Spin, jet-feedback and black-hole growth

1. Spin, jet-feedback and black-hole growth Steve Rawlings (sr@astro.ox.ac.uk) & Tom Mauch (txm@astro.ox.ac.uk) Sub-Department of Astrophysics, University of Oxford The Project Observations of distant quasars and their local dormant counterparts can be used to infer the build up of supermassive black holes subject to assumptions about accretion efficiency and how rotational energy is stored in, and released from, the ergosphere of spinning black holes. Simple-minded calculations suggest that constraints on efficiency may be uncomfortably close to maxima suggested by theories for spinning black holes. This project will couple state-of-the-art datasets with theories to determine the role of black hole spin in the growth of black holes. For the first time in astronomy, some regions of the sky are becoming so deeply observed at all wavebands from X-ray through to radio that it should be possible to use this information to measure both the active accretion onto black holes, and the energy output in terms of jets powered by spinning black holes. Active Galactic Nuclei Black-hole Growth Observational constraints on the growth of massive black holes in galactic nuclei are obtained by measuring the current mass density of black holes comparing this to the accretion rate of black holes throughout the history of the Universe. Limits on the accretion rate can be measured from observations of AGN in a wide range of wavelengths. The figure below shows a measurement of the build-up of black holes between z=5 and 0. The presence of supermassive black holes in the cores of galaxies has been inferred from observations of Active Galactic Nuclei (AGN). These are characterised by enhanced emission at all wavelengths in galaxy nuclei which is fuelled by accretion of matter onto a central compact object believed to be a black hole. In AGN matter is accreting onto the supermassive black hole from an accretion disk surrounded by a dusty torus (see schematic on top right). In many AGN energy is transported by via jets into the surrounding intergalactic medium (see figure to left). Their present day mass density has been determined by exploiting a relation between the velocity dispersions of galaxy bulges and black hole mass. The accretion rate has been determined from an optical survey of QSOs. The local black hole mass density is recovered assuming an accretion efficiency close to the Eddington limit. Photo-z’s In order to quantify the physical properties of each galaxy, templates will be fitted to multi-wavelength photometry. This will provide probability distributions for the redshift and accretion rate of black holes. Survey Astronomy In the past decade we have witnessed an explosion in the amount of survey data coming from telescopes. The techniques required for efficient and productive exploitation of these datasets are still in their infancy. During this project you will have the opportunity to help in the collection and processing of deep survey data and to develop novel data extraction and data mining algorithms. Observations In this project you will be have the opportunity to observe with state-of the-art telescopes all over the world. The GMRT is a radio telescope located east of Mumbai in India. It consists of 30 steerable antennae and uses aperture synthesis techniques to produce deep, high resolution images of the radio sky. 1.4 GHz WSRT survey image Tasks • Develop robust ways of measuring jet output using new deep radio observations with the GMRT in India, and the WSRT in Holland. • Develop a new and sophisticated `photometric redshift' code that will start with input catalogues covering all wavebands from X-ray to radio, and output probability distributions for redshift and accretion rate. • Apply the photo-z code to data from the VISTA Deep Extragalactic Observations (VIDEO) survey to be carried out on the ESO VISTA telescope in Chile. • Determine whether it is possible to prove that the storage of spin, and feedback via jets, is a key part of the build-up of black holes. • Collect a PhD, and hopefully go on to a glorious career in astrophysics! VISTA is a 4m near-infrared survey telescope located close to the VLT site at Paranal in Chile. When online in mid 2008, VISTA will undertake a deep survey in regions of sky with extensive multi-wavelength data (VIDEO).