Past X-ray observations by ASCA suggest that warm absorbers (O VII and O VIII edges) are apparently rare in high luminosity AGNs (quasars) while they are more common in low luminosity AGNs (Seyferts). However, this could be a selection effect if high luminosity AGNs have mostly narrow absorption lines (with no strong bound free edges), which escaped detection by the low resolution of ASCA. To check this hypothesis we are studying the high-resolution X-ray spectra of quasars from grating spectrometers on board Chandra and XMM-Newton in search for absorption lines. In this contribution we present spectra of three quasars. The spectra show narrow (several hundred km s−1) absorption and emission X-ray lines from H-like and He-like ions of O, Ne, Mg, and other abundant elements. We also detect absorption from iron L-shell lines and iron M-shell unresolved transition array. We present the analysis of MR2251-178 where we find that at least two, and probably three, distinct warm absorbers are needed to explain the high resolution spectrum of this object. We re-analyze the high-resolution X-ray spectrum of PG 1211+143 and suggest that an outflow velocity of ∼3000 km s−1 provides an adequate explanation to these data. We also present preliminary results form the Chandra/HETGS observation of the quasar 4C74.26.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We study the NLR emission line spectrum of 12 NLS1s to constrain the EUV – soft X-ray continuum SED using accurate photoionization modeling. We find that the NLR emission line ratios, which we measure for several NLS1 galaxies, can be reproduced within ±15% without a strong BBB component in the framework of a two-component model.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The cross-correlating cosmic microwave background (CMB) fluctuations caused by the Sunyaev-Zel'dovich effect from observed clusters of galaxies with their redshifts can be used to measure the mean squared cluster peculiar velocity with an error $\sigma_{C_S^2}\simeq (300{\rm km/s})^2$. This can be done around $z\gt0.3$ with clusters of flux above 200 mJy which will be detected by PLANCK, coupled with high resolution microwave images to eliminate the cosmological part of the CMB fluctuations. The latter can be achieved with observations by the planned ALMA array or the NSF South Pole telescope and other surveys. By measuring the rms peculiar velocity of clusters and their bulk flow in, e.g., 4 spheres of $\sim 100h^{-1}$ Mpc at $z=0.3$, we could have a direct measurement of the matter density $0.21\lt\Omega_m\lt0.47$ at 95% confidence level.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Measuring stellar velocity dispersion (σ) in Narrow-Line Seyfert 1 (NLS1) with optical spectra, can be very difficult because of the large and bright Fe II multiplets, which completely suppress the typically used stellar absorption lines. Indeed, σ values are to date available only for 2 NLS1s. Here we present new σ measurements of three NLS1s observed in the spectral range centered around the Ca II triplet (λ∼8600Å). Moreover, we compare σ with the gaseous velocity dispersion finding that the σ = FWHM([O III]5007Å)/2.35 relation (Nelson & Whittle 1995) is not satisfied by our galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present Very Large Array observations at 1.4 and 5 GHz of a sample of 16 quasi-stellar objects (QSOs) at z = 1.78 to 2.71. These sources were chosen to have similar optical properties (MB, spectra) as samples of (z ≥ 3.7 QSOs) for which we have comparable (sub)millimeter (250 GHz or 350 GHz) and centimeter observations. Half of the chosen quasars are bright at 250 or 350 GHz while the other half have not been detected at (sub)mm wavelengths. All eight submm-loud sources in our study were detected at 1.4 GHz, the majority of these at high significance (≥0.2±0.02 mJy). Only three of the submm-quiet QSO's were detected at radio frequencies, and these at lower significance (≤0.17 mJy). These results argue for a real physical difference between the submm-luminous and submm-quiet sources, and against a continuum of submm luminosities. Four of these sources have radio spectral indices and radio-to-FIR ratios consistent with star forming galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

J and K-band imaging with Gemini N has resolved the host galaxies of QSOs of redshifts 4.7 to 5.2. We also discuss I and Z band imaging of two QSOs of redshift above 6.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We explore possible correlations between the light profile shapes of early-type galaxies, as parameterized by the Sérsic index $n$, and relevant stellar population parameters, which were obtained from spectra of extremely high signal–to–noise and stellar population models that provide an age indicator that is virtually free of the effects of metallicity. We do not find any robust correlation between $n$ and mean age or metallicity. However, we find evidence for a strong positive correlation between $n$ and [Mg/Fe] abundance ratio. We speculate that early-type galaxies settle up their structure on short time-scales in agreement with those imposed by their [Mg/Fe] ratios, suggesting that the global structure was already at place at high $z$.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

