1,721,128 research outputs found
Internal dynamics of the massive cluster Abell 697: a multi-wavelength analysis
No full textAims.We conduct an intensive study of the rich, X-ray luminous, and hot galaxy cluster Abell 697 (at z=0.282), likely containing a diffuse radio-emission, to determine its dynamical status.
Methods: .Our analysis is based on new spectroscopic data obtained at the TNG telescope for 93 galaxies and on new photometric data obtained at the INT telescope in a large field. We combine galaxy velocity and position information to select 68 cluster members (out to 1.3 {h70-1} Mpc from the cD galaxy), determine global dynamical properties, and detect possible substructures. The investigation of the dynamical status is also performed by using X-ray data stored in the Chandra archive.
Results: .We compute the line-of-sight (LOS) velocity dispersion of galaxies, σv=1334-95+114 km s-1, in agreement with the high average X-ray temperature T_X=(10.2±0.8) keV recovered from Chandra data, as expected in the case of energy-density equipartition between galaxies and gas. Assuming that the cluster is in dynamical equilibrium and mass follows the galaxy distribution, we find that A697 is a very massive cluster obtaining M(<{R}_max=0.75 {h70-1} Mpc)=9.5+1.8-1.5 × 1014 {h70-1} Msun and M(<{R}_vir=3.85 {h70-1} Mpc)=4.5-1.3+1.4 × 1015 {h70-1} Msun for the region well sampled by the spectroscopic data and for the entire virialized region, respectively. Further investigations find that A697 is not fully relaxed, as shown by the non Gaussianity of the velocity distribution, the elongation of the X-ray emission, and the presence of small-size substructures in the central region.
Conclusions: .Our results suggest that we are observing a cluster that has undergone a complex cluster merger occurring mainly along the LOS, with a transverse component in the SSE-NNW direction. The importance and the phase of the merging event is discussed. The spatial correlation between the (likely) radio halo and the optical and X-ray cluster structure supports the hypothesis of a relation between extended radio emission and merging phenomena
Internal dynamics of Abell 2294: a massive, likely merging cluster
No full textContext. The mechanisms giving rise to diffuse radio emission in galaxy clusters, and in particular their connection with cluster mergers, are still debated.
Aims: We seek to explore the internal dynamics of the cluster Abell 2294, which has been shown to host a radio halo.
Methods: Our analysis is mainly based on redshift data for 88 galaxies acquired at the Telescopio Nazionale Galileo. We combine galaxy velocities and positions to select 78 cluster galaxies and analyze its internal dynamics. We also use both photometric data acquired at the Isaac Newton Telescope and X-ray data from the Chandra archive.
Results: We re-estimate the redshift of the large, brightest cluster galaxy (BCG) obtaining = 0.1690, which closely agrees with the mean cluster redshift. We estimate a quite large line-of-sight (LOS) velocity dispersion σ_V ~ 1400 km s-1 and X-ray temperature TX ~ 10 keV. Our optical and X-ray analyses detect substructure. Our results imply that the cluster is composed of two massive subclusters separated by a LOS rest frame velocity difference Vrf ~ 2000 km s-1, very closely projected in the plane of sky along the SE-NW direction. This observational picture, interpreted in terms of the analytical two-body model, suggests that Abell 2294 is a cluster merger elongated mainly in the LOS direction and captured during the bound outgoing phase, a few fractions of Gyr after the core crossing. We find that Abell 2294 is a very massive cluster with a range of M = 2-4 × 1015 h70-1 Msun, depending on the adopted model. In contrast to previous findings, we find no evidence of Hα emission in the spectrum of the BCG galaxy.
Conclusions: The emerging picture of Abell 2294 is that of a massive, quite “normal” merging cluster, like many clusters hosting diffuse radio sources. However, perhaps because of its particular geometry, more data are needed for reach a definitive, more quantitative conclusion
Optical analysis of the poor clusters Abell 610, Abell 725, and Abell 796, containing diffuse radio sources
No full textAims: We study the dynamical status of the poor, low X-ray luminous galaxy clusters Abell 610, Abell 725, and Abell 796 (at z = 0.1, 0.09, and 0.16, respectively), containing diffuse radio sources (relic, relic, and possible halo, respectively).
Methods: Our analysis is based on new spectroscopic data obtained at the William Herschel Telescope for 158 galaxies, new photometry obtained at the Isaac Newton Telescope with the addition of data recovered from the Data Release 5 of the Sloan Digital Sky Survey. We use statistical tools to select 57, 36, and 26 cluster members and to analyze the kinematics of cluster galaxies, as well as to study the 2D cluster structure.
