We present and discuss results concerning a study of stellar populations in the galaxies belonging to CL 0048-2942, a cluster at intermediate redshift (z = 0.64), and to the field. This study gives insight on the evolutionary stage of the cluster galaxies at different radial distances from the cluster centre. We find a population gradient within the cluster: centre galaxies host older stars whereas galaxies located towards the cluster outskirts are predominantly made of less evolved stars. This effect is even more pronounced as we move outside the cluster, into the field. This is interpreted as star formation being more intense in the field, or rather, suppressed within the cluster, particulary as we move towards its centre.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present results of our wide-field redshift survey of galaxies in a 285 square degree region of the Shapley Supercluster (SSC).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

There is now firm evidence that the ICM consists of a mixture of hot plasma, magnetic fields and relativistic particles. The most important pieces of evidence for non-thermal phenomena in galaxy clusters come from the diffuse Mpc-scale synchrotron radio emission (radio halos), observed in a growing number of massive clusters (Feretti 2003), and from hard X-ray (HXR) excess emission (detected in a few cases), which can be explained in terms of IC scattering of relativistic electrons off the cosmic microwave background photons (Fusco-Femiano et al. 2003). There is now growing evidence that giant radio halos may be naturally accounted for by synchrotron emission from relativistic electrons reaccelerated by some kind of turbulence generated in the cluster volume during merger events (Brunetti 2003). With the aim of investigating the connection between thermal and non-thermal properties of the ICM, we have developed a statistical magneto-turbulent model which describes the evolution of the thermal and non-thermal emission from clusters. We calculate the energy and spectrum of the magne-!tosonic waves generated during cluster mergers, the acceleration and evolution of relativistic electrons and thus the resulting synchrotron and inverse Compton spectra. Here we give a brief description of the main results, while a more detailed discussion will be presented in a forthcoming paper (Cassano & Brunetti, in preparation). Einstein-De Sitter cosmology, $H_0=50$ km s$^{-1}$ Mpc$^{-1}$, $q_0=0.5$, is assumed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We investigate the interplay between active nuclei and their surrounding ISM by interferometric radio continuum and mm line observations at high angular resolution and high sensitivity of a sample of active galaxies (e.g. NGC3718), carried out with MERLIN, EVN and the IRAM Plateau de Bure interferometer. They are part of an ongoing international study-NUGA (NUclei of GAlaxies)-about the nature, i.e. basically the fueling mechanisms, of nearby active galaxies. The mm line observations provide information about the distribution and kinematics of the molecular gas in these galaxies, which are regarded to be an important part of the matter feeding the central engine. We find a variety of molecular gas structures in our sample ranging from spirals, bars, warped disks, rings to asymmetric disks. The MERLIN/EVN measurements at 18 cm, as well as 6 cm, allow us to investigate the nature of the central engine itself. Also, the radio observations unveil extended structures on all observed angular scales (from VLA to MERLIN and EVN), like jets, diffuse components, as well as compact features. Moreover, the spectra are flat to steep, depending on the respective source components. The combination of the mm line and radio continuum results allow us to discuss possible interactions between the observed jets and the surrounding interstellar medium.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We have analized XMM-Newton data of A2199, a nearby ($z\,=\,0.030$), relaxed, rich cluster of galaxies, whose X-ray emission is strongly peaked on the central galaxy, NGC6166, suggesting the existence of a cluster cool core (Peres et al. 1998). The background subtraction is performed using an observation characterized by features similar to those of the A2199 observation. We have selected, in the XMM-Newton archive, a field observation presenting the following properites:

[bull] duration of about 90 ksec;

[bull] performed with the same filter as the A2199 observation;

