TY - THES A1 - Husemann, Bernd T1 - The AGN-host galaxy connection : new insights from the extended ionised gas T1 - Die AGN-Galaxien Verbindung : neue Erkenntnisse durch das ausgedehnte ionisierte Gas N2 - Active Galactic Nuclei (AGN) are powered by gas accretion onto supermassive Black Holes (BH). The luminosity of AGN can exceed the integrated luminosity of their host galaxies by orders of magnitude, which are then classified as Quasi-Stellar Objects (QSOs). Some mechanisms are needed to trigger the nuclear activity in galaxies and to feed the nuclei with gas. Among several possibilities, such as gravitational interactions, bar instabilities, and smooth gas accretion from the environment, the dominant process has yet to be identified. Feedback from AGN may be important an important ingredient of the evolution of galaxies. However, the details of this coupling between AGN and their host galaxies remain unclear. In this work we aim to investigate the connection between the AGN and their host galaxies by studying the properties of the extendend ionised gas around AGN. Our study is based on observations of ~50 luminous, low-redshift (z<0.3) QSOs using the novel technique of integral field spectroscopy that combines imaging and spectroscopy. After spatially separating the emission of AGN-ionised gas from HII regions, ionised solely by recently formed massive stars, we demonstrate that the specific star formation rates in several disc-dominated AGN hosts are consistent with those of normal star forming galaxies, while others display no detectable star formation activity. Whether the star formation has been actively suppressed in those particular host galaxies by the AGN, or their gas content is intrinsically low, remains an open question. By studying the kinematics of the ionised gas, we find evidence for non-gravitational motions and outflows on kpc scales only in a few objects. The gas kinematics in the majority of objects however indicate a gravitational origin. It suggests that the importance of AGN feedback may have been overrated in theoretical works, at least at low redshifts. The [OIII] line is the strongest optical emission line for AGN-ionised gas, which can be extended over several kpc scales, usually called the Narrow-Line Region (NLR). We perform a systematic investigation of the NLR size and determine a NLR size-luminosity relation that is consistent with the scenario of a constant ionisation parameter throughout the NLR. We show that previous narrow-band imaging with the Hubble Space Telescope underestimated the NLR size by a factor of >2 and that the continuum AGN luminosity is better correlated with the NLR size than the [OIII] luminosity. These affects may account for the different NLR size-luminosity relations reported in previous studies. On the other hand, we do not detect extended NLRs around all QSOs, and demonstrate that the detection of extended NLRs goes along with radio emission. We employ emission line ratios as a diagnostic for the abundance of heavy elements in the gas, i.e. its metallicity, and find that the radial metallicity gradients are always flatter than in inactive disc-dominated galaxies. This can be interpreted as evidence for radial gas flows from the outskirts of these galaxies to the nucleus. Recent or ongoing galaxy interactions are likely responsible for this effect and may turn out to be a common prerequisite for QSO activity. The metallicity of bulge-dominated hosts are systematically lower than their disc-dominated counterparts, which we interpret as evidence for minor mergers, supported by our detailed study of the bulge-dominated host of the luminous QSO HE 1029-1401, or smooth gas accretion from the environment. In this line another new discovery is that HE 2158-0107 at z=0.218 is the most metal poor luminous QSO ever observed. Together with a large (30kpc) extended structure of low metallicity ionised gas, we propose smooth cold gas accretion as the most likely scenario. Theoretical studies suggested that this process is much more important at earlier epochs of the universe, so that HE 2158-0107 might be an ideal laboratory to study this mechanism of galaxy and BH growth at low redshift more detailed in the furture. N2 - Aktive Galaxienkerne (AGN) entstehen durch die Akkretion von Gas auf massive Schwarze Löcher, welche im Zentrum jeder Galaxie mit einer spherodialen Komponente vermutet werden. Die Leuchtkraft eines AGN kann die seiner gesamten Muttergalaxie um Größenordnungen übersteigen. In diesem Fall werden AGN oft als Quasi-Stellare Objekte (Quasare) bezeichnet. Spezielle Mechanismen müssen für das Auslösen dieser Kernaktivität in Galaxien verantwortlich sein. Verschiedene Prozesse wurden bereits identifiziert, aber der entscheidende Mechanismus wurde bisher noch nicht entdeckt. Die Wechselwirkung mit einem AGN könnte außerdem einen