3,581 research outputs found
The dynamical status of ZwCl 2341.1+0000: a very elongated galaxy structure with a complex radio emission
We study the dynamical status of the galaxy system ZwCl 2341.1+0000, a
filamentary multi-Mpc galaxy structure associated with a complex diffuse radio
emission. Our analysis is mainly based on new spectroscopic data for 128
galaxies acquired at the TNG telescope. We also use optical data available in
the SDSS and X-ray data from the Chandra archive. We select 101 cluster member
galaxies and compute the cluster redshift ~0.2693 and the global LOS
velocity dispersion ~1000 km/s. Our optical analysis agrees with the presence
of at least three, likely four or more, optical subclusters causing the SSE-NNW
elongation of the galaxy distribution and a significant velocity gradient in
the S-N direction. In particular, we detect an important low-velocity subclump
in the southern region, roughly coincident with the brightest peak of the
diffuse radio emission but with a clear offset between the optical and radio
peaks. We also detect one (or two) optical subcluster(s) at north, in
correspondence with the second brightest radio emission, and another one in the
central cluster region, where a third diffuse radio source has been recently
detected. A more refined analysis involving the study of the 2D galaxy
distribution suggests an even more complex structure. As for the X-ray
analysis, we confirm the SSE-NNW elongation of the intracluster medium and
detect four significant peaks. The X-ray emission is strongly asymmetric and
offsetted with respect to the galaxy distribution, thus suggesting a merger
caught in the phase of post-core-core passage. Our findings support two
possible hypotheses for the nature of the diffuse radio emission of ZwCl
2341.1+0000: a 2 relics+halo scenario or diffuse emission associated with the
infall and merging of several galaxy groups during the first phase of the
cluster formation.Comment: 14 pages, 14 figures, 4 tables; MNRAS in pres
Internal dynamics of the galaxy cluster Abell 959
The connection of cluster mergers with the presence of extended, diffuse
radio sources in galaxy clusters is still being debated. In this paper we aim
to obtain new insights into the internal dynamics of Abell 959, showing
evidence of a diffuse radio source, analyzing velocities and positions of
member galaxies. Our analysis is based on redshift data for 107 galaxies in the
cluster field acquired at the Telescopio Nazionale Galileo. We also use
photometric data from the Sloan Digital Sky Survey (Data Release 6). We combine
galaxy velocities and positions to select 81 galaxies recognized as cluster
members and determine global dynamical properties. We analyze the cluster
searching for substructures by using several statistical methods. We also study
the 2D galaxy distribution in the field of the cluster. We compare our results
with those from X-ray and gravitational lensing analyses. We estimate a cluster
redshift of z=0.2883 +/- 0.0004. We detect an NE high velocity group at 5' from
the cluster center with a relative line--of--sight (LOS) velocity of ~ +1900
km/s with respect to the main system. We also detect a central, dense structure
elongated along the SE--NW direction likely connected with the two dominant
galaxies and their surrounding cores. This elongated central structure is
probably the trace of an old cluster merger. The LOS velocity dispersion of
galaxies is very high (1025 (-75/+104) km/s). The virial mass is M(<R=1.48
Mpc)= 1.15 (-0.19/+0.25) Msun. Our results suggest that this cluster is forming
along two main directions of mass accretion and show the typical
characteristics of radio clusters; i.e., it is very massive and shows a young
dynamical state. However, deeper radio observations are needed to clarify the
nature of the diffuse radio emission in Abell 959.Comment: 12 pages, 13 figures, 3 tables. Accepted for publication on Astronomy
and Astrophysic
The puzzling merging cluster Abell 1914: new insights from the kinematics of member galaxies
We analyze the dynamical state of Abell 1914, a merging cluster hosting a
radio halo, quite unusual for its structure. Our study considers spectroscopic
data for 119 galaxies obtained with the Italian Telescopio Nazionale Galileo.
We select 89 cluster members from spatial and velocity distributions. We also
use photometry Canada-France-Hawaii Telescope archives. We compute the mean
cluster redshift, =0.168, and the velocity dispersion which shows a high
value, sigma_v=1210_{-110}^{+125} km/s. From the 2D analysis we find that Abell
1914 has a NE-SW elongated structure with two galaxy clumps, that mostly merge
in the plane of the sky. Our best, but very uncertain estimate of the velocity
dispersion of the main system is sigma_v~1000 km/s. We estimate a virial mass
M_sys=1.4--2.6 10^{15} h_{70}^{-1} Msun for the whole system. We study the
merger through a simple two-body model and find that data are consistent with a
bound, outgoing substructure observed just after the core crossing. By studying
the 2D distribution of the red galaxies, photometrically selected, we show that
Abell 1914 is contained in a rich large scale structure, with two close
companion galaxy systems, known to be at z~0.17. The system at SW supports the
idea that the cluster is accreting groups from a filament aligned in the NE-SW
direction, while that at NW suggests a second direction of the accretion NW-SE.
