2,068 research outputs found
Isotropic Heating of Galaxy Cluster Cores via Rapidly Reorienting AGN Jets
AGN jets carry more than sufficient energy to stave off catastrophic cooling
of the intracluster medium (ICM) in the cores of cool-core clusters. However,
in order to prevent catastrophic cooling, the ICM must be heated in a
near-isotropic fashion and narrow bipolar jets with
ergs/s, typical of radio AGNs at cluster centres, are inefficient at heating
the gas in the transverse direction to the jets. We argue that due to existent
conditions in cluster cores, the SMBHs will, in addition to accreting gas via
radiatively inefficient flows, experience short stochastic episodes of enhanced
accretion via thin discs. In general, the orientation of these accretion discs
will be misaligned with the spin axis of the black holes and the ensuing
torques will cause the black hole's spin axis (and therefore, the jet axis) to
slew and rapidly change direction. This model not only explains recent
observations showing successive generations of jet-lobes-bubbles in individual
cool-core clusters that are offset from each other in the angular direction
with respect to the cluster center, but also shows that AGN jets {\it can} heat
the cluster core nearly isotropically on the gas cooling timescale. Our model
{\it does} require that the SMBHs at the centers of cool-core clusters be
spinning relatively slowly. Torques from individual misaligned discs are
ineffective at tilting rapidly spinning black holes by more than a few degrees.
Additionally, since SMBHs that host thin accretion discs will manifest as
quasars, we predict that roughly 1--2 rich clusters within should have
quasars at their centers.Comment: 10 pages; accepted in ApJ; updated to conform with the accepted
Journal versio
An XMM-Newton View of the Radio Galaxy 3C 411
We present the first high signal-to-noise XMM-Newton observations of the
broad-line radio galaxy 3C 411. After fitting various spectral models, an
absorbed double power-law continuum and a blurred relativistic disk reflection
model (kdblur) are found to be equally plausible descriptions of the data.
While the softer power-law component (=2.11) of the double power-law
model is entirely consistent with that found in Seyfert galaxies (and hence
likely originates from a disk corona), the additional power law component is
very hard (=1.05); amongst the AGN zoo, only flat-spectrum radio
quasars have such hard spectra. Together with the very flat radio-spectrum
displayed by this source, we suggest that it should instead be classified as a
FSRQ. This leads to potential discrepancies regarding the jet inclination
angle, with the radio morphology suggesting a large jet inclination but the
FSRQ classification suggesting small inclinations. The kdblur model predicts an
inner disk radius of at most 20 r and relativistic reflection
A deep Chandra observation of Abell 4059: a new face to radio-mode AGN feedback?
A deep Chandra observation of the cooling core cluster Abell 4059 (A4059) is
presented. Previous studies have found two X-ray cavities in the central
regions of A4059 together with a ridge of X-ray emission 20kpc south-west of
the cluster center. These features are clearly related to the radio galaxy
PKS2354-35 which resides in the cD galaxy. Our new data confirm these previous
findings and strengthen previous suggestions that the south-western ridge is
colder and denser than, but in approximate pressure equilibrium with, the
surrounding ICM atmosphere. In addition, we find evidence for a weak shock that
wraps around the north and east sides of the cavity structure. Our data allow
us to map the 2-dimensional distribution of metals in the ICM of A4059 for the
first time. We find that the SW ridge possesses an anomalously high
(super-solar) metalicity. The unusual morphology, temperature structure and
metal distribution all point to significant asymmetry in the ICM atmosphere
prior to the onset of radio-galaxy activity. Motivated by the very high
metalicity of the SW ridge, we hypothesize that the ICM asymmetry was caused by
the extremely rapid stripping of metal enriched gas from a starburst galaxy
that plunged through the core of A4059. Furthermore, we suggest that the onset
of powerful radio-galaxy activity in the cD galaxy may have been initiated by
this starburst/stripping event, either via the tidal-shocking of cold gas
native to the cD galaxy, or the accretion of cold gas that had been stripped
from the starburst galaxy.Comment: Accepted for publication in the Astrophysical Journal. 12 pages, 11
figures. A version of this paper including full resolution figures can be
found at http://www.astro.umd.edu/~chris/publications/papers/a4059_2008.pd
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