1,721,021 research outputs found
The dynamical status of ZwCl 2341.1+0000: a very elongated galaxy structure with a complex radio emission
No full textWe 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 Italian Telescopio Nazionale Galileo. We also use optical data available in the Sloan Digital Sky Survey and X-ray data from the Chandra archive.
We select 101 cluster member galaxies and compute the cluster redshift ̃ 0.2693 and the global line-of-sight velocity dispersion σV ̃ 1000 km s-1.
Our optical analysis agrees with the presence of at least three, likely four or more, optical subclusters causing the south-south-east-north-north-west (SSE-NNW) elongation of the galaxy distribution and a significant velocity gradient in the south-north 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. Depending on the adopted model, we obtain a mass estimate Msys ̃ 1-3 × 10^{15}h_{70}^{-1}M_{⊙} for the whole system.
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 two relics + halo scenario or diffuse emission associated with the infall and merging of several galaxy groups during the first phase of the cluster formation
The puzzling merging cluster Abell 1914: new insights from the kinematics of member galaxies
No full textWe analyse 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, σV = 1210{^{+ 125}_{- 110}} km s-1. From the 2D analysis we find that Abell 1914 has a north-east (NE)-south-west (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 σV, main ̃ 1000 km s-1. We estimate a virial mass Msys = 1.4-2.6 × 1015 h{^{- 1}_{70}} 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 haloes. 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
Structure of Abell 1995 from optical and X-ray data: a galaxy cluster with an elongated radio halo
No full textContext. Abell 1995 is a puzzling galaxy cluster hosting a powerful radio halo, but it has not yet been recognized as a obvious cluster
merger, as usually expected for clusters with diffuse radio emission.
Aims. We aim at an exhaustive analysis of the internal structure of Abell 1995 to verify that this cluster is really dynamically relaxed,
as reported in previous studies.
Methods. We base our analysis on new and archival spectroscopic and photometric data for 126 galaxies in the field of Abell 1995.
The study of the hot intracluster medium was performed on X-ray archival data.
Results. Based on 87 fiducial cluster members, we have computed the average cluster redshift z = 0.322 and the global radial
velocity dispersion σV ∼ 1300 km s−1. We detect two main optical subclusters separated by 1.5 that cause the known NE-SW
elongation of the galaxy distribution and a significant velocity gradient in the same direction. As for the X-ray analysis, we confirm
that the intracluster medium is mildly elongated, but we also detect three X-ray peaks. Two X-ray peaks are offset with respect to
the two galaxy peaks and lie between them, thus suggesting a bimodal merger caught in a phase of post core-core passage. The third
X-ray peak lies between the NE galaxy peak and a third, minor galaxy peak suggesting a more complex merger. The difficulty of
separating the two main systems leads to a large uncertainty on the line-of-sight (LOS) velocity separation and the system mass:
ΔVrf,LOS = 600–2000 km s−1 and Msys = 2–5 × 1015 h−1
70 M, respectively. Simple analytical arguments suggest a merging scenario
for Abell 1995, where two main subsystems are seen just after the collision with an intermediate projection angle.
Conclusions. The high mass of Abell 1995 and the evidence of merging suggest it is not atypical among clusters with known radio
halos. Interestingly, our findings reinforce the previous evidence for the peculiar dichotomy between the dark matter and galaxy
distributions observed in this cluster
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Dynamics of the Radio–halo Cluster A2744: An Optical StudyGroups of Galaxies in the Nearby Universe
No full textWe present the results of a dynamical analysis of the radio-halo cluster A2744 based on optical data. We find that this cluster is in an advanced merging phase, with two galaxy subsystems impacting along a direction close to the line- of-sight, likely observed just after the core passage
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