Table of contents

We are pleased to present the proceedings from the Astronomy at High Angular Resolution 2011: The central kiloparsec in galactic nuclei conference. The conference took place in the Physikzentrum of the Deutsche Physikalische Gesellschaft (DPG), Bad Honnef, Germany, from 28 August to 2 September 2011. It was the second conference of this kind, following the Astronomy at High Angular Resolution conference held in Bad Honnef, three years earlier in 2008.

The main objective of the conference was to frame the discussion of the broad range of physical processes that occur in the central 100pc of galactic nuclei. In most cases, this domain is difficult to probe through observations. This is mainly because of the lack of angular resolution, the brightness of the central engine and possible obscurations through dust and gas, which play together in the central regions of host galaxies of galactic nuclei within a broad range of activity. The presence of large amounts of molecular and atomic (both neutral and ionized) gas, dust and central engines with outflows and jets implies that the conditions for star formation in these regions are very special, and probably different from those in the disks of host galaxies.

Numerous presentations covering a broad range of topics, both theoretical and experimental, those related to research on Active Galactic Nuclei and on a wide range of observed wavelengths were submitted to the Scientific Organizing Committee. Presentations have been grouped into six sessions:

• The nuclei of active galaxies

• The Galactic Center

• The immediate environment of Super Massive Black Holes

• The physics of nuclear jets and the interaction of the interstellar medium

• The central 100pc of the nuclear environment

• Star formation in that region

The editors thank all participants of the AHAR 2011 conference for their enthusiasm and their numerous and vivid contributions to this conference. We would especially like to thank John Hugh Seiradakis from the Aristotle University of Thessaloniki in Greece for giving the dinner talk on the most astounding ancient Antikythera mechanism. We would also like to thank Victor Gomer and the staff of the Physikzentrum of the Deutsche Physikalische Gesellschaft in Bad Honnef where the conference took place. Last but not least we would like to thank all unnamed helpers, without whom the organisation of this conference would not have been possible.

Financial support for this conference was granted by the Deutsche Forschungsgemeinschaft (DFG) Sonderforschungsbereich project number SFB 956. We also acknowledge support from the European Community Framework Programme 7, Advanced Radio Astronomy in Europe, grant agreement no. 227290.

Christof Iserlohe, Vladimir Karas, Melanie Krips, Andreas Eckart, Silke Britzen and Sebastian Fischer

The Editors

Conference Group Photo, 1 September 2011

The PDF also contains additional photographs from the conference and the Contents of the Proceedings.

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

The latest results from our Quasar-ULIRG Evolution Study (QUEST) are described with an emphasis on the recent scientific breakthroughs on the issue of quasar feedback.

We summarize our recent results on the evolution of super-massive black holes in the cores of galaxies. Our models are based on the viscous, Eddington-limited evolution of self-gravitating accretion disks. We find that, within this framework, one can explain the growth time scales and the luminosities of individual objects as well as the variation of these quantities for AGN with different black hole masses.

The sheer range of scales in the Universe makes it impossible to model all at once. It is necessary, therefore, when conducting numerical experiments, that we employ sub-resolution prescriptions that can represent the scales we are unable to model directly. In this article we present a prescription for black hole growth that incorporates a different accretion regime from the standard approach used in the literature, and discuss the results of dedicated simulations of intermediate processes between small-scale accretion flows and large-scale cosmological volumes that can strongly enhance the accretion rate onto the black hole at the centre of a galaxy.

We present near-to-mid-infrared spectral energy distributions (SEDs) for 21 Seyfert galaxies, using subarcsecond resolution imaging data. Our aim is to compare the properties Seyfert 1 (Sy1) and Seyfert 2 (Sy2) tori using clumpy torus models and a Bayesian approach to fit the infrared (IR) nuclear SEDs. These dusty tori have physical sizes smaller than 6 pc radius, as derived from our fits. Active galactic nuclei (AGN) unification schemes account for a variety of observational differences in terms of viewing geometry. However, we find evidence that strong unification may not hold, and that the immediate dusty surroundings of Sy1 and Sy2 nuclei are intrinsically different. The Type 2 tori studied here are broader, have more clumps, and these clumps have lower optical depths than those of Type 1 tori. The larger the covering factor of the torus, the smaller the probability of having direct view of the AGN, and vice-versa. In our sample, Sy2 tori have larger covering factors (C_T = 0.95±0.02) and smaller escape probabilities than those of Sy1 (C_T = 0.5±0.1). Thus, on the basis of the results presented here, the classification of a Seyfert galaxy may depend more on the intrinsic properties of the torus rather than on its mere inclination, in contradiction with the simplest unification model.

We present MERLIN 18 cm radio continuum observations of three 0.4 < z < 0.8 broad-absorption-line (BAL) quasi-stellar objects (QSOs). The question, whether BAL QSOs can be interpreted in a pure orientation scheme, or whether evolutionary aspects have to be taken into account, is still a matter of debate. Radio-interferometric observations can provide additional information about both aspects. The presence of jets, their orientation, and beaming can provide clues on the orientation of the nuclear components. On the other hand, the compactness of the nuclear radio emission and its spectral index can provide information about the evolutionary state of the AGN, and of starbursts, if present.

The inner structure of AGNs is expected to change below a certain luminosity limit. The big blue bump, footprint of the accretion disk, is absent for the majority of low-luminosity AGNs (LLAGNs). Moreover, recent simulations suggest that the torus, a keystone in the Unified Model, vanishes for nuclei with L_bol ≲ 10⁴² erg s⁻¹ . However, the study of LLAGN is a complex task due to the contribution of the host galaxy, which light swamps these faint nuclei. This is specially critical in the IR range, at the maximum of the torus emission, due to the contribution of the old stellar population and/or dust in the nuclear region. Adaptive optics imaging in the NIR (VLT/NaCo) together with diffraction limited imaging in the mid-IR (VLT/VISIR) permit us to isolate the nuclear emission for some of the nearest LLAGNs in the Southern Hemisphere. These data were extended to the optical/UV range (HST), radio (VLA, VLBI) and X-rays (Chandra, XMM-Newton, Integral), in order to build a genuine spectral energy distribution (SED) for each AGN with a consistent spatial resolution (< 0''.5) across the whole spectral range. From the individual SEDs, we construct an average SED for LLAGNs sampled in all the wavebands mentioned before. Compared with previous multiwavelength studies of LLAGNs, this work covers the mid-IR and NIR ranges with high-spatial resolution data. The LLAGNs in the sample present a large diversity in terms of SED shapes. Some of them are very well described by a self-absorbed synchrotron (e.g. NGC 1052), while some other present a thermal-like bump at ∼ 1 μm (NGC 4594). All of them are significantly different when compared with bright Seyferts and quasars, suggesting that the inner structure of AGNs (i.e. the torus and the accretion disk) suffers intrinsic changes at low luminosities.

The F-GAMMA program is a coordinated effort to investigate the physics of Active Galactic Nuclei (AGNs) via multi-frequency monitoring of Fermi blazars. In the current study we show and discuss the evolution of broad-band radio spectra, which are measured at ten frequencies between 2.64 and 142 GHz using the Effelsberg 100-m and the IRAM 30-m telescopes. It is shown that any of the 78 sources studied can be classified in terms of their variability characteristics in merely 5 types of variability. It is argued that these can be attributed to only two classes of variability mechanisms. The first four types are dominated by spectral evolution and can be described by a simple two-component system composed of: (a) a steep quiescent spectral component from a large scale jet and (b) a time evolving flare component following the "Shock-in-Jet" evolutionary path. The fifth type is characterised by an achromatic change of the broad band spectrum, which could be attributed to a different mechanism, likely involving differential Doppler boosting caused by geometrical effects. Here we present the classification, the assumed physical scenario and the results of calculations that have been performed for the spectral evolution of flares.

We review how the masses of black holes in active galactic nuclei are measured and outline the current limitations and uncertainties. Masses have been measured directly by emission-line reverberation for nearly 50 relatively nearby AGNs, but uncertainties due to the unknown geometry and projection effects limit the accuracy of these masses to ∼ 0.3 dex. Reverberation studies show that there is a very tight relationship between the broad-line region radius and the AGN luminosity, with an intrinsic scatter of ∼ 0.1 dex, which shows (1) that the largest source of systematic uncertainty in the black hole mass determinations is how the velocity field of the broad-line region is characterized, not the size of the broad-line region, and (2) that the size of the broad-line region can be estimated to fairly high accuracy from the AGN luminosity alone, thus providing a powerful indirect method of estimating black hole masses in even distant AGNs.

