Structure and Evolution of Galaxy Clusters: Internal Dynamics of ABCG 209 at z~0.21

We study the internal dynamics of the rich galaxy cluster ABGC 209 on the basis of new spectroscopic and photometric data. The distribution in redshift shows that ABCG 209 is a well isolated peak of 112 detected member galaxies at z=0.209, characterised by a high value of the line-of-sight velocity dispersion, sigma_v=1250-1400 Km/s, on the whole observed area (1 Mpc/h from the cluster center), that leads to a virial mass of M=1.6-2.2x10^15 M_sun within the virial radius, assuming the dynamical equilibrium. The presence of a velocity gradient in the velocity field, the elongation in the spatial distribution of the colour-selected likely cluster members, the elongation of the X-ray contour levels in the Chandra image, and the elongation of cD galaxy show that ABCG 209 is characterised by a preferential NW-SE direction. We also find a significant deviation of the velocity distribution from a Gaussian, and relevant evidence of substructure and dynamical segregation. All these facts show that ABCG 209 is a strongly evolving cluster, possibly in an advanced phase of merging.Comment: 26 pages, 14 figures. A&A in pres

Extended stellar kinematics of elliptical galaxies in the Fornax cluster

We present extended stellar kinematics for a sample of 13 elliptical galaxies in the Fornax cluster. Major-axis velocity dispersion profiles (VDPs) and rotation curves (RCs) are given for 12 of the galaxies. A major feature of this data is the spatial extension: for 8 galaxies the data extends beyond 1 R_e, and for 5 it extends beyond 2 R_e. Compared to the previously available data, this corresponds to an increase in spatial coverage by a factor from 1 to 5. Five of the ellipticals in the sample turn out to be rotationally-supported systems, having positive rotation parameter log (V/sigma)*. One of these five, and another 3 galaxies from the remaining sample, display evidence for bar-like kinematics. The data indicate that the true number of `dynamically hot' stellar systems, is much lower than previously thought: of the Es in the present sample only 1/4 are confirmed as `pressure-supported' systems. The data reveal a host of individual peculiarities, like: wiggles, strong gradients, and asymmetries in the rotation curve and/or in the velocity dispersion profile, thus showing that the presence of kinematically distinct components and/or triaxiality is a common characteristic of this class of object.Comment: 27 pages, includes 15 eps figures. Accepted for publication in A&A Sup

Shapley Supercluster Survey: Ram-Pressure Stripping vs. Tidal Interactions in the Shapley Supercluster

We present two new examples of galaxies undergoing transformation in the Shapley supercluster core. These low-mass (stellar mass from 0.4E10 to 1E10 Msun) galaxies are members of the two clusters SC-1329-313 (z=0.045) and SC-1327-312 (z=0.049). Integral-field spectroscopy complemented by imaging in ugriK bands and in Halpha narrow-band are used to disentangle the effects of tidal interaction (TI) and ram-pressure stripping (RPS). In both galaxies, SOS-61086 and SOS-90630, we observe one-sided extraplanar ionized gas extending respectively 30kpc and 41kpc in projection from their disks. The galaxies' gaseous disks are truncated and the kinematics of the stellar and gas components are decoupled, supporting the RPS scenario. The emission of the ionized gas extends in the direction of a possible companion for both galaxies suggesting a TI. The overall gas velocity field of SOS-61086 is reproduced by ad hoc N-body/hydrodynamical simulations of RPS acting almost face-on and starting about 250Myr ago, consistent with the age of the young stellar populations. A link between the observed gas stripping and the cluster-cluster interaction experienced by SC-1329-313 and A3562 is suggested. Simulations of ram pressure acting almost edge-on are able to fully reproduce the gas velocity field of SOS-90630, but cannot at the same time reproduce the extended tail of outflowing gas. This suggests that an additional disturbance from a TI is required. This study adds a piece of evidence that RPS may take place in different environments with different impacts and witnesses the possible effect of cluster-cluster merger on RPS.Comment: 27 pages, 28 figures, MNRAS accepte

Oscillating universes as eigensolutions of cosmological Schr\"odinger equation

We propose a cosmological model which could explain, in a very natural way, the apparently periodic structures of the universe, as revealed in a series of recent observations. Our point of view is to reduce the cosmological Friedman--Einstein dynamical system to a sort of Schr\"odinger equation whose bound eigensolutions are oscillating functions. Taking into account the cosmological expansion, the large scale periodic structure could be easily recovered considering the amplitudes and the correlation lengths of the galaxy clusters.Comment: 12 pages, Latex, submitted to Int. Jou. of Theor. Phy

ACCESS - V. Dissecting ram-pressure stripping through integral-field spectroscopy and multi-band imaging

We study the case of a bright (L>L*) barred spiral galaxy from the rich cluster A3558 in the Shapley supercluster core (z=0.05) undergoing ram-pressure stripping. Integral-field spectroscopy, complemented by multi-band imaging, allows us to reveal the impact of ram pressure on the interstellar medium. We study in detail the kinematics and the physical conditions of the ionized gas and the properties of the stellar populations. We observe one-sided extraplanar ionized gas along the full extent of the galaxy disc. Narrow-band Halpha imaging resolves this outflow into a complex of knots and filaments. The gas velocity field is complex with the extraplanar gas showing signature of rotation. In all parts of the galaxy, we find a significant contribution from shock excitation, as well as emission powered by star formation. Shock-ionized gas is associated with the turbulent gas outflow and highly attenuated by dust. All these findings cover the whole phenomenology of early-stage ram-pressure stripping. Intense, highly obscured star formation is taking place in the nucleus, probably related to the bar, and in a region 12 kpc South-West from the centre. In the SW region we identify a starburst characterized by a 5x increase in the star-formation rate over the last ~100 Myr, possibly related to the compression of the interstellar gas by the ram pressure. The scenario suggested by the observations is supported and refined by ad hoc N-body/hydrodynamical simulations which identify a rather narrow temporal range for the onset of ram-pressure stripping around t~60 Myr ago, and an angle between the galaxy rotation axis and the intra-cluster medium wind of ~45 deg. Taking into account that the galaxy is found ~1 Mpc from the cluster centre in a relatively low-density region, this study shows that ram-pressure stripping still acts efficiently on massive galaxies well outside the cluster cores.Comment: 46 pages, 21 figures, accepted for publication; MNRAS 201

