Interactions between galaxies are suggested to be a mechanism responsible for feeding Active Galactic Nuclei (AGN). Theoretical models show that interactions are an efficient way to drive gas from the galaxy to the nucleus, however, the observational evidence on this subject is controversial. Here we review results in this field, discuss possible limitations of previous studies and the importance of dealing with selection effects. We also show that there is no significant difference in the percentage of low luminosity AGN and normal galaxies with companions, and discuss possible interpretations of this result.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We predict the metallicity distribution of stars for 6 Dwarf Spheroidal (dSph) galaxies of the Local Group by means of a chemical evolution model which is able to reproduce several observed abundance ratios and the present day total mass and gas content of these galaxies. The model adopts up to date nucleosynthesis and takes into account the role played by supernovae of different types (II, Ia). Each galaxy model is specified by the prescriptions of the star formation rate and by the galactic wind efficiency chosen to reproduce the main features of these galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the results of L-band spectroscopic observations of local bright ULIRGs, performed with ISAAC at VLT. The excellent sensitivity of the telescope and instrument provided spectra of unprecedented quality for this class of objects, which allowed a detailed study of the relative AGN/starburst contribution to the energy output, and of the composition of the circumnuclear absorber. A new mid-infrared diagnostic diagram is proposed, in which starbursts and AGNs are clearly separated.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The XMM–LSS project is detecting distant clusters of low mass, quite comparable in mass to the ones in the local universe. This allows a direct comparison of galaxy properties at different redshifts in “similar” clusters. We present here first results on the evolution of the reddest galaxies in 25 clusters/groups at $0.3\la z \la 1.0$ and for the whole galaxy population in the same clusters. The emerging picture from the current study is that the counterparts of present day clusters tend to show two or more distinct populations: a relatively old ($z_f \gt 2-5$) population evolving passively, together with a younger population, ostensibly responsible for the apparent brightening of the characteristic magnitudes, $m^*$.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

For the past 10 years there has been an active debate over whether fast shocks play an important role in ionizing emission line regions in Seyfert galaxies. To investigate this claim, we have studied the Seyfert 2 galaxy Mkn 78, using HST UV/optical images and spectroscopy. Since Mkn 78 provides the archetypal jet-driven bipolar velocity field, if shocks are important anywhere they should be important in this object. Having mapped the emission line fluxes and velocity field, we first compare the ionization conditions to standard photoionization and shock models. We find coherent variations of ionization consistent with photoionization model sequences which combine optically thick and thin gas, but are inconsistent with either autoionizing shock models or photoionization models of just optically thick gas. Furthermore, we find absolutely no link between the ionization of the gas and its kinematic state, while we do find a simple decline of ionization degree with radius. We feel this object provides the strongest case to date against the importance of shock related ionization in Seyferts.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the results from a new 120 ks XMM-Newton observation of Sérsic 159-03. A previous XMM-Newton observation of this cluster shows the presence of a soft X-ray excess in the outer parts of the cluster, which is possibly connected to the interaction between the cluster and the gas from the surrounding filaments. We exploit the long exposure time to constrain the excess emission and discuss the relation to the warm-hot intergalactic medium. Furthermore, we show a high-resolution RGS spectrum of the core of the cluster and radial profiles from EPIC, which allow us to constrain the internal temperature structure and elemental abundances.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We perform a statistical analysis to study the infall of galaxies onto groups and clusters in the nearby Universe. The study is based on the UZC/SSRS2 group catalogs and galaxy peculiar velocity data. We find a clear signature of infall of galaxies onto groups in a large range of scales 5 Mpc h$^{-1} < r < 30$ Mpc h$^{-1}$. We obtain a significant increase of the infall amplitude with group mass derived from virial equilibrium and from the luminosity of the member galaxies. We compare the observational results with mock catalogs derived from numerical simulations of semi-analytical models where we obtain a behavior similar to observations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We investigate the relation between circular velocity vc and bulge velocity dispersion σ in spiral galaxies, based on literature data and new spectroscopic observations. We find a strong, nearly linear vc−σ correlation with a negligible intrinsic scatter, and a striking agreement with the corresponding relation for elliptical galaxies. The least massive galaxies (σ<80 km s−1) significantly deviate from this relation. We combine this vc−σ correlation with the well-known MBHσ relation to obtain a tight correlation between circular velocity and supermassive black hole mass, and interpret this as observational evidence for a close link between supermassive black holes and the dark matter haloes in which they presumably formed. Apart from being an important ingredient for theoretical models of galaxy formation and evolution, the relation between MBH and circular velocity has the potential to become an important practical tool in estimating supermassive black hole masses in spiral galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present results from a set of high ($512^3$ effective resolution), and ultra-high ($1024^3)$ SPH adiabatic cosmological simulations of cluster formation aimed at studying the internal structure of the intracluster medium (ICM). We discuss the radial structure and scaling relations expected from purely gravitational collapse, and show that the choice of a particular halo model can have important consequences on the interpretation of observational data. The validity of the approximations of hydrostatic equilibrium and a polytropic equation of state are checked against results of our simulations. We also show the first results from an unprecedented large-scale simulation of 500 $h^{-1}$ Mpc and $2\times 512^3$ gas and dark matter particles. This experiment will make possible a detailed study of the large-scale distribution of clusters as a function of their X-ray properties.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The nuclear region of the barred spiral galaxy M83 has been imaged at near-infrared wavelengths with the HST NICMOS, showing a new region of star formation activity.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We analyze quasi-2-dimensional slices of the SDSS EDR. Gaussian smoothing with weighting by the inverse of the selection function provides 2D density fields across the full survey depth. Superclusters (SC) are characterized by a percolation algorithm in the large-scale smoothed field. Group candidates are identified with density maxima in the small-scale smoothed field. The group mass function depends on the SC environmental density. We derive the shape-dependent 3-point correlation function and the void size distribution. These are well reproduced by the galaxies identified in high-resolution $\Lambda$CDM simulations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We announce the construction of an Atlas of STIS-HST Spectra of Seyfert Galaxies, covering the UV and/or optical spectral range. Nuclear spectra of these galaxies have been extracted in windows of width 0.2″ for an optimized sampling (as this is the width of the slit in most cases), from a long-slit spectrum usually covering 52″. Extranuclear spectra have also been extracted, usually using larger windows to improve signal-to-noise ratio. Spectra obtained with different gratings have been combined in order to provide the largest possible wavelength coverage for each galaxy.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We have mapped, for the first time, the full velocity extent of the water maser emission in NGC 3079. Based on the analysis of the spectral-line maps, we propose a nearly edge-on, massive, thick, and flared disk for the geometric model of the inner parsec. The disk orbits a mass of $\sim2\times 10^6 M_{\odot}$ enclosed within 0.4 pc, most likely a supermassive black hole. The disk is most likely self-gravitating, clumpy, and supportive of star formation. The presence in our VLBI continuum images of an aging synchrotron component, which is not collinear with the previously imaged jet, might be suggestive of changes in jet orientation. The jet may coexist on pc-scales with a wide-angle outflow, that is related to the kpc-scale superbubble and that is inferred from the observation of dense molecular material at high latitudes above the disk.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present an overview of the initial data processing of near-IR bi-dimensional spectroscopy of the central region of two nearby (v < 3000 km s−1) Active Galactic Nuclei, obtained using the CIRPASS IFU at Gemini South.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We describe a semi-analytic model for the X-ray emitting gas in clusters and groups in which the gas is preheated before halo formation. The model relies on physically sound prescriptions for the formation and evolution of halo structure. For a gas temperature gradient corresponding to a polytropic index of 1.2 and an energy injection of 0.6 keV per gas particle, this model successfully reproduces the observed correlations between gas luminosity, gas temperature and halo mass. We use the model to investigate the detailed entropy structure of groups and clusters of galaxies and compare the results with the observational data.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Can we determine spin parameters of black holes by observations of black hole shadows in accretion disks? In order to answer this question, we have investigated shapes and positions of black hole shadows in optically thick accretion disks around Kerr black holes. In conclusion, in order to measure black hole spin parameters from shapes and positions of black hole shadows, it is crucially important to determine a position of a mass centers of a black hole in a region of a black hole shadow.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

