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Sample records for agn feedback models

  1. Models of AGN feedback

    NASA Astrophysics Data System (ADS)

    Combes, Françcoise

    2015-02-01

    The physical processes responsible of sweeping up the surrounding gas in the host galaxy of an AGN, and able in some circumstances to expel it from the galaxy, are not yet well known. The various mechanisms are briefly reviewed: quasar or radio modes, either momentum-conserving outflows, energy-conserving outflows, or intermediate. They are confronted to observations, to know whether they can explain the M-sigma relation, quench the star formation or whether they can also provide some positive feedback and how the black hole accretion history is related to that of star formation.

  2. Hydrodynamic models of AGN feedback in cooling core clusters

    NASA Astrophysics Data System (ADS)

    Vernaleo, John C.

    X-ray observations show that the Intra Cluster Medium (ICM) in many galaxy clusters is cooling at a rapid rate, often to the point that it should have radiated away all of its energy in less than the age of the cluster. There is however a very clear lack of enough cool end products of this gas in the centers of the clusters. Energetic arguments indicate that Active Galactic Nuclei (AGN) should be capable of heating the inner regions of clusters enough to offset the radiative cooling; truncating massive galaxy formation and solving the cooling flow problem. We present three sets of high resolution, ideal hydrodynamic simulations with the ZEUS code to test this AGN heating paradigm. For the first set of simulations, we study the dependence of the interaction between the AGN jets and the ICM on the parameters of the jets themselves. We present a parameter survey of two-dimensional (axisymmetric) models of back-to-back jets injected into a cluster atmosphere. We follow the passive evolution of the resulting structures. These simulations fall into roughly two classes, cocoon-bounded and non-cocoon bounded. We find that the cocoon-bounded sources inject significantly more entropy into the core regions of the ICM atmosphere, even though the efficiency with which the energy is thermalized is independent of the morphological class. In all cases, a large fraction of the energy injected by the jet ends up as gravitational potential energy due to the expansion of the atmosphere. For the second set, we present three-dimensional simulations of jetted AGN that act in response to cooling-mediated accretion of an ICM atmosphere. We find that our models are incapable of producing a long term balance of heating and cooling; catastrophic cooling can be delayed by the jet action but inevitably takes hold. At the heart of the failure of these models is the formation of a low density channel through which the jet can freely flow, carrying its energy out of the cooling core. Finally, we

  3. Signatures of AGN feedback

    NASA Astrophysics Data System (ADS)

    Wylezalek, D.; Zakamska, N.

    2016-06-01

    Feedback from active galactic nuclei (AGN) is widely considered to be the main driver in regulating the growth of massive galaxies. It operates by either heating or driving the gas that would otherwise be available for star formation out of the galaxy, preventing further increase in stellar mass. Observational proof for this scenario has, however, been hard to come by. We have assembled a large sample of 133 radio-quiet type-2 and red AGN at 0.1AGN-ionized gas, the stellar masses of the host galaxies and their star formation rates. We then investigate the relationships between AGN luminosities, specific star formation rates (sSFR) and outflow strengths W_{90} - the 90% velocity width of the [OIII]λ5007Å line power and a proxy for the AGN-driven outflow speed. Outflow strength W_{90} is independent of sSFR for AGN selected based on their mid-IR luminosity. This is in agreement with previous work that demonstrates that star formation is not sufficient to produce the observed ionized gas outflows which have to be powered by AGN activity. More importantly, we find a negative correlation between W_{90} and sSFR in the AGN hosts with the highest star formation rates, i.e., with the highest gas content. This relationship implies that AGN with strong outflow signatures are hosted in galaxies that are more `quenched' considering their stellar mass than galaxies with weaker outflow signatures. This correlation is only seen in AGN host galaxies with SFR >100 M_{⊙} yr^{-1} where presumably the coupling of the AGN-driven wind to the gas is strongest. This observation is consistent with the AGN having a net suppression, or `negative' impact, through feedback on the galaxies' star formation history.

