We have studied the host-galaxy morphologies of narrow- and broad-line Seyfert 1 galaxies (NLS1s and BLS1s) based on broad-band optical images from the Hubble Space Telescope archives. We find that large-scale stellar bars, spanning 1–10 kpc from the nucleus, are much more common in NLS1s than BLS1s. Furthermore, the fraction of NLS1 spirals that have bars increases with decreasing full-width at half-maximum (FWHM) of the broad component of Hβ. This suggests a link between the large-scale bars, which can support high fueling rates to the inner kpc, and the high mass-accretion rates associated with the supermassive black holes in NLS1s. A preliminary examination of the inner (<1 kpc) dust morphologies has revealed no significant differences between NLS1s and BLS1s, except that we confirm the previous finding that galaxies with large-scale bars have a much higher frequency of “grand design” nuclear dust spirals.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

I briefly report on the work conducted to probe the gravitational potential of active and non-active disk galaxies using gas and stellar kinematics.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In an effort to elevate to higher grounds our understanding on the impact of the formation and evolution of bars in the formation and evolution of galaxies, we have developed a diagnostic tool to distinguish between recently formed and evolved bars. Our method was applied in the study of a sample of 14 galaxies and revealed that, apparently, AGN activity tends to appear in galaxies which have young bars rather than evolved bars. This suggests that the time scale for the fueling of AGN by bars is short, and may help to explain, for instance, why there is not a clear correlation between the presence of bars and AGN in galaxies.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

Nuclear spirals can provide a wealth of information about the nuclear potential in disc galaxies. They form naturally as a gas response to non-axisymmetry in the gravitational potential, even if the degree of this asymmetry is very small. Linear wave theory well describes weak nuclear spirals, but stronger asymmetries in the potential induce waves beyond the linear regime, which appear as spiral shocks. If a central massive black hole (MBH) is present, spiral shocks can extend all the way to its immediate vicinity, and generate gas inflow up to 0.03 M$_{\odot}\,$ yr−1. This coincides with the accretion rates needed to power local Active Galactic Nuclei.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We identify 175 Seyfert galaxies from the Southern Sky Redshift Survey – SSRS2. We use the entire SSRS2 catalog to investigate the correlation between the presence of AGN with host environment. The AGN phenomenon is more strongly correlated with the internal host properties than with the external environment. In particular, we find that Seyferts reside in more luminous galaxies, and are twice as frequent in barred galaxies and systems showing signs of advanced merger condition, when compared to a control sample.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Atomic gas in the central kiloparsec of young radio galaxies is quite prevalent, as revealed by 21cm H I absorption line observations using the WSRT. The column depths are anti-correlated with the linear sizes of the radio sources, but VLBI reveals that sometimes the neutral hydrogen is situated in a disk or torus on parsec or sub-kiloparsec scales around the central engine, while in other cases the H I is probably associated with star-forming regions along the jets. NGC 1052 is a nearby example, in which, next to some isolated clouds along the jets, there appears to be an atomic and molecular torus with a radius of a few parsecs, but with a central hole of about 0.5 pc, in which the gas is mostly ionised.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

From hydrodynamical simulations for the response of gaseous disks to imposed potentials, including those of a bar and supermassive black hole (SMBH), we found that the morphology of nuclear features developed by gas flows driven by the bar depends strongly on the sound speed of gas and the mass of SMBH which governs the potential shape in the central kiloparsec. Thus, nuclear features seem to provide a promising diagnostic for the inner dynamics of spiral galaxies. Specifically, a tightly wound grand-design nuclear spiral that winds more than 2π indicates the presence of an SMBH which is massive enough to remove the IILR.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

During the last decades many authors have concentrated their efforts on understanding what are the most efficient mechanisms to feed an AGN. Several solutions have been proposed, as the presence of circumnuclear star clusters, nuclear bars/disks/spirals, and the interaction between galaxies, in form of close encounters and mergers. Here we present new results about an isolated, intermediate-type Seyfert galaxy, Mrk315. The analysis of broad- and narrow-band images, and integral field spectra revealed a spiral-like structure hidden under the E/S0 morphology of the galaxy, and confirmed the presence of a nuclear jet-like feature, forming a sort of very extended “hook”. Moreover, our data confirmed the supposed nature of the already known knot, located at 2” from the active nucleus, as a secondary nucleus, residual of a minor merger bewteen the galaxy and a small nucleated companion.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

