216,617 research outputs found
Radio-mode feedback in local AGNs: dependence on the central black hole parameters
Radio mode feedback, in which most of the energy of an active galactic
nucleus (AGN) is released in a kinetic form via radio-emitting jets, is thought
to play an important role in the maintenance of massive galaxies in the
present-day Universe. We study the link between radio emission and the
properties of the central black hole in a large sample of local radio galaxies
drawn from the Sloan Digital Sky Survey (SDSS), based on the catalogue of Best
and Heckman (2012). Our sample is mainly dominated by massive black holes
(mostly in the range ) accreting at very low Eddington
ratios (typically ). In broad agreement with previously
reported trends, we find that radio galaxies are preferentially associated with
the more massive black holes, and that the radio loudness parameter seems to
increase with decreasing Eddington ratio. We compare our results with previous
studies in the literature, noting potential biases. The majority of the local
radio galaxies in our sample are currently in a radiatively inefficient
accretion regime, where kinetic feedback dominates over radiative feedback. We
discuss possible physical interpretations of the observed trends in the context
of a two-stage feedback process involving a transition in the underlying
accretion modes.Comment: accepted for publication in Monthly Notices of the Royal Astronomical
Societ
Incompleteness of Representation Theory: Hidden symmetries and Quantum Non-Integrability
Representation theory is shown to be incomplete in terms of enumerating all
integrable limits of quantum systems. As a consequence, one can find exactly
solvable Hamiltonians which have apparently strongly broken symmetry. The
number of these hidden symmetries depends upon the realization of the
Hamiltonian.Comment: 4 pages, Revtex, Phys. Rev. Lett. , July 27 (1997), in pres
Chemical and kinetic equilibrations via radiative parton transport
A hot and dense partonic system can be produced in the early stage of a
relativistic heavy ion collision. How it equilibrates is important for the
extraction of Quark-Gluon Plasma properties. We study the chemical and kinetic
equilibrations of the Quark-Gluon Plasma using a radiative transport model.
Thermal and Color-Glass-Condensate motivated initial conditions are used. We
observe that screened parton interactions always lead to partial pressure
isotropization. Different initial pressure anisotropies result in the same
asymptotic evolution. Comparison of evolutions with and without radiative
processes shows that chemical equilibration interacts with kinetic
equilibration and radiative processes can contribute significantly to pressure
isotropization.Comment: Presented at 24th International Nuclear Physics Conference
(INPC2010), Vancouver, Canada, 4-9 July 201
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