We have undertaken an imaging survey of low surface brightness dwarf galaxies in nearby groups with the main goal of studying the faint-end of the galaxy luminosity function at z $\sim 0$. Here we describe the results on the search for LSB dwarf galaxies in two compact groups: HCG44 and HCG68. Our study explores the surface brightness, sizes, magnitudes and colours of these candidate dwarf galaxies. The selection criteria were their central surface brightness, scale factors and diameters at the limiting isophote of 26 R mag$/"^{2}$. We estimate the faint end of the luminosity function of galaxies through Monte Carlo simulations. The observed magnitude distribution of the candidate dwarf galaxies in the groups (down to $M_{R} \sim - 13$) is compatible with a Schechter function with a slope $\alpha \sim -1.2$.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present a multi-wavelength study of a pair of head-tailed radio galaxies in an in-falling filament of the A3125/A3128 cluster complex which is located at the centre of the massive Horologium Reticulum Supercluster (HRS). We compare the large-scale structure evident from extensive optical observations of the region with the dynamical information gleaned from the morphology of the radio jets. We argue that in addition to the acceleration produced by in-fall toward the centre of A3125, the closest galaxy cluster, the radio jets show some evidence of bulk motion along the major filament of the HRS.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

From hydrodynamical simulations for the response of gaseous disks to imposed potentials, including those of a bar and supermassive black hole (SMBH), we found that the morphology of nuclear features developed by gas flows driven by the bar depends strongly on the sound speed of gas and the mass of SMBH which governs the potential shape in the central kiloparsec. Thus, nuclear features seem to provide a promising diagnostic for the inner dynamics of spiral galaxies. Specifically, a tightly wound grand-design nuclear spiral that winds more than 2π indicates the presence of an SMBH which is massive enough to remove the IILR.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We have compared galaxies hosting an active nucleus with non-active galaxies in the SDSS by analyzing their stellar populations. We conclude that the Seyfert 2 phenomenon appears in galaxies of intermediate masses (∼2 × 1010 M$_\odot$), while low mass galaxies do not produce active nuclei, and high mass galaxies tend to produce a low level of non-stellar activity. We also compared the environment of active and non-active galaxies of similar masses and concluded that there is no excess of close neighbors among the Seyferts when compared with non-active galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The kinematics of black hole and neutron star X-ray binaries in the Galaxy should help to know their birth place and constrain their evolution. We have used multiple tools of modern astronomy to determine the trajectories in the Galaxy and track the origins of black hole and neutron star X-ray binaries that are of topical interest in astrophysics. We find three distinct classes of black hole and neutron star X-ray binaries: (1) low mass X-ray binaries that move at high velocities on galactocentric orbits similar to the most ancient stars born in the Galactic bulge and the halo, (2) those that move in the Galactic disk along paths that resemble the circular orbits of massive stars formed in the disk, and (3) high and intermediate mass X-ray binaries running away from their parent regions of star formation. Here we discuss some of the cases studied.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Recent detection of a large optical depth to Thomson scattering by Wilkinson Microwave Anisotropy Probe (WMAP) implicates in new considerations about reionization epoch. Nowadays it is possible to simulate hydrogen reionization for redshift 15 < z < 20, although the greater difficult problem consists to know what are the first ionizing sources in the universe. Observations on Gunn-Peterson effect reconciled with WMAP findings suggests z ∼6 as the redshift for complete reionization. Study on the formation history of supermassive black holes (SMBHs) in galaxies suggests an interplay among QSOs activity and star rate formation. On this aspect, QSOs work as clocks of star formation in spheroids. Observations of magnesium abundance in QSOs for various redshifts show that star formation in these systems began very early.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In an effort to elevate to higher grounds our understanding on the impact of the formation and evolution of bars in the formation and evolution of galaxies, we have developed a diagnostic tool to distinguish between recently formed and evolved bars. Our method was applied in the study of a sample of 14 galaxies and revealed that, apparently, AGN activity tends to appear in galaxies which have young bars rather than evolved bars. This suggests that the time scale for the fueling of AGN by bars is short, and may help to explain, for instance, why there is not a clear correlation between the presence of bars and AGN in galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We analyse statistically the infall of mass onto clusters in $\Lambda$-CDM numerical simulations. Also, we consider numerical simulations which include galaxy formation through semi-analytical models to compare the expected infall of mass and galaxies. We find the most probable values at $V \sim 300-400$ km/s and a significant tail of large infall velocities ($V > 1000$ km/s). The flow onto cluster is more pronounced for high local density regions. Mass and galaxies behave similarly although with a slightly lower amplitude.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The last decade has seen an explosion in the number and scope of wide-field surveys. The data provided by these surveys will greatly increase our understanding of the relationships between the outskirts and the cluster centers and the field. I summarize the status of current deep-wide optical surveys and describe the plans for the next generations of surveys, with particular emphasis on the applications of these surveys to weak gravitational lensing. As a concrete example of such a survey, I will present results from the Deep Lens Survey (DLS).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Gas in galaxy centers may be irradiated by far-ultraviolet, X-ray photons or both. We discuss the observational line diagnostics for PDRs (FUV) and XDRs (X-ray).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We carried out a spectroscopic survey of a sample of 59 Seyfert nuclei (observed both in the northern and in the southern hemisphere) around the stellar absorption lines of Calcium II at 8498.02, 8542.09 and 8662.14 Å (CaT). Our main goal is to determine their stellar velocity dispersions. These measurements, along with photometric information, will allow us to obtain the M/L ratio, useful to determine the nature of the ∼33% of “ambiguous” Seyfert 2.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The properties of stellar populations in the centers of nearby lenticular galaxies are investigated by means of 2D spectroscopy. All the galaxies are divided into 4 groups depending on the environment type; every subsample contains more than 10 galaxies. Clear distinctions between the mean stellar ages and abundance ratios are found both for the nuclei and for the bulges of the S0s in the different environments.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