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

MRC B1221–423 is a powerful, nearby (z = 0.17) compact radio source, which lies within the envelope of a galaxy which is undergoing a tidal interaction with a companion. Broad-band optical/NIR colours show evidence of several distinct episodes of star formation. The evidence points to this being a radio source “caught in the act” of its first ignition.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

Studies in optical starlight have failed to reach a consensus on the importance of either galaxy interactions, bars, or nuclear spirals in triggering luminous active galactic nuclei (AGNs). Here, we present the first systematic imaging study of Seyfert (disk) galaxies in the 21-cm line of neutral atomic hydrogen (HI) gas. HI is the most sensitive and enduring tracer of galaxy interactions, and can reveal tidal features not otherwise visible in optical starlight. Our sample comprises all twenty-eight galaxies in the Véron-Cetty & Véron (1998) catalog with nuclear magnitudes −19 ≥ MB > −23 (including Seyfert, LINER, and HII galaxies) at 0.015 ≤ z ≤ 0.017 in the northern hemisphere, and a matched control sample of twenty-seven inactive galaxies at z≈0.008. We have detected nearly all the galaxies observed, and find a much higher incidence of tidal interactions — usually not seen in optical starlight — among the Seyfert galaxies by comparison with the matched control sample. Those Seyferts with uncertain or no clear tidal features show disturbed HI morphologies and/or kinematics, as well as HI companion galaxies, more frequently than the control sample. Our study suggests that the undisturbed optical appearence of active galaxies may be deceptive, and imply that galaxy-galaxy interactions trigger a significant fraction luminous AGNs at low redshifts. The majority of the Seyfert galaxies in our sample appear to be at a relatively early stage of an encounter rather than late in a merger.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We have compared galaxies hosting an active nucleus with non-active galaxies in the SDSS by analyzing their stellar populations. We conclude that the Seyfert 2 phenomenon appears in galaxies of intermediate masses (∼2 × 1010 M$_\odot$), while low mass galaxies do not produce active nuclei, and high mass galaxies tend to produce a low level of non-stellar activity. We also compared the environment of active and non-active galaxies of similar masses and concluded that there is no excess of close neighbors among the Seyferts when compared with non-active galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We study AGN jet formation by means of exact solutions of the relativistic magnetohydrodynamic equations. This is an original extension in Schwarzchild's metric of previous meridionally self-similar models. The outflow is mainly thermally driven to high asymptotic speeds from the central region where the escape speed is also high. The jet solutions are magnetically collimated on the sub-parsec scale.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

Global three-dimensional (3D) magneto-hydrodynamical (MHD) simulations of accretion flow have been extensively performed recently. We calculate the emergent spectra from 3D MHD flows by the Monte Carlo radiative transfer simulations, and examine to what extent simulated MHD flows can account for the observed spectrum of Sagittarius A* (Sgr A*). It is found that the emergent spectrum from the inner part of the MHD flow (r<10rs) is consistent with the observations in the X-ray flaring state of Sgr A*, where rs is the Schwarzschild radius. However, the MHD flow can not reproduce the spectrum in the quiescent state.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Using N-body numerical simulations, we investigate the stability of a nuclear disk of a few pc characteristic radius, around a supermassive black hole (SBH), and embedded in a galactic bulge. We find that with an SBH of a suitable range of mass, placed at its center, the nuclear disk is subject to one-armed (m=1) natural instabilities. We propose a feedback cycle for this mode, based on waves between corotation and OLR, and where the “indirect term”, and the massive bulge play a fundamental role. Nuclear disks formed from accreted gas could be the precursors of this type of structure and may be common in central regions of galaxies. Density waves could be an efficient mechanism of fueling the gas in the central few tens of parsecs in galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We compare the circumnuclear stellar population and environmental properies of Seyfert and Composite (Seyfert + Starburst) nuclei with those of LINERs and LINER/HII transition galaxies (TOs), and discuss evidence for evolution from Seyfert/Composite to LINER/TO nuclei.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html