Kinematics of the southern galaxy cluster Abell 3733

We report radial velocities for 99 galaxies with projected positions within 30 arcmin of the center of the cluster A3733 obtained with the MEFOS multifiber spectrograph at the 3.6-m ESO telescope. These measurements are combined with 39 redshifts previously published by Stein (1996) to built a collection of 112 galaxy redshifts in the field of A3733, which is used to examine the kinematics and structure of this cluster. We assign cluster membership to 74 galaxies with heliocentric velocities in the interval 10500-13000 km/s. From this sample of cluster members, we infer a heliocentric systemic velocity for A3733 of 11653{+74}{-76} km/s, which implies a mean cosmological redshift of 0.0380, and a velocity dispersion of 614{+42}{-30} km/s. The application of statistical substructure tests to a magnitude-limited subset of the latter sample reveals evidence of non-Gaussianity in the distribution of ordered velocities in the form of lighter tails and possible multimodality. Spatial substructure tests do not find, however, any significant clumpiness in the plane of the sky, although the existence of subclustering along the line-of-sight cannot be excluded.Comment: AA-LaTeX2e style; 10 pages, 2 Postscript figures, Table 1 appended. To be published in Astronomy and Astrophysics. Also available at ftp://pcess1.am.ub.es/pub/AA/a3733.ps.g

The HI Content of Spirals. I. Field-Galaxy HI Mass Functions and HI Mass-Optical Size Regression

A standard parametric maximum-likelihood technique is used to determine both the probability distribution over total HI mass $M_{\rm HI}$ and the regression of this quantity on the linear optical diameter $D_{\rm o}$ for field giant spirals (Sa-Sc) from a complete HI-flux-limited data set of these objects. Gaussian and Schechter parametrizations of the HI mass function are explored. We find that the available data are equally well described by both models, and that the different morphological classes of giant spirals have HI mass functions which, in general, agree well within the errors. The largest discrepancy corresponds to the Sb-type systems which exhibit a deficit of low HI-mass objects relative to the other types. Using a straightforward generalization of the gaussian model, we have also investigated the linear dependence of $M_{\rm HI}$ on $D_{\rm o}$. We confirm that the HI content of spirals is much better predicted by the size of their optical disks than by their morphological types alone. The inferred correlations imply a considerable decrease of the ratio $M_{\rm HI}/D_{\rm o}^2$ with increasing galaxy size for types earlier than Sc.Comment: 23 pages, uuencoded gzipped postscript; 3 Tables and 12 Figures available upon request from [email protected]

The Spatial Distribution, Kinematics, and Dynamics of the Galaxies in the Region of Abell 2634 and 2666

A total of 663 galaxies with known redshifts in a $6\deg\!\times 6\deg$ field centered on A2634, including 211 new measurements, are used to study the structure of this cluster and its surroundings. Two samples, ---one containing 200 galaxies within two degrees from the cluster center and a second, magnitude-limited, of 118 galaxies within the central half degree---, are used to examine the structure, kinematics, dynamics of A2634. We show that early-type galaxies appear to be a relaxed system, while the spiral population eschews the center of the cluster and exhibits both a multimodal velocity distribution and a much larger velocity dispersion than the ellipticals. We find no evidence of significant substructure in the central regions supportive of a recent merger of two subclusters, a scenario that has been suggested to explain the bending of the tails of the cluster central radio source (3C 465). We also conclude that the adoption of lenient membership criteria that ignore the dynamical complexity of A2634 are unlikely to be responsible for the conflictual results reported on the motion of this cluster with respect to the CMB. The kinematical and dynamical analysis is extended to A2634's close companion, A2666, and to two distant background clusters at 18,000 and 37,000 $\rm km s^{-1}$.Comment: 52 pages (AAS LaTeX macro v3.0). 5 Tables and 18 Figures available on request. To appear in the ApJ. JMS-94-0

Virialization of Galaxy Clusters and Beyond

Using samples of structures identified by a multi-scale decomposition from numerical simulation, we analyze the scale-dependence of the virialization of clusters. We find that beyond the scale of full virialization there exists a radius range over which clusters are quasi-virialized, i.e. while the internal structure of an {\it individual} cluster is at substantial departure from dynamical relaxation, some {\it statistical} properties of the multi-scale identified clusters are approximately the same as those for the virialized systems. The dynamical reason of the existence of quasi-virialization is that some of the scaling properties of dynamically relaxed systems of cosmic gravitational clustering approximately hold beyond the full virialization regime. The "individual-statistical" duality of the quasi-virialization provides an explanation of the observed puzzle that the total masses of clusters derived from virial theorem are statistically the same as the gravitational lensing determined masses, in spite of the presence of irregular configuration and substructures in individual clusters. It also explains the tight correlation between the velocity dispersion of optical galaxies and the temperature of X-ray emitting gas. Consequently, the virial mass estimators based on the assumptions of isothermal and hydrostatic model are statistically applicable to scales on which the clusters are quasi-virialized. In the quasi-virialization regime, the temperature functions of clusters also show scaling. This feature is a useful discriminator among cosmological models.Comment: AAS Latex file, 22 pages+ 14 figures, accepted for publication in Ap