LLAGN that include low-ionization nuclear emission-line regions (LINERs), and transition-type objects (TOs) represent the most common type of nuclear activity. Here, a study of the central stellar population of LLAGN is presented. Our goal is to search for spectroscopic signatures of young and intermediate age stars, and to investigate their relationship with the ionization mechanism in LLAGN. The method used is based on the stellar population synthesis of the UV-optical continuum of the innermost (20-100 pc) regions in these galaxies. Half of the LINERs and TOs of the Palomar catalogue are analysed. It is found that weak-[OI] ([OI]/Hα≤0.25) LLAGN have an intermediate age stellar population that dominates the optical light. But young stellar clusters dominate the UV continuum in these objects. These clusters can co-exist with a black-hole in spatial scales of a few pc. Most of the strong-[OI] LLAGN have a predominantly old stellar population. These results suggest that young and intermediate age stars do not play a significant role in the ionization of LLAGN with strong [OI].To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We report the discovery of a probable large-scale structure composed of many galaxy clumps around the known twin clusters at $z=1.26$ and $z=1.27$ in the Lynx region. Our analysis is based on deep, panoramic, and multi-colour imaging with the Suprime-Cam on the 8.2 m Subaru telescope. We apply a photometric redshift technique to extract plausible cluster members at $z\sim1.27$ down to $\sim M^\ast+2.5$. From the 2-D distribution of these photometrically selected galaxies, we newly identify seven candidates of galaxy groups or clusters where the surface density of red galaxies is significantly high ($>$5$\sigma$), in addition to the two known clusters, comprising the largest most distant supercluster ever identified.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We study the formation and evolution of voids in the dark matter distribution using various simulations of the popular $\Lambda$ Cold Dark Matter Universe. We identify voids by requiring them to be spherical or elliptical regions of space with a mean overdensity of $-0.8$ or less. The distribution of void sizes in the different simulations shows good overlap. The size of a void is related to the depth of the smoothed density field at that position in the initial conditions. The rescaled mass profiles of voids in the different simulations agree remarkably well. We find a universal void mass profile of the form $\rho(\ltr)/\rho(r_{\rm eff}) \propto \exp[(r/r_{\rm eff})^\alpha]$ where $r_{\rm eff}$ is the effective void radius and $\alpha\sim 2$. The mass function of haloes in voids is steeper than that of haloes which populate denser regions.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We have established under which conditions core collapse of a spherical cluster occurs before massive stars have time to evolve off the main sequence (MS). We consider cluster central velocity dispersions of 100 km s−1 and higher, appropriate for galactic nuclei. At such high velocities, binary stars play little dynamical role and are therefore neglected. On the other hand whether collisions allow the growth of very massive stars (VMS, with $\ensuremath{M_{\ast}} \gg 100\,\ensuremath{M_{\odot}}$) or, on the contrary, grind them down is a central unknown addressed in this work. We find that, in spite of the high relative velocities, run-away growth of a VMS, a likely progenitor for an intermediate-mass BH (IMBH), occurs in all clusters with short enough a core collapse time.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In this paper we present some preliminary results of a 3-mm (86 GHz) radio continuum survey of selected Seyfert galaxies made with the Berkley-Maryland Illinois Millimeter Array (BIMA) in D configuration. The images shown here have spatial resolutions of about two arcminutes after gaussian tapering. At this observing wavelength, we expect to have a negligible non-thermal emission as the spectra is certainly dominated by free-free radio emission. We have measured flux densities and 3 mm luminosities which agree with a thermal blackbody spectra expected from data obtained with the IRAS satellite at wavelengths shorter than 80 μm. Data is presented for NGC3982, NGC5597, NGC5253, NGC1667, and NGC2997 and the main astrophysical consequences of such studies are discussed in this poster. We also argue that radio continuum at millimeter wavelengths is a better observational tool to study the star-formation in active galaxies than conventional infrared photometry.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