Interferometric resolution at IR wavelengths offers for the first time the possibility to zoom into the nuclei of galaxies beyond the circumnuclear stellar structures and spatially resolve gas and dust in the innermost regions (0.05-5pc), dominated by the central black hole. Ultimate goal is to reveal new aspects of AGN feeding, and interaction with its host galaxy. After first successes of resolving AGN with infrared interferometry (VLTI, Keck-IF), the second generation of high-resolution interferometric imagers behind 8m class telescopes is currently being built. I will summarize current aspects and successes of the field, and present our activities to provide extended capabilities for VLTI-Midi and -Matisse, LBT-Linc-Nirvana and Keck-Astra to study a larger sample of AGN in greater detail.

We analyze the emission properties of a new sample of 3 596 type 1 AGN, selected from the SDSS DR7 based on the detection of broad Hα emission. The sample extends over a broad Hα luminosity L_bHα of 10⁴⁰–10⁴⁴ erg s⁻1 and a broad Hα FWHM of 1 000–25 000 km s⁻¹, which covers the range of black hole mass 10⁶ < M_BH/M⊙ < 10^9.5 and luminosity in Eddington units 10⁻³ < L/L_Edd < 1. We combine ROSAT, GALEX and 2MASS observations to form the SED from 2.2 μm to 2 keV. We find the following: 1. The distribution of the Hα FWHM values is independent of luminosity. 2. The observed mean optical-UV SED is well matched by a fixed shape SED of luminous quasars, which scales linearly with L_bHα, and a host galaxy contribution. 3. The host galaxy r-band (fibre) luminosity function follows well the luminosity function of inactive non-emission line galaxies (NEG), consistent with a fixed fraction of ∼ 3% of NEG hosting an AGN, regardless of the host luminosity. 4. The optical-UV SED of the more luminous AGN shows a small dispersion, consistent with dust reddening of a blue SED, as expected for thermal thin accretion disc emission. 5. There is a rather tight relation of νL_ν(2 keV) and L_bHα, which provides a useful probe for unobscured (true) type 2 AGN.

We present recent results of magnetohydrodynamic (MHD) simulations of jet formation and propagation, discussing a variety of astrophysical setups. In the first approach the role of the disk magnetic flux profile and disk mass flux profile concerning the jet collimation degree is investigated. Our results suggest (and quantify) that in general magnetized outflows launched from a compact region close to the inner disk radius tend to be less collimated. The second setup considers simulation of relativistic MHD jet formation, considering jet launched from the surface of a Keplerian disks, demonstrating - for the first time - the self-collimating ability of relativistic MHD jets. We obtain Lorentz factors up to ≃ 10 while acquiring a high degree of collimation of about 1 degree. We then present MHD jet formation simulations taking into account radiation pressure of a central luminous source. We investigate radiative effects on jet collimation and propagation - an environment which is interesting for outflows from massive young stars and active galactic nuclei. Finally, we present a model which explains a possible jet rotation by shock compression of an intrinsic helical magnetic field.

Spectral energy distributions (SEDs) of the central few tens of parsecs of some of the nearest active galactic nuclei [AGN] have been used to construct a genuine redshift-zero SED template [1]. This paper presents the comparison between this redshift-zero template and those of the radio loud and radio quiet quasar templates by [2]. Despite the four orders of magnitude difference in power between the redshift-zero AGNs, mostly Seyfert galaxies, and that of quasars, they all show a remarkable similarity. The distinction relays on the importance of the so-called blue bump component – emission from the accretion disk - which is absent in Seyfert type 2, mildly present in Seyfert type 1, seen in full realm in quasars. Conversely, the characteristic red bump component - dust reprocessed emission in the IR - is present in all cases. The difference between the three AGN classes can be ascribed in terms of central dust obscuration and progressive view angle of the nuclear core.

Strong broad emission lines are the most important signatures of active galactic nuclei. These lines allowed to discover the cosmological nature of quasars, and at present these lines allow for convenient method of weighting the black holes residing in their nuclei. However, a question remains why such strong lines form there in the first place. Specifically, in the case of Low Ionization Lines, there must be a mechanism which leads to an efficient rise of the material from the surface of the accretion disk surrounding a black hole but at the same time should not give a strong signature of the systematic outflow, as the Balmer lines are not significantly shifted with respect to the Narrow Line Region. We determine the effective temperature of the accretion disk underlying the Hβ line at the basis of the time delay measured from reverberation and the simple Shakura-Sunyaev theory of accretion disks. We obtain that this temperature is universal, and equal 995 ± 74 K, independently from the black hole mass and accretion rate of the source. This result suggests to us that the dust formation in the disk atmosphere is responsible for the strong rise of the material. However, as the material gains height above the disk it becomes irradiated, the dust evaporates, the radiation pressure force suddenly drops and the material fall back again at the disk. Therefore, a failed wind forms. In the simple version of the model the disk irradiation is neglected, but in the present paper we also discuss this irradiation and we use the observed variation of the Broad Line Region in NGC 5548 to constrain the character of this non-local non-stationary phenomenon. The current instruments cannot resolve the Broad Line Region but future instrumentation may allow to test the model directly.

NGC 4151 is a Seyfert 1.5 galaxy. Due to its proximity of only 13 Mpc it is an ideal testbed and therefore one of the most intensively studied Seyfert galaxies. NGC4151 shows an outflow in the Narrow Line Region (NLR) along the NE and SW direction. This outflow has been modelled by several authors ([9], [10] and [11]) as two hollow bi-cones. The excitation conditions in the NLR have been investigated by [11] and have been attributed to photoionization due to the central engine. [4] also observed a linear radio structure in the inner few parsec with a pronounced S-like curvature which is slightly misaligned with the bi-cones major axes. Here we compare these findings with our results and discuss the role of the radio jet. We also refer the reader to the full paper (Iserlohe et. al., 2012) which will be published soon.

We present the results of near-infrared (NIR) H+K ESO-SINFONI integral field spectroscopy (IFS) of the Seyfert 2 galaxy NGC 7172. The aim is to investigate the central 800pc, concentrating on excitation conditions, morphology and stellar content. The NIR is less influenced by dust extinction than optical light and therefore yields a close undisturbed look at the central region.

In this proceedings we concentrate on emission line measurements in the central 800pc of NGC 7172. The detection of [SiVI] and broad Paa and Brγ components are clear signs of an accreting super-massive black hole (SMBH) which hides behind the prominent dustlane. Temperatures of about 1400K show evidence of hot dust in the nuclear region. Narrow components of Paα and Brγ allow for an extinction measurement. The molecular hydrogen lines, hydrogen recombination lines and [FeII] point out that the excitation of these lines is caused by an AGN. The findings show evidence for nuclear activity located behind the prominent dustlane crossing the central region of the galaxy. The nucleus of NGC 7172 is a Seyfert 1 nucleus either surrounded or hidden by a molecular dust torus. Our observation aids the unified model scheme in its basic proposition, however, we can not conclude the shape of the torus due to our spatial resolution.

We report on measurements of the luminosity function of early (young) and late-type (old) stars in the central 0.5 pc of the Milky Way nuclear star cluster as well as the density profiles of both components. The young (∼ 6 Myr) and old stars (> 1 Gyr) in this region provide different physical probes of the environment around a supermassive black hole; the luminosity function of the young stars offers us a way to measure the initial mass function from star formation in an extreme environment, while the density profile of the old stars offers us a probe of the dynamical interaction of a star cluster with a massive black hole. The two stellar populations are separated through a near-infrared spectroscopic survey using the integral-field spectrograph OSIRIS on Keck II behind the laser guide star adaptive optics system. This spectroscopic survey is able to separate early-type (young) and late-type (old) stars with a completeness of 50% at K' = 15.5. We describe our method of completeness correction using a combination of star planting simulations and Bayesian inference. The completeness corrected luminosity function of the early-type stars contains significantly more young stars at faint magnitudes compared to previous surveys with similar depth. In addition, by using proper motion and radial velocity measurements along with anisotropic spherical Jeans modeling of the cluster, it is possible to measure the spatial density profile of the old stars, which has been difficult to constrain with number counts alone. The most probable model shows that the spatial density profile, n(r) ∝ r^−γ, to be shallow with γ = 0.4 ± 0.2, which is much flatter than the dynamically relaxed case of γ = 3/2 to 7/4, but does rule out a 'hole' in the distribution of old stars. We show, for the first time, that the spatial density profile, the black hole mass, and velocity anisotropy can be fit simultaneously to obtain a black hole mass that is consistent with that derived from individual orbits of stars at distances < 1000 AU from the Galactic center.

