We present a new analysis of galaxy colours and star formation rates as a function of environment, from the Sloan Digital Sky Survey and the 2dF Galaxy Redshift Survey. The galaxy distribution is well characterised by only two distinct populations: one that is blue and star–forming, and one that is red and quiescent. The colour and H$\alpha$ distribution of each of these populations is approximately independent of environment, while their relative abundances depend strongly on local galaxy density. Even in the lowest-density environments, a substantial ($\sim 30$ per cent) population of galaxies have red colours and exhibt no detectable H$\alpha$ emission. We compare these data with theoretical predictions of galaxy formation, properly accounting for observational selection biasses and uncertainties. We conclude that galaxy transformations must either be rapid (with a timescale $\tau\lesssim0.5$ Gyr), or must occur preferentially at high redshift.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Most of the baryons in the universe remain undetected. They are thought to be floating in intergalactic space, and their thermal state is highly uncertain. The only places where we have reasonably complete observations of the overall baryon population are in clusters of galaxies, where the baryons reveal themselves through their X-ray emission. There we find that only about 10% of the baryons have turned into stars, probably because feedback processes intervene to prevent more baryons from condensing. These galaxy formation processes seem to have left an imprint on the thermal state of the intracluster medium, but in order to interpret that imprint, one needs to pay close attention to how entropy develops in the intergalactic gas. Many of the global properties of clusters turn out to be determined primarily by the entropy threshold for cooling within a Hubble time. However, XMM-Newton observation are revealing a sort of altered similarity among the entropy profiles of clusters seeming to indicate that galactic winds may have smoothed the local intergalactic medium before it accreted onto clusters.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We make use of extensive HST optical and VLA radio observations of the Seyfert galaxy Markarian 78 to analyse the properties of the jet flow. Our starting assumption is that the jet's power can be inferred from the energy stored in the radio lobe, and the jet's momentum flux can be inferred from the momentum of the ionized gas. Using the properties of three regions, we derive a jet flow power of ∼1040.5 erg s−1 and momentum flux of ∼1033.5 dyne. Assuming the jet contains both thermal and relativistic material, we find that the thermal component dominates both the jet's luminosity and its momentum flux. We find the jet to be mildly transonic, with speed only a few times that of the [OIII] velocities. The jet is, however, quite dense, with sufficient ram pressure to accelerate the ionized gas to the observed velocities. Over the region lifetime, the jet can provide the thermal component of the lobes, and likely does this by entraining ISM material en route. These jet properties seem, at least to us, to be eminently plausible, suggesting an approach of this kind may be appropriate for other radio quiet objects.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Using adaptive optics on Keck and the VLT in the H- and K-bands, we have begun a project to probe the dynamics and star formation around AGN on scales of 0.1″. The stellar content of the nucleus is traced through the 2.29 µm CO 2-0 and 1.62 µm CO 6-3 absorption bandheads. These features are directly spatially resolved, allowing us to measure the extent and distribution of the nuclear star forming region. The dynamics are traced through the 2.12 µm H2 1-0 S(1) and 1.64 µm [FeII] emission lines, as well as stellar absorption features. Matching disk models to the rotation curves at various position angles allows us to determine the mass of the stellar and gas components, and constrain the mass of the central black hole. In this contribution we summarise results for the two type 1 AGN Mkn 231 and NGC 7469.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present new observations from Gemini-South for two unusual AGNs: the recently-discovered, largest-known FR I radio galaxy (>1.1 Mpc), and a FR I radio galaxy originating from a spiral host (the wrong kind of galaxy!). Both AGNs may represent missing classes of objects, not present in current surveys and samples.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Stellar velocity dispersions in AGN are useful indicators of the black-hole mass (through the M[bull ]−σ[sstarf ] relation) and nuclear stellar populations (through the M/L ratio). We have collected near-infrared spectra of ∼40 Seyferts in the CaII triplet range in order to measure σ[sstarf ] and investigate the connection between stellar populations and AGN properties. In this poster we present a comparison between two methods to measure velocity dispersions: (1) direct fitting (DFM) and (2) cross-correlation (CCM). (1) In DFM the spectra in the CaII triplet range is modeled as a combination of a broadened and shifted stellar spectrum (observed through the same instrumental setup) and a featureless continuum. This method has the advantage of making it easy to mask out noisy regions and sky residuals. (2) CCM converts the width of the star-galaxy cross-correlation function onto a velocity dispersion. We find that these methods yield velocity dispersions consistent to within 20 km s−1 on-average. Our results are consistent to within 20 km s−1 with those objects available in the literature.