We report on some of the recent work that has come from our Hubble Space Telescope programme to find massive black holes in nearby spiral galaxies. Determining black hole masses from gas kinematics in spiral galaxies is difficult, but results have been reported for NGC 4041 and new results are soon to be reported for NGC 1300 and NGC 2748. Complementary programmes are also looking for the presence of nuclear star clusters in our Space Telescope Imaging Spectrograph (STIS) and archival Near-infrared Camera and Multi-Object Spectrometer (NICMOS) images. We are also currently analysing United Kingdom Infrared Telescope (UKIRT) Fast Track Imager (UFTI) near-infrared images to determine the surface brightness profiles for 37 of the galaxies in the sample.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the preliminary results of 235 MHz, 327 MHz and 610 MHz observations of the galaxy cluster A3562 in the core of the Shapley Concentration (SC). The purpose of these observations, carried out with the Giant Metrewave Radio Telescope (GMRT, Pune, India) was to study the radio halo located at the centre of A3562 and determine the shape of its radio spectrum at low frequencies, in order to understand the origin of this source. In the framework of the re–acceleration model, the preliminary analysis of the halo spectrum suggests that we are observing a young source (few $10^8$ yrs) at the beginning of the re–acceleration phase.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In this paper, we revisit the constraints obtained by several authors (Reichart et al. 1999; Eke et al. 1998; Henry 2000) on the estimated values of $\Omega_{\rm m}$, $n$ and $\sigma_8$ in the light of recent theoretical developments: 1) new theoretical mass functions (Sheth & Tormen 1999, Sheth, Mo & Tormen 2001, Del Popolo 2002b); 2) a more accurate mass-temperature relation, also determined for arbitrary $\Omega_{\rm m}$ and $\Omega_{\rm \Lambda}$ (Del Popolo 2002a).

Firstly, using the quoted improvements, we re-derive an expression for the X-ray Luminosity Function (XLF), similarly to Reichart et al. (1999), and then we get some constraints to $\Omega_{\rm m}$ and $n$, by using the ROSAT BCS and EMSS samples and maximum-likelihood analysis. Then we re-derive the X-ray Temperature Function (XTF), similarly to Henry (2000), re-obtaining the constraints on $\Omega_{\rm m}$, $n$, $\sigma_8$. Both in the case of the XLF and XTF, the changes in the mass function and M-T relation produces an increase in $\Omega_{\rm m}$ of $\simeq 20\%$ and similar results in $\sigma_8$ and $n$.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We discuss the results so far of a program to image in the rest-frame optical and near-UV the host galaxies of a sample of 5 high redshift (z∼2−3) radio-quiet quasars with nuclear luminosities lower than most samples studied at high z. We found that in the rest-frame optical the hosts have luminosities of about L∗, comparable to the Lyman break galaxies at similar redshifts. From the rest-frame UV imaging, we can derive optical–UV colors, and find they show a great deal of variation, but may be somewhat redder and less starforming than the LBGs. We are supplementing this work at high z with study of the hosts of z∼1 radio-quiet quasars with similar low nuclear luminosities.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In this contribution we investigate the connection between clusters of galaxies and their large-scale environment, with an emphasis on clusters which are well characterized by their X-ray emission. We show that this connection is so tight that clusters can be used as perfect tracers of the large-scale matter distribution and thus for cosmological tests. The correlation of the X-ray traced cluster mass and the optical luminosity of the galaxy content of clusters shows that the dark matter and galaxy distribution are tightly connected, but we also observe a scatter which is so far not well understood. We further explore the correlation of the galaxy population mix with the geometry of the large-scale structure features. On larger scales we also find correlations of the properties of galaxy clusters with the density of their large-scale structure environment.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Magnetic fields are crucial to the generation of turbulence and the dynamics of accretion and energy dissipation in accretion disks. Nevertheless, until now, there has been no self-consistent analytic formalism that puts the evolution of turbulent magnetic fields on the same footing as other dynamical processes such as mass flow and energy generation. We have developed a self-consistent framework for turbulent, magnetized accretion disks with the aim of studying the processes that power hot coronae. Utilizing this framework we have identified the possible magnetic sources of power for the coronae of black hole accretion disks. The most promising is the Poynting flux associated with the azimuthal-vertical magnetic stress. We also determine how the emission from the disk is modified by the processes that power the corona and related winds.