entscheidenden Einfluss auf die Entwicklung von Galaxien haben. Es ist noch unklar wie diese Wechselwirkung genau abläuft und ob es die Sternentstehung in Galaxien beeinflusst. In dieser Arbeit studieren wir die Eigenschaften des ausgedehnten ionisierten Gases in AGN-Muttergalaxien, um mögliche Wechselwirkungen zu untersuchen. Wir benutzen dazu eine Stichprobe von ~50 Quasaren bei geringer Rotverschiebung (z<0.3), die mit der neuartigen Technik der Integralfeld-Spektroskopie beobachtet wurden. Diese Technik kombiniert bildgebende und spektroskopische Verfahren. Wir können mit unserer Analyse zeigen, dass die spezifische Sternentstehungsrate in einigen Scheiben-dominierten AGN-Muttergalaxien vergleichbar mit denen von normalen Galaxien ohne Kernaktivität ist. Allerdings können wir in einigen AGN-Muttergalaxien keine Anzeichen von Sternentstehung feststellen. Ob Sternentstehung in diesen Galaxien momentan durch die Wechselwirkung mit dem AGN unterdrückt wird, ist daher nicht eindeutig. Hinweise auf Gasausflüsse liefert die Kinematik des ionisierten Gases für einige wenige Objekte, doch die Kinematik für die meisten AGN-Muttergalaxien kann allein durch das Wirken der Gravitation erklärt werden. Daraus schließen wir, dass der Einfluss von AGN auf ihre Muttergalaxien geringer sein könnte als theoretisch angenommen wird. Die [OIII] Emissionslinie ist die stärkste optische Linie für AGN-ionisiertes Gas und kann sich über eine Region von mehreren kpc vom Kern erstrecken, die als "Narrow-Line Region" (NLR) bezeichnet wird. Durch eine systematische Untersuchung der NLR-Ausdehnung können wir eine Beziehung zwischen NLR-Radius und AGN-Leuchtkraft bestimmen. Diese Relation ist konsistent mit einem konstanten Ionisationsparameter über die gesamte Ausdehnung der NLR. Frühere Studien mit dem Hubble Weltraumteleskop unterschätzten die Größe der NLR um mehr als einen Faktor 2. Andererseits können wir nicht für alle Quasare eine ausgedehnte NLR nachweisen, wobei eine NLR-Detektion bei einer höheren Radioleuchtkraft des Quasars wahrscheinlicher ist. Dies deutet auf eine Wechselwirkung eines Radio-Jets mit dem kernumgebenden Gas hin. Wir benutzen Emissionslinien des ionisierten Gases, um den Anteil von schweren Elementen im Gas, die so genannte Metallizität, zu bestimmen. Dabei finden wir, dass die radialen Metallizitätsgradienten in Scheiben-dominierten AGN-Muttergalaxien deutlich flacher sind als in vergleichbaren Galaxien ohne Kernaktivität, was wir als Anzeichen für radialen Gastransport vom Rand der Galaxien zum Kern interpretieren. Dies könnte durch kürzliche oder immer noch andauernde gravitative Wechselwirkungen zwischen Nachbargalaxien entstanden sein und stellt eventuell eine Voraussetzung für Kernaktivität dar. Sehr interessant ist unser Ergebnis, dass die ellptischen AGN-Muttergalaxien eine geringere Metallizität aufweisen als die Spiralgalaxien. Dies könnte z.B. durch das Verschmelzen mit kleinen Nachbargalaxien induziert werden, welche eine intrinsisch geringe Metallizität aufweisen. Am Beispiel der elliptischen Muttergalaxie des Quasars HE 1029-1401 können wir durch eine detaillierte Analyse des ionisierten Gases verschiedene Indizien für einen solchen Prozess nachweisen. Eine weiteres Resultat dieser Arbeit ist die Entdeckung eines leuchtkräftigen Quasars mit der geringsten Metallizität, die bisher für solche Objekte nachgewiesen werden konnte. Wir interpretieren die geringe Metallizität und die Ausdehnung des ionisierten Gases über 30kpc als deutliche Indizien für die Akkretion von intergalaktischem Gas. Dieser Prozess findet viel häufiger im frühen Universum statt. HE 2158-0107 könnte daher ein ideales Objekt sein, um diesen Prozess im nahen Universum detaillierter studieren zu können. KW - Quasare KW - Integralfeld-Spectroskopie KW - Galaxien KW - Interstellares Medium KW - Quasars KW - Integral field spectroscopy KW - Galaxies KW - Interstellar medium Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-55556 ER - TY - JOUR A1 - Blaha, Karen A. A1 - Pikovskij, Arkadij A1 - Rosenblum, Michael A1 - Clark, Matthew T. A1 - Rusin, Craig G. A1 - Hudson, John L. T1 - Reconstruction of two-dimensional phase dynamics from experiments on coupled oscillators JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - Phase models are a powerful method to quantify the coupled dynamics of nonlinear oscillators from measured data. We use two phase modeling methods to quantify the dynamics of pairs of coupled electrochemical oscillators, based on the phases of the two oscillators independently and the phase difference, respectively. We discuss the benefits of the two-dimensional approach relative to the one-dimensional approach using phase difference. We quantify the dependence of the coupling functions on the coupling magnitude and coupling time delay. We show differences in synchronization predictions of the two models using a toy model. We show that the two-dimensional approach reveals behavior not detected by the one-dimensional model in a driven experimental oscillator. This approach is broadly applicable to quantify interactions between nonlinear oscillators, especially where intrinsic oscillator sensitivity and coupling evolve with time. