The excellent spatial resolution of the Chandra satellite allowed us to see a wide variety of new types of substructures in the intergalactic gas in clusters of galaxies. The most promising scenarios to explain at least some of the phenomenology in the clusters centers involve processes that result from the interaction of the central active galaxy and its surroundings. Here, we present preliminary results of a Chandra velocity analysis of the Centaurus cluster. The results suggest that some of the core features may be interacting with pre-existent bulk gas flows in the cluster.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We use low resolution, near-IR spectra of eight of the most distant quasars known, with redshifts in the range 4.9<z<6.4, to investigate the gas and dust properties in their circumnuclear regions. Half of these quasars are characterized by deep, broad and blueshifted absorption features associated with both high and low ionization species, i.e. they belong to the class of Broad Absorption Line (BAL) quasars, which are associated with powerful outflows of dense gas. The large fraction of BAL quasars, the depth and ionization state of the absorption features suggest that these most distant quasars are surrounded by a much larger amount of dense gas than lower redshift (z<4) quasars. We discuss the possible interpretation of this result in terms of extremely high accretion rates and the association with the early formation of quasars.

The spectral shape of all these very distant quasars, and in particular of the BAL quasars, is bluer than for quasars at z<4, suggesting an evolution of the properties of the dust responsible for the quasar reddening. We show that the observed spectral shape can be explained by an extinction curve due to dust produced by SNe. This finding would address the problem of the dust production at z>6, when the age of the universe was lower than the evolutionary timescales of AGB stars.