  4. How to model AGN feedback in cosmological simulations?

    NASA Astrophysics Data System (ADS)

    Sijacki, Debora

    2015-08-01

    Hydrodynamical cosmological simulations are one of the most powerful tools to study the formation and evolution of galaxies in the fully non-linear regime. Despite several recent successes in simulating Milky Way look-alikes, self-consistent, ab-initio models are still a long way off. In this talk I will review numerical and physical uncertainties plaguing current state-of-the-art cosmological simulations of galaxy formation. I will then discuss which feedback mechanisms are needed to reproduce realistic stellar masses and galaxy morphologies in the present day Universe and argue that the black hole feedback is necessary for the quenching of massive galaxies. I will then demonstrate how black hole - host galaxy scaling relations depend on galaxy morphology and colour, highlighting the implications for the co-evolutionary picture between galaxies and their central black holes. In the second part of the talk I will present a novel method that permits to resolve gas flows around black holes all the way from large cosmological scales to the Bondi radii of black holes themselves. I will demonstrate that with this new numerical technique it is possible to estimate much more accurately gas properties in the vicinity of black holes than has been feasible before in galaxy and cosmological simulations, allowing to track reliably gas angular momentum transport from Mpc to pc scales. Finally, I will also discuss if AGN-driven outflows are more likely to be energy- or momentum-driven and what implications this has for the redshift evolution of black hole - host galaxy scaling relations.

  5. Assessing AGN feedback models with c iii* measurement and photoionization modeling

    NASA Astrophysics Data System (ADS)

    McGinnis, Daniel J.

    2013-12-01

    Mass outflows in active galactic nuclei (AGN) have been hypothesized to represent a feedback mechanism through which black hole growth and galaxy formation are linked. In order to assess this claim, typical outflow kinetic luminosities must be compared to calculated minimum values that are needed to produce feedback relevance. We have developed a method for placing lower limits on the kinetic luminosity by combining photoionization modeling with column density measurements of a select few ionic species, including C III* 1175 as a measure of gas density. This method is applied to sample AGNs representative of those observed with the Sloan Digital Sky Survey (SDSS) and the Cosmic Origins Spectrograph (HST/COS). We find that although measured kinetic luminosity lower limits for the quasar SDSS J170322.41+23124.3 and Seyfert galaxy Akn 564 are several orders of magnitude less than that required for feedback relevance, our method can be drastically improved with increased signal to noise ratios.

  6. Comparing Simulations of AGN Feedback

    NASA Astrophysics Data System (ADS)

    Richardson, Mark L. A.; Scannapieco, Evan; Devriendt, Julien; Slyz, Adrianne; Thacker, Robert J.; Dubois, Yohan; Wurster, James; Silk, Joseph

    2016-07-01

    We perform adaptive mesh refinement (AMR) and smoothed particle hydrodynamics (SPH) cosmological zoom simulations of a region around a forming galaxy cluster, comparing the ability of the methods to handle successively more complex baryonic physics. In the simplest, non-radiative case, the two methods are in good agreement with each other, but the SPH simulations generate central cores with slightly lower entropies and virial shocks at slightly larger radii, consistent with what has been seen in previous studies. The inclusion of radiative cooling, star formation, and stellar feedback leads to much larger differences between the two methods. Most dramatically, at z=5, rapid cooling in the AMR case moves the accretion shock to well within the virial radius, while this shock remains near the virial radius in the SPH case, due to excess heating, coupled with poorer capturing of the shock width. On the other hand, the addition of feedback from active galactic nuclei (AGNs) to the simulations results in much better agreement between the methods. For our AGN model, both simulations display halo gas entropies of 100 keV cm2, similar decrements in the star formation rate, and a drop in the halo baryon content of roughly 30%. This is consistent with the AGN growth being self-regulated, regardless of the numerical method. However, the simulations with AGN feedback continue to differ in aspects that are not self-regulated, such that in SPH a larger volume of gas is impacted by feedback, and the cluster still has a lower entropy central core.