The Galactic Center (GC) hosts a population of young stars some of which seem to form a system of mutually inclined warped discs. While the presence of young stars in the close vicinity of the massive black hole is already problematic, their orbital configuration makes the situation even more puzzling. We present a possible warped disc origin scenario for these stars, which assumes an initially flat accretion disc which develops a warp through Pringle instability, or Bardeen-Petterson Effect. By working out the critical radii and the time scales involved, we argue that disc warping is plausible for GC parameters. We construct time evolution models for such discs considering the discs' self-gravity, and the torques exerted by the surrounding old star cluster. Our simulations suggest that the best agreement for a purely self-gravitating model is obtained for a disc-to-black hole mass ratio of M_d/M_bh ∼ 0.001.

Origin of several hundreds of young stars in within the distance ≲ 1pc from the Galactic supermassive black hole still represents an open problem of contemporary astrophysics. In this contribution we further investigate the model which assumes their formation in situ via fragmentation of a self-gravitating gaseous disc. We show that currently observed configuration of the system of young stars can be obtained as an outcome of a dynamical evolution of a single, initially very thin stellar disc. Our model assumes the long-term evolution of the stellar disc to be determined by gravitational influence of a distant molecular torus (CND) and mutual resonances of stellar orbits within the disc.

We present for the first time, an infrared data-cube of the central parsec of our Galaxy in the 2.8 to 4.2 micron range. This spectral band (the L-band) harbors important signatures of the interstellar and circumstellar medium, since the water ice absorption feature at 3 micron traces the dense medium and the hydrocarbon absorption at 3.4 micron is only observed in the diffuse gas.

Thanks to a calibrator spectrum of the foreground extinction in the L-band derived in a previous paper, we corrected our data-cube for the line of sight extinction. Our observations performed with ISAAC spectrograph at the VLT-ESO telescope suggest that part of the absorption features takes place in the local environment of the Galactic center. This induces the presence of very low temperatures in the central parsec.

The central black hole of the Milky Way, Sagittarius A* (SgrA*) is, in terms of Eddington luminosity, the weakest accreting object of its class accessible to detailed observations. It is therefore key to the refinement of theoretical models of radiatively inefficient accretion. Unfortunately, our knowledge of the mean SED of Sgr A* is very limited. Current models rely almost exclusively on cm to mm mean flux measurements and only on upper limits at infrared to soft X-ray wavelengths. Here, we present a new analysis of imaging data of the Galactic center (GC) at 2.2 to 8.6 microns, obtained with NACO and VISIR at the ESO VLT. We used the VISIR burst mode combined with a novel implementation of the holographic image reconstruction algorithm to obtain mid-infrared images with a Strehl ratio ≫ 90% even under conditions of ∼2 – 3" seeing in the visual. No counterpart of Sgr A* is detected at 8.6 microns. At this wavelength, Sgr A* is located right on top of a dust ridge, which considerably complicates the search for a potential point-source. Based on the available data, it is argued that Sgr A* cannot be detected in the MIR with currently available instruments, not even during flares. At 3.8 and 4.8 μm SgrA* is detected at all times. We measure the time-averaged mean fluxes of Sgr A* at these wavelengths. From the literature there is evidence that SgrA* is also detected at 2.2 μm most of the time. The new measurements of the mean, quiescent emission of SgrA* fill a gap of almost 6 orders of magnitude in its known mean SED and provide novel constraints on accretion/emission models.

The GC offers unique opportunities to study stellar and bow-shock polarization effects in a dusty environment. NIR polarimetry of the stellar and bow-shock sources in the central parsec is presented for the first time at NACO resolution (AO assisted, ESO VLT). We present polarization maps of the central 3"×19" and spatially resolved polarimetry of the known extended bow-shock sources in this region. The measured foreground polarization is largely parallel to the Galactic plane, with average values of 5.5% at 15° (Ks-band) and 9.5% at 20° (H-band) in the center of the FOV. These values vary over the field-of-view, and we suggest that this may be caused by local dichroic extinction on dust grains in the Northern Arm of the Minispiral. It was possible to isolate the intrinsic polarization of the two bow-shock sources contained in the sample, IRS 21 and 1W, and both show similar intrinsic polarization degrees of 5.5% respectively 7.8% (Ks) and 6.9% (H, only 1W) at polarization angles coincident with previous MIR findings, both in total and spatially resolved. The spatial polarization pattern of both sources hints at the processes likely responsible for the intrinsic polarization: scattering on and emission from elongated, aligned grains.

Based on Bremer et al. (2011) and Eckart et al. (2012) we report on simultaneous observations and modeling of the millimeter, near-infrared, and X-ray flare emission of the source Sagittarius A* (SgrA*) associated with the super-massive (4×10⁶ M⊙) black hole at the Galactic Center. We study physical processes giving rise to the variable emission of SgrA* from the radio to the X-ray domain. To explain the statistics of the observed variability of the (sub-)mm spectrum of SgrA*, we use a sample of simultaneous NIR/X-ray flare peaks and model the flares using a synchrotron and SSC mechanism. The observations reveal flaring activity in all wavelength bands that can be modeled as the signal from adiabatically expanding synchrotron self-Compton (SSC) components. The model parameters suggest that either the adiabatically expanding source components have a bulk motion larger than v_exp or the expanding material contributes to a corona or disk, confined to the immediate surroundings of SgrA*. For the bulk of the synchrotron and SSC models, we find synchrotron turnover frequencies in the range 300-400 GHz. For the pure synchrotron models this results in densities of relativistic particles of the order of 10^6.5 cm⁻³ and for the SSC models, the median densities are about one order of magnitude higher. However, to obtain a realistic description of the frequency-dependent variability amplitude of SgrA*, models with higher turnover frequencies and even higher densities are required. We discuss the results in the framework of possible deviations from equilibrium between particle and magnetic field energy. We also summarize alternative models to explain the broad-band variability of SgrA*.

Ongoing millimeter VLBI observations with the Event Horizon Telescope allow unprecedented study of the innermost portion of black hole accretion flows. Interpreting the observations requires relativistic, time-dependent physical modeling. We discuss the comparison of radiative transfer calculations from general relativistic MHD simulations of Sagittarius A* and M87 with current and future mm-VLBI observations. This comparison allows estimates of the viewing geometry and physical conditions of the Sgr A* accretion flow. The viewing geometry for M87 is already constrained from observations of its large-scale jet, but, unlike Sgr A*, there is no consensus for its millimeter emission geometry or electron population. Despite this uncertainty, as long as the emission region is compact, robust predictions for the size of its jet launching region can be made. For both sources, the black hole shadow may be detected with future observations including ALMA and/or the LMT, which would constitute the first direct evidence for a black hole event horizon.

The Galactic center stellar disk and the circumnuclear ring provide a unique opportunity to study in detail the dynamics and physical conditions of distant molecular disks in the nuclei of galaxies. One of the key questions is how these disks form so close to their host black holes and under what condition they form stars in a tidally stressed environment. We argue that disk formation around a massive black hole is due to partial accretion of extended molecular clouds that temporarily pass through the central region of the Galaxy. The cancellation of angular momentum of the gravitationally focused gas naturally creates a compact gaseous disk. The disk can potentially become gravitationally unstable and form stars. We apply these ideas to explain the origin of sub-parsec megamaser disks found in the nuclei of Seyfert 2 galaxies. We show that an empirical scaling relation between the mass of the black hole and the size of the disk can be understood in the context of the cloud capture scenario. We conclude that the stellar and gas disks found in our Galactic center act as a bridge to further our understanding of more distant mega-maser disks in the nuclei of Seyfert 2 galaxies.

Sparse aperture masking (SAM) interferometry combined with Adaptive Optics (AO) is a technique that is uniquely suited to investigate structures near the diffraction limit of large telescopes. The strengths of the technique are a robust calibration of the Point Spread Function (PSF) while maintaining a relatively high dynamic range. We used SAM+AO observations to investigate the circumstellar environment of several bright sources with infrared excess in the central parsec of the Galaxy. For our observations, unstable atmospheric conditions as well as significant residuals after the background subtraction presented serious problems for the standard approach of calibrating SAM data via interspersed observations of reference stars. We circumvented these difficulties by constructing a synthesized calibrator directly from sources within the field-of-view. When observing crowded fields, this novel method can boost the efficiency of SAM observations because it renders interspersed calibrator observations unnecessary. Here, we presented the first NaCo/SAM images reconstructed using this method.

