We present the results of a new stellar population synthesis code which mixes both evolutionary and empirical population synthesis techniques. The code decomposes a given galaxy spectrum into a base of high resolution spectra from the recent evolutionary synthesis models of Bruzual & Charlot (2003). The main novelty is that now we synthesize the whole Fλ spectrum, rather than a handful of absorption lines and colors.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We have imaged $\sim 1$ deg$^{2}$ in the V-band in the direction of the Hercules cluster (Abell 2151). The data are used to compute, for the first time, the luminosity function (LF) of galaxies in the cluster down to the dwarf regime (M$_{lim}$ $\sim -13.85$ ). The global LF is well described by a Schechter function (Schechter 1976) with best-fit parameters $\alpha = -1.30 \pm 0.06$ and M$_V^* = -21.25 \pm 0.25$. The radial dependence of the LF has also been studied, finding that it turns out to be almost constant within the errors even further away than the virial radius. Given the presence of significant substructure within the cluster, we have analized the LFs in different regions. While the LFs of the two subclusters present are consistent with each other and with the global one, the southernmost one exhibits a somewhat steeper faint-end slope.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the first homogeneous sample of intermediate-mass black hole candidates in active galactic nuclei. Starting with broad-line active nuclei from the Sloan Digital Sky Survey, we use the linewidth-luminosity-mass scaling relation to select a sample of 19 galaxies in the mass range $M_{\mathrm{BH}} \approx 8 \times 10^4 - 10^6\,\ensuremath{M_{\odot}}$. In contrast to the local active galaxy population, the host galaxies are ∼1 mag fainter than M* and thus are probably late-type systems. The active nuclei are also faint, with $M_g \approx -15$ to −18 mag, while the bolometric luminosities are close to the Eddington limit. The spectral properties of the sample are compared to the related class of objects known as narrow-line Seyfert 1 galaxies. We discuss the importance of our sample as observational analogues of primordial black holes, contributors to the integrated signal for future gravitational wave experiments, and as a valuable tool in the calibration of the MBM–σ∗ relation.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the preliminary results of BVRI imaging of six clusters chosen from a follow-up project of the CNOC cluster survey. In an attempt to ascertain the evolution of galaxies in the cluster environment, we focus on the infalling galaxy groups, especially on their characteristics reflected by their color properties. To investigate the role of cluster environment in the evolution of galaxy groups, the color properties of galaxy groups are explored as a function of cluster radius and the local density of cluster galaxies. Both the radius and the local density affect the properties of groups, but evidence suggests that density may be more important in the relationship between cluster environment and galaxy characteristics.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We investigate whether the spectral-type of a locally dominant (most luminous) galaxy can be used to select sets of galaxies that are physically associated (groups). We assume that passive dominants trace a group-like potential, and SF-dominants a field-like environment. The group sample includes 988 groups selected in the 2dFGRS applying a maximum magnitude difference criterion. We find that the average number of passive galaxies associated to a dominant is larger when the dominant is passive, a result supporting our assumption that galaxy associations around a passive dominant are reliable groups. Finally we show that, to reduce the contamination by unbound galaxy associations (SF-dominant), ${\rm a}\geq 3$ passive-members criterion is more efficient than ${\rm a}\geq 6$ all-members criterion.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the results of a spectrophotometric study of star forming regions in HII galaxies. In particular, we find that, besides their “blobbiness”, HII galaxies are quite homogenous in their chemical properties, though we do see important fluctuations in some physical properties (e.g. extinction).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present an X-ray binary population synthesis model, and use it to simulate the evolution of X-ray binaries formed in a burst of star formation of duration 20 Myr and star-formation rate 10 M$_{\odot}$ yr−1. We find that the X-ray luminous phase persists long after the star-formation episode has ended. The 2-10 keV X-ray luminosity can reach values of 1040−1041 erg s−1, comparable to those of some Seyfert galaxies. These models are directly applicable to starburst galaxies as well as LINERs powered by vigorous star formation.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Seyfert narrow line regions (NLR) have emission line ratios which are remarkably uniform, displaying only ∼0.5 dex variation between different galaxies. Existing models have been unable to explain these observations without the introduction of ad hoc assumptions, geometrical restrictions or new parameters. Here we introduce a new model: dusty radiation pressure dominated photoionization, which provides a natural self-regulating characteristic, leading to an invariance of the spectrum over a very wide range (>100) of ionization parameter. The dusty model is able to reproduce both the range and the absolute value of the observational line ratios not only in the standard optical diagnostic diagrams but also in UV diagnostic plots, providing an explanation to the problem in NLR observations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In this paper we present results of a detailed morphological and radio polarization study of the nearby radio galaxy 3C33.1 (4C72.01, 0106+729, z = 0.18) made with the Very Large Array at 18 and 21 cm. Recently, this galaxy has been re-classified within a sample of large core-dominated radio sources and it has an exceedingly high projected linear size of ∼450 kpc. The jet shows little Faraday rotation, with rotation measures |RM|<20 rad m−2, whereas the hotspots exhibit higher values. The low rotation measures indicate that this radio source has a visible jet, which can be a naked jet or stripped from a dense environment. A spectral ageing analysis, based on syncrotron power losses arguments of the integrated spectra, suggest that the radio structure is not younger than 20 Myrs. Further observational properties of this radio galaxy are also discussed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Secular evolution and fueling is driven by bars in spiral galaxies, and the related dynamical processes are reviewed. It is shown that gravity torques dominate over viscous torques, and produce gas infall to the center. In this infall, the bar wave accepts the angular momentum, which produces its destruction. In the end, a central mass concentration is built, which also contributes to this destruction. While gas can be stalled at ILR for a while, secondary bars then take over the fueling. In a galaxy life-time, several bar episodes can successively develop. Through external gas accretion, disks are replenished by intermittence, between two bar phases. While the general trend for a galaxy is to evolve towards early-types, its morphology can oscillate, and turn back transiently to later-types.