This contribution reviews two topics of current interest in the study of black hole demographics in active galaxies: Can the stellar velocity dispersions of quasar host galaxies be measured? And can we constrain the black hole mass function below 106 M$_\odot$?To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We explore the stellar halo of the Milky Way to search for fossil signatures of past mergers. We use the Beers et al. (2000) catalog of non-kinematically selected metal poor stars in the solar neighborhood to select subsets of halo stars within 1-2 kpc of the Sun. Motivated by the results of high resolution CDM simulations, we look for substructure in the kinematics of the fastest stars. When a two-point velocity correlation function is applied to these subsets, statistical evidence of substructure is found. This appears to be due to a small moving group with dynamical properties similar to the stellar “stream” previously discovered by Helmi et al. (1999).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present a statistical analysis of the Chandra observation of the source field around the 3C 295 galaxy cluster ($z=0.46$). Three different methods of analysis, namely a chip by chip LogN-LogS, a two-dimentional Kolmogorov-Smirnov (KS) test, and the angular correlation function (ACF) show a strong overdensity of sources in the North-East of the field, that may indicate a filament of the large scale structure of the universe towards 3C 295.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Clusters of galaxies are the largest bound gravitational systems in the universe. They outline the large-scale structure and thus are able to test predictions of cosmological models. Detailed studies of galaxy populations in clusters at high $z$ offer insights into galaxy evolution as a function of look-back time. Unfortunately, large homogeneous samples of galaxy clusters only exist at redshifts $<$0.5. There are around 1000 candidate clusters with photometric or otherwise estimated redshifts above 0.5, but spectroscopically confirmed clusters are still scarce in this redshift regime. Some clusters with $z>1$ have recently been identified from X-ray surveys.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The structure of the universe is believed to have formed by clustering hierarchically from small to large scales. Much of this evolution occurs very slowly but at a few special times more rapid, violent activity may occur as major subunits collide at high velocities. The Abell 2125 complex ($z=0.247$) appears to be undergoing such an event as shown by modeling of the optical velocity field and by the detection with the VLA of an unusually large number of associated radio active galaxies. We present an 80 ksec Chandra imaging of Abell 2125, together with extensive complementary multi-wavelength data. We show direct evidence for galaxy transformation and destruction during the cluster formation. The Chandra data unambiguously separate the X-ray contributions from discrete sources and large-scale diffuse gas in the Abell 2125 complex, which consists of various merging clusters/groups of galaxies and low-surface brightness emission. This enables us to study processes affecting galaxy evolution during this special time from scales of Mpc down to a few kpc. The overall level of activity plus the special time for the cluster-cluster merger suggests that an important phase of galaxy evolution can take place during such events.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present a new sample of 30 nearby (z < 0.2) BL Lacs, selected to study the nuclear as well as the large scale properties of low power radio sources. New VLA and VLBA radio data have been obtained to discuss the morphology, physical properties, and overall properties of the sample. We show that the distributions of total radio power and intrinsic core radio power for BL Lacs are consistent with their being drawn from the same population as FR I radio galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

High resolution radio and X-ray observations of a subsample of composite LINER/H II galaxies with arcsec-scale radio cores were obtained. These observations yield a 12% detection rate of low luminosity AGN among the entire composite sample in the Palomar survey. Four of these low luminosity AGN also possess sub-parsec jet-like radio extensions. While canonical advection-dominated accretion flows may be responsible for the radio and X-ray emission in submillijansky cores like NGC 7331, they do not appear consistent with the radio emission in these milliarcsecond-scale radio cores; the latter sources are more likely to have an energetically important contribution from a radio-emitting jet.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We identify the dominant emission processes in 3C 270 in the infrared to be non-thermal, and emission from its dusty disk does not contribute significantly to the total infrared output. This implies that such disks can be hard to find through their infrared emission, and that any circumnuclear torus, if at all present, is small and thin.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We discuss follow-up X-ray observations of giant-amplitude, non-recurrent X-ray flares, interpreted as tidal disruptions of stars by supermassive black holes at the centers of the flaring galaxies. The flare observations open up a new window to study supermassive black holes and their environment, and the physics of accretion events, in non-active galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Galaxy clusters at $z\sim1$ are particularly important in the study of cluster evolution and the application of clusters to cosmological studies. We briefly discuss the difficulties in creating well-defined, large, high-redshift cluster samples, and some of the techniques used in optical/IR imaging to overcome them. We give a summary of the current state of optical/IR observations of the relatively small number of high-redshift clusters identified so far, including discussions of the galaxy luminosity function, the Fundamental Plane, the color-magnitude relation, and the Butcher-Oemler effect. The application of photometric redshift techniques is also highlighted.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

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