1,487 research outputs found
Tomographic filtering of geodynamic models: Implications for model interpretation and largeâscale mantle structure
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94833/1/jgrb15038.pd
Energy non-equipartition in systems of inelastic, rough spheres
We calculate and verify with simulations the ratio between the average
translational and rotational energies of systems with rough, inelastic
particles, either forced or freely cooling. The ratio shows non-equipartition
of energy. In stationary flows, this ratio depends mainly on the particle
roughness, but in nonstationary flows, such as freely cooling granular media,
it also depends strongly on the normal dissipation. The approach presented here
unifies and simplifies different results obtained by more elaborate kinetic
theories. We observe that the boundary induced energy flux plays an important
role.Comment: 4 pages latex, 4 embedded eps figures, accepted by Phys Rev
A direct limit on the turbulent velocity of the intracluster medium in the core of Abell 1835 from XMM-Newton
We examine deep XMM-Newton Reflection Grating Spectrometer (RGS) observations
of the X-ray luminous galaxy cluster A1835. For the first time in a galaxy
cluster we place direct limits on turbulent broadening of the emission lines.
This is possible because the coolest X-ray emitting gas in the cluster, which
is responsible for the lines, occupies a small region within the core. The most
conservative determination of the 90 per cent upper limit on line-of-sight,
non-thermal, velocity broadening is 274 km/s, measured from the emission lines
originating within 30 kpc radius. The ratio of turbulent to thermal energy
density in the core is therefore less than 13 per cent. There are no emission
lines in the spectrum showing evidence for gas below ~3.5 keV. We examine the
quantity of gas as a function of temperature and place a limit of 140 Msun/yr
(90 per cent) for gas cooling radiatively below 3.85 keV.Comment: 5 pages, accepted by MNRAS, includes minor change suggested by
refere
Systematic study of X-ray Cavities in the brightest galaxy of the Draco Constellation NGC 6338
We present results based on the systematic analysis of currently available
Chandra archive data on the brightest galaxy in the Draco constellation NGC
6338, in order to investigate the properties of the X-ray cavities. In the
central ~6 kpc, at least a two and possibly three, X-ray cavities are evident.
All these cavities are roughly of ellipsoidal shapes and show a decrement in
the surface brightness of several tens of percent. In addition to these
cavities, a set of X-ray bright filaments are also noticed which are spatially
coincident with the H{\alpha} filaments over an extent of 15 kpc. The H{\alpha}
emission line filaments are perpendicular to the X- ray cavities. Spectroscopic
analysis of the hot gas in the filaments and cavities reveal that the X-ray
filaments are cooler than the gas contained in the cavities. The emission line
ratios and the extended, asymmetric nature of the H{\alpha} emission line
filaments seen in this system require a harder ionizing source than that
produced by star formation and/or young, massive stars. Radio emission maps
derived from the analysis of 1.4 GHz VLA FIRST survey data failed to show any
association of these X-ray cavities with radio jets, however, the cavities are
filled by radio emission. The total power of the cavities is 17\times 1042 erg
s-1 and the ratio of the radio luminosity to cavity power is ~ 10-4, implying
that most of the jet power is mechanical.Comment: The paper contains 12 figures and 3 tables, Accepted 2011 December 7
for publication in MNRA
AGN-Induced Cavities in NGC 1399 and NGC 4649
We present an analysis of archival Chandra and VLA observations of the E0
galaxy NGC 1399 and the E2 galaxy NGC 4649 in which we investigate cavities in
the surrounding X-ray emitting medium caused by the central AGN. We calculate
the jet power required for the AGN to evacuate these cavities and find values
of ~8x10^{41} erg/s and ~14x10^{41} erg/s for the lobes of NGC 1399 and
~7x10^{41} erg/s and ~6x10^{41} erg/s for those of NGC 4649. We also calculate
the k/f values for each cavity, where k is the ratio of the total particle
energy to that of electrons radiating in the range of 10 MHz to 10 GHz, and f
is the volume filling factor of the plasma in the cavity. We find that the
values of k/f for the lobes of NGC 1399 are ~93 and ~190, and those of the
lobes of NGC 4649 are ~15000 and ~12000. We conclude that the assumed spectrum
describes the electron distribution in the lobes of NGC 1399 reasonably well,
and that there are few entrained particles. For NGC 4649, either there are many
entrained particles or the model spectrum does not accurately describe the
population of electrons.Comment: 8 pages, 2 figures, accepted for publication in MNRA
The X-ray luminous cluster underlying the bright radio-quiet quasar H1821+643
We present a Chandra observation of the only low redshift, z=0.299, galaxy
cluster to contain a highly luminous radio-quiet quasar, H1821+643. By
simulating the quasar PSF, we subtract the quasar contribution from the cluster
core and determine the physical properties of the cluster gas down to 3 arcsec
(15 kpc) from the point source. The temperature of the cluster gas decreases
from 9.0\pm0.5 keV down to 1.3\pm0.2 keV in the centre, with a short central
radiative cooling time of 1.0\pm0.1 Gyr, typical of a strong cool-core cluster.
The X-ray morphology in the central 100 kpc shows extended spurs of emission
from the core, a small radio cavity and a weak shock or cold front forming a
semi-circular edge at 15 arcsec radius. The quasar bolometric luminosity was
estimated to be 2 x 10^{47} erg per sec, requiring a mass accretion rate of 40
Msolar per yr, which corresponds to half the Eddington accretion rate. We
explore possible accretion mechanisms for this object and determine that Bondi
accretion, when boosted by Compton cooling of the accretion material, could
provide a significant source of the fuel for this outburst. We consider
H1821+643 in the context of a unified AGN accretion model and, by comparing
H1821+643 with a sample of galaxy clusters, we show that the quasar has not
significantly affected the large-scale cluster gas properties.Comment: 20 pages, 19 figures, accepted by MNRA
Development of finite strain in the convecting lower mantle and its implications for seismic anisotropy
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94627/1/jgrb13518.pd
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