The Galactic nuclear bulge hosts significant populations of young stars, within a few hundred parsecs around the Galactic Centre, unlike the more extended bulge. Recently, we discovered classical Cepheid variable stars (hereinafter Cepheids) in the Galactic nuclear bulge. Their ages are estimated to be ∼ 25 Myr based on the period-age relation of Cepheids. They are the first clear evidence of star formation a few tens of Myr ago. In addition, the period distribution of the Cepheids indicates that star formation rate was enhanced around ∼ 25 Myr ago compared to between 30 and 70 Myr ago. Such detailed star formation history has never been obtained for central parts of other galaxies. The timescale of the change in star formation seems to be consistent with the value, ∼ 20 Myr, suggested for gas inflow into the nuclear bulge. We discuss its implication on the evolution of the nuclear bulge.

From a large-scale study of the Galactic center (GC) region in SiO(2 – 1), HCO⁺(1 – 0), and H¹³CO⁺(1 – 0), we identify shock regions as traced by the enhancement of SiO emission. We selected 9 positions called by us as "interaction regions", because they mark the places where gas in the GC could be interacting with gas coming from higher latitude ("disk-halo interaction") or from larger galactocentric radius. These positions were studied using the ¹²C/¹³C isotopic ratio to trace gas accretion/ejection. We found a systematically higher ¹²C/¹³C isotopic ratio (> 40) toward the interaction regions than for the GC "standard" molecular clouds (20 – 25). These high isotopic ratios are consistent with the accretion of the gas from higher galactic latitudes or from larger galactocentric distances. There are two kinetic temperature regimes (one warm at ∼ 200 K and one cold at ∼ 40 K) for all the positions, except for the positions associated to the giant molecular loops where only the warm component is present. Relative molecular abundances suggest that the heating mechanism in the GC is related to shocks. We mapped one molecular cloud placed at the foot points of the giant molecular loops in 3-mm molecular lines to reveal the morphology, chemical composition and the kinematics of the shocked gas.

We discuss the role of general relativity frame dragging acting on magnetic field lines near a rotating (Kerr) black hole. Near ergosphere the magnetic structure becomes strongly influenced and magnetic null points can develop. We consider aligned magnetic fields as well as fields inclined with respect to the rotation axis, and the two cases are shown to behave in profoundly different ways. Further, we construct surfaces of equal values of local electric and magnetic intensities, which have not yet been discussed in the full generality of a boosted rotating black hole.

We report the detection of the first VLBI ring-structure around the core of an AGN - around the core of the quasar 3C454.3. This ring-structure starts being visible in VLBI maps around 1996. It expands with an apparent velocity between 0.11±0.01mas/yr and 0.18±0.01mas/yr and dominates the pc-scale structure for at least 14 years. This is the result of a re-analysis of 41 VLBA data sets at six different radio frequencies observed between 1995.57 and 2011.48. We observe a correlation between radio flaring, flux-density variability, a ring-structure and kinematic properties of the jet. Taken together, it is tempting to see a causal connection and to explain all of this geometrically. The kinematic changes as well as the changes in the flaring characteristics might be caused by a change of the angle to the line of sight towards the observer. This behaviour resembles our findings for 0735+178 - with 3C454.3 being the second AGN to reveal kinematic mode changes.

These mode changes could be explained by the presence of a supermassive binary black hole. 3C454.3 had been modelled as a binary black hole before.

Recent discoveries by VERITAS, H.E.S.S., and MAGIC indicate that very-high-energy (VHE) gamma-rays may be produced in all types of blazars, including radio-loud quasars. In the dense nuclear radiation fields (BLR, dust torus IR) in these objects, VHE gamma-rays may be efficiently absorbed and initiate Compton-supported pair cascades. We have developed a Monte-Carlo code following the full 3-dimensional development of pair cascades in AGN environments. We have shown that even very weak magnetic fields may lead to efficient quasi-isotropization of the cascade emission, escaping predominantly in MeV – GeV gamma-rays. We propose this as a potential contributor to the Fermi gamma-ray flux from several radio galaxies, and present model fits to the Fermi-detected radio galaxies NGC 1275 and Cen A.

Accounting for ∼20% of the total QSO population, Broad Absorption Line QSOs are still an unsolved problem in the AGN context. They present wide troughs in the UV spectrum, due to material with velocities up to 0.2 c toward the observer. The two models proposed in literature try to explain them as a particular phase of the evolution of QSOs or as normal QSOs, but seen from a particular line of sight.

We built a statistically complete sample of Radio-Loud BAL QSOs, and carried out an observing campaign to piece together the whole spectrum in the cm wavelength domain, and highlight all the possible differences with respect to a comparison sample of Radio-Loud non-BAL QSOs. VLBI observations at high angular resolution have been performed, to study the pc-scale morphology of these objects. Finally, we tried to detect a possible dust component with observations at mm-wavelengths.

Results do not seem to indicate a young age for all BAL QSOs. Instead a variety of orientations and morphologies have been found, constraining the outflows foreseen by the orientation model to have different possible angles with respect to the jet axis.

Quasars and Active Galactic Nuclei (AGNs) are often obscured by dust and gas. It is normally assumed that the obscuration occurs in an oblate "obscuring torus", that begins at the radius at which the most refractive dust can remain solid. The most famous form of this torus is a donut-shaped region of molecular gas with a large scale-height. While this model is elegant and accounts for many phenomena at once, it does not hold up to detailed tests. Instead the obscuration in AGNs must occur on a wide range of scales and be due to a minimum of three physically distinct absorbers. Slicing the "torus" into these three regions will allow interesting physics of the AGN to be extracted.

With mid-IR and near-IR long-baseline interferometers, we are now mapping the radial distribution of the dusty accreting material in AGNs at sub-pc scales. We currently focus on Type 1 AGNs, where the innermost region is unobscured and its intrinsic structure can be studied directly. As a first systematic study of Type 1s, we obtained mid-/near-IR data for small samples over ∼3–4 orders of magnitudes in UV luminosity L of the central engine. Here we effectively trace the structure by observing dust grains that are radiatively heated by the central engine. Consistent with a naive expectation for such dust grains, the dust sublimation radius R_in is in fact empirically known to be scaling with L^1/2 from the near-IR reverberation measurements, and this is also supported by our near-IR interferometry. Utilizing this empirical relationship, we normalize the radial extent by R_in and eliminate the simple L^1/2 scaling for a direct comparison over the samples. We then find that, in the mid-IR, the overall size in units of R_in seems to become more compact in higher luminosity sources. More specifically, the mid-IR brightness distribution is rather well described by a power-law, and this power-law becomes steeper in higher luminosity objects. The near-IR flux does not seem to be a simple inward extrapolation of the mid-IR power-law component toward shorter wavelengths, but it rather comes from a little distinct brightness concentration at the inner rim region of the dust distribution. Its structure is not well constrained yet, but there is tentative evidence that this inner near-IR-emitting structure has a steeper radial distribution in jet-launching objects. All these should be scrutinized with further observations.

We present ground-based high-spatial resolution mid-infrared (MIR) observations of 20 nearby low-luminosity AGN (LLAGN) with VLT/VISIR and the preliminary analysis of a new sample of 10 low-luminosity Seyferts observed with Gemini/Michelle. LLAGN are of great interest because these objects are the most common among active galaxies, especially in the nearby universe. Studying them in great detail makes it possible to investigate the AGN evolution over cosmic timescale. Indeed, many LLAGN likely represent the final stage of an AGN's lifetime. We show that even at low luminosities and accretion rates nuclear unresolved MIR emission is present in most objects. Compared to lower spatial resolution Spitzer/IRS spectra, the high-resolution MIR photometry exhibits significantly lower fluxes and different PAH emission feature properties in many cases. By using scaled Spitzer/IRS spectra of typical starburst galaxies, we show that the star formation contribution to the 12 μm emission is minor in the central parsecs of most LLAGN. Therefore, the observed MIR emission in the VISIR and Michelle data is most likely emitted by the AGN itself, which, for higher luminosity AGN, is interpreted as thermal emission from a dusty torus. Furthermore, the 12 /amemission of the LLAGN is strongly correlated with the absorption corrected 2-10 keV luminosity and the MIR- X-ray correlation found previously for AGN is extended to a range from 10⁴⁰ to 10⁴⁵ erg/s. This correlation is independent of the object type, and in particular the low-luminosity Seyferts observed with Michelle fall exactly on the power-law fit valid for brighter AGN. In addition, no dependency of the MIR-X-ray ratio on the accretion rate is found. These results are consistent with the unification model being applicable even in the probed low-luminosity regime.