More than half of all low-redshift AGN exhibit UV and X-ray absorption by highly ionized gas. The observed UV and X-ray absorption lines are almost aiways blue-shifted at velocities of hundreds of km s−1, indicating that the absorbing gas is outflowing from the active nucleus. In some cases the inferred mass flux rivals the Eddington limit of the central black hole, an indication that these outflows are intimately related to the mass accretion and energy generation mechanism in AGN. The ejected material can also have an affect on the interstellar medium of the host galaxy and the surrounding intergalactic medium. Over the past several years, coordinated UV and X-ray observations of several bright AGN at high spectral resolution using HST, FUSE, Chandra, and XMM-Newton have contributed greatly to our understanding of these outflows. I will give an overview of these recent observations, summarize our FUSE survey of low-redshift AGN, and interpret the results in the context of models of winds from accretion disks and thermally driven winds from the obscuring torus.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present completed results of a high resolution radio imaging survey of the Palomar Spectroscopic Sample of all (∼470) nearby bright northern galaxies. Almost half the Palomar sample's galaxies have nuclei with emission-lines characteristic of AGN but with LHα ≤ 1040 erg s−1. These are referred to as low-luminosity AGNs or LLAGNs. The power source of such LLAGNs has been long debated. High resolution radio surveys of the sample – with the VLA at 15 GHz (150 mas resolution), and the VLBA at 5 GHz (2 mas resolution) – have now revealed a high incidence of pc-scale radio cores with implied brightness temperatures [gsim ]108K, and sub-parsec scale jets. The results support the presence of accreting black holes in ≥50% of all LLAGNs; there is no evidence against all LLAGNs being mini-AGNs. The detected parsec-scale radio nuclei are preferentially found in massive ellipticals and in type 1 nuclei (i.e. nuclei with broad Hα emission). These nuclei follow the usual correlations between radio and emission-line gas properties found in more powerful AGNs. The radio luminosity function (RLF) of Palomar Sample LLAGNs extends three orders of magnitude below, and is continuous with, that of ‘classical’ AGNs. We find marginal evidence for a low-power turnover in the RLF; nevertheless LLAGNs are responsible for a significant fraction of accretion in the local universe. Low accretion rates (≤10−2−10−3 of the Eddington rate) are implied in both advection- and jet-type models. Within the context of jet models, the accretion energy output is dominated by the energy in the observed jets rather than the radiated bolometric luminosity. These jets would be able to dump sufficient energy into the innermost parsecs to significantly slow the accretion inflow. Detailed results can be found in Nagar et al. (2002, 2004) and references therein.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present some preliminary results from an on-going study of the evolution of stellar populations in rich clusters of galaxies. Our baseline sample contains core line-strength measurements from 183 galaxies with $b_{\rm J} \le 19.5$ from four clusters with $\bar{z}\sim0.04$, against which observations of higher-redshift clusters can be compared. Using predictions from stellar population models to compare with our measured line strengths we can derive relative luminosity-weighted mean ages and metallicities for the stellar populations in each of our clusters. It must be stressed that these ages and metallicities are only accurate when used in a relative sense as the stellar population models, due to differing abundance ratios used in the models compared to those observed in elliptical galaxies, provide inaccurate absolute ages and metallicities. We also investigate the ${\rm Mg}b^\prime$-$\sigma_0$ and H$\beta_G^\prime$-$\sigma_0$ scaling relations. We find that ${\rm Mg}b^\prime$ is correlated with $\sigma_0$, the likely explanation being that larger galaxies are better at retaining their heavier elements due to their larger potentials. ${\rm H}\beta_G^\prime$, on the other hand, we find to be anti-correlated with $\sigma_0$. This result implies that the stellar populations in larger galaxies are older than in smaller galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The intrinsic emission of obscured active galactic nuclei (AGN) cannot be measured