1,721,070 research outputs found
Multi-object spectroscopy of CL1821+643: a dynamically relaxed cluster with a giant radio halo?
Full text linkWe present the study of the dynamical status of the galaxy cluster CL1821+643, a rare and intriguing cool-core cluster hosting a giant radio halo. We base our analysis on new spectroscopic data for 129 galaxies acquired at the Italian Telescopio Nazionale Galileo. We also use spectroscopic data available from the literature and photometric data from the Sloan Digital Sky Survey. We select 120 cluster member galaxies and compute the cluster redshift ̃ 0.296 and the global line-of-sight velocity dispersion σV ̃ 1100 km s-1. The results of our analysis are consistent with CL1821+643 being a massive (M > 1015 M⊙) dynamically relaxed cluster dominated by a big and luminous elliptical at the centre of the cluster potential well. None of the tests employed to study the cluster galaxies kinematics in the 1D (velocity information), 2D (spatial information), and 3D (combined velocity and spatial information) domains is able to detect significant substructures. While this picture is in agreement with previous results based on X-ray data and on the existence of the central cool core, we do not find any evidence of a merging process responsible for the radio halo discovered in this cluster. Thus, this radio halo remains an open problem that raises doubts about our understanding of diffuse radio sources in clusters
A spectroscopic survey of Abell 1703: is it a rare relaxed cluster hosting a radio halo or a usual merging system?
Full text linkWe present the study of the internal dynamics of the intriguing galaxy cluster Abell 1703, a system hosting a probable giant radio halo whose dynamical status is still controversial. Our analysis is based on unpublished spectroscopic data acquired at the Italian Telescopio Nazionale Galileo and data publicly available in the literature. We also use photometric data from the Sloan Digital Sky Survey. We select 147 cluster members and compute the cluster redshift ̃ 0.277 and the global line-of-sight velocity dispersion σv ̃ 1300 km s-1. We infer that Abell 1703 is a massive cluster: M200 ̃ 1-2 × 1015 M☉. The results of our study disagree with the picture of an unimodal, relaxed cluster as suggested by previous studies based on the gravitational lensing analysis and support the view of a perturbed dynamics proposed by recent works based on Chandra X-ray data. The first strong evidence of a dynamically disturbed cluster comes from the peculiarity of the BCG velocity with respect to the first moment of the velocity distribution of member galaxies. Moreover, several statistical tests employed to study the cluster galaxies kinematics find significant evidence of substructure, being Abell 1703 composed by at least two or three subclumps probably caught after the core-core passage. In this observational scenario, the suspected existence of a radio halo in the centre of this cluster is not surprising and well agrees with the theoretical models describing diffuse radio sources in clusters
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
Hydrodinamic interactions between karst conduits and matrix: some example from Classical Karst
No full textOptical 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
The redshift-space two-point correlation functionof galaxy groups in the CfA2 and SSRS2 surveys
No full textWe measure the two-point redshift-space correlation function of loose groups of galaxies, {xi {GG}(s)} , for the combined CfA2 and SSRS2 surveys. Our combined group catalog constitutes the largest homogeneous sample available (885 groups). We compare {xi {GG}(s)} with the correlation function of galaxies, {xi {gg}(s)} , in the same volume. We find that groups are significantly more clustered than galaxies: {xi {GG}/xi {gg}} m=1.64+/-0.16. A similar result holds when we analyze a volume-limited sample (distance limit 78 {{h}-1 Mpc} h) of 139 groups. For these groups, with median velocity dispersion sigma {v} ~ 200 {km s-1} and mean group separation d ~ 16 {{h}-1 Mpc} h, we find that the correlation length is s{0}=8+/-1 {{h}-1 Mpc} h, which is significantly smaller than that found for rich clusters. We conclude that clustering properties of loose groups of galaxies are intermediate between galaxies and rich clusters. Moreover, we find evidence that group clustering depends on physical properties of groups: correlation strengthens for increasing sigma {v}
Optical mass estimates of galaxy clusters
No full textWe evaluate in a homogeneous way the optical masses of 170 nearby clusters (z <= 0.15). The sample includes both data from the literature and the new ESO Nearby Abell Clusters Survey (ENACS) data. On the assumption that mass follows the galaxy distribution, we compute the mass of each cluster by applying the virial theorem to the member galaxies. We constrain the masses of very substructured clusters (about 10% of our clusters) between two limiting values. After appropriate rescaling to the X-ray radii, we compare our optical mass estimates to those derived from X-ray analyses, which we compiled from the literature (for 66 clusters). We find a good overall agreement. This agreement is expected in the framework of two common assumptions: that mass follows the galaxy distribution and that clusters are not far from a situation of dynamical equilibrium, with both gas and galaxies reflecting the same underlying mass distribution. We stress that our study strongly supports the reliability of present cluster mass estimates derived from X-ray analyses and/or (appropriate) optical analyses
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
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