Warm gas and dust surround the innermost regions of active galactic nuclei (AGN). They provide the material for accretion onto the super-massive black hole and they are held responsible for the orientation-dependent obscuration of the central engine. The AGN-heated dust distributions turn out to be very compact with sizes on scales of about a parsec in the mid-infrared. Only infrared interferometry currently provides the necessary angular resolution to directly study the physical properties of this dust. Size estimates for the dust distributions derived from interferometric observations can be used to construct a size–luminosity relation for the dust distributions. The large scatter about this relation suggests significant differences between the dust tori in the individual galaxies, even for nuclei of the same class of objects and with similar luminosities. This questions the simple picture of the same dusty doughnut in all AGN. The Circinus galaxy is the closest Seyfert 2 galaxy. Because its mid-infrared emission is well resolved interferometrically, it is a prime target for detailed studies of its nuclear dust distribution. An extensive new interferometric data set was obtained for this galaxy. It shows that the dust emission comes from a very dense, disk-like structure which is surrounded by a geometrically thick, similarly warm dust distribution as well as significant amounts of warm dust within the ionisation cone.

We have obtained high-resolution mid-infrared (MIR) imaging, nuclear spectral energy distributions (SEDs) and archival Spitzer spectra for 22 low-luminosity active galactic nuclei (LLAGN; L_bol < 5 × 10⁴² erg s⁻¹). Infrared (IR) observations may advance our understanding of the accretion ows in LLAGN, the fate of the obscuring torus at low accretion rates, and, perhaps, the star formation histories of these objects. However, while comprehensively studied in higher-luminosity Seyferts and quasars, the nuclear IR properties of LLAGN have not yet been well-determined. In these proceedings we summarise the results for the LLAGN at the relatively high-luminosity, high-Eddington ratio end of the sample. Strong, compact nuclear sources are visible in the MIR images of these objects, with luminosities consistent with or slightly in execss of that predicted by the standard MIR/X-ray relation. Their broadband nuclear SEDs are diverse; some resemble typical Seyfert nuclei, while others possess less of a well-defined MIR "dust bump". Strong silicate emission is present in many of these objects. We speculate that this, together with high ratios of silicate strength to hydrogen column density, could suggest optically thin dust and low dust-to-gas ratios, in accordance with model predictions that LLAGN do not host a Seyfert-like obscuring torus.

The detection of powerful near-infrared emission in high redshift (z > 5) quasars demonstrates that very hot dust is present close to the active nucleus also in the very early universe. A number of high-redshift objects even show significant excess emission in the rest frame NIR over more local AGN spectral energy distribution (SED) templates. In order to test if this is a result of the very high luminosities or redshifts, we construct mean SEDs from the latest SDSS quasar catalogue in combination with MIR data from the WISE preliminary data release for several redshift and luminosity bins. Comparing these mean SEDs with a large sample of z > 5 quasars we could not identify any significant trends of the NIR spectral slope with luminosity or redshift in the regime 2.5 < z ≲ 6 and 10⁴⁵ < νL_ν (1350Å) ≲ 10⁴⁷ erg/s. In addition to the NIR regime, our combined Herschel and Spitzer photometry provides full infrared SED coverage of the same sample of z > 5 quasars. These observations reveal strong FIR emission (L_FIR ≳ 10¹³ L_⊙) in seven objects, possibly indicating star-formation rates of several thousand solar masses per year. The FIR excess emission has unusally high temperatures (T∼65K) which is in contrast to the temperature typically expected from studies at lower redshift (T∼45K). These objects are currently being investigated in more detail.

A multiple molecular line and line transition study is presented for the circumnuclear disk (CND) of the proto-typical Seyfert galaxy NGC 1068. A detailed analysis of the kinematics and excitation conditions of the molecular gas, as traced by ¹²CO, ¹³CO, HCN and HCO⁺, suggests that part of the molecular gas in the CND is shocked, expanding and heated to high kinetic temperatures most likely as a consequence of an interaction between the radio jet and the CND. We further find support for an X-ray altered chemistry of the molecular gas in the CND based on the significantly elevated abundance of HCN when compared to star-forming, starbursting or quiescent gas regions.

We aimed to study the chemistry of the circumnuclear molecular gas of NGC 1068, and to compare it with those of the starburst galaxies M 82 and NGC 253. Using the IRAM-30 m telescope, we observed the inner 2kpc of NGC 1068 between 86.2 GHz and 115.6 GHz. We identified 35 spectral features, corresponding to 24 different molecular species. Among them, HC₃N, SO, N₂H⁺, CH₃CN, NS, ¹³CN, and HN¹³C are detected for the first time in NGC 1068. Assuming local thermodynamic equilibrium (LTE), we calculated the column densities of the detected molecules, as well as the upper limits to the column densities of some undetected species. The comparison among the chemistries of NGC 1068, M 82, and NGC 253, suggests that, apart from X-rays, shocks also determine the chemistry of NGC 1068. We propose the column density ratio between CH₃CCH and HC₃N as a prime indicator of the imprints of starburst and AGN environments in the circumnuclear interstellar medium. This ratio is, at least, 64 times larger in M 82 than in NGC 1068, and, at least, 4 times larger in NGC 253 than in NGC, 1068. Finally, we used the UCL_CHEM and UCL_PDR chemical codes to constrain the origin of the species, as well as to test the influence of UV radiation fields and cosmic rays on the observed abundances.

Recent advances in general relativistic magnetohydrodynamic modeling of jets offer unprecedented insights into the inner workings of accreting black holes that power the jets in active galactic nuclei (AGN) and other accretion systems. I will present the results of recent studies that determine spin-dependence of jet power and discuss the implications for the AGN radio loud/quiet dichotomy and recent observations of high jet power in a number of AGN.

How does the gas get in nuclear regions to fuel black holes? How efficient is the feedback? The different processes to cause rapid gas inflow (or outflow) in galaxy centers are reviewed. Non axisymmetries can be created or maintained by internal disk instabilities, or galaxy interactions. Simulations and observations tell us that the fueling is a chaotic and intermittent process, with different scenarios and time-scales, according to the various radial scales across a galaxy.

Astrochemistry is rapidly becoming one of the most powerful tools to study the structure and evolution of the central kiloparsec in spiral nuclei. Imagining the distribution of quiescent ion-molecule, photon-dominated region (PDR) and shock chemistry permits the triggers of nuclear starbursts to be identified and the bursts subsequent feedback to be constrained. Two new chemical methods for identifying the evolutionary phase of the starbursts in IC 342, NGC 6946 and Maffei 2 are discussed. The first method is to use the HCO⁺/N₂H⁺ ratio to constrain the degree of penetration of dense clumps by UV radiation. The second determines the evolutionary phase by mapping the amount and physical conditions of the densest molecular component via multi-transition HC₃N observations. With the full capabilities of radio facilities such as the VLA and ALMA, probing the changing gas chemistry on sub arcsecond scales in external galaxies will very soon be routine.

We present the images and kinematics of circumnuclear molecular gas from 100 pc scale down to 10 pc scale in nearby active galactic nuclei (AGNs) using the Submillimeter Array (SMA) and the Plateau de Bure Interferometer (PdBI). We have observed several nearby galaxies that host AGNs, such as the nearest radio galaxy Centaurus A (NGC 5128), the Seyfert 2 galaxy M51 (NGC 5194), the Seyfert 2 galaxy NGC 1068, the Seyfert 1 galaxy NGC 1097, and the Seyfert 2 / starburst composite galaxy NGC 4945, in CO lines to see whether the molecular gas distribution, kinematics, and physical conditions at 10 – 100 pc scale follows the AGN unified model or not. In 100 pc scale, most of the circumnuclear molecular gas shows smooth velocity gradient, suggesting a regular rotating feature, and also shows abnormal line ratios, suggesting the existence of active sources to make the circumnuclear molecular gas dense and/or warm conditions or abnormal chemical compositions. In 10 pc scale, on the other hand, the molecular gas kinematics shows various characteristics, some shows very disturbed kinematics such as a jet-entrained feature in the galaxies that have jets, but some still shows regular rotation feature in a galaxy that does not have obvious jets. These results indicate that the kinematics and physical/chemical conditions of the circumnuclear molecular gas at the scale less than 100 pc is highly affected by the AGN activities, and at this scale, there is no clear evidence of any unified feature seen in the circumnuclear molecular gas.