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We characterize the stellar population of a complete sample of the closest southern radio-galaxies – 12 Fanaroff-Riley I (FR I), 8 FR II and 4 with undefined FRx type – and a comparison sample of 18 non-active elliptical and SO galaxies. We measured equivalent widths and continuum colours and their radial variations, and performed spectral synthesis as a function of distance from the nucleus. Only 4 of the radio-galaxies have more than 10% of the total flux at 4020Å contributed from 100 Myr old or younger stellar population components – including a featureless continuum due to an AGN. All 4 are FRII or FRx. The main difference between the stellar population of the radio-galaxies and that of the non-active ones is that the former have a larger contribution of the intermediate age component, suggesting a relation between the present radio activity and a past episode of star formation which occurred about 1 Gyr ago.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We derive here the mean temperature profile for a sample of hot, medium distant clusters recently observed with XMM-Newton, whose profiles are available from the literature, and compare it with the mean temperature profile found from BeppoSAX data. The XMM-Newton and BeppoSAX profiles are in good agreement between 0.05 and 0.25 $r_{180}$. From 0.25 to about 0.5 $r_{180}$ both profiles decline; however the BeppoSAX profile does so much more rapidly than the XMM-Newton profile.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Central regions of superclusters are the ideal places where to study cluster merging phenomena: in fact the accretion activity is enhanced, as predicted by the cosmological simulations. In this paper I review the case-study of the Shapley Concentration, aimed to understand the effect of major mergings on the intracluster medium and the galaxy population of the involved clusters.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present first results for spectroscopic observations of galaxies in 4 clusters at $z=0.7-0.8$ and one cluster at $z=0.5$ observed by the ESO Distant Cluster Survey (EDisCS). Our spectroscopic catalogues contain 236 cluster members of our 5 clusters, and the number of members per cluster ranges from 30 to 67. Our cluster velocity dispersions are between $\sim$400 and over 1000 $\rm{km s}^{-1}$. Galaxy redshift distributions are found to be non-Gaussian and we find evidence for significant substructure in two clusters, one at $z \sim 0.79$ and another at $z \sim 0.54$; both clusters have velocity dispersions exceeding 1000 $\rm{km~s}^{-1}$. These systems have clearly not yet virialised at these epochs in qualitative agreement with CDM scenarios and their cluster velocity dispersions should not be used in the measurement of cluster mass. Our clusters have a wide range of different cluster velocity dispersions, richnesses and substructuring, and our spectroscopic data set is allowing a comprehensive insight into cluster galaxy evolution as a function of redshift and environment.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Using extensive ground-based spectroscopy, we isolate the E+A population in three intermediate redshift clusters ($z=0.33$, 0.58 and 0.83) and study their physical properties using HST/WFPC2 imaging. Our analysis includes galaxy colors, luminosities, Hubble types, and quantitative structural parameters as well as measured and estimated internal velocity dispersions. We find E+A galaxies make up a non-negligible fraction ($\sim7-13\%$) of cluster members at these redshifts, and their diverse nature indicates a heterogeneous parent population. From their velocity dispersions and half-light radii, we infer that the descendants of the E+A's in our highest redshift clusters are massive early-type galaxies, and we estimate that $\gtrsim30\%$ of the E-S0 members have undergone an E+A phase. We also find the characteristic E+A mass decreases with decreasing redshift; this is similar to the decrease in luminosity of rapidly star-forming field galaxies since $z\sim1$, i.e. galaxy “down-sizing”.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present preliminary results from a wide-field spectroscopic survey of two galaxy clusters at $z=0.4$, separated by $\lt$10 $h^{-1}$ Mpc on the sky. Both clusters are similarly optically rich, have velocity dispersions $\sim 700$ km s$^{-1}$, but differ in X-ray luminosity by a factor of $\sim$20.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present results from dynamical Monte Carlo simulations of dense star clusters near the Galactic center (GC). While these clusters spiral in toward the GC by dynamical friction, they could undergo core collapse and form an intermediate mass black hole (IMBH) by runaway collisions. Clusters can reach within a parsec of the GC where, following tidal disruption, they would inject many young stars still bound to the IMBH into the GC region. This scenario (Gerhard 2001; Hansen & Milosavljević 2003) provides a possible explanation for the youth paradox raised by recent IR observations (Ghez et al. 2003).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