[bull] characterized by a galactic HI column density and a soft X-ray background, the latter being calculated from the ROSAT All-Sky survey diffuse background maps, which differ from those of the A2199 observation ($N_H\,=\,8.7 \times 10^{19}\,\,{\rm cm}^{-2}, R_{45}\,=\,208.2 \times 10^{-6}\,\,{\rm cts/arcmin}^2$) by 3% and 30% respectively.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In this paper we interpret C and X-band radio continuum observations of a sample of Markarian galaxies. The results are briefly discussed. Seyfert 2 galaxies show sistematically higher HI mass-to-blue magnitude than Seyfert 1 galaxies, as well as higher radio to far-infrared luminosities. The observational properties are interpreted in terms of simple non-thermal and dust emission. We obtained radio brightness temperatures, equipartion magnetic fields and total magnetic densities for the disks. Upper limits for thermal densities are derived from simple free-free emission. Star formation rates and mean supernova rates are estimated for individual Markarian galaxies. The SFR values of the most luminous Markarian galaxies are considerably higher than those found in compact blue dwarf galaxies and also in gas-rich, early-type spirals.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present a unique multiwavelength dataset of the Abell 901/902 supercluster at $z=0.16$. The environment of the structure is well characterized by weak lensing analysis, galaxy dynamics, and X-ray imaging, and we examine how galaxy properties correlate with these measures of environment. We examine the star-formation–density relation and find a surface mass density threshold above which star-formation in supercluster galaxies is truncated, and that this transformation affects primarily the faint end of the star-forming galaxy population (down to $M^*+6$). In addition, we present a preliminary dynamical analysis of the spectroscopic sample ($n\sim 300$ galaxies), revealing a bimodal distribution of galaxy velocities and significant substructure.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present Chandra observations of the nuclear region of nearby inactive galaxies. The sample is selected based on the absence or weakness of optical emission lines in the nucleus. X-ray nuclei are detected in four out of six galaxies. This result, along with previous observations, suggests that more than half of galaxies, for which no evidence for nuclear activity is known, possess an ultra-low-luminosity “active” nucleus. X-ray emission from hot gas is detected in at least four galaxies. We estimate the Bondi accretion rate from the gas density, temperature, and central black hole mass and suggest that the accretion luminosity is not simply determined by the Bondi rate.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the initial results of a deep submillimeter survey of ten $z\sim 1$ galaxy clusters with the SCUBA bolometer array on the JCMT. Recently, an excess number of dust enshrouded starbursts in high-redshift galaxy cluster fields was reported (Best 2002) and has been interpreted as increased star-formation within young clusters. An alternative explanation is that these starbursts are background objects behind clusters with enhanced lensing cross-sections, over that predicted from simple lensing models, so-called “super-lenses” seen in recent optical cluster surveys. To investigate this issue, we are studying a set of clusters which show strong optical arcs (super-lenses) and a set of clusters of equal redshift and richness but which are not super-lenses. The preliminary results, based on 50% of the sample, tentatively suggest that, while the dusty starbursts are limited to the super-lensing cluster fields, they are not background objects but lie within the clusters themselves. Cluster-cluster merging offers a means of increasing both the lensing cross-section, thereby accounting for the multiple strong optical arcs, and increasing the star formation within the clusters through galaxy interactions.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Based on our previous work about a co-evolution of massive black holes (MBH) and their host spheroids, we estimate the cosmic star formation history associated with AGN accretion by ROSAT X-ray All sky surveys. We show: 1) the total amount of star formation associated with MBH growth is at least half of the net star formation at high redshift, which probably totally missed by the current UV/optical deep surveys; 2) the FIR emission from the dust heated by star formation on-going during the MBH growth could be a significant energy source for SCUBA populations; 3)the peak redshift of the massive spheroid formation in this case is around 1.5, not necessary to be at much higher redshift.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We investigate the broadband optical emission of diffuse intergalactic stars in galaxy clusters at $z\sim0.25$ by means of an image stacking technique. The images of 654 clusters, selected with the max-BCG algorithm from a subsample of the SDSS-Data Release 1 (DR1), have been stacked after masking all the sources detected down to very low S/N. The resulting images in the g, r and i bands provide reliable photometric data at the level of $\gtrsim30$ mag$/\square$” (r band), out to $\gtrsim 600$ kpc from the Brightest Cluster Galaxy (BCG). Our analysis shows that: i) the IntraCluster Light (ICL) is much more concentrated than the galaxy light, contributing $\sim$30% of the total cluster optical emission at $R=100$ kpc, but less than 10% at $R > 500$ kpc; ii) the ICL contributes between 15 and 20% of the total cluster optical luminosity between the optical radius ($\mu_r=25$ mag$/\square$”) of the BCG and 500 kpc; iii) the colours of the ICL are consistent with the global colours of the cluster galaxies, with little evidence for redder g$-$r.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

It appears that the dynamical status of clusters and groups of galaxies is related to the large-scale structure of the Universe. A few interesting trends have been established:

(1) The Cluster Substructure-Alignment Connection by which clusters show a strong correlation between their tendency to be aligned with their neighbors and their dynamical state (as indicated by the existence of significant substructres).

(2) The Cluster Dynamics-Cluster Clustering Connection by which dynamically young clusters are more clustered than the overall cluster population.

(3) The Cluster-Supercluster Alignment Connection by which clusters of galaxies show a statistical significant tendency to be aligned with the projected major axis orientation of their parent supercluster.

(4) The Galaxy Alignment-Cluster Dynamics Connection by which red-sequence cluster bright galaxies show a significant trend to be aligned with their parent cluster major axis, especially in dynamically young clusters.

(5) The Group Richness-Shape Connection by which groups of galaxies are flatter the poorer they are.

