model of planetestimal evolution to date. The goal is to develop a complete account of planet formation. This technique will be highly efficient, and able to evolve newly formed planetesimals all the way through to planets. The results will seamlessly connect the final two stages of planet formation and capture feedback processes in which evolving protoplanets can replenish the reservoir of planetesimals. During the course of this work answers to many questions surrounding planet formation will emerge, e.g., a realistic collision evolution model for planetesimals will allow accurate growth timescales to be calculated, which will in turn determine whether giant planet cores can plausibly form from the gradual growth of planetesimals or if some faster mechanism is required. In addition, this work will predict the amount of debris produced by planetesimals during planet formation, which will be vital to interpret observations of protoplanetary disks. This work will also be useful in interpreting our own solar system. Here is a of a numerical simulation of an impact between two "planetesimals". The result is very similar to dwarf planet Haumea and the dynamical family associated with it (, Dobinson).
Galaxies and cosmologyIn optical astronomy we are studying galaxy populations and their evolution using surveys of nearby galaxies to look for previously undetected low surface brightness and compact galaxies, and observations of more distant clusters and groups to look for evidence of the evolution of their galaxy content. The uses the 2dF multi-object spectrograph on the Anglo-Australian Telescope to measure redshifts for complete samples of objects detected in the direction of the Fornax Cluster, while the Hubble Space Telescope has used the HST to image the nearest extremely massive cluster at high resolution, in order to explore the galaxy population in such an environment in great detail ().
Other survey work concentrates on the highest redshift galaxies, thus exploring the first structures that formed in the universe and the `epoch of reionization', the era when photons from the first generations of stars and quasars ionized the universe (, Davies, Husband).
Clusters of Galaxies and CosmologyClusters of galaxies can be used as powerful cosmological probes with which to measure the fundamental properties of our Universe. In order to do this effectively, their masses must be measured. This is an observational challenge as clusters are dominated by dark matter, and we must estimate their masses from our observations of their luminous matter. By combining observations of the hot gas in clusters made with X-ray observatories (such as and ), with measurements of the Sunyaev-Zel'dovich effect (from experiments such as OCRA and ), and measurements of the gravitational lensing effect of clusters (from optical telescopes), we are attempting to measure the most accurate masses possible for a large number of galaxy clusters. (, Giles).
We are also using X-ray observations to measure the temperatures of a sample of very distant galaxy clusters. The numbers of distant galaxy clusters of different temperatures and the evolution of this distribution relative to nearby clusters is very sensitive to underlying cosmological parameters. By comparing our observations with the predictions of different cosmological models we will gain new insight into the values of the parameters which describe the Universe. (, Koens).
Cooling FlowsSuch clusters of galaxies often contain cooling flows, in which the high-density hot gas trapped in the centre of the cluster is thought to cool rapidly, allowing slow inflow of material. This gives rise to strong X-ray emission in the centres of clusters which is easily detected. However, evidence for the cooled material in other wavebands has been difficult to find, requiring the use of new instrumentation, larger telescopes and novel techniques. We are carrying out detailed study of this gas in the optical and IR with the new generation of 8-m telescopes. ().
Active galaxiesA number of group members are involved in the study of active galactic nuclei (AGN), particularly , using radio, infra-red, optical, and X-ray techniques (, , , Bliss, Mannering). Interests include the environments and dynamics of radio sources, unified models for both high-power and low-power objects, observation and modelling of jets and the X-ray/radio relationship in radio galaxies and quasars. Instruments used by the group include the , the , , the , , , the , , , and .
Active galaxies can also be used as cosmological probes. Powerful radio sources are markers of massive structures (clusters of galaxies); by we can find massive structures in the early universe, which allows us to test models of structure formation, a key goal of cosmology. Once these structures are found, multi-waveband observations are being used to determine key parameters such as mass, dynamical state and baryon content. Radio observations (e.g. of the Sunyaev-Zel'dovich effect), optical (peculiar velocities, weak lensing) and X-ray observations (measurement of the hot intracluster plasma properties) all contribute to these studies. (, , , ).
Plasma ProcessesMany of the observable properties of active galaxies are related to plasma processes in the sources, and this relates closely to terrestrial fusion plasma physics. Work in the group on particle acceleration and radiation has led to collaborations with the UKAEA fusion physics research group at Culham (, James, Moon, Newton).
Black holesBlack holes have a profound impact on their environment. Gas falling towards a super-massive black hole can produce tremendous quantities of radiation (often outshining an entire galaxy), and can also produce very high velocity outflows such as relativistic jets. The feedback between inflowing gas and outflowing jets and radiation plays an important role in regulating structure (e.g. galaxy and galaxy cluster) formation and evolution. We study the environment immediately surrounding black holes using space-based X-ray observatories (including Chandra and Suzaku), in addition to observations at other wavelengths. X-ray spectroscopy of gas deep in the potential well of the black hole, where the effects of strong gravity are important, allows us to probe the properties of the black hole itself (, Momtahan).
Microwave background radiationStudies of the cosmic microwave background radiation revolve about the use of the Sunyaev-Zel'dovich (SZ) effect as a cosmological probe. We are involved with two new SZ experiments: the One Centimetre Receiver Array (OCRA) and the . Both instruments will ultimately perform blind surveys for galaxy clusters and in the interim are observing clusters known from X-ray and optical surveys in order to constrain physical models of the cluster atmospheres. We are also investigating other structures induced on the background radiation by relatively local (within a few Gpc) astrophysical phenomena, such as effects due to the propagation of the CMB through changing gravitational fields. (, Alareedh, Talaganis).
Galactic Line EmissionResearch on the photo-excited component of the interstellar medium, continues through our (Masheder, , Morris) involvement with the international of the Galactic plane and some other important Galactic and extragalactic regions, using observations taken with the at the Anglo-Australian Observatory, and the northern equivalent, called , carried out with the Isaac Newton Telescope on La Palma There is a separate page on H-alpha research .
The Coldrick ObservatoryThe telescopes of the will be used for research (including studies of masers and AGN) when they are fully commissioned.
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