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Register a new userDiffuse light and building history of the galaxy cluster Abell 2667
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We have searched for diffuse intracluster light in the galaxy cluster Abell 2667 (z=0.233) from HST images in three filters. We have applied to these images an iterative multi-scale wavelet analysis and reconstruction technique, which allows to subtract stars and galaxies from the original images. We detect a zone of diffuse emission south west of the cluster center (DS1), and a second faint object (ComDif), within DS1. Another diffuse source (DS2) may be detected, at lower confidence level, north east of the center. These sources of diffuse light contribute to 10-15% of the total visible light in the cluster. Whether they are independent entities or are part of the very elliptical external envelope of the central galaxy remains unclear. VLT VIMOS integral field spectroscopy reveals a faint continuum at the positions of DS1 and ComDif but do not allow to compute a redshift. A hierarchical substructure detection method reveals the presence of several galaxy pairs and groups defining a similar direction as the one drawn by the DS1-central galaxy-DS2 axis. The analysis of archive XMM-Newton and Chandra observations shows X-ray emission elongated in the same direction. The X-ray temperature map shows the presence of a cool core, a broad cool zone stretching from north to south and hotter regions towards the north east, south west and north west. This possibly suggests shock fronts along these directions produced by infalling material. These various data are consistent with a picture in which diffuse sources are concentrations of tidal debris and harassed matter expelled from infalling galaxies by tidal stripping and undergoing an accretion process onto the central cluster galaxy; as such, they are expected to be found along the main infall directions.
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Based on HST and MUSE data, we probe the stellar and gas properties (i.e. kinematics, stellar mass, star formation rate) of the radio-loud brightest cluster galaxy (BCG) located at the centre of the X-ray luminous cool core cluster Abell 2667 (z = 0.2343). The bi-dimensional modelling of the BCG surface brightness profile reveals the presence of a complex system of substructures extending all around the galaxy. Clumps of different size and shape plunged into a more diffuse component constitute these substructures, whose intense blue optical colour hints to the presence of a young stellar population. Our results depict the BCG as a massive (M_star ~ 1.38 x 10^11 M_sun) dispersion-supported spheroid (v_star < 150 km/s, sigma_0 ~ 216 km/s) hosting an active supermassive black hole (M_SMBH ~ 3.8 x 10^9 M_sun) whose optical features are typical of low ionisation nuclear emission line regions. Although the velocity pattern of the stars in the BCG is irregular, the stellar kinematics in the regions of the clumps show a positive velocity of ~ 100 km/s, similarly to the gas component. An analysis of the mechanism giving rise to the observed lines in the clumps through empirical diagnostic diagrams points out that the emission is composite, suggesting the contribution from both star formation and AGN. We conclude our analysis describing how scenarios of both chaotic cold accretion and merging with a gas-rich disc galaxy can efficaciously explain the phenomena the BCG is undergoing.
(abridged) We present extensive multi-color imaging and low resolution VIMOS Integral Field Unit spectroscopic observations of the X-ray luminous cluster Abell 2667 (z=0.233). An extremely bright giant gravitational arc (z=1.0334) is easily identified as part of a triple image system and other fainter multiple images are also revealed by the HST-WFPC2 images. The VIMOS-IFU observations cover a field of view of 54 x 54 and enable us to determine the redshift of all galaxies down to V=22.5. Furthermore, redshifts could be identified for some sources down to V=23.2. In particular we identify 21 cluster members in the cluster inner region, from which we derive a velocity dispersion of sigma=960 km/s, corresponding to a total mass of 7.1 x 10^{13} solar masses within a 110 kpc radius. Using the multiple images constraints and priors on the mass distribution of cluster galaxy halos we construct a detailed lensing mass model leading to a total mass of 2.9 x 10^{13} solar masses within the Einstein radius (16 arcsec). The lensing mass and dynamical mass are in good agreement although the dynamical one is much less accurate. Comparing these measurements with published X-ray analysis, is however less conclusive. Although the X-ray temperature matches the dynamical and lensing estimates, the published NFW mass model derived from the X-ray measurement with its small concentration of c ~3 can not account for the large Einstein radius observed in this cluster. A larger concentration of ~6 would however match the strong lensing measurements. These results are likely reflecting the complex structure of the cluster mass distribution, underlying the importance of panchromatic studies from small to large scale in order to better understand cluster physics.
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, <z>=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 $10^{15}$ M$_odot$ 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.
We report extensive VLA and ATCA observations of the two diffuse radio sources in the cluster of galaxies Abell 548b, which confirm their classification as relics. The two relics (named A and B) show similar flux density, extent, shape, polarization and spectral index and are located at projected distances of about 430 and 500 kpc from the cluster center, on the same side of the clusters X-ray peak. On the basis of spectral indices of discrete radio sources embedded within the diffuse features, we have attempted to distinguish emission peaks of the diffuse sources from unrelated sources. We have found that both relics, in particular the B-relic, show possible fine structure, when observed at high resolution. Another diffuse source (named C) is detected close in projection to the cluster center. High-resolution images show that it contains two discrete radio sources and a diffuse component, which might be a candidate for a small relic source. The nature and properties of the diffuse radio sources are discussed. We conclude that they are likely related to the merger activity in the cluster.
Using the CLASH-VLT survey, we assembled an unprecedented sample of 1234 spectroscopically confirmed members in Abell~S1063, finding a dynamically complex structure at z_cl=0.3457 with a velocity dispersion sigma_v=1380 -32 +26 km s^-1. We investigate cluster environmental and dynamical effects by analysing the projected phase-space diagram and the orbits as a function of galaxy spectral properties. We classify cluster galaxies according to the presence and strength of the [OII] emission line, the strength of the H$delta$ absorption line, and colours. We investigate the relationship between the spectral classes of galaxies and their position in the projected phase-space diagram. We analyse separately red and blue galaxy orbits. By correlating the observed positions and velocities with the projected phase-space constructed from simulations, we constrain the accretion redshift of galaxies with different spectral types. Passive galaxies are mainly located in the virialised region, while emission-line galaxies are outside r_200, and are accreted later into the cluster. Emission-lines and post-starbursts show an asymmetric distribution in projected phase-space within r_200, with the first being prominent at Delta_v/sigma <~-1.5$, and the second at Delta_v/ sigma >~ 1.5, suggesting that backsplash galaxies lie at large positive velocities. We find that low-mass passive galaxies are accreted in the cluster before the high-mass ones. This suggests that we observe as passives only the low-mass galaxies accreted early in the cluster as blue galaxies, that had the time to quench their star formation. We also find that red galaxies move on more radial orbits than blue galaxies. This can be explained if infalling galaxies can remain blue moving on tangential orbits.
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