  7. The Abundance of Distant and Extremely Red Galaxies: The Role of AGN Feedback in Hierarchical Models

    NASA Astrophysics Data System (ADS)

    Menci, N.; Fontana, A.; Giallongo, E.; Grazian, A.; Salimbeni, S.

    2006-08-01

    We investigate the effect of AGN feedback associated with the bright QSO phase on the color distribution of galaxies from z=0 up to z=4. To this aim, we insert a blast-wave model of AGN feedback in our semianalytic model of galaxy formation, which includes the growth of supermassive black holes and the AGN activity triggered by interactions of the host galaxies. The AGN feedback is directly related to the impulsive, luminous quasar phase. We test our model by checking the consistency of its results against (1) the QSO luminosity functions from z=0 to 4, and (2) the observed local relation between the black hole mass mBH and the mass of the host galaxy. At low redshift the inclusion of AGN feedback enhances the number of red bright galaxies so that the color distribution of Mr<-22 objects is entirely dominated by red (u-r>1.5) galaxies; at 0.5model yields an ERO surface density of 6.3×103 deg2, matching existing data. Extending our analysis to z=4, the model matches the observed surface density 1.5×103 deg2 of distant red galaxies (DRGs) at mK=20; such a population is predicted to be dominated by galaxies with old stellar populations for z>2.5.

  8. AGN feedback in galaxy clusters and groups

    NASA Astrophysics Data System (ADS)

    Hardcastle, Martin

    2016-07-01

    Mechanical feedback via Active Galactic Nuclei (AGN) jets in the centres of galaxy groups and clusters is a crucial ingredient in current models of galaxy formation and cluster evolution. Jet feedback is believed to regulate gas cooling and thus star formation in the most massive galaxies, but a robust physical understanding of this feedback mode is currently lacking. Athena will provide (1) the first kinematic measurements on relevant spatial scales of the hot gas in galaxy, group and cluster haloes as it absorbs the impact of AGN jets, and (2) vastly improved ability to map thermodynamic conditions on scales well-matched to the jets, lobes and gas disturbances produced by them. I will present new predictions of Athena's ability to measure the energetic impact of powerful jets based on our most recent set of numerical models.

  9. A comparative study of AGN feedback algorithms

    NASA Astrophysics Data System (ADS)

    Wurster, J.; Thacker, R. J.

    2013-05-01

    Modelling active galactic nuclei (AGN) feedback in numerical simulations is both technically and theoretically challenging, with numerous approaches having been published in the literature. We present a study of five distinct approaches to modelling AGN feedback within gravitohydrodynamic simulations of major mergers of Milky Way-sized galaxies. To constrain differences to only be between AGN feedback models, all simulations start from the same initial conditions and use the same star formation algorithm. Most AGN feedback algorithms have five key aspects: the black hole accretion rate, energy feedback rate and method, particle accretion algorithm, black hole advection algorithm and black hole merger algorithm. All models follow different accretion histories, and in some cases, accretion rates differ by up to three orders of magnitude at any given time. We consider models with either thermal or kinetic feedback, with the associated energy deposited locally around the black hole. Each feedback algorithm modifies the region around the black hole to different extents, yielding gas densities and temperatures within r ˜ 200 pc that differ by up to six orders of magnitude at any given time. The particle accretion algorithms usually maintain good agreement between the total mass accreted by dot{M} dt and the total mass of gas particles removed from the simulation, although not all algorithms guarantee this to be true. The black hole advection algorithms dampen inappropriate dragging of the black holes by two-body interactions. Advecting the black hole a limited distance based upon local mass distributions has many desirably properties, such as avoiding large artificial jumps and allowing the possibility of the black hole remaining in a gas void. Lastly, two black holes instantly merge when given criteria are met, and we find a range of merger times for different criteria. This is important since the AGN feedback rate changes across the merger in a way that is dependent