Circumnuclear starburst rings are effective barriers against gas inflow. The large 'pile-up' of gas leads to distinct star forming events in the rings of NGC 5248 and NGC 6951. In our work, the rings are distinctly seen as the locations where the bulk of the central kiloparsec star formation in the last 2 Gyr has taken place. This in turn has direct implications for the large scale bars that have driven the formation of the circumnuclear rings in these galaxies. They have to be at least as old. The system of large-scale bar and circumnuclear ring has therefore ample time to stop gas inflow on the scale of the last 100 pc. The stars formed in the ring will help build the (pseudo-)bulge and eventually alter the gravitational potential.

We study star formation (SF) in very active environments, in luminous IR galaxies, which are often interacting. A variety of phenomena are detected, such as central starbursts, circumnuclear SF, obscured SNe tracing the history of recent SF, massive super star clusters, and sites of strong off-nuclear SF. All of these can be ultimately used to define the sequence of triggering and propagation of star-formation and interplay with nuclear activity in the lives of gas rich galaxy interactions and mergers. In this paper we present analysis of high-spatial resolution integral field spectroscopy of central regions of two interacting LIRGs. We detect a nuclear 3.3 μm PAH ring around the core of NGC 1614 with thermal-IR IFU observations. The ring's characteristics and relation to the strong star-forming ring detected in recombination lines are presented, as well as a scenario of an outward expanding starburst likely initiated with a (minor) companion detected within a tidal feature. We then present NIR IFU observations of IRAS 19115-2124, aka the Bird, which is an intriguing triple encounter. The third component is a minor one, but, nevertheless, is the source of 3/4 of the SFR of the whole system. Gas inflows and outflows are detected in their nuclei locations. Finally, we briefly report on our on-going NIR adaptive optics imaging survey of several dozen LIRGs. We have detected highly obscured core-collapse SNe in the central kpc, and discuss the statistics of "missing SNe" due to dust extinction. We are also determining the characteristics of hundreds of super star clusters in and around the core regions of LIRGs, as a function of host-galaxy properties.

While the existence of a starburst-AGN connection is undisputed, there is no consensus on what the connection is. In this contribution, we begin by noting that the mechanisms which drive gas inwards in disk galaxies are generally inefficient at removing angular momentum, leading to stalled inflows. Thus, a tiered series of such processes is required to bring gas to the smallest scales, each of which on its own may not correlate with the presence of an AGN. Similarly, each may be associated with a starburst event, making it important to discriminate between 'circumnuclear' and 'nuclear' star formation. In this contribution, we show that stellar feedback on scales of tens of parsecs plays a critical role in first hindering and then helping accretion. We argue that it is only after the initial turbulent phases of a starburst that gas from slow stellar winds can accrete efficiently to smaller scales. This would imply that the properties of the obscuring torus are directly coupled to star formation and that the torus must be a complex dynamical entity. We finish by remarking on other contexts where similar processes appear to be at work.

High-resolution observations of the central few 100 pc of the galactic nuclear environments remain prohibitive for large statistical samples, which are crucial for tracing the links between central black hole formation, galaxy formation and AGN activity over cosmic time. With this contribution, we present novel ways of connecting the physics of black hole accretion with its immediate environs via a new quantitative evaluation of the degree to which the strength and spatial configuration of the water maser emission is associated with the nuclear nebular galactic activity. We discuss possible evolutionary/causal connections between these two types of emission, together with criteria that could dramatically enhance our search for mega-maser systems in nearby galactic centers. These are timely results given the interest in combining high-resolution observations with extremely large optical telescopes and large arrays that start to conquer the sub-millimeter window.

The starburst/Seyfert composite galaxy IRAS 01072+4954 (z = 0.0236) is an enigmatic source that combines a Seyfert 1-like X-ray emission with a starburst optical spectrum that lacks broad line emission. We performed High Angular Resolution observations of the central kiloparsec of this galaxy in the near-infrared. Combining our data with 2MASS images of the whole galaxy, we obtain and model the surface brightness profile. We find indications for the presence of an elongated bar-like structure in both data sets. We also model the line of sight velocity distribution of the stars in the bulge. The derived photometrical and kinematical parameters of the bulge are used to evaluate the black hole mass through scaling relations. We find that all reliable estimations of the black hole mass are consistent with the presence of an intermediate mass black hole of M_BH ≲ 10⁵ M_⊙.

Gas materials in the inner Galactic disk continuously migrate toward the Galactic center (GC) due to interactions with the bar potential, magnetic fields, stars, and other gaseous materials. Those in forms of molecules appear to accumulate around 200 pc from the center (the central molecular zone, CMZ) to form stars there and further inside. The bar potential in the GC is thought to be responsible for such acculmulation of molecules and subsequent star formation, which is believed to have been continous throughout the lifetime of the Galaxy. We present hydrodynamic simulations of gas clouds in the central kpc region of the Milky Way that is modeled with a three-dimensional bar potential. Our simulations consider realistic gas cooling and heating, star formation, and supernova feedback. A torus of dense gas clouds forms as a result of X₁–X₂ orbit transfer, and its size (∼ 200 pc radius) coincides with the extraordinary reservoir of dense molecular clouds in the inner bulge, the Central Molecular Zone (CMZ). We also present some results from our preliminary simulations for gas transportation from the CMZ to the circumnuclear disk of molecular clouds located at a few parsecs from the GC.

What are the main drivers of activity in the local universe? Observations have been instrumental in identifying the mechanisms responsible for fueling activity in galaxy nuclei. In this context we summarize the main results of the NUclei of GAlaxies (NUGA) survey. The aim of NUGA is to map, at high resolution and high sensitivity, the distribution and dynamics of the molecular gas in the central kiloparsec region of 25 galaxies, and to study the different mechanisms responsible for gas fueling of low-luminosity AGNs (LLAGN). Gas flows in NUGA maps reveal a wide range of instabilities. The derived gravity torque maps show that only ∼1/3 of NUGA galaxies show evidence of ongoing fueling. Secular evolution and dynamical decoupling are seen to be key ingredients to understand the AGN fueling cycle. We discuss the future prospects for this research field with the advent of instruments like the Atacama Large Millimeter Array (ALMA).

Radio continuum observations of barred galaxies revealed strong magnetic fields of ≥ 50 – 100μG in the circumnuclear starbursts. Such fields are dynamically important and give rise to magnetic stress that causes inflow of gas towards the center at a rate of several solar masses per year, possibly along the spiral field seen in radio polarization and as optical dust lanes. This may solve the long-standing question of how to feed active nuclei, and explain the relation between the bolometric luminosity of AGN nuclei and the star-formation rate of their hosts. The strong magnetic fields generated in young galaxies may serve as the link between star formation and accretion onto supermassive black holes. – Magnetic fields of ≥ 160 μG strength were measured in the central region of the almost edge-on starburst galaxy NGC 253. Four filaments emerging from the inner disk delineate the boundaries of the central outflow cone of hot gas. Strong Faraday rotation of the polarized emission from the background disk indicates a large-scale helical field in the outflow walls.

The question whether or not the initial mass function (IMF) is universal, i.e. the same in all kinds of environments, is subject to intense debate. A number of recent observations have been interpreted as evidence for a nonstandard IMF. Hydrodynamical simulations indicate that the kinetic temperature of the collapsing molecular gas is crucial for the shape of the resulting IMF. Unfortunately, the kinetic temperature of the molecular gas in external galaxies is often not well constrained. We demonstrate the diagnostic power of a selected set of para-formaldehyde lines as tracers of the kinetic temperature as well as the gas density in external galaxies using our non-LTE radiative transfer model. With this new observational tool, we have engaged in characterizing the properties of the dense molecular gas phase in a number of nearby starburst galaxies and near AGN. Our first results suggest the existence of a dense molecular gas phase in these active environments that is significantly warmer than the dust and much warmer than dense molecular gas found in the disk of our own Galaxy.