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present a semi-analytic model able to trace the thermalisation history of the ISM in a Starburst region and determine the SN heating efficiency evolution.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We have analyzed the position angle (PA) differences between radio jets and dust distributions in the centers of Fanaroff & Riley Type 1 (FRI) radio galaxies. We model the observed PA differences to infer the three-dimensional relative orientation of jet and dust. Our main conclusion is that there is a dichotomy in dust-jet-galaxy orientation both in projection and in three-dimensional space. The orientation dichotomy can explain the contradictory results obtained in previous studies. We briefly mention scenarios that might explain the dichotomy.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Near-infrared and optical imaging of BL Lac host galaxies is used to investigate their colour properties. We find that the R–H colour and colour gradient distributions of the BL Lac hosts are much wider than those for normal ellipticals, and many objects have very blue hosts and/or steep colour gradients. The blue colours are most likely caused by recent star formation. The lack of obvious signs of interaction may, however, require a significant time delay between the interaction event with associated star formation episodes and the onset of the nuclear activity.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In this paper I address three topics. The first regards the use of composite spectra as a tool to study the spectral evolution of galaxies in intermediate-redshift clusters. This technique is used to demonstrate the robustness of measurements of strong H$\delta$ absorption, indicative of mild-to-moderate starbursts, in a significant fraction of galaxies in these clusters. Second, I present some spectroscopic data on Abell 851 ($z=0.41$) that suggests that the starbursts in this cluster have been triggered by tidal encounters in infalling groups in the cluster. Third, I briefly describe the IMACS imaging-spectrograph, which has been built for the Magellan-Baade telescope, and, following the idea that the outskirts of clusters are “where the action is,” describe a large spectroscopic program to study “cluster building” using IMACS.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We estimate the gas mass fractions for a sample of 39 high-$z$ galaxy clusters using a combination of three different data sets: Chandra X-ray data, OVRO/BIMA centimeter-wave Sunyaev-Zel'dovich Effect (SZE) data, and published weak gravitational lensing data. The gas mass fraction $f_g$ is calculated in three different ways. The X-ray surface brightness and SZE decrement are used independently to determine the number of baryons in the intracluster gas and subsequently the gas mass; the total mass follows assuming spherical symmetry and hydrostatic equilibrium (HSE). The third, less model-dependent approach is to calculate the projected SZE gas mass along a cylinder and divide by the total mass derived from the lensing data. The goal of this study is to compare the $f_g$ results from the three different methods to investigate systematic uncertainties associated with clumping of the intracluster medium, cluster elongation, and the HSE assumption.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A solid observational characterization of cluster regions around the virial radius would allow us to improve considerably our understanding of the physics of galaxy clusters as a whole: sadly current and planned experiments will not allow us to study these regions. Unbeknownst to most but not all, the development of an experiment sensitive to cluster outer regions could be achieved with currently available technology, with no need for breakthroughs. Amongst the major factors that will decide whether and when such an experiment will be flown are the awareness of the cluster community of the importance of such a mission and its determination at supporting it.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We show that Massive Black Holes of AGNs follow the same approximately linear relation with the luminosity of the host spheroid (bulge) found in normal (quiescent) galaxies, with the black hole mass being 0.002 that of the bulge. We also demonstrate that Narrow line AGNs seem to have a significantly lower Mbh/Lbulge ratio, which implies a new strong correlation between Mbh/Lbulge and the width of the broad emission lines of AGNs (Wandel 2002). Combining existing data, new observations and extrapolation schemes based on the Faber-Jackson relation, the relation between the BH mass and the stellar velocity dispersion in the host bulge of AGNs is constructed. It too agrees with the relation found in quiescent galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

By means of 2D spectroscopy we have found a lot of compact inner stellar and gaseous disks in morphologically normal galaxies. The evolution and spatial orientation of these inner structures are often decoupled from the evolution and spatial orientation of the large-scale galactic disks and bulges. We argue that this finding requires substantial change of common approaches to investigations of the central parts of galaxies, including central black hole studies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We report the results of combined Chandra, HST/STIS, and FUSE observations of the intrinsic absorption in the Seyfert 1 galaxy NGC 4151. Our previous studies revealed an unusually large column of outflowing gas, very close to the nucleus, which responds rapidly to changes in the ionizing continuum due to its high density. With the latest observations, we have discovered evidence that the large absorbing column consists of individual high and low ionization components, and that the column density of the latter has decreased due to bulk motion across our line-of-sight. The Chandra spectra have revealed the signature of both very high ionization lines such as H-like and He-like Si, and inner-shell lines from low ionization species which may be associated with the UV absorbers. With the FUSE observations, we have detected lines from less abundant elements, which have permitted us to constrain the physical conditions and covering factors of the UV absorbers. These results indicate a complex and heterogeneous absorbing system, the extreme properties of which are likely the result of a relatively large viewing angle with respect to the accretion-disk axis.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Using N-body numerical simulations, we investigate the stability of a nuclear disk of a few pc characteristic radius, around a supermassive black hole (SBH), and embedded in a galactic bulge. We find that with an SBH of a suitable range of mass, placed at its center, the nuclear disk is subject to one-armed (m=1) natural instabilities. We propose a feedback cycle for this mode, based on waves between corotation and OLR, and where the “indirect term”, and the massive bulge play a fundamental role. Nuclear disks formed from accreted gas could be the precursors of this type of structure and may be common in central regions of galaxies. Density waves could be an efficient mechanism of fueling the gas in the central few tens of parsecs in galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html