  10. Uncovering AGN Fueling and Feedback in Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Mushotzky, Richard

    2014-09-01

    While massive black holes (BHs) are ubiquitous in massive galaxies, their presence in dwarf galaxies is less certain. This constitutes a major gap in our understanding of BH-galaxy co-evolution. Identifying low-mass BHs in local dwarfs could also constrain BH seed formation at high z. Active BHs in dwarfs can reveal BH fueling and feedback in a vastly different regime than the well-studied AGN in massive hosts. Most AGN feedback models focus on the latter, as star formation is thought to suffice to drive feedback in dwarfs. However, AGN are increasingly found in dwarfs, where their effect on hosts may be most dramatic. We propose an unprecedented program to detect and characterize AGN fueling and feedback in the low-mass regime, using a unique sample of Swift-BAT AGN in dwarf

  11. Kinetic Modeling of Electron Conduction-Driven Microinstabilities and Their Relevance for AGN Feedback

    NASA Astrophysics Data System (ADS)

    Roberg-Clark, Gareth; Swisdak, M.; Reynolds, Christopher S.; Drake, James

    2016-04-01

    Since the Intracluster Medium (ICM) is a weakly collisional plasma, the standard Spitzer conduction rate (which relies on collisionality) does not necessarily describe the transport of heat in clusters. In addition, many plasma microinstabilities become unstable at high beta since the magnetic field is easily pliable in the presence of induced pressure anisotropies. These properties imply that the true rate of conduction in an ICM-like plasma could be highly dependent on small-scale effects. We perform 2D kinetic Particle-In-Cell simulations and derive an analytic theory of a conduction-driven electron microinstability present in high-beta collisionless plasmas. We find that scattering by electromagnetic waves significantly reduces the conductive heat flux of electrons in our model. Our results have implications for 1) cool-core clusters in which AGN feedback may play a crucial role in maintaing overall thermodynamic stability, 2) heat flux suppression and scattering by other microinstabilities and 3) basic plasma physics questions that up until this point have not been explored fully.

  12. The Importance of Winds for AGN Feedback

    NASA Astrophysics Data System (ADS)

    Crenshaw, D. M.; Kraemer, S. B.; Schmitt, H. R.; Fischer, T. C.; Gagne, J.

    2014-01-01

    Active galactic nuclei (AGN) are fed by accretion of matter onto supermassive black holes (SMBHs), generating huge amounts of radiation from very small volumes. AGN also provide feedback to their environments via mass outflows of ionized gas, which could play a critical role in the formation of large-scale structure in the early Universe, chemical enrichment of the intergalactic medium, and self-regulation of SMBH and galactic bulge growth. We provide an update on our research on the winds in nearby moderate-luminosity AGN, In particular, we concentrate on winds that occur on relatively large scales (hundreds of parsecs) that are revealed through spatially resolved HST spectra of emission-line gas in the narrow line regions (NLRs) of nearby AGN. We discuss the techniques for measuring the mass outflow rates and kinetic luminosities of these AGN winds and gauge their importance for providing significant AGN feedback.

  13. Calibrating AGN Feedback in Clusters

    NASA Astrophysics Data System (ADS)

    Wise, M. W.

    2009-12-01

    Whether caused by AGN jets, shocks, or mergers, the most definitive evidence for heating in cluster cores comes from X-ray spectroscopy. Unfortunately such spectra are essentially limited to studying the emission spectrum from the cluster as a whole. However since the same underlying emission measure distribution produces both the observed CCD and RGS spectra, X-ray imaging can still provide spatial information on the heating process. Using Chandra archival data for a sample of 9 clusters, we demonstrate how imaging data can be used to constrain departures from a canonical, isobaric cooling flow model as a function of position in a given cluster. The results of this analysis are also shown for the deep archival exposure of the Perseus cluster. Such ``heating maps'' can provide constraints on both the location and magnitude of the heating in the cores of clusters. When combined with detections and spectral index maps from low-frequency radio observations, these maps can be used to distinguish between different models for heating in these objects.