There is ever mounting evidence for a connection between the evolution of AGN and starburst-activity, as, for instance, suggested by a relation between the mass of the central black hole and the velocity dispersion of the bulge stars. However, the nature of this connection remains unclear, raising a number of questions, e. g.: Is the AGN triggered by the starburst or is the starburst activity caused by AGN? Which physical processes link starbursts and AGN? Here we will give a short review of crucial observations and theoretical work and describe our plans in that regard.

Here we present the preliminary results of the analysis of VIMOS observations of the central 4.5 kpc of the double-barred galaxy NGC 5850. We use optical diagnostic diagrams to study the main ionization mecahnism across the field of view confirming the LINER nature in the continuum peak location. Also a star-forming (SF) region is found close to it (0.46kpc), a second SF region is located east of the center (1.6kpc). Further the data reveals a complex nuclear gas kinematics which is likely to be dominated by the secondary bar.

We analyze the time variability of the X-ray emission of RE J1034+396, an active galactic nucleus with the first firm detection of a quasi-periodic oscillations (QPO). Based on the results of a wavelet analysis, we find a drift in the QPO central frequency. The change in the QPO frequency correlates with the change in the X-ray flux with a short time delay. Linear structures such as shocks, spiral waves, or very distant flares seem to be a favored explanation for this particular QPO event.

We revisit the lamp-post geometry of the black-hole accretion disc with a primary illuminating source on the rotational axis. The primary X-ray power-law radiation is Compton reflected from the disc towards the observer. The gravitational field of a rotating black hole influences the photon properties on its way from the primary source to the disc and from the primary source and accretion disc to a distant observer. We study the polarization properties of the radiation how they would be observed in this scenario. The degree and the angle of polarization are examined as functions of the black hole spin, observers inclination angle and the position of the primary source.

We present SINFONI adaptive optics assisted and seeing limited NIR integral field spectroscopy of the central hundreds of pc of ten z < 0.01 Seyfert 2 galaxies. The main goal of this study is to assess the significance of star formation and extinction in the circumnuclear region of Seyfert 2s. The immediate surroundings of the nuclei are resolved at linear scales of about 50-100 parsecs for most of the observed sources. The intensity and line-of-sight velocity distribution of different species is derived from the 3D SINFONI data by calculating the higher order moments of the emission lines. As part of this work in progress, the resulting maps are currently analyzed following the approach of generalized surface photometry, which allows us to identify the multiple kinematical components in the circumnuclear region of Seyfert 2s.

Q0957+561 was the first discovered gravitationally lensed quasar. The mirage shows two images of a radio-loud quasar at redshift z = 1.41. The time lag between these two images is well established around one year. We detected a very prominent variation in the optical brightness of Q0957+561A at the beginning of 2009, which allowed us to predict the presence of significant intrinsic variations in multi-wavelength light curves of Q0957+561B over the first semester of 2010. To study the predicted brightness fluctuations of Q0957+561B, we conducted an X-ray, NUV, optical and NIR monitoring campaign using both ground-based and space-based facilities. The continuum NUV-optical light curves revealed evidence of a centrally irradiated, standard accretion disk. In this paper, we focus on the radial structure of the standard accretion disk and the nature of the central irradiating source in the distant radio-loud active galactic nucleus (AGN).

We investigate, by means of direct numerical N-body integration, the orbital evolution of an initially thin stellar disc around a dominating central mass. As a perturbation to the Keplerian stellar motions, we consider the gravitational influence of an extended spherically symmetric stellar cusp and the mutual gravitational interaction of the stars within the disc. Our results suggest that the two-body relaxation of the disc, which is often neglected in similar analyses, leads to significant changes of its radial density profile on time-scales of 10⁵–10⁶ yr for systems with dimensions of the young stellar disc observed in the Sgr A* region.

SDSS J094533.99+100950.1 is a weak line quasar (WLQ) characterised by a low equivalent widths of the high-ionization emission lines such as CIV or HeII, typical iron emission, radio quiescence and X-ray weakness. In our work we tried to answer the question if it is possible that observed emission is intrinsically weak and come from not fully developed broad emission-line region (BELR). We also analyse the observed continuum to check if it is able to ionize a BELR gas and reproduce a weakness of emission-lines or this spectral feature can be simply explained by an intrinsic absorption. Our conclusion is that the minimal active galactic nuclei (AGN) engine consisting of an unobscured accretion disk with a partially ionized gas just expanding from the disk atmosphere is enough to explain observed features of SDSS J094533.99+100950.1.

We investigate star formation (SF) activity in the central kpc of a sample of nearby Active Galactic Nuclei (AGNs). AGN activities are expected to either trigger SF via accreting ISM to the central regions of the host galaxies or quench the SF via the energy feedback of the AGNs. To study the AGN-SF relation we select 113 nearby galaxies that host 8 GHz central radio sources. We use 8 GHz radio emission to represent the AGN activity and 8 micron dust emission in the central kpc regions of these galaxies to estimate the SF rate (SFR). The SFR is found to be correlated with the stellar mass for stellar mass greater than 10¹⁰ solar mass and looks scattered for stellar mass less than 10¹⁰ solar mass. There is no correlation between the specific SFR (SSFR) and the AGN activity for all sources. However, if we exclude the sources with the central stellar mass greater than 10¹⁰ solar mass, we find that the 8 GHz radio emission is well correlated with the SSFR. These results suggest that the AGN activity is significant in triggering SF activity only for small galaxies. Besides, we also select about 20 nearby AGN galaxies to investigate the radial variation of their surface specific star formation rate.

An accretion scenario in which the material captured by a black hole from its environment is assumed to be magnetized (β ∼ 1) is discussed. We show that the accretion picture in this case is strongly affected by the magnetic field of the flow itself. The accretion power within this Magnetically Controlled Accretion (MCA) scenario is converted predominantly into the magnetic energy of the accretion flow. The rapidly amplified field prevents the accretion flow from forming a homogeneous Keplerian disk. Instead, the flow is decelerated by its own magnetic field at a large distance (Shvartsman radius) from the black hole and switches into a non-Keplerian dense magnetized slab. The material in the slab is confined by the magnetic field and moves towards the black hole on the time scale of the magnetic field annihilation. The basic parameters of the slab are evaluated. Interchange instabilities in the slab may lead to a formation of Z-pinch type configuration of the magnetic field over the slab in which the accretion power can be converted into jets and high-energy radiation.

The Galactic centre mini-spiral region is a mixture of gas and dust with temperatures ranging from a few hundred K to 10⁴ K. We report results from 1.3 and 3 mm radio interferometric observations of this region with CARMA, and present a spectral index map of this region. We find a range of emission mechanisms in the region, including the inverted synchrotron spectrum of Sgr A*, free-free emission from the mini-spiral arms, and a possible dust emission contribution indicated by a positive spectral index.

A number of studies have dealt with the link between distant powerful radio sources and the most massive galaxies in the early Universe. Despite major advances in our understanding of high redshift radio galaxies (HzRGs), we still only have a rudimentary picture of the physical conditions (i.e. gas density, temperature, ambient UV-field) prevailing in the interstellar medium (ISM) of these objects. Here we report on ongoing CI, [CII] and CO observations of TNJ 1338–1942 at z = 4.11 with the IRAM 30m telescope, the JCMT and ATCA. With these observations we will make a first attempt at constraining the average ISM conditions in TNJ 1338–1942.

Recent modeling of multi-waveband spectroscopic and maser observations suggests that the ionized outflows in the nuclear region of the archetypal Seyfert-2 galaxy NGC 1068 are inclined with respect to the vertical axis of the obscuring torus. Based on this suggestion, we build a complex reprocessing model of NGC 1068 for the optical/UV band. We apply the radiative transfer code stokes to compute polarization spectra and images. The effects of electron and dust scattering and the radiative coupling occurring in the inner regions of the multi-component object are taken into account and evaluated at different polar and azimuthal viewing angles. The observed type-1/type-2 polarization dichotomy of active galactic nuclei is reproduced. At the assumed observer's inclination toward NGC 1068, the polarization is dominated by scattering in the polar outflows and therefore it indicates their tilting angle with respect to the torus axis. While a detailed analysis of our model results is still in progress, we briefly discuss how they relate to existing polarization observations of NGC 1068.