directly, but the obscured examples uniquely allow determination of the physical conditions near the central engine on 10–100 pc scales. The reprocessed radiation that emerges at X-ray and infrared energies, in particular, reveals the distribution of the obscuring medium. In general, X-ray spectroscopy shows the total column density along the line of sight, and in extremely obscured (Compton thick) cases, the fluorescent iron Kα emission line is sensitive to viewing angle and covering fraction. Observed near- and mid-infrared spectra require an inhomogeneous distribution of material around the AGN, and they specifically depend on parameters such as the optical depth per obscuring cloud and the number of clouds along the line of sight. The total spatial extent of the obscuring region determines the shape of the far-infrared spectrum.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We study the effects of radiative cooling, star formation and stellar feedback on the properties and evolution of galaxy clusters using high-resolution Adaptive Mesh Refinement N-body+gasdynamics simulations of clusters forming in the $\Lambda$CDM universe. Cooling leads to the condensation of gas in the inner regions of clusters, which in turn leads to steepening of the dark matter profile. The cooling gas is replaced by the higher-entropy gas from the outer regions, which raises the entropy and temperature of gas in the cluster core. The magnitude of these effects is likely overestimated in the current simulations because they suffer from the overcooling problem: a much larger fraction of baryons is in the form of cold gas and stars than is observed. We find that the thermal stellar feedback alone does not remedy this problem. Additional ad-hoc preheating can lower the amount of cold gas but a simple uniform preheating results in incorrect star formation history, as it delays the bulk of star formation until $z<1$. Our analysis shows that the overcooling in a cluster as a whole is really the overcooling in the central galaxy and its progenitors at high redshifts. This indicates that an additional heating mechanism that can continuously heat the gas in the cluster core is required to reproduce the observed cluster properties. Energy injection by the Active Galactic Nuclei, which may provide such heating, may thus be an important missing ingredient in the current theoretical models of cluster formation.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Here we present a self-consistent stationary solution for spherically symmetric winds driven by massive star clusters under the impact of radiative cooling. We demonstrate that cooling may modify drastically the distribution of temperature and the observational appearance of star cluster winds if the rate of injected energy approaches a critical value, and that the stationary wind solution does not exist if the energy deposition rate exceeds this limit.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The discovery of diffuse synchrotron radio emission and, more recently, of the hard X-ray (HXR) tails have triggered a growing interest about non-thermal phenomena in galaxy clusters. After a brief review of the most important evidences for non-thermal emission, I will focus on the origin of the emitting particles and of the hadronic component. In particular I will describe the particle-injection and -acceleration mechanisms at work in the intra-cluster medium (ICM) and, at the same time, discuss the possibility to test current modellings of these phenomena with future radio, HXR, and gamma ray observatories.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present a method for deriving light-weighted stellar metallicities and ages from high-resolution galaxy spectra, based on the new population synthesis code of Bruzual & Charlot (2003). The method relies on the simultaneous fit of several optical spectral absorption features that are sensitive to either age or metallicity, but not to the $\alpha$-elements abundance ratio. We have constructed a library of stochastic star formation histories, which we have used to derive median-likelihood estimates of ages and metallicities for $\sim10^5$ galaxies extracted from the Sloan Digital Sky Survey Data Release One (SDSS DR1), spanning the full range in star formation activities, from dormant early type to actively star forming. Here we discuss the results for early-type galaxies. We show that the $g-r$, $M_r$ color-magnitude relation for these galaxies is driven primarily by changes in metallicity and in heavy-element abundance ratios. Changes in light-weighted age contribute mainly to the scatter about the relation. This is consistent with previous interpretations of this relation based on lower resolution models.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html