We conclude that Abell 1914 well fits among typical clusters with radio halos.
We argue that the unusual radio emission is connected to the complex cluster
accretion and suggest that Abell 1914 resembles the well-known nearby merging
cluster Abell 754 for its particular observed phenomenology.Comment: 14 pages, 10 figures, 2 table
Recommended from our members
Trade intensity and output synchronisation: On the endogeneity properties of the EMU
Using annual bilateral data over the period 1988-2011 for a panel of 24 industrialised and emerging economies, we analyse in a time-varying framework the determinants of output synchronisation in EMU (European Monetary Union) distinguishing between core and peripheral member states. The results support the specialisation paradigm rather than the endogeneity hypothesis. Evidence is found in the euro period of diverging patterns between the core and the peripheral EMU countries raising questions about the future stability of EMU
Evolution of zero-metallicity massive stars
We discuss the evolutionary properties of primordial massive and very massive
stars, supposed to have formed from metal-free gas. Stellar models are
presented over a large range of initial masses (8 Msun <= Mi <= 1000 Msun),
covering the hydrogen- and helium-burning phases up to the onset of carbon
burning. In most cases the evolution is followed at constant mass. To estimate
the possible effect of mass loss via stellar winds, recent analytic formalisms
for the mass-loss rates are applied to the very massive models (Mi >= 120
Msun).Comment: Invited talk at IAU Symp. 212, ``A Massive Star Odyssey, from Main
Sequence to Supernova'', K.A. van der Hucht, A. Herrero, C. Esteban (eds.), 7
pages, 5 postscript figure
On Simulating Liouvillian Flow From Quantum Mechanics Via Wigner Functions
The interconnection between quantum mechanics and probabilistic classical
mechanics for a free relativistic particle is derived in terms of Wigner
functions (WF) for both Dirac and Klein-Gordon (K-G) equations. Construction of
WF is achieved by first defining a bilocal 4-current and then taking its
Fourier transform w.r.t. the relative 4-coordinate. The K-G and Proca cases
also lend themselves to a closely parallel treatment provided the Kemmer-
Duffin beta-matrix formalism is employed for the former. Calculation of WF is
carried out in a Lorentz-covariant fashion by standard `trace' techniques. The
results are compared with a recent derivation due to Bosanac.Comment: 9 pages, Latex; email: [email protected]
The structure of Abell 1351: a bimodal galaxy cluster with peculiar diffuse radio emission
We aim to review the internal structure and dynamics of the Abell 1351
cluster, shown to host a radio halo with a quite irregular shape. Our analysis
is based on radial velocity data for 135 galaxies obtained at the Telescopio
Nazionale Galileo. We combine galaxy velocities and positions to select 95
cluster galaxy members and analyse the internal dynamics of the whole cluster.
We also examine X-ray data retrieved from Chandra and XMM archives. We measure
the cluster redshift, =0.325, the line-of-sight (LOS) velocity dispersion,
\sigma_v~1500 km/s, and the X-ray temperature, kT~9 keV. From both X-ray and
optical data independently, we estimate a large cluster mass, in the 1--4
M range. We attribute the extremely high value of \sigma_v to
the bimodality in the velocity distribution. We find evidence of a significant
velocity gradient and optical 3D substructure. The X-ray analysis also shows
many features in favour of a complex cluster structure, probably supporting an
ongoing merger of substructures in Abell 1351. The observational scenario
agrees with the presence of two main subclusters in the northern region, each
with its brightest galaxy (BCG1 and BCG2), detected as the two most important
X-ray substructures with a rest-frame LOS velocity difference of \Delta v~2500
km/s (in the rest frame) and probably being in large part aligned with the LOS.
We conclude that Abell 1351 is a massive merging cluster. The details of the
cluster structure allow us to interpret the quite asymmetric radio halo as a
`normal' halo plus a southern relic, strongly supporting a previous suggestion
based only on inspection of radio and preliminary X-ray data.Comment: 13 pages, 13 figures, 1 tabl
- …