Finally, these spectra allow to investigate the Fe/α-element abundance ratio, which is a tracer of the star formation history, through the relative strengths of the FeII UV bump and the MgII doublet. We find indications for a large abundance of Fe even in the most distant quasars at z∼6. This finding requires that a strong burst of star formation occurred in the hosts of these quasars already at z>9.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We analyse the stellar content of a large number of HII galaxies based on the continuum and absorption features of their spectra using population synthesis methods, in order to gain information about the star formation histories of these objects. We find that all galaxies of our sample contain an old stellar population (≥1 Gyr) that dominates the stellar mass, and in a great majority of these, we also found evidence for an intermediate-age population ≥100 Myr apart from the presently bursting, ionizing young generation ≤107 yrs.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the black hole mass–bulge velocity dispersion relation for a complete sample of 75 soft X-ray selected AGNs. We find that the AGNs with highest accretion rates relative to Eddington lie below the MBH–σ relation of broad line Seyfert 1s, confirming the Mathur et al. (2001) result. The statistical result is robust and not due to any systematic measurement error. This has important consequences towards our understanding of black hole formation and growth: black holes grow by accretion in well formed bulges. As they grow, they get closer to the MBH–σ relation for normal galaxies. The accretion is highest in the beginning and dwindles as time goes by. Our result does not support theories of the MBH–σ relation in which the black hole mass is a constant fraction of the bulge mass/velocity dispersion at all times or those in which bulge growth is controlled by AGN feedback.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The CAIRNS (Cluster And Infall Region Nearby Survey) project is a large spectroscopic survey of the infall regions surrounding nine nearby rich clusters of galaxies. I describe the survey and use the kinematics of galaxies in the infall regions to estimate the cluster mass profiles. At small radii, these mass profiles are consistent with independent mass estimates from X-ray observations and Jeans analysis. I demonstrate the dependence of mass-to-light ratios on environment by combining these mass profiles with Two-Micron All-Sky Survey (2MASS) photometry. Near-infrared light is more extended than mass in these clusters, suggesting that dense cluster cores are less efficient at forming galaxies and/or more efficient at disrupting them. At large radii, galaxy populations in cluster infall regions closely resemble those in the field. The mass-to-light ratio at these radii should therefore be a good probe of the global mass-to-light ratio. The mass-to-light ratio in the infall region yields a surprisingly low estimate of $\Omega_m \sim 0.1$.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We analysed 246 scanned ACO clusters and we do not find any dependence of galaxy cluster ellipticity on redshift.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We use the photoionization code MAPPINGS Ic to model optical emission-line ratios of the extended emission-line regions of 24 Seyfert galaxies. Although most line ratios can be reproduced by varying the ionization parameter, gas density and/or the shape of the ionizing continuum, the ratio [NII]λλ6548,84/[OII]λ3727 can only be reproduced if we allow for a range of oxygen abundances of 0.5≤ (O/H)/(O/H)$_{\odot} \leq$ 3 for the whole sample. We propose a calibration to obtain (O/H) in terms of [NII]/[OII]. Also, in order to reproduce the emission-line spectra beyond 2 kpc from the nucleus, we had to introduce the contribution from hot stars to the ionizing spectra. We conclude that this is due to an increasing contribution of HII regions with distance from the nucleus to the emission-line regions.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The “Herschel Space Observatory” is an ESA mission to perform imaging photometry and spectroscopy in the far-IR & submm 57–670 μm range. It carries a 3.5 m diameter radiatively cooled telescope. The scientific instruments – two cameras/medium resolution spectrometers (PACS and SPIRE) and a very high resolution heterodyne spectrometer (HIFI) – are housed in a superfluid helium cryostat. Herschel will be placed in orbit around the Earth-Sun L2 point in 2007 and will operate for a minimum of 3 years. Roughly 2/3 of the observing time is open to the general astronomical community through a competitive proposal procedure.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the values of CN and Mg overabundances with respect to Fe, for early-type galaxies in 8 clusters over a range of richness and morphology. Spectra were taken from the Sloan Digital Sky Survey (SDSS) DR1 spectroscopic database, and from WHT and CAHA observations. Abundances were derived from absorption lines and single burst population models, by comparing galaxy spectra with appropriately broadened synthetic model spectra. We find robust correlations between [Mg/CN] and [CN/Fe] abundance ratios and cluster X-ray luminosity. No correlation was observed for [Mg/Fe]. We also see a clear trend with the richness and morphology of the clusters. This behavior is interpreted given varying formation timescales for CN, Mg and Fe, combined with a different star formation history in early-type galaxies as a function of their environment. This result supports the scenario in which early-type galaxies in more massive clusters are assembled on shorter timescales than those galaxies within less massive clusters.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We introduce our project that investigates the kinematic properties of early–type galaxies in 6 distant poor clusters at $z\approx0.25$. This study represents a continuation of our efforts to understand galaxy evolution in low-density environments. Higher–resolution MOSCA spectra have been obtained at the Calar Alto 3.5-m telescope with which we can measure absorption line strengths and velocity dispersions. In conjunction with our HST/F702W images of all the clusters, we are able to construct the Fundamental Plane of ellipticals and S0 galaxies in poor clusters at a look-back time of $\approx3$ Gyr. For galaxies outside the HST field, we concentrate our analysis on the Mg–$\sigma$ and Faber–Jackson relations. With the line strength diagrams age/metallicity distributions can be derived in densities between the field and rich cluster environments. Comparing with our rich clusters at the same cosmic epochs, the dependence of galaxy formation models on the local environment can be tested more quantitatively.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Using the results of an extended set of high-resolution non-radiative hydrodynamic simulations of galaxy clusters we obtain simple analytic formulae for the dark matter and hot gas distribution, in the spherical approximation.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the study of the gas mass fraction, $f_{\rm gas}$, properties of distant galaxy clusters observed within the XMM-$\Omega$project, based on a sample of distant ($z\sim 0.5$) clusters of median luminosity. These clusters were previously detected as serendipity ROSAT clusters surveys. We first study the $f_{\rm gas}$ profiles traced up to the virial radius in both Einstein de Sitter (EdS) and concordance cosmologies. We find that the mean gas fraction profile of our high-$z$ sample is similar to the local mean profile and in good agreement with numerical simulations predictions. This result confirms the self-similarity of the shape predicted by the simple scenario of structure formation up to high redshifts. We observe $f_{\rm gas}$ in the central part of distant clusters to lie below the local ones in the case of an EdS model, consistently with the observed evolution in the $\hbox{$L_{\rm X}$--$T$}$ relation, which is indeed found to be weaker than expected in a self-similar model. We investigate quantitatively this departure from scaling laws by comparing $f_{\rm gas}$ in our distant XMM clusters with those derived from the local sample at fixed scaled radii. We show that the internal structure is very complex, i.e. the variation of the gas mass fraction with radius, with temperature and with redshift reveals differences that cannot be described in a simple scaling scheme. The observed variations in the central parts are a clear indication that, in these regions, the argument based on the non-evolving $f_{\rm gas}$ with redshift cannot be used to infer the cosmological parameters, given the present (lack of) understanding of the gas physics in clusters. At the virial radius, where this argument could be valid, we find that the $\Lambda$CDM model is excluded at more than 3-$\sigma$.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

I present preliminary results and discussion from a K-band imaging study of the host galaxies of samples of ULIRGs and IR-bright QSOs, designed to match in terms of their FIR luminosities and redshift distributions. Large K-band bulges are found to be present in all of the quasars, with the majority of the ULIRGs being best-fit by a disc. Despite the apparent difference, a significant overlap exists between the two populations in terms of their nuclear luminosity. A significant unresolved nuclear component is present in all of the objects, and this is found to correlate with the luminosity of the K-band host across the sample.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

