We present first results of numerical simulations of the dynamics of all three components of a galaxy cluster: the dark matter, the intracluster gas, and the member galaxies. Our first aim is to understand the enrichment of the gas component by studying various interaction processes between cluster galaxies and the intracluster gas, notably ram-pressure stripping and galactic winds. Our second aim is to find out how fast metals originating from such interaction processes diffuse throughtout the cluster, in order to understand observed metallicity maps of galaxy clusters obtained from X-ray observations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We have modeled the time-variable profiles of the Hα emission line from the non-axisymmetric disk and debris tail created in the tidal disruption of a solar-type star by a $10^{6} M_{\odot}$ black hole. We find that the line profiles at these very early stages of the evolution of the post-disruption debris do not resemble the double peaked profiles expected from a rotating disk since the debris has not yet settled into such a stable structure. The predicted line profiles vary on fairly short time scales (of order hours to days). As a result of the uneven distribution of the debris and the existence of a ‘tidal tail’ (the stream of returning debris), the line profiles depend sensitively on the orientation of the tail relative to the line of sight. Given the illuminating UV/X-ray light curve, we also model the Hα light curve from the debris.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present results of a self-consistent model of the spectral energy distribution (SED) of starburst galaxies. Two parameters control the IR SED, the mean pressure in the ISM and the destruction timescale of molecular clouds. Adding a simplified AGN spectrum provides mixing lines on IRAS color : color diagrams. This reproduces the observed colors of both AGNs and starbursts.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

VLA observations of selected FR-II jets (3C208, 3C352, 3C434, 3C9 and 3C14) between 5 and 15 GHz are used to derive astrophysical properties in the jets of these radio sources. We interpret the results as giving support for unifying schemes of radio galaxies and quasars. We have also determined the Faraday rotation for jets and counter-jet sides. Rotation measures are used to constrain the internal density and mach numbers of the jets, obtaining values similar to those of quasar jets but higher than those of radio galaxies. The radio brightness can be explained by doppler boosting of the synchrotron radiation, giving evidence for orientation effects as an origin for the Laing-Garrington effect.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the first determination of the pairwise velocity dispersion of galaxies at different luminosity with the final release of the Two-Degree Field Galaxy Redshift Survey (2dFGRS). Our result surprisingly shows that the random velocities of the faint galaxies are very high, around $700 {\rm km\,s}^{-1}$, reaching similar values as the brightest galaxies. At intermediate luminosities slightly brighter than the characteristic luminosity $M_*$, the velocities exhibit a well defined steep minimum near $400 {\rm km\,s}^{-1}$. The result challenges the current halo model of galaxies of Yang et al. that was obtained by matching the clustering and luminosity function of 2dFGRS, and can be an important constraint in general on theories of galaxy formation, e.g., the semi-analytical model. Combining the observed luminosity dependence of clustering, our result implies that quite a fraction of faint galaxies are in massive halos of galaxy clusters as the brightest ones, but most of the $M_*$ galaxies are in galactic halos.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Using spectra of normal emission line galaxies from the First Data Release of the Sloan Digital Sky Survey (SDSS) we have investigated the relations between the extinction C(Hβ) as derived from the Hα/Hβ emission line ratio and various global parameters of the galaxies. Our main findings include: C(Hβ) is linked with the galaxy spectral type and colour, decreasing from early- to late-type spirals. It also increases with increasing metallicity and is larger for more luminous galaxies and those with older stellar populations. The extinction of the stellar light is correlated with both the extinction of the nebular light and the intrinsic galaxy colours. The optical properties of the luminous infrared galaxies in our SDSS sample are very similar to those of our entire sample of SDSS galaxies. These results have implications for the determination of global star formation rates and total stellar masses in normal galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Our view of galaxy evolution has been dramatically enhanced by recent deep field surveys at far-infrared and submillimeter wavelengths. Current evidence suggests that the number density of the most luminous far-infrared sources evolves strongly with redshift, and that the luminosity density in the far-infrared/submillimeter may exceed that in the optical/ultraviolet by factors of 3−10 at redshifts z > 1. If true, then as much as 80-90% of the “activity” in galaxies at z > 1 may be hidden by dust. Surveys of complete samples of luminous infrared galaxies in the local Universe show that the majority, if not all objects with log $(L_{\rm ir}/L_\odot) \simgt 11.6$, appear to be major mergers of molecular gas-rich disks accompanied by dust-enshrouded nuclear starbursts and powerful AGN. If the majority of the deep-field sources are simply more distant analogs of local luminous infrared galaxies, then we may be witnessing at z ∼1−3 the primary epoch in the formation of spheroids and massive black holes. This major event in galaxy evolution is largely missed by current deep optical/ultraviolet surveys.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present HST/STIS FUV images of the Lyα and FUV continuum emission of the luminous emission line nebulae in the cooling core cluster A1795. The Lyα and FUV continuum emission consist of a diffuse component (∼60%) and more compact features (knots and filaments) which lie preferentially along the radio source edges. The correlations between the FUV continuum flux and the Lyα emission line flux implies that the nebulae are mainly ionized locally. We suggest that the FUV knots are star clusters with ongoing star formation with rates of several solar masses per year. It appears that star formation occurs through out the nebula, though it is strongly enhanced along the edges of the radio source. The radio source may play a key role in the ionization and morphology of the nebula, e.g., by snow-plowing the gas, shocking and ionizing the gas, triggering star formation, and destroying clouds that it has engulfed. The observed FUV continuum is consistent with about half the number of hot stars which are required to ionize the nebula. We note that we may be missing some of the FUV flux due to obscuration. Thus, we find that young hot stars (e.g., O5) probably provide the bulk of the photons which ionize the nebula, though other sources of ionization may contribute in selected regions of the nebula. We suggest that the mass accretion rates are comparable to the star formation rates (of order 10 M[odot] yr−1). This is consistent with the lack of intermediate temperature gas (<1 keV) being due to energy input to the cooling gas, rather than to “hiding” the cooling gas.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We have carried out aperture synthesis CO(J=1-0) observations of the FRI radio galaxy 3C 31 (NGC 383), using the Nobeyama Millimeter Array (NMA) and the RAINBOW interferometer, which achieves a large collecting area by adding the NRO 45m telescope. Our high-resolution (1.9″×1.4″) CO 3D observations reveal a very massive ($\sim 10^9 M_\odot$), circularly-rotating molecular gas ring, which coincides nicely with the silhouette disk seen in the Hubble Space Telescope (HST) optical images. This is the first map depicting the molecular gas distribution and kinematics associated with a silhouette disk in the heart of a radio galaxy.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We describe MUSYC, a 1 square degree multiwavelength survey that will make unique contributions in several areas and is particularly well suited for the study of high redshift AGN.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

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