According to the current paradigm, galaxies form and reside in extended cold dark matter (CDM) halos and in turn are key tracers of cosmological structure. Understanding how different types of galaxies occupy halos of different masses is one of the major challenges facing extragalactic astrophysics. The observed galaxy properties depend on the environment surrounding the galaxy. Within the framework of most galaxy formation models the environmental dependence of the galaxy population is mainly due to the change of the halo mass function with large-scale environment. Such models make precise predictions for how galaxy clustering should depend on environment. We will illustrate this by presenting analytical models of dark matter and galaxy clustering along with results obtained from numerical simulations. With these results we can hope to obtain a better understanding of the link between galaxies and dark matter and thereby constrain galaxy formation models.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A single web link is provided to a maintained site giving detailed descriptions of telescope and instrumentation combinations available – and planned for the near future – at Gemini South, CTIO, SOAR and SMARTS for observers of AGN.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the analysis of Hubble Space Telescope blue spectra at intermediate spectral resolution for the nuclei of 23 nearby disk galaxies. These objects were selected to have nebular emission in their nuclei, and span a range of emission-line classifications as well as Hubble types. Here we focus on the stellar population as revealed by the continuum spectral energy distribution measured within the central 0.″13 (∼8 pc) of these galaxies. The data were modeled with linear combinations of single-age stellar population synthesis models. The large majority (∼80%) of the surveyed nuclei have spectra whose features are consistent with a predominantly old ($\gtrsim 5 \times 10^9$ yr) stellar population. Approximately 25% of these nuclei show evidence of a component with age younger than 1 Gyr, with the incidence of these stars related to the nebular classification. Successful model fits imply an average reddening corresponding to AV∼0.4 mag and stellar metallicity of (1–2.5)$Z_\odot$. Our findings reinforce the picture wherein Seyfert nuclei and the majority of low-ionization nuclear emission-line regions (LINERs) are predominantly accretion-powered, and suggest that much of the central star formation in HII nuclei is actually circumnuclear.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present results from new high angular resolution observations of the neutral hydrogen absorption using global VLBI, MERLIN, and VLA observations of the peculiar radio galaxy 3C 293. These results reveal extensive HI absorption against the inner kiloparsec of the radio jet in this source over a wide range of angular scales. In additional to these sub-arcsecond resolution radio observations we also present infrared imaging of the jet.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

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