We present the multiple line observations carried out with interferometry. We observed the circumnuclear region of the barred galaxy NGC 7552 in molecular lines tracing diffuse molecular gas (¹²CO J = 2 - 1; observed by SMA) and relatively dense molecular gas (HCN J = 1 - 0; observed by ATCA). We also reprocessed a published HI image which covers the entire galaxy to gain an analytical image with higher resolution.

The displacement between HCN (J = 1 – 0) and radio knots (3 cm continuum; ATCA archive data) is clearly seen in the circumnuclear starburst ring of NGC 7552. The propagation time derived from ¹²CO J = 2 - 1 and HI based rotation curve between the HCN (J = 1 – 0) and radio knots implies the timescale between the formation and death of massive stars. The timescale of NGC 7552 is about an order of magnitude shorter than 5 – 10 Myr timescale for OB stars to become supernovae. It is possible that star formation in the ring is top heavy, resulting in a shorter timescale.

It has recently been proposed that the jets of low-luminosity radio galaxies are powered by direct accretion of the hot phase of the IGM onto the central black hole. Cold gas remains a plausible alternative fuel supply, however. The most compelling evidence that cold gas plays a role in fueling radio galaxies is that dust is detected more commonly and/or in larger quantities in (elliptical) radio galaxies compared with radio-quiet elliptical galaxies. On the other hand, only small numbers of radio galaxies have yet been detected in CO (and even fewer imaged), and whether or not all radio galaxies have enough cold gas to fuel their jets remains an open question. If so, then the dynamics of the cold gas in the nuclei of radio galaxies may provide important clues to the fuelling mechanism. The only instrument capable of imaging the molecular component on scales relevant to the accretion process is ALMA, but very little is yet known about CO in southern radio galaxies. Our aim is to measure the CO content in a complete volume-limited sample of southern radio galaxies, in order to create a well-defined list of nearby targets to be imaged in the near future with ALMA. APEX has been equipped with a receiver (APEX-1) able to observe the 230 GHz waveband. This allows us to search for CO(2-1) line emission in our target galaxies. Here we present the results of CO(2-1) APEX-1 spectroscopy taken in 2008 and 2010 for our southern sample. The experiment was successful with nearly all targets detected, and several indications for double-horned CO line profiles, consistent with ordered rotation.

Supernovae play an integral role in the feedback of processed material into the ISM of galaxies and are responsible for most of the chemical enrichment of the universe. The rate of supernovae can also reveal the star formation histories. Supernova rate is usually measured through the non-thermal radio continuum luminosity, but in this paper we establish a quantitative relationship between the [FeII]_1.26 luminosity and supernova rate in a sample of 11 near-by starburst galaxies. SINFONI data cubes are used to perform a pixel pixel analysis of this correlation. Using Bry equivalent width and luminosity as the only observational inputs into Starburst 99, the supernova rate is derived at each pixel and a map of supernova rate is created. This is then compared morphologically and quantitatively to [FeII]_1.26 luminosity map. We find a strong linear and morphological correlation between supernova rate and [FeII]_1.26 on a pixel-pixel basis: The Starburst 99 derived supernova rates are also in good agreement with the radio derived supernova rates, which further demonstrates the strength of [FeII] as a tracer of supernova rate. With the strong correlation found in this sample of galaxies, we now qualitatively use [FeII]_1.26 to derive supernova rate on either a pixel-pixel or integrated galactic basis.

Broad emission line flux ratios are a powerful diagnostic of the physical conditions of the broad-line region gas in Active Galactic Nuclei. With recent advances in infrared spectroscopy, previously unstudied emission lines provide a new means to investigate the physical nature of the BELR gas. The hydrogen emission lines are particularly sensitive to the upper limits of both the radius from the central ionising source and the number density of the gas. Using an existing subset of near-infrared quasar spectra from the Glikman et al. (2006) sample [1] together with Cloudy photoionization simulations, we confirm the Locally Optimally emitting Cloud (LOC) model's ability to reproduce observed emission line flux ratios. The model is then used to constrain physical conditions for individual sources. The photoionization models show that high number density, low incident flux gas is required to reproduce observed near-infrared hydrogen emission line ratios. We also find that comparison to individual sources, rather than composites, is vital.

The quasar 3C 345 is one of the best examples of an active galactic nucleus (AGN) showing structural and flux variability on parsec scales around a compact unresolved radio core. Over the past 30 years, it has been followed up closely from radio to gamma-ray wavebands with a special focus on very long baseline interferometry (VLBI) observations in the range of 1–100 GHz. The complex parsec-scale jet of 3C 345 exemplifies an archetypical 'superluminal' jet with an apparent helical morphology. Here we present first results from a study of the long-term jet evolution, especially focusing on the evolution of trajectories, kinematics, and emission in more than 20 enhanced emission regions embedded in the jet. A "closeup" on physical properties of individual features implies that the outer jet is most likely dominated by Kelvin-Helmholtz instability. Studies of general trends in properties of those features provide certain evidence for their apparent trajectories to result from an underlying (slowly evolving) pattern lit up by passages of plasma condensations ejected during the nuclear flares. The long-term evolution of this pattern indicates its possible relation either to the elliptical mode of Kelvin-Helmholtz instability or precession of the jet direction.

Balanced black ring solutions of pure Einstein-Maxwell theory in five dimensions are presented here. Those solutions are asymptotically flat, and their tension and gravitational self-attraction are balanced by the repulsion due to rotation and electrical charge. Hence they are free of conical singularities and possess a regular horizon which exhibits the topology S¹ × S² of a torus. The global charges and the horizon properties of the solutions are discussed, and it is shown that they satisfy a Smarr relation. These black ring solutions are constructed numerically, and are restricted to the case of black rings with a rotation in the direction of the S¹ .

For the purpose of analyzing the spectral evolution of stellar population, we derive spectral energy distributions of simple stellar population in different ages from GALAXEV. Then, from stellar populations spectra, physical parameters are obtained for observational spectra of galaxies in the wavelength range from 3200 Å to 9500 Å. We use spectral data of Coleman and Wu for plotting the spectra of four types of galaxies. These observational data are combined and averaged from different sources; also they are extrapolated to high redshifts. In addition, we plot 16 synthesized spectra by considering Salpeter Initial Mass Function (IMF), exponential and constant Star Formation Rate (SFR) and solar metallicity for all spectra. Comparing the observational spectra with stellar population spectra, we analyze the age distribution for elliptical, irregular and two types of spiral field galaxies and obtain age and time scale parameters for each.

The near-infrared (NIR) emission of Sagittarius A* (Sgr A*), the source associated with the supermassive black hole (4.4 × 10⁶M_⊙) at the center of our galaxy, is polarized and highly variable. Correlations between intensity and polarimetric parameters of the observed light curves compared with the predicted ones for different configurations, allow us to extract information about the geometry of the radiating region. Here we present the theoretical polarimetric light curves expected in the case of optically thin NIR emission from overdense regions close to the marginal stable orbit. Using a numerical code we track the time evolution of detectable polarization properties produced by synchrotron emission of compact sources in the vicinity of the black hole. We show that the different setups lead to very distinctive patterns in the time profiles of polarized flux and the orientation of the polarization vector and as such may be used for determining the geometry of the accretion flow around Sgr A*.

We analyze the evolution of galaxy spectral properties up to z = 1 by using galaxies from the zCOSMOS-Bright 20k spectroscopic survey. We divide the sample in several mass-redshift bins to obtain stacked galaxy spectra and measure emission lines with a higher S/N. The aim of this work is to investigate whether it is possible to highlight some evidence of AGN activity in suppressing star formation during the transitional phase of galaxies from late to early type, with a particular look on a possible trend of the galaxy total stellar mass.

Our main finding is a clear role of the total stellar mass in leading galaxy evolution. As the diagnostic diagrams indicate, the objects show a progressive shift towards the AGNs region with increasing total stellar mass. Additionally, the composites follow, for a fixed redshift bin, evolutionary tracks that move from the upper part of the SF galaxies sequence down to the same metallicity sequence. For stellar masses greater than 1.6 × 10¹⁰ solar masses, the objects start being classified as composites or AGNs. This indicates that AGNs mostly act at the highest mass bins, where our sample is firstly populated by passive galaxies that have experienced the quenching.

The evidence that older stellar populations inhabit more massive galaxies, together with the increasing AGN detection rate with increasing masss, suggest a scenario in which AGNs might act to quench the star formation and, then, contribute to the transformation from young blue late-type galaxies to old red early-type galaxies.