AGN activity is known to drive fast outflows of gas. We report the discovery of fast outflows of neutral gas with velocities over 1000 km/s in a number of radio galaxies. In the best studied object, 3C 293, the kinematical properties of the neutral and ionised outflows are similar, indicating a common origin. Moreover, the outflow appears to be located near the radio lobes and not near the nucleus. This suggests that the interaction between the radio jet and the ISM is driving the outflow.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

By fitting to the quiescent galaxy MBH−σ∗ relation, we calculate the average shift required to scale reverberation-mapped AGN masses to the same zero-point. We use reanalyzed virial products (rV2/G) and both new and published velocity dispersions to find the offset in the AGN calibration. This scaling factor, 〈f〉, accounts for the detailed dynamics and geometry of the broad-line region (BLR). Finally, we confirm the rough correlation between σ∗ and FWHM([O III]) for these 16 AGNs.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We explore the region of influence of a galaxy cluster using numerical simulations of cold dark matter halos. Many of the observed galaxies in a cluster are expected to be infalling for the first time. Half of the halos at distances of one to two virial radii today have previously orbited through the cluster, most of them have even passed through the dense inner regions of the cluster. Some halos at distances of up to three times the virial radius have also passed through the cluster core. We do not find a significant “infall age” versus present day position for substructures and the scatter at a given position is very large. This relation may be much more significant if we could resolve the physically overmerged galaxies in the central region.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Atomic gas in the central kiloparsec of young radio galaxies is quite prevalent, as revealed by 21cm H I absorption line observations using the WSRT. The column depths are anti-correlated with the linear sizes of the radio sources, but VLBI reveals that sometimes the neutral hydrogen is situated in a disk or torus on parsec or sub-kiloparsec scales around the central engine, while in other cases the H I is probably associated with star-forming regions along the jets. NGC 1052 is a nearby example, in which, next to some isolated clouds along the jets, there appears to be an atomic and molecular torus with a radius of a few parsecs, but with a central hole of about 0.5 pc, in which the gas is mostly ionised.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

First results from the AGN-Heidelberg program aimed at spatially resolving the central pc region of the closest Active Galactic Nuclei are presented. The core region of prototype active nuclei are clearly unveiled at IR waves and at distances from the nucleus – few pc- where circumnuclear starforming regions appear not to be present. Within that perspective, classical active nuclei as Circinus and NGC 1097, reveal with unprecedented detail clear channels of material being driven to the core whereas others as Centaurus A and NGC 5506, show a “clean” core environment. At the very center, a central compact region of ∼2 pc scale is resolved in Circinus but not in the other cases challenging thus the universal presence of the putative obscuring torus.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Analysing mid–infrared ISOCAM images of the cluster of galaxies J1888.16CL, we identified among its members several particularly active galaxies with total infrared luminosities well above $10^{11}~\Lo$. If powered by dust enshrouded starbursts, as suggested by their optical spectra, these Luminous Infrared Galaxies would exhibit star formation rates surprisingly high in the cluster environment. The triggering mechanism is unclear but could be tidal collisions within sub-structures or infalling groups.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In this paper we report on our recent results connected with the direct environment of the super massive black hole of the Milky Way. The data are obtained using the VLT facilities (ISAAC and NAOS/CONICA instruments) in the near- and mid-infrared wavelength ranges. We provide a calibration of the foreground and local differential (in wavelength and spatially) extinction of the Galactic Center and report on the discovery of a new complex of infrared excess sources (possibly young stars) located at the northern part of the IRS 13 cluster. Finally, we discuss the origin of filamentary structures observed in the L-band images.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html