Download this poster - Astrophysics

Spin, jet-feedback and black-hole growth
Steve Rawlings ([email protected]) & Tom Mauch ([email protected])
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
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).
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.
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.
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.
Survey Astronomy
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.
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 multiwavelength data (VIDEO).
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.
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!