Photometric properties (effective surface brightness, effective radius, radial profile index, axis ratio, color, color gradient) of 328 galaxies in the Coma cluster fainter than $R=15$ mag are examined as a function of the distance from the cluster center. No significant gradient is found for the effective surface brightness, effective radius and radial profile index. The distribution of axis ratios shows a concentration of round galaxies at the cluster center in the magnitude range $16.5 \lt R \lt 18$; most of these are found to be old and to have intermediate metal abundance, suggesting that they are nucleated dwarf ellipticals. On the other hand, we find a significant gradient in color, in the sense that galaxy colours become bluer with increasing distance from the cluster center. We conclude that this color gradient represents a metallicity gradient.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The H I deficiency pattern of the spiral population in the Virgo cluster region reveals a significant number of galaxies at very large clustercentric distances with gaseous deficiencies comparable to those measured in the cluster centers. We have used the output of cosmological $N$-body simulations to investigate whether the gas-deficient galaxies on the outskirts of the Virgo cluster may have previously passed through its core. We find that the maximum radius reached by infalling galaxies as they bounce out of a Virgo-like cluster must be less than 2.5 virial radii, which results in a predicted velocity-distance diagram noticeably different from the one drawn by the data. The latter is fairly well reproduced, however, after including in the simulations distance errors at the 20% relative rms level. Yet, for several objects apparently over 5 Mpc in front or behind the Virgo center the assumption that they are instead close enough to the cluster to have passed already through its core strains the bounds of plausibility. Hence, unless these outlying H I-deficient Virgo's spirals have grossly incorrect distances, they cannot have lost their gas by interactions with the intracluster medium. This suggests that the evolution of spirals might begin already on the suburbs of clusters.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The warm-hot intergalactic medium contains a major part of all baryons in the universe. Despite this, it is very hard to observe in X-rays due to its relatively low temperature and the poor spectral resolution of most instruments. The high sensitivity and good spectral resolution of XMM-Newton allowed for the first time to show the presence of the warm-hot intergalactic medium in the outskirts of several nearby clusters of galaxies. In this contribution these results are presented. The physical state of the gas such as temperature, density, mass and chemical composition are discussed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The cluster soft excess emission indicates the presence of large amounts of warm gas ($T\sim10^6$ K) in the neighborhood of galaxy clusters. Among the clusters that display this phenomenon is the Coma cluster, the nearest rich galaxy cluster. The excess emission is more prominent at the cluster's outskirts than at its center. Detailed studies of its large-scale emission–up to $\sim 2.6$ Mpc from the cluster's center–reveal that these warm baryons are as massive as, or possibly more massive than, the well-known hot intra-cluster medium ($T\sim10^8$ K). A possible interpretation of the excess emission from the Coma cluster is radiation from low-density filaments located in the neighborhood of the cluster. In this case, the filaments would extend for much larger distances, or feature higher density, than predicted by current cosmological simulations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present near-infrared imaging of the host galaxies of 17 quasars at 1 < z < 2, obtained with ISAAC at the ESO VLT UT1 under excellent seeing (∼0.4 arcsec). The radio-loud (RLQ) and radio-quiet (RQQ) quasars in the sample have similar distribution of redshift and optical luminosity. Both RLQ and RQQ hosts follow the cosmic evolution of massive inactive ellipticals undergoing passive evolution. This indicates that nuclear activity can occur in all luminous ellipticals without producing a significant change in their global properties and evolution. However, there is a systematic difference by a factor ∼2 in the host luminosity between RLQs and RQQs, which remains the same from z = 2 to z = 0. Quasar hosts are already well formed at z ∼2, in disagreement with hierarchical models of AGN and galaxy formation and evolution models. No correlation is found between the nuclear and the host luminosities. If the host luminosity is proportional to the black hole mass, as in nearby massive spheroids, both types of quasars emit at very different levels with respect to their Eddington luminosity.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We have analyzed the frequency and properties of the nuclear activity in two samples of galaxies, with and without circumnuclear rings and spirals (CNRs). We discuss the relevance of the results in the framework of the AGN feeding processes and some results are: (i) bright companion galaxies seem not to be important for the appearance of CNRs, therefore these would be more related to intrinsic properties of the host galaxies or to minor merger processes; (ii) the proportion of strong bars in AGN galaxies with a CNR is higher than the expected rate of strongly barred AGN galaxies from the sample of Ho and co-workers; (iii) the incidence of Seyfert activity coeval with CNRs is clearly larger than the expected rate from the morphological distribution of the host galaxies; (iv) the rate of Sy 2 to Sy 1 in galaxies with CNRs is larger than the expected proportion for galaxies without CNRs; this proportion would be in the opposite sense as expected from the geometric paradigm of the classical unified model for AGNs, but supports a scenario where Sy 2 activity is linked to circumnuclear star formation.