Extended stellar kinematics of elliptical galaxies in the Fornax cluster

We present extended stellar kinematics for a sample of elliptical galaxies in the Fornax cluster. Out of the 13 galaxies presented here, five (FCC 119, FCC 136, NGC 1373, NGC 1428, FCC 335) have no previously published kinematical data. Major-axis velocity dispersion profiles (VDPs) and rotation curves (RCs) are given for 12 of the galaxies. A major feature of this data is the spatial extension: for 8 galaxies the data extends beyond 1 R_e, and for 5 it extends beyond 2 R_e. Compared to the previously available data, this corresponds to an increase in spatial coverage by a factor from 1 to 5. The present sample represents 86% of the ellipticals in Fornax brighter than B_T = 15 mag. Five of the ellipticals in the sample turn out to be rotationally-supported systems, having positive rotation parameter log ((V)/(sigma ))(*) . One of these five, and another 3 galaxies from the remaining sample, display evidence for bar-like kinematics. The data indicate that the yes number of ``dynamically hot'' stellar systems, is much lower than previously thought: of the Es in the present sample only 1/4 are confirmed as ``pressure-supported'' systems. The data reveal a host of individual peculiarities, like: wiggles, strong gradients, and asymmetries in the rotation curve and/or in the velocity dispersion profile, thus showing that the presence of kinematically distinct components and/or triaxiality is a common characteristic of this class of object. Based on observations collected at Siding Spring Observatory. Table 3 is presented in electronic form only, and is available from the CDS, Strasbourg via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.htm

Evolution of UV -- NIR Structural Properties of Cluster Galaxies

Structural parameters (half light radius r_e, mean surface brightness _e and Sersic index n) are derived for the galaxy cluster A 209, at z = 0.21, in UV and optical restframe, and for the cluster EIS 0048, at z = 0.64, in UV, optical and NIR restframe. This data set, together with previous optical and NIR measurements for the cluster AC 118 at z=0.31}, constitutes the first large sample (N~250) of cluster galaxies whose UV - NIR structure can be investigated up to a look-back time of ~6 Gyr (Omega_m=0.3, Omega_L=0.7 and H_0=70 Km/s/Mpc). The analysis is performed (1) by direct comparison of log r_e, and log n, in UV-OPT and OPT-NIR, and (2) by using the structural parameters to estimate UV-OPT and OPT-NIR internal colour gradients of galaxies. We classify the galaxies as spheroids or disks according to the shape of the optical light profile of galaxies, and investigate separately the evolution in the properties of both populations. On the average, we find that the bulk of spheroids and disks are more concentrated at longer wavelengths, having Delta(log r_e) > 0, and Delta(log n) < 0. The mean value of Delta(log n) in OPT-NIR seems to be the quantity more dependent on z, in the sense that it decreases at higher redshift. In particular, we find a strong decrease in the ratio of OPT to NIR Sersic indices for the disks at z~0.64. By comparing the estimated colour gradients (grad(UV-OPT) and grad(OPT-NIR)) with age and metallicity models, we find that, for the spheroids, both grad(UV-OPT) and grad(OPT-NIR) are weakly dependent on the redshift, confirming that metallicity is the primary effect to drive the gradients. For the disks, metallicity is not able at all to describe the observed range of colour gradients. Age or age+metallicity are responsible for the radial colour distribution of disk dominated galaxies

Cosmic dance in the Shapley Concentration Core - I. A study of the radio emission of the BCGs and tailed radio galaxies

The Shapley Concentration ($z\approx0.048$) covers several degrees in the Southern Hemisphere, and includes galaxy clusters in advanced evolutionary stage, groups of clusters in the early stages of merger, fairly massive clusters with ongoing accretion activity, and smaller groups located in filaments in the regions between the main clusters. With the goal to investigate the role of cluster mergers and accretion on the radio galaxy population, we performed a multi-wavelength study of the BCGs and of the galaxies showing extended radio emission in the cluster complexes of Abell 3528 and Abell 3558. Our study is based on a sample of 12 galaxies. We observed the clusters with the GMRT at 235, 325 and 610 MHz, and with the VLA at 8.46 GHz. We complemented our study with the TGSS at 150 MHz, the SUMSS at 843 MHz and ATCA at 1380, 1400, 2380, and 4790 MHz data. Optical imaging with ESO-VST and mid-IR coverage with WISE are also available for the host galaxies. We found deep differences in the properties of the radio emission of the BCGs in the two cluster complexes. The BCGs in the A3528 complex and in A3556, which are relaxed cool-core objects, are powerful active radio galaxies. They also present hints of restarted activity. On the contrary, the BCGs in A3558 and A3562, which are well known merging systems, are very faint, or quiet, in the radio band. The optical and IR properties of the galaxies are fairly similar in the two complexes, showing all passive red galaxies. Our study shows remarkable differences in the radio properties of the BGCs, which we relate to the different dynamical state of the host cluster. On the contrary, the lack of changes between such different environments in the optical band suggests that the dynamical state of galaxy clusters does not affect the optical counterparts of the radio galaxies, at least over the life-time of the radio emission.Comment: 24 pages, 11 figures, accepted for publication in Astronomy & Astrophysic