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We describe recent discoveries of low column density (N$_{\rm HI} = 10^{12.5-16.0}$ cm$^{-2}$) H I Ly$\alpha$ absorbers made with the Hubble Space Telescope (HST) which have allowed us a first look at gas in local intergalactic space; i.e., between us and the “Great Wall”. These absorbing clouds account for 29 $\pm$ 4% of all baryons at $z$=0 and are, in general, only loosely related to individual galaxies. Owing to the proximity of these absorbers to the Earth, the 187 absorbers in our combined GHRS + STIS sample provide our best view of the relationship between Ly$\alpha$ absorbers and galaxies, voids, and supercluster filaments. While only a few of the very strongest absorbers in our sample appear associated with individual galaxies, the majority (78%) are associated with large-scale filamentary structures of galaxies, while 22% are found in galaxy “voids”. Amongst the highest column density absorbers (with N$_{\rm HI}\approx$ 10$^{16}$ cm$^{-2}$) in our sample, we find a low-ionization, metal-bearing absorber associated with a post-starburst dwarf galaxy $\sim$ 70h$^{-1}_{70}$ kpc away. The detailed properties of the absorber and the galaxy provide strong evidence that these two are causally related. We argue that many/most weak metal absorption systems could be due to outflowing “superwinds” from dwarf galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We pursue the dynamics of dusty gas clouds that are blown out of circumnuclear starburst regions, taking into consideration the growth of clouds by inelastic cloud-cloud collision and the resultant change of the optical depth. As a result, we find that the clouds originating in the circumnuclear starburst can contribute to the obscuration to produce type 2 Seyfert galaxies. Also, it is shown that, if the AGN luminosity overwhelms the starburst one, almost all clouds are ejected from the galaxy by the radiation pressure of the AGN, resulting in the formation of quasar-like objects.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

I review the evidence in favour of the existence of intermediate mass black holes (IMBH) in a sub-set of the class of ultraluminous X-ray source (ULX). Their X-ray properties and information on their local environments is beginning to point towards the presence of IMBHs in some, and perhaps the most luminous, ULX.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We analyze the properties of quasar variability using repeated SDSS imaging data in five UV-to-far red photometric bands, accurate to 0.02 mag, for ∼13,000 spectroscopically confirmed quasars. The observed time lags span the range from 3 hours to over 3 years, and constrain the quasar variability for rest-frame time lags of up to two years, and at rest-frame wavelengths from 1000Å to 6000Å. We demonstrate that ∼66,000 SDSS measurements of magnitude differences can be described within the measurement noise by a simple function of only three free parameters. The addition of POSS data constrains the long-term behavior of quasar variability and provides evidence for a turn-over in the structure function. This turn-over indicates that the characteristic time scale for optical variability of quasars is of the order 1 year.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Interactions between galaxies are suggested to be a mechanism responsible for feeding Active Galactic Nuclei (AGN). Theoretical models show that interactions are an efficient way to drive gas from the galaxy to the nucleus, however, the observational evidence on this subject is controversial. Here we review results in this field, discuss possible limitations of previous studies and the importance of dealing with selection effects. We also show that there is no significant difference in the percentage of low luminosity AGN and normal galaxies with companions, and discuss possible interpretations of this result.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We predict the metallicity distribution of stars for 6 Dwarf Spheroidal (dSph) galaxies of the Local Group by means of a chemical evolution model which is able to reproduce several observed abundance ratios and the present day total mass and gas content of these galaxies. The model adopts up to date nucleosynthesis and takes into account the role played by supernovae of different types (II, Ia). Each galaxy model is specified by the prescriptions of the star formation rate and by the galactic wind efficiency chosen to reproduce the main features of these galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the results of L-band spectroscopic observations of local bright ULIRGs, performed with ISAAC at VLT. The excellent sensitivity of the telescope and instrument provided spectra of unprecedented quality for this class of objects, which allowed a detailed study of the relative AGN/starburst contribution to the energy output, and of the composition of the circumnuclear absorber. A new mid-infrared diagnostic diagram is proposed, in which starbursts and AGNs are clearly separated.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The XMM–LSS project is detecting distant clusters of low mass, quite comparable in mass to the ones in the local universe. This allows a direct comparison of galaxy properties at different redshifts in “similar” clusters. We present here first results on the evolution of the reddest galaxies in 25 clusters/groups at $0.3\la z \la 1.0$ and for the whole galaxy population in the same clusters. The emerging picture from the current study is that the counterparts of present day clusters tend to show two or more distinct populations: a relatively old ($z_f \gt 2-5$) population evolving passively, together with a younger population, ostensibly responsible for the apparent brightening of the characteristic magnitudes, $m^*$.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