This work reports our recent results of an HI line and radio continuum imaging survey of selected southern Active galaxies made with the Very Large Array and the Australian Telescope Compact Array. Radio images are presented and rotation curves for individual galaxies were obtained. The HI total mass content in Seyfert galaxies is larger than those seen in starburst galaxies. Our trends confirm that the infrared luminosity correlates well with the total neutral gas content, which supports the scenario that star formation in the bulges of Seyfert galaxies is considerably higher than in regular late-type galaxies or spirals. We also find a trend between various observational quantities which are also discussed in this work.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The observed properties of supermassive black holes suggest a fundamental link between their assembly and the formation of their host spheroids. We model the growth and activity of black holes in galaxies using ΛCDM cosmological hydrodynamic simulations. We study the evolution of the metal enrichment in quasar hosts and hence explore the relationship between star/spheroid formation and black hole growth/activity in galaxies. Using the simulations we approach the epoch of the first quasars and the first significant star formation activity. We show that the hosts of the rare bright quasars at z∼5−6 have star formation rates of several hundred $\rm\thinspace M_{\odot}\yr^{-1},$ and halo masses of order ∼1012 $\rm\thinspace M_{\odot}$. Already at these redshifts they have supersolar ($Z/Z_{\odot} \sim 2-3$) central metallicities, with a mild dependence of metallicity on luminosity, consistent with observed trends.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In order to analyse the large numbers of Seyfert galaxy spectra available at present, we are testing new techniques to derive their physical parameters fastly and accurately.

We present an experiment on such a new technique to segregate old and young stellar populations in galactic spectra using machine learning methods. We used an ensemble of classifiers, each classifier in the ensemble specializes in young or old populations and was trained with locally weighted regression and tested using ten-fold cross-validation. Since the relevant information concentrates in certain regions of the spectra we used the method of sequential floating backward selection offline for feature selection.

Very interestingly, the application to Seyfert galaxies proved that this technique is very insensitive to the dilution by the Active Galactic Nucleus (AGN) continuum. Comparing with exhaustive search we concluded that both methods are similar in terms of accuracy but the machine learning method is faster by about two orders of magnitude.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

I briefly report on the work conducted to probe the gravitational potential of active and non-active disk galaxies using gas and stellar kinematics.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html