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We investigate the environmental dependence of galaxy properties in the local universe based on the data of the Sloan Digital Sky Survey. We focus on how star formation and morphology of galaxies correlate with luminosity, local environment, and global environment. We find that galaxy properties abruptly change at a critical local density of $\log \Sigma_{\rm crit}\sim 0.4\ {\rm galaxies}\ h_{75}^{2}\ \rm Mpc^{-2}$. The ‘break’ at the critical density is found only for faint galaxies ($M^*_r+1 < M_r < M^*_r+2$). Bright galaxies ($M_r < M^*_r+1$) show no break. That is, the star formation-density and the morphology-density relations depend on galaxy luminosity. Next, we focus on global environment, i.e., richness of galaxy groups and clusters. Most galaxies are not forming stars in groups as poor as $\sigma\sim200\rm\ km\ s^{-1}$. This fact suggests that environmental mechanisms that are effective only in rich clusters, such as ram-pressure stripping of cold gas and harassment, have not played a major role in suppressing galaxy star formation. Our results may suggest that evolution of bright galaxies is not strongly related to galaxy systems such as groups and clusters. On the other hand, evolution of faint galaxies may have a close connection.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We investigate environmental effects on evolution of bright cluster galaxies in a $\Lambda$-dominated cold dark matter universe using a combination of dissipationless $N$-body simulations and a semi-analytic galaxy formation model. We incorporate effects of ram-pressure stripping (RPS) and minor merger-induced small starburst (minor burst) into our model. By considering minor burst, the observed morphology-radius relation is successfully reproduced. When we do not consider minor burst, the RPS hardly increases the intermediate B/T population. In addition, the RPS and minor burst are not important for colours or star formation rates of galaxies in the cluster core if star formation time-scale is properly chosen, because the star formation is sufficiently suppressed by consumption of the cold gas. We also find that SF in bulge-dominated galaxies is mainly terminated by starburst induced by major mergers in all environments.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We discuss how the energy feedback from active galactic nuclei and quasars is essential in explaining the observed X-ray luminosities and entropy levels of the intracluster and intragroup medium.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We analyzed 13 narrow-line Seyfert 1 galaxies (NLS1s) observed with XMM-Newton. Their X-ray continua are well parameterized by a combination of a hard power law and thermal emission from a standard Shakura-Sunyaev accretion disk. However, the observed disk temperatures are significantly higher than the prediction from the standard disk, and the temperatures are distributed within an extremely narrow range (0.15–0.22 keV) in spite of the wide range of luminosities (LX = 1041–45 erg s−1). Furthermore, we found an anti-correlation between the disk temperature and luminosity of PKS 0558–504. These results strongly indicate the breakdown of the standard accretion picture in NLS1s. We suggest that a slim disk, which is a stable disk solution under a high mass-accretion rate, could be able to explain the observational results, if the photon trapping effect is properly taken into account.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A systematic study of 30 Radio Loud AGNs available in the BeppoSAX archive has been carried out. The sample consists of 9 Broad Line radio Galaxies, 5 Steep Spectrum Radio Quasars and 16 Flat Spectrum Radio Quasars. These objects represent, according to Unified Models, objects with decreasing viewing angles. Our analysis shows considerable differences between FSRQs and BLRGs'SSRQS. As expected in the AGN Unified Model: i) the X-Ray spectrum of FSRQs is a simple power law with a hard spectral slope (the only exception being 3C273), ii) Broad Line and Steep Radio Spectrum AGNs show a steeper X-Ray continuum and Seyfert like features. We also find that the Fe line is weaker than in radio quiet objects. However no strong evidence emerges that a jet contamination may be the main responsible for the EW shrinking in BLRGs and SSRQs. Recent XMM-Newton observations of Pictor A, 3C445 and PKS 2152-69 confirm the nuclear BeppoSAX results and better constrain the Fe line parameters.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

New infrared spectroscopy of 22 high-luminosity high-redshift AGNs helps to test several suggestions regarding the mass, composition and size of the emission line regions in active galacic nuclei (AGN). A plot of the metalicity luminosity correlation over more than five orders of magnitude in luminosity shows that most narrow line Seyfert 1 galaxies fall outside of the general trend. However, when L/LEdd is plotted instead of luminosity, all sources follow the same trend suggesting this to be the primary driver of the correlation. Regarding the narrow emission lines in the most luminous sources, there is a dichotomy in the observed properties where 2/3 of the sources show very strong [O III] lines while the remaining 1/3 have no detectable NLR. On the basis of this I argue that earlier proposed relations of the type $R_{NLR}\propto L_{{\rm [O III]}}^{1/2}$ must break down for RNLR exceeding a few kpc. Thus, NLRs in high luminosity AGN may be very different from those observed in nearby sources. In particular, some high luminosity sources may be in a phase of violent star-formation that produce a large quantity of high density gas in their central kpc.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The NUGA project is a high-resolution (0.5″−1″) CO survey of low luminosity AGN including the full sequence of activity types (Seyferts, LINERs and transition objects). NUGA aims to systematically study the different mechanisms for gas fueling of AGNs in the Local Universe. In this paper we discuss the latest results of this recently completed survey, which now includes newly acquired subarcsec resolution observations for all targets of the sample. The large variety of circumnuclear disk morphologies found in NUGA galaxies (m = 1, m = 2 and stochastic instabilities) is a challenging result that urges the refinement of current dynamical models. In this paper we report on new results obtained in 4 study cases for NUGA: NGC 4826, NGC 7217, NGC 4579 and NGC 6951.