For the past 10 years there has been an active debate over whether fast shocks play an important role in ionizing emission line regions in Seyfert galaxies. To investigate this claim, we have studied the Seyfert 2 galaxy Mkn 78, using HST UV/optical images and spectroscopy. Since Mkn 78 provides the archetypal jet-driven bipolar velocity field, if shocks are important anywhere they should be important in this object. Having mapped the emission line fluxes and velocity field, we first compare the ionization conditions to standard photoionization and shock models. We find coherent variations of ionization consistent with photoionization model sequences which combine optically thick and thin gas, but are inconsistent with either autoionizing shock models or photoionization models of just optically thick gas. Furthermore, we find absolutely no link between the ionization of the gas and its kinematic state, while we do find a simple decline of ionization degree with radius. We feel this object provides the strongest case to date against the importance of shock related ionization in Seyferts.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the results from a new 120 ks XMM-Newton observation of Sérsic 159-03. A previous XMM-Newton observation of this cluster shows the presence of a soft X-ray excess in the outer parts of the cluster, which is possibly connected to the interaction between the cluster and the gas from the surrounding filaments. We exploit the long exposure time to constrain the excess emission and discuss the relation to the warm-hot intergalactic medium. Furthermore, we show a high-resolution RGS spectrum of the core of the cluster and radial profiles from EPIC, which allow us to constrain the internal temperature structure and elemental abundances.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We perform a statistical analysis to study the infall of galaxies onto groups and clusters in the nearby Universe. The study is based on the UZC/SSRS2 group catalogs and galaxy peculiar velocity data. We find a clear signature of infall of galaxies onto groups in a large range of scales 5 Mpc h$^{-1} < r < 30$ Mpc h$^{-1}$. We obtain a significant increase of the infall amplitude with group mass derived from virial equilibrium and from the luminosity of the member galaxies. We compare the observational results with mock catalogs derived from numerical simulations of semi-analytical models where we obtain a behavior similar to observations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We investigate the relation between circular velocity vc and bulge velocity dispersion σ in spiral galaxies, based on literature data and new spectroscopic observations. We find a strong, nearly linear vc−σ correlation with a negligible intrinsic scatter, and a striking agreement with the corresponding relation for elliptical galaxies. The least massive galaxies (σ<80 km s−1) significantly deviate from this relation. We combine this vc−σ correlation with the well-known MBHσ relation to obtain a tight correlation between circular velocity and supermassive black hole mass, and interpret this as observational evidence for a close link between supermassive black holes and the dark matter haloes in which they presumably formed. Apart from being an important ingredient for theoretical models of galaxy formation and evolution, the relation between MBH and circular velocity has the potential to become an important practical tool in estimating supermassive black hole masses in spiral galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present results from a set of high ($512^3$ effective resolution), and ultra-high ($1024^3)$ SPH adiabatic cosmological simulations of cluster formation aimed at studying the internal structure of the intracluster medium (ICM). We discuss the radial structure and scaling relations expected from purely gravitational collapse, and show that the choice of a particular halo model can have important consequences on the interpretation of observational data. The validity of the approximations of hydrostatic equilibrium and a polytropic equation of state are checked against results of our simulations. We also show the first results from an unprecedented large-scale simulation of 500 $h^{-1}$ Mpc and $2\times 512^3$ gas and dark matter particles. This experiment will make possible a detailed study of the large-scale distribution of clusters as a function of their X-ray properties.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The nuclear region of the barred spiral galaxy M83 has been imaged at near-infrared wavelengths with the HST NICMOS, showing a new region of star formation activity.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html