Human-robot cooperation for robust surface treatment using non-conventional sliding mode control

© 2018 ISA This work presents a human-robot closely collaborative solution to cooperatively perform surface treatment tasks such as polishing, grinding, deburring, etc. The method considers two force sensors attached to the manipulator end-effector and tool: one sensor is used to properly accomplish the surface treatment task, while the second one is used by the operator to guide the robot tool. The proposed scheme is based on task priority and adaptive non-conventional sliding mode control. The applicability of the proposed approach is substantiated by experimental results using a redundant 7R manipulator: the Sawyer cobot

A Sliding Mode Control Architecture for Human-Manipulator Cooperative Surface Treatment Tasks

© 2018 IEEE. This paper presents a control architecture readily suitable for surface treatment tasks such as polishing, grinding, finishing or deburring as carried out by a human operator, with the added benefit of accuracy, recurrence and physical strength as administered by a robotic manipulator partner. The shared strategy effectively couples the human operator propioceptive abilities and fine skills through his interactions with the autonomous physical agent. The novel proposed control scheme is based on task prioritization and a non-conventional sliding mode control, which is considered to benefit from its inherent robustness and low computational cost. The system relies on two force sensors, one located between the last link of the robot and the surface treatment tool, and the other located in some place of the robot end-effector: the former is used to suitably accomplish the conditioning task, while the latter is used by the operator to manually guide the robotic tool. When the operator chooses to cease guiding the tool, the robot motion safely switches back to an automatic reference tracking. The paper presents the theories for the novel collaborative controller, whilst its effectiveness for robotic surface treatment is substantiated by experimental results using a redundant 7R manipulator and a mock-up conditioning tool

HI 2334+26: An Extended HI Cloud near Abell 2634

We report the serendipitous discovery of a large HI cloud with an associated HI mass of $6(\pm1.5)\times 10^9 h^{-2}$ M$_\odot$ and a heliocentric velocity 8800 \kms, located near the periphery of the cluster of galaxies Abell 2634. Its velocity field appears to be very quiescent, as no gradients in the peak velocity are seen over its extent of 143$h^{-1}$ by 103$h^{-1}$ kpc. The distribution of gas is poorly resolved spatially, and it is thus difficult at this time to ascertain the nature of the cloud. At least two relatively small, actively star--forming galaxies appear to be embedded in the HI gas, which may (a) be an extended gaseous envelope surrounding one or both galaxies, (b) have been spread over a large region by a severe episode of tidal disruption or (c) have been affected by the ram pressure resulting from its motion through the intracluster gas of A2634.Comment: 12 pages plus 2 tables (AAS LaTeX macro v3.0), 4 figures not included. To appear in the A

Two-Temperature Intracluster Medium in Merging Clusters of Galaxies

We investigate the evolution of intracluster medium during a cluster merger, explicitly considering the relaxation process between the ions and electrons by N-body and hydrodynamical simulations. When two subclusters collide each other, a bow shock is formed between the centers of two substructures and propagate in both directions along the collision axis. The shock primarily heats the ions because the kinetic energy of an ion entering the shock is larger than that of an electron by the ratio of masses. In the post-shock region the energy is transported from the ions to electrons via Coulomb coupling. However, since the energy exchange timescale depends both on the gas density and temperature, distribution of electron temperature becomes more complex than that of the plasma mean temperature, especially in the expanding phase. After the collision of two subclusters, gas outflow occurs not only along the collision axis but also in its perpendicular direction. The gas which is originally located in the central part of the subclusters moves both in the parallel and perpendicular directions. Since the equilibrium timescale of the gas along these directions is relatively short, temperature difference between ions and electrons is larger in the directions tilted by the angles of $\pm 45^\circ$ with respect to the collision axis. The electron temperature could be significantly lower that the plasma mean temperature by $\sim 50$ at most. The significance of our results in the interpretation of X-ray observations is briefly discussed.Comment: 20 pages, 11 figures, Accepted for publication in Ap