Results: The low values we compute for the global line-of-sight velocity dispersion of galaxies (σV = 420-700 km s-1) confirm that these clusters are low-mass clusters. Abell 610 shows a lot of evidence of substructure. It seems to be formed by two structures separated by ~700 km s-1 in the cluster rest-frame, having comparable σV ~ 200 km s-1 and likely causing a velocity gradient. The velocity of the brightest cluster member (BCMI; a bright radio source) is very close to the mean velocity of the higher velocity structure. A third small, low-velocity group hosts the second brightest cluster member (BCMII). The analysis of the 2D galaxy distribution shows a bimodal distribution in the core elongated in the SE-NW direction and likely associated to BCMI and BCMII groups. Abell 725 and Abell 796, which are less sampled, show marginal evidence of substructure in the velocity space. They are elongated in the 2D galaxy distribution. For both Abell 610 and Abell 725 we shortly discuss the possible connection with the hosted diffuse radio relic.
Conclusions: Our results show that relic radio sources are likely connected with merger events, but are not limited to massive clusters. About the possible halo source in Abell 796, there is some evidence of a merger event in this non-massive cluster, but a pointed radio observation is necessary to confirm this halo
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
Internal dynamics of Abell 1240: a galaxy cluster with symmetric double radio relics
No full textContext: The mechanisms giving rise to diffuse radio emission in galaxy clusters, and in particular their connection with cluster mergers, are still debated.
Aims: We aim to obtain new insights into the internal dynamics of the cluster Abell 1240, which appears to contain two roughly symmetric radio relics, separated by ~2 h_70-1 Mpc.
Methods: Our analysis is based mainly on redshift data for 145 galaxies mostly acquired at the Telescopio Nazionale Galileo and on new photometric data acquired at the Isaac Newton Telescope. We also use X-ray data from the Chandra archive and photometric data from the Sloan Digital Sky Survey (Data Release 7). We combine galaxy velocities and positions to select 89 cluster galaxies and analyze the internal dynamics of the Abell 1237 + Abell 1240 cluster complex, Abell 1237 being a close companion of Abell 1240 in its southern direction.
Results: We estimate similar redshifts for Abell 1237 and Abell 1240, = 0.1935 and = 0.1948, respectively. For Abell 1237, we estimate a line-of-sight (LOS) velocity dispersion of σV ~ 740 km s-1and a mass of M ~ 6 × 1014 h_70-1 Msun. For Abell 1240, we estimate a LOS σV ~ 870 km s-1and a mass in the range M ~ 0.9-1.9 × 1015 h_70-1 Msun, which takes account of its complex dynamics. Abell 1240 is shown to have a bimodal structure with two galaxy clumps roughly aligned along its N-S direction, the same as defined by the elongation of its X-ray surface brightness and the axis of symmetry of the relics. The two brightest galaxies of Abell 1240, associated with the northern and southern clumps, are separated by a LOS rest-frame velocity difference Vrf ~ 400 km s-1and a projected distance D ~ 1.2 h_70-1 Mpc. The two-body model agrees with the hypothesis that we are looking at a cluster merger that occurred largely in the plane of the sky, the two galaxy clumps being separated by a rest-frame velocity difference Vrf ~ 2000 km s-1at a time of 0.3 Gyr after the crossing core, while Abell 1237 is still infalling onto Abell 1240. Chandra archive data confirm the complex structure of Abell 1240 and allow us to estimate a global X-ray temperature of TX = 6.0±0.5 keV.
Conclusions: In agreement with the findings from radio data, our results for Abell 1240 strongly support the “outgoing merger shocks” model to explain the presence of the relics
The dynamical status of the galaxy cluster Abell 115
No full textAims:We present the results of a new spectroscopic and photometric survey of the hot, binary X-ray cluster A115 at z = 0.193, containing a radio relic.
Methods: Our analysis is based on new spectroscopic data obtained at the Telescopio Nazionale Galileo for 115 galaxies and on new photometric data obtained at the Isaac Newton Telescope in a large field. We combine galaxy velocity and position information to select 85 galaxies recognized as cluster members, determine global dynamical properties and detect substructures.
Results: We find that A115 appears as a well isolated peak in the redshift space, with a global line-of-sight (LOS) velocity dispersion σ_v=1362-108+126 km s-1. Our analysis confirms the presence of two structures of cluster-type well recognizable in the plane of the sky and shows that they differ of 2000 km s-1in the LOS velocity. The northern, high velocity subcluster (A115N) is likely centred on the second brightest cluster galaxy (BCM-A, coincident with radio source 3C28) and the northern X-ray peak. The southern, low velocity subcluster (A115S) is likely centred on the first brightest cluster galaxy (BCM-B) and the southern X-ray peak. We estimate that A115S is slightly dynamically more important than A115N having σv = 900-1100 km s-1 vs. σv = 750-850 km s-1. Moreover, we find evidence for two small groups at low velocities. We estimate a global cluster virial mass of 2.2-3.5 × 1015 h70-1 Msun.
Conclusions: Our results agree with a pre-merging scenario where A115N and A115S are colliding with a LOS impact velocity Δ {{v}_rf} ̃ 1600 km s-1. The most likely solution to the two-body problem suggests that the merging axis lies at 20 degrees from the plane of the sky and that the cores will cross after 0.1 Gyr. The radio relic with its largest dimension perpendicular to the merging axis is likely connected to this merger
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
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