529 research outputs found
The Cluster of Galaxies Abell 970
We present a dynamical analysis of the galaxy cluster Abell 970 based on a
new set of radial velocities measured at ESO, Pic du Midi and Haute-Provence
observatories. Our analysis indicates that this cluster has a substructure and
is out of dynamical equilibrium. This conclusion is also supported by
differences in the positions of the peaks of the surface density distribution
and X-ray emission, as well as by the evidence of a large scale velocity
gradient in the cluster. We also found a discrepancy between the masses
inferred with the virial theorem and with the X-ray emission, what is expected
if the galaxies and the gas inside the cluster are not in hydrostatic
equilibrium. Abell 970 has a modest cooling flow, as is expected if it is out
of equilibrium as suggested by Allen (1998). We propose that cooling flows may
have an intermittent behavior, with phases of massive cooling flows being
followed by phases without significant cooling flows after the acretion of a
galaxy group massive enough to disrupt the dynamical equilibrium in the center
of the clusters. A massive cooling flow will be established again, after a new
equilibrium is achieved.Comment: 24 pages, 9 figures, submitted to A&
The cluster of galaxies Abell 376
We present a dynamical analysis of the galaxy cluster Abell 376 based on a
set of 73 velocities, most of them measured at Pic du Midi and Haute-Provence
observatories and completed with data from the literature. Data on individual
galaxies are presented and the accuracy of the determined velocities is
discussed as well as some properties of the cluster. We obtained an improved
mean redshift value z=0.0478^{+0.005}_{-0.006} and velocity dispersion
sigma=852^{+120}_{-76}km/s. Our analysis indicates that inside a radius of
900h_{70}^{-1}kpc (15 arcmin) the cluster is well relaxed without any
remarkable feature and the X-ray emission traces fairly well the galaxy
distribution. A possible substructure is seen at 20 arcmin from the centre
towards the Southwest direction, but is not confirmed by the velocity field.
This SW clump is, however, kinematically bound to the main structure of Abell
376. A dense condensation of galaxies is detected at 46 arcmin (projected
distance 2.6h_{70}^{-1}Mpc) from the centre towards the Northwest and analysis
of the apparent luminosity distribution of its galaxies suggests that this
clump is part of the large scale structure of Abell 376. X-ray spectroscopic
analysis of ASCA data resulted in a temperature kT = 4.3+/-0.4 keV and metal
abundance Z = 0.32+/-0.08 Z_solar. The velocity dispersion corresponding to
this temperature using the T_X-sigma scaling relation is in agreement with the
measured galaxies velocities.Comment: 11 pages, 10 figures, accepted for publication in A&
The structure and dynamics of the AC114 galaxy cluster revisited
We present a dynamical analysis of the galaxy cluster AC114 based on a
catalogue of 524 velocities. Of these, 169 (32%) are newly obtained at ESO
(Chile) with the VLT and the VIMOS spectrograph. Data on individual galaxies
are presented and the accuracy of the measured velocities is discussed.
Dynamical properties of the cluster are derived. We obtain an improved mean
redshift value z= 0.31665 +/- 0.0008 and velocity dispersion \sigma= 1893+73-82
\kms. A large velocity dispersion within the core radius and the shape of the
infall pattern suggests that this part of the cluster is in a radial phase of
relaxation with a very elongated radial filament spanning 12000 \kms. A radial
foreground structure is detected within the central 0.5/h Mpc radius,
recognizable as a redshift group at the same central redshift value. We analyze
the color distribution for this archetype Butcher-Oemler galaxy cluster and
identify the separate red and blue galaxy sequences. The latter subset contains
44% of confirmed members of the cluster, reaching magnitudes as faint as R_{f}=
21.1 (1.0 magnitude fainter than previous studies). We derive a mass M_{200}=
(4.3 \pm 0.7) x 10^15 Msun/h. In a subsequent paper we will utilize the
spectral data presented here to explore the mass-metallicity relation for this
intermediate redshift cluster.Comment: 17 pages, 11 figures, 4 tables, accepted for publication in MNRA
Heat transport in Bi_{2+x}Sr_{2-x}CuO_{6+\delta}: departure from the Wiedemann-Franz law in the vicinity of the metal-insulator transition
We present a study of heat transport in the cuprate superconductor
Bi_{2+x}Sr_{2-x}CuO_{6+\delta} at subkelvin temperatures and in magnetic fields
as high as 25T. In several samples with different doping levels close to
optimal, the linear-temperature term of thermal conductivity was measured both
at zero-field and in presence of a magnetic field strong enough to quench
superconductivity. The zero-field data yields a superconducting gap of
reasonable magnitude displaying a doping dependence similar to the one reported
in other families of cuprate. The normal-state data together with the results
of the resistivity measurements allows us to test the Wiedemann-Franz(WF) law,
the validity of which was confirmed in an overdoped sample in agreement with
previous studies. In contrast, a systematic deviation from the WF law was
resolved for samples displaying either a lower doping content or a higher
disorder. Thus, in the vicinity of the metal-insulator cross-over, heat
conduction in the zero-temperature limit appears to become significantly larger
than predicted by the WF law. Possible origins of this observation are
discussed.Comment: 9 pages including 7 figures, submitted to Phys. Rev.