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The formation and growth of supermassive black holes (SMBHs) physically linked with bulges are considered. We focus on the radiation hydrodynamic process for the growth of SMBH in the optically thick starburst phase, where radiation from bulge stars drives the mass accretion on to a galactic center through radiation drag effect. In the present scenario, the AGN luminosity-dominant phase (QSO phase) is preceded by the host luminosity-dominat phase, which is called “proto-QSO phase”. In this phase, there exists the massive dusty disks within younger bulges. Also, the proto-QSO phase is anticipated by an optically-thick ultraluminous infrared galaxy (ULIRG) phase. Furthermore, such radiation hydrodynamic model has been also applied to disk galaxies. It turns out that the mass of a SMBH primarily correlates with a bulge component even in a disk galaxy. Thus, by analogy to proto-QSOs, the BH growing phase in disk galaxies may have massive dusty disks within younger bulges.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Despite many years of effort, observational studies have not found a strong correlation between the presence of any proposed fueling mechanism and low-luminosity AGN. After a discussion of the mass requirements for fueling, I summarize this observational work and provide a number of hypotheses for why the nature of AGN fueling has remained unresolved. In particular, I stress the potential importance of the increasing number of candidate fueling mechanisms with decreasing mass accretion rate, the relevant spatial scales for different fueling mechanisms, and the lifetime of an individual episode of nuclear accretion. The episodic AGN lifetime is a particularly relevant complication if it is comparable to or shorter than the time that the responsible fueling mechanisms are observationally detectable. I conclude with a number of relatively accessible areas for future investigation.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We summarize the detection rates at wavelengths other than optical for ∼99,000 galaxies from the Sloan Digital Sky Survey (SDSS) Data Release 1 “main” spectroscopic sample. The analysis is based on positional cross-correlation with source catalogs from ROSAT, 2MASS, IRAS, GB6, FIRST, NVSS and WENSS surveys. We find that the rest-frame UV-IR broad-band galaxy SEDs form a remarkably uniform, nearly one parameter, family. As an example, the SDSS u and r band data, supplemented with redshift, can be used to predict K band magnitudes measured by 2MASS with an rms scatter of only 0.2 mag; when measurement uncertainties are taken into account, the astrophysical scatter appears not larger than ∼0.1 mag.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Metal enrichment of intracluster medium (ICM) is reanalysed in the hierarchical galaxy formation scenario. In order to investigate metal abundances of $\alpha$ and iron-peak elements, we incorporate metal production processes by type Ia supernovae (SNe Ia) as well as type II supernovae (SNe II) into the GALFORM model of semi-analytic galaxy formation. We find that a top-heavy initial mass function (IMF) of stars with a power index $x\simeq 0.35$ for starburst is required under the constraint that the IMF for quiescent disc star formation is the Kennicutt IMF. Our model shows an only mild evolution of [Fe/H] as suggested by a recent observation.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The emission line spectra of active galactic nuclei fall into three main categories: star formation nuclei (or HII regions), Seyfert nuclei and LINERs (low ionization narrow emission-line regions). A subset of these galactic nuclei has intermediate characteristics between LINERs and HII regions. These so-called transition objects were the subject of numerous studies in the past, but their true nature has remained elusive. It's almost impossible to explain these objects with models that take into account only one ionization mechanism, being it stars, an AGN or shocks. We show how the use of a set of elaborated photoionization models, that account consistently for these parameters (ionization by stars, shocks and/or AGN and dust), constrained by a detailed study of the stellar population properties, can help us understand the nature of these transition objects.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We use numerical simulations of galaxy clusters to study the dynamical and thermal evolution of the ICM from high redshift to the present time. We measure the properties of the satellites accreting on the cluster main progenitor and then measure their self-bound mass fraction as a function of time after the merging. We also calculate the mean properties of their orbits and investigate the time evolution of their internal velocity dispersion and gas temperature. We measure and model the mean pericentric and apocentric times, distances and velocities. Finally we show how the properties of the ICM at redshift zero can be understood by decomposing them as a function of the cluster merging history.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We analyse the rest–frame (U$-$V) colour–magnitude relation for 2 clusters at redshift 0.7 and 0.8, drawn from the ESO Distant Cluster Survey. By comparing them with the population of red galaxies in the Coma cluster, we show that the high redshift clusters exhibit a deficit of passive faint red galaxies. Our results show that the red–sequence population cannot be explained in terms of a monolithic and synchronous formation scenario. A large fraction of faint passive galaxies in clusters today has moved onto the red sequence relatively recently as a consequence of the fact that their star formation activity has come to an end at $z<0.8$.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html