These are strong indications that clusters develop in a hierarchical fashion by anisotropic merging of smaller units along the large-scale filamentary structures within which they are embedded.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the ability of weak lensing surveys to locate massive clusters. We use both analytic models of dark matter halos and mock weak lensing surveys generated from a large cosmological $N$-body simulation. We find that, for a weak lensing survey with a galaxy number density of $n_g=30$ arcmin$^{-2}$ with a mean redshift $z=1$, the mean number of galaxy clusters which are expected to be identified is $N({\rm S/N}>4)=7$ per 1 deg$^2$. Weak lensing surveys thus provide a reasonably efficient way to search for massive clusters. We also describe our project on the weak lensing cluster survey exploiting Suprime-Cam (the wide-field prime focus camera on the 8m Subaru telescope), called Suprime-33 and present current status. We also present results from its pilot survey in the Suprime-Cam 2.1 deg$^2$ field.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

An increasing number of AGNs exhibit broad, double-peaked Balmer emission lines, which arise from the outer regions of the accretion disk which fuels the AGN. The line profiles vary on timescales of 5–10 years. Our group has monitored a set of 20 double-peaked emitters for the past 8 years (longer for some objects). Here we describe a project to characterize the variability patterns of the double-peaked Hα line profiles and compare with those of two simple models: a circular disk with a spiral arm and an elliptical disk.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Ab-initio modeling of galaxy formation is becoming ever more detailed and is including ever more physical processes in a bid to describe the process of galaxy formation more realistically. We will describe some recent advances and applications of the semi-analytic model of galaxy formation, GALFORM. In particular, we will describe a preliminary study of the effects of environment on galaxy morphology in a $z=0.4$ cluster.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present a spectroscopic sample of 48 early-type galaxies in the rich cluster Abell 2218 and 50 galaxies in Abell 2390. Since both samples are very similar, we combine them and investigate a total number of 98 early-type galaxies at $z \sim 0.2$. A subsample of 34 galaxies with HST structural properties is used to construct the Fundamental Plane. Elliptical and S0 galaxies show a zeropoint offset of $\overline{m}_{r}\sim0.43$ mag with respect to the local Coma FP. Both sub-samples, ellipticals and lenticulars, exhibit a similar, mild evolution and small scatter. The moderate amount of luminosity evolution is consistent with stellar population models of passive evolution, if $z_{f}\ge2$ is assumed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

WFPC2 continuum images of the low metallicity Blue Compact Dwarf Galaxy SBS 0335-052 revealed 6 intense point source that were deemed to be super star clusters. Subsequent observations with NICMOS in the infrared continuum and Paschen α reveals that only 2 of the sources have very young stars with the other point sources as clusters that may have ended their episodes of star formation. The optical images show a probable supernova created cavity to the north of the present clusters, while the currently active star forming clusters lie at the southern end of the cluster. This indicates a possible string of induced star formation propagating from the north to the south. The presence of a large number of O stars in a small volume raises the question of whether super star clusters might be the breeding grounds for intermediate mass black holes.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We have investigated the stellar kinematics of two brightest cluster galaxies (BCGs) to large distances from the cluster centre. In both galaxies, the velocity dispersion rises with radius. Orbital anisotropy is ruled out as the cause and we conclude that the kinematics in the outer parts of BCGs are dark matter dominated. This result contrasts with the current problem for intermediate luminosity ellipticals, which appear to have less dark matter than predicted by CDM. Combining the present results with our previous work, the fraction of BCGs with outwardly rising dispersions ($\sim60\%$) is much higher than that found previously ($\sim7\%$) from the inner parts of BCGs. We argue that this phenomenon may be more common than previously thought. The agreement with radial trends expected for a smooth galaxy/cluster transition, and the lack of dependence on cD/BCG dominance and cluster environment, suggest that the outwardly rising dispersion is a genuine response of the stars to the underlying cluster potential. There is evidence that BCG in Abell 2063 is not at the centre of the cluster potential.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We compare the circumnuclear stellar population and environmental properies of Seyfert and Composite (Seyfert + Starburst) nuclei with those of LINERs and LINER/HII transition galaxies (TOs), and discuss evidence for evolution from Seyfert/Composite to LINER/TO nuclei.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We have discovered four intergalactic HII regions in the Stephan's quintet, at more than 25 kpc projected distance from the center of the nearest group galaxy, with no apparent optical connection to it. They have ${\rm M}_B$ ranging from −11.9 to −12.5 mag, colors B$-$R=0.7 to 1.1 mag, radial velocities from 6565 to 6651 km/s and they are superposed onto the HI tail east of NGC 7319, with a mean radial velocity of 6610 km/s. In addition, they have metalicities of the order of 12+log(O/H)=8.58$\pm$0.25, which suggests that they were formed from pre-enriched material. We derive a mean age of $4.6 \pm 0.6$ Myr and a mean stellar mass of $(2.9 \pm 1.4)\times10^4~M_\odot$ for the four objects. The masses, ages, colors, velocities, metalicities and location of the objects suggest that they are HII regions that were formed far away from the galaxies through compression of the intergalactic HI gas by galaxy collisions.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html