  14. AGN feedback in the Perseus cluster

    NASA Astrophysics Data System (ADS)

    Gendron-Marsolais, Marie-Lou; Hlavacek-Larrondo, Julie; Clarke, Tracy E.; Intema, Huib; Fabian, Andrew C.; Taylor, Gregory B.; Blundell, Katherine

    2016-04-01

    Deep Chandra images of the Perseus cluster of galaxies have revealed a succession of cavities created by the jets of the central supermassive black hole, pushing away the X-ray emitting gas and leaving bubbles filled with radio emission. Perseus is one of the rare examples showing buoyantly rising lobes from past radio outbursts, characterized by a steep spectral index and known as ghost cavities. All of these structures trace the complete history of mechanical AGN feedback over the past 500 Myrs. I will present results on new, ultra deep 230-470 MHz JVLA data. This low-frequency view of the Perseus cluster will probe the old radio-emitting electron population and will allow us to build the most detailed map of AGN feedback in a cluster thus far.

  15. Inverse Compton X-ray signature of AGN feedback

    NASA Astrophysics Data System (ADS)

    Bourne, Martin A.; Nayakshin, Sergei

    2013-12-01

    Bright AGN frequently show ultrafast outflows (UFOs) with outflow velocities vout ˜ 0.1c. These outflows may be the source of AGN feedback on their host galaxies sought by galaxy formation modellers. The exact effect of the outflows on the ambient galaxy gas strongly depends on whether the shocked UFOs cool rapidly or not. This in turn depends on whether the shocked electrons share the same temperature as ions (one-temperature regime, 1T) or decouple (2T), as has been recently suggested. Here we calculate the inverse Compton spectrum emitted by such shocks, finding a broad feature potentially detectable either in mid-to-high energy X-rays (1T case) or only in the soft X-rays (2T). We argue that current observations of AGN do not seem to show evidence for the 1T component. The limits on the 2T emission are far weaker, and in fact it is possible that the observed soft X-ray excess of AGN is partially or fully due to the 2T shock emission. This suggests that UFOs are in the energy-driven regime outside the central few pc, and must pump considerable amounts of not only momentum but also energy into the ambient gas. We encourage X-ray observers to look for the inverse Compton components calculated here in order to constrain AGN feedback models further.

  16. Impact of AGN and stellar feedback on the gas of a simulated z~2 star-forming galaxy

    NASA Astrophysics Data System (ADS)

    Roos, Orianne; Bournaud, Frédéric; Juneau, Stephanie; Gabor, Jared

    2015-08-01

    With high-resolution simulations of star-forming disk galaxies at high redshift, we study the effects of combined AGN and stellar feedback models on the gas of the host-galaxy. AGN feedback is modeled using a standard thermal recipe of feedback (gas is heated and pushed away) plus a post-processing method to compute AGN ionization. We first consider AGN feedback only and show that, even though the AGN generates powerful outflows, the effects of AGN feedback on star formation is relatively weak on time-scales up to a few 100s of Myrs, even when long-range radiative feedback is accounted for. Furthermore, as the combination of stellar feedback models generates outflows that are more powerful than the sum of the models taken separately, we check whether combined AGN and stellar feedback also couple non-linearly. We then include several stellar feedback sources on top of AGN feedback, such as young stars creating HII regions through radiative pressure and supernovae releasing thermal and kinetic energy in the ISM. We follow their impact on the gas of high-resolution simulations and study the coupling between the different sources of outflows (AGN, young stars, supernovae) , which could produce very fast outflows, with important outflow rates. How do these feedback-driven winds affect the host? What is the amount of expelled gas? What is its density and temperature and what is the consequence for in place and future star formation? Can such outflows change the distribution of existing stars?

  17. Studying AGN Feedback with Galactic Outflows in Luminous Obscured Quasar

    NASA Astrophysics Data System (ADS)

    Sun, Ai-Lei

    2016-01-01

    Feedback from Active galactic nuclei (AGN) has been proposed as an important quenching mechanism