High resolution B, V, I imaging of the inner region of the spiral barred galaxy NGC 7479 suggests this galaxy contains a pseudo nuclear ring and possibly a nuclear bar.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We investigate the relation between the asymptotic circular velocity, $V_{\rm circ}$, and the central stellar velocity dispersion, $\sigma_{\rm c}$, in galaxies. We consider a new sample of high surface brightness spiral galaxies (HSB), low surface brightness spiral galaxies (LSB), and elliptical galaxies with HI-based $V_{\rm circ}$ measurements. We find that: 1) elliptical galaxies with HI measurements fit well within the relation; 2) a linear law can reproduce the data as well as a power law (used in previous works) even for galaxies with $\sigma_{\rm c} \lt 70$ km/s; 3) LSB galaxies, considered for the first time with this respect, seem to behave differently, showing either larger $V_{\rm circ}$ values or smaller $\sigma_{\rm c}$ values.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present near-IR, diffraction limited imaging of the nucleus of NGC 1068 obtained with NAOS-CONICA at VLT. These observations provide an accute view on the distribution of hot dust in the vicinity of the central source, at a 0.1” resolution. The use of a new type of coronagraph allowed us to detect and identify new structures at K, to calculate more accurate color indices, and derive the state of the dust in this very complex morphology. We also used deconvolution on images aquired in other bands to get an accute view of these structures.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Modern kinematic diagnostics from high-S/N spectroscopy provide useful tests on the collisionless merger hypothesis for the formation of elliptical galaxies. Bender, Saglia & Gerhard (1994) show that the skewness of the line-of-sight velocity distributions (LOSVD) has opposite sign to the rotation velocity and follows a distinct pattern. Previous N-body experiments (Bendo & Barnes 2000, Naab & Burkert 2001) disagree as to whether the relation is reproduced by the models.

We present first results from an ongoing effort to explain the skewness properties of the LOSVD's of ellipticals. We use large N-body simulations of disk-disk galaxy mergers ($10^6$ particles), with mass ratios 1:1 and 3:1. Our 1:1 models fail to reproduce the H3 vs. $V/\sigma$ relation, in agreement with Naab & Burkert (2001). 3:1 mergers yield trends similar to the observations for large values of $V/\sigma$, but with overall lower H3 values in the models than in real galaxies. And we fail to reproduce high H3 values for low $V/\sigma$. So far, it is unclear whether the disagreement is related to the lack of rotation in the bulge components of our initial model galaxies, or to a more general shortcoming of dissipationless mergers to reproduce the properties of real ellipticals.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Surface brightness measurements of the diffuse intracluster light (ICL) in centrally concentrated, relaxed clusters have demonstrated that stars bound only to the cluster potential can contain anywhere from 5 to 50% of the total cluster flux. These stars are a by-product of the evolution of galaxies in clusters, and can be used to constrain models for the structure and evolution of clusters and their member galaxies. The ICL will be an important test of cosmological models as it is a baryonic component of clusters that is likely to evolve with redshift. To learn about these processes we are undertaking a program to measure the characteristics of the ICL (total flux, color, and substructure) as a function of cluster mass, morphology, and redshift. We have obtained data for a sample of 10 clusters at low and moderate redshifts. We discuss here our preliminary results for one cluster in that sample, A3888. With 4-5 hour integration times on-source per filter (V & gunn-r), we reach a 1 sigma surface brightness limit of 29.9 mag/arcsec$^{2}$ in the V band. We have identified an intracluster light component that is $\sim10\%$ of total cluster light, extends to 600 kpc from the center of the cluster, and is redder in color than the cluster galaxies ($V-r = 0.4$ near the center, increasing to $V-r = 0.8$ at r = 500 kpc). In addition we find 3 low surface brightness features which are blue ($V-r \simeq 0$), and in total are equivalent to one $m_V = 20.8$ mag galaxy.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Low-luminosity nebular emission is found in the centers of a large fraction of galaxies, and in many cases the energy source powering these systems is ambiguous. This is particularly true for H II/LINER “transition” objects, although a reasonable explanation for these sources is that their emission is the composite result of a weak accretion-powered system surrounded by star-forming regions. This contribution describes results from a Hubble Space Telescope spectroscopic survey that probes the structure of nearby transition objects and other emission nuclei. The results provide only limited support for the composite picture for these sources; the emission nuclei do not show a strong tendency for the nebular classification to depend on aperture size. The strongest variations in forbidden line ratios appear to be mediated by a gradient of decreasing nebular density with increasing radius.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The gravitationally lensing clusters A370, A2218, A1689 and Cl0024+1654 were observed with the Infrared Space Observatory (ISO) using ISOCAM at 6.7 $\mu$m and 14.3 $\mu$m (hereafter 7 $\mu$m and 15 $\mu$m respectively).

A total of 178 sources were detected in the whole set, 70 of them being cluster objects. The spectral energy distribution of a subset of sources was calculated using GRASIL. The results for the total infrared luminosity and the estimation of the star formation rate are presented for the non stellar objects for which the SED has been determined. The majority of the cluster galaxies in A2218 are best fit by models of quiescent ellipticals. In Cl0024+1654, most of the galaxies lying on the Butcher-Oemler region of the colour-magnitude diagram are best fit by disk galaxies, while those on the main sequence area have in general SEDs corresponding to post-starburst galaxies.

The population of each cluster is compared with the field population, as well as with the population of other clusters. A significant number of Luminous IR Galaxies (LIRGs) is detected in Cl0024+1654, while only one LIRG has been observed in total in A370, A1689, and A2218. This result supports the link between LIRGs in clusters and recent or ongoing cluster merger activity as well as the need for extending the observations to the outer parts of clusters.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html