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevE.84.046201 SN - 1539-3755 VL - 84 IS - 4 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Mulansky, Mario A1 - Ahnert, Karsten A1 - Pikovskij, Arkadij A1 - Shepelyansky, Dima L. T1 - Strong and weak chaos in weakly nonintegrable many-body hamiltonian systems JF - Journal of statistical physics N2 - We study properties of chaos in generic one-dimensional nonlinear Hamiltonian lattices comprised of weakly coupled nonlinear oscillators by numerical simulations of continuous-time systems and symplectic maps. For small coupling, the measure of chaos is found to be proportional to the coupling strength and lattice length, with the typical maximal Lyapunov exponent being proportional to the square root of coupling. This strong chaos appears as a result of triplet resonances between nearby modes. In addition to strong chaos we observe a weakly chaotic component having much smaller Lyapunov exponent, the measure of which drops approximately as a square of the coupling strength down to smallest couplings we were able to reach. We argue that this weak chaos is linked to the regime of fast Arnold diffusion discussed by Chirikov and Vecheslavov. In disordered lattices of large size we find a subdiffusive spreading of initially localized wave packets over larger and larger number of modes. The relations between the exponent of this spreading and the exponent in the dependence of the fast Arnold diffusion on coupling strength are analyzed. We also trace parallels between the slow spreading of chaos and deterministic rheology. KW - Lyapunov exponent KW - Arnold diffusion KW - Chaos spreading Y1 - 2011 U6 - https://doi.org/10.1007/s10955-011-0335-3 SN - 0022-4715 VL - 145 IS - 5 SP - 1256 EP - 1274 PB - Springer CY - New York ER - TY - JOUR A1 - Komarov, Maxim A1 - Pikovskij, Arkadij T1 - Effects of nonresonant interaction in ensembles of phase oscillators JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - We consider general properties of groups of interacting oscillators, for which the natural frequencies are not in resonance. Such groups interact via nonoscillating collective variables like the amplitudes of the order parameters defined for each group. We treat the phase dynamics of the groups using the Ott-Antonsen ansatz and reduce it to a system of coupled equations for the order parameters. We describe different regimes of cosynchrony in the groups. For a large number of groups, heteroclinic cycles, corresponding to a sequential synchronous activity of groups and chaotic states where the order parameters oscillate irregularly, are possible. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevE.84.016210 SN - 1539-3755 VL - 84 IS - 1 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Lueck, S. A1 - Pikovskij, Arkadij T1 - Dynamics of multi-frequency oscillator ensembles with resonant coupling JF - Modern physics letters : A, Particles and fields, gravitation, cosmology, nuclear physics N2 - We study dynamics of populations of resonantly coupled oscillators having different frequencies. Starting from the coupled van der Pol equations we derive the Kuramoto-type phase model for the situation, where the natural frequencies of two interacting subpopulations are in relation 2 : 1. Depending on the parameter of coupling, ensembles can demonstrate fully synchronous clusters, partial synchrony (only one subpopulation synchronizes), or asynchrony in both subpopulations. Theoretical description of the dynamics based on the Watanabe-Strogatz approach is developed. KW - Oscillator populations KW - Kuramoto model KW - Resonant interaction Y1 - 2011 U6 - https://doi.org/10.1016/j.physleta.2011.06.016 SN - 0375-9601 VL - 375 IS - 28-29 SP - 2714 EP - 2719 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Kralemann, Björn A1 - Pikovskij, Arkadij A1 - Rosenblum, Michael T1 - Reconstructing phase dynamics of oscillator networks JF - Chaos : an interdisciplinary journal of nonlinear science N2 - We generalize our recent approach to the reconstruction of phase dynamics of coupled oscillators from data [B. Kralemann et al., Phys. Rev. E 77, 066205 (2008)] to cover the case of small networks of coupled periodic units. Starting from a multivariate time series, we first reconstruct genuine phases and then obtain the coupling functions in terms of these phases. Partial norms of these coupling functions quantify directed coupling between oscillators. We illustrate the method by different network motifs for three coupled oscillators