Structure and dynamics of the supercluster of galaxies SC0028-0005
According to the standard cosmological scenario, superclusters are objects
that have just passed the turn around point and are collapsing. The dynamics of
very few superclusters have been analysed up to now. In this paper we study the
supercluster SC0028-0005, at redshift 0.22, identify the most prominent groups
and/or clusters that make up the supercluster, and investigate the dynamic
state of this structure. For the membership identification, we have used
photometric and spectroscopic data from SDSS-DR10, finding 6 main structures in
a flat spatial distribution. We have also used a deep multi-band observation
with MegaCam/CFHT to estimate de mass distribution through the weak-lensing
effect. For the dynamical analysis, we have determined the relative distances
along the line of sight within the supercluster using the Fundamental Plane of
early-type galaxies. Finally, we have computed the peculiar velocities of each
of the main structures. The 3D distribution suggests that SC0028-005 is indeed
a collapsing supercluster, supporting the formation scenario of these
structures. Using the spherical collapse model, we estimate that the mass
within ~Mpc should lie between 4 and . The
farthest detected members of the supercluster suggest that within ~Mpc
the density contrast is with respect to the critical density at
, implying a total mass of --,
most of which in the form of low-mass galaxy groups or smaller substructures.Comment: 12 pages, 9 figures, Accepted for publication in MNRA
Competing types of quantum oscillations in the 2D organic conductor (BEDT-TTF)8Hg4Cl12(C6H5Cl)2
Interlayer magnetoconductance of the quasi-two dimensional organic metal
(BEDT-TTF)8Hg4Cl12(C6H5Cl)2 has been investigated in pulsed magnetic fields
extending up to 36 T and in the temperature range from 1.6 to 15 K. A complex
oscillatory spectrum, built on linear combinations of three basic frequencies
only is observed. These basic frequencies arise from the compensated closed
hole and electron orbits and from the two orbits located in between. The field
and temperature dependencies of the amplitude of the various oscillation series
are studied within the framework of the coupled orbits model of Falicov and
Stachowiak. This analysis reveals that these series result from the
contribution of either conventional Shubnikov-de Haas effect (SdH) or quantum
interference (QI), both of them being induced by magnetic breakthrough.
Nevertheless, discrepancies between experimental and calculated parameters
indicate that these phenomena alone cannot account for all of the data. Due to
its low effective mass, one of the QI oscillation series - which corresponds to
the whole first Brillouin zone area - is clearly observed up to 13 K.Comment: 8 pages, 8 figures. To be published in Phys. Rev.
Electron-Phonon Dynamics in an Ensemble of Nearly Isolated Nanoparticles
We investigate the electron population dynamics in an ensemble of nearly
isolated insulating nanoparticles, each nanoparticle modeled as an electronic
two-level system coupled to a single vibrational mode. We find that at short
times the ensemble-averaged excited-state population oscillates but has a
decaying envelope. At long times, the oscillations become purely sinusoidal
about a ``plateau'' population, with a frequency determined by the
electron-phonon interaction strength, and with an envelope that decays
algebraically as t^-{1/2} We use this theory to predict electron-phonon
dynamics in an ensemble of Y_2 O_3 nanoparticles.Comment: 11 pages, 3 figure
Physics of the Merging Clusters Cygnus A, A3667, and A2065
We present ASCA gas temperature maps of the nearby merging galaxy clusters
Cygnus A, A3667, and A2065. Cygnus A appears to have a particularly simple
merger geometry that allows an estimate of the subcluster collision velocity
from the observed temperature variations. We estimate it to be ~2000 km/s.
Interestingly, this is similar to the free-fall velocity that the two Cygnus A
subclusters should have achieved at the observed separation, suggesting that
merger has been effective in dissipating the kinetic energy of gas halos into
thermal energy, without channeling its major fraction elsewhere (e.g., into
turbulence). In A3667, we may be observing a spatial lag between the shock
front seen in the X-ray image and the corresponding rise of the electron
temperature. A lag of the order of hundreds of kiloparsecs is possible due to
the combination of thermal conduction and a finite electron-ion equilibration
time. Forthcoming better spatial resolution data will allow a direct
measurement of these phenomena using such lags. A2065 has gas density peaks
coincident with two central galaxies. A merger with the collision velocity
estimated from the temperature map should have swept away such peaks if the
subcluster total mass distributions had flat cores in the centers. The fact
that the peaks have survived (or quickly reemerged) suggests that the
gravitational potential also is strongly peaked. Finally, the observed specific
entropy variations in A3667 and Cygnus A indicate that energy injection from a
single major merger may be of the order of the full thermal energy of the gas.
We hope that these order of magnitude estimates will encourage further work on
hydrodynamic simulations, as well as more quantitative representation of the
simulation results.Comment: Corrected the Cyg-A figure (errors shown were 1-sigma not 90%); text
unchanged. ApJ in press. Latex, 5 pages, 3 figures (2 color), uses
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