and for random networks of five and nine units. We also discuss nonlinear effects in coupling. Y1 - 2011 U6 - https://doi.org/10.1063/1.3597647 SN - 1054-1500 VL - 21 IS - 2 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Burylko, Oleksandr A1 - Pikovskij, Arkadij T1 - Desynchronization transitions in nonlinearly coupled phase oscillators JF - Physica :D, Nonlinear phenomena N2 - We consider the nonlinear extension of the Kuramoto model of globally coupled phase oscillators where the phase shift in the coupling function depends on the order parameter. A bifurcation analysis of the transition from fully synchronous state to partial synchrony is performed. We demonstrate that for small ensembles it is typically mediated by stable cluster states, that disappear with creation of heteroclinic cycles, while for a larger number of oscillators a direct transition from full synchrony to a periodic or a quasiperiodic regime occurs. KW - Coupled oscillators KW - Oscillator ensembles KW - Kuramoto model KW - Nonlinear coupling KW - Bifurcations Y1 - 2011 U6 - https://doi.org/10.1016/j.physd.2011.05.016 SN - 0167-2789 VL - 240 IS - 17 SP - 1352 EP - 1361 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Levnajic, Zoran A1 - Pikovskij, Arkadij T1 - Network reconstruction from random phase resetting JF - Physical review letters N2 - We propose a novel method of reconstructing the topology and interaction functions for a general oscillator network. An ensemble of initial phases and the corresponding instantaneous frequencies is constructed by repeating random phase resets of the system dynamics. The desired details of network structure are then revealed by appropriately averaging over the ensemble. The method is applicable for a wide class of networks with arbitrary emergent dynamics, including full synchrony. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevLett.107.034101 SN - 0031-9007 VL - 107 IS - 3 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Pikovskij, Arkadij A1 - Rosenblum, Michael T1 - Dynamics of heterogeneous oscillator ensembles in terms of collective variables JF - Physica :D, Nonlinear phenomena N2 - We consider general heterogeneous ensembles of phase oscillators, sine coupled to arbitrary external fields. Starting with the infinitely large ensembles, we extend the Watanabe-Strogatz theory, valid for identical oscillators, to cover the case of an arbitrary parameter distribution. The obtained equations yield the description of the ensemble dynamics in terms of collective variables and constants of motion. As a particular case of the general setup we consider hierarchically organized ensembles, consisting of a finite number of subpopulations, whereas the number of elements in a subpopulation can be both finite or infinite. Next, we link the Watanabe-Strogatz and Ott-Antonsen theories and demonstrate that the latter one corresponds to a particular choice of constants of motion. The approach is applied to the standard Kuramoto-Sakaguchi model, to its extension for the case of nonlinear coupling, and to the description of two interacting subpopulations, exhibiting a chimera state. With these examples we illustrate that, although the asymptotic dynamics can be found within the framework of the Ott-Antonsen theory, the transients depend on the constants of motion. The most dramatic effect is the dependence of the basins of attraction of different synchronous regimes on the initial configuration of phases. KW - Coupled oscillators KW - Oscillator ensembles KW - Kuramoto model KW - Nonlinear coupling KW - Watanabe-Strogatz theory KW - Ott-Antonsen theory Y1 - 2011 U6 - https://doi.org/10.1016/j.physd.2011.01.002 SN - 0167-2789 VL - 240 IS - 9-10 SP - 872 EP - 881 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Straube, Arthur V. A1 - Pikovskij, Arkadij T1 - Pattern formation induced by time-dependent advection JF - Mathematical modelling of natural phenomena N2 - We study pattern-forming instabilities in reaction-advection-diffusion systems. We develop an approach based on Lyapunov-Bloch exponents to figure out the impact of a spatially periodic mixing flow on the stability of a spatially homogeneous state. We deal with the flows periodic in space that may have arbitrary time dependence. We propose a discrete in time model, where reaction, advection, and diffusion act as successive operators, and show that a mixing advection can lead to a pattern-forming instability in a two-component system where only one of the species is advected. Physically, this can be explained as crossing a threshold of Turing instability due to effective increase of one of the diffusion constants. KW - pattern formation KW - reaction-advection-diffusion equation Y1 - 2011 U6 - https://doi.org/10.1051/mmnp/20116107 SN - 0973-5348 VL - 6 IS - 1 SP - 138 EP - 148 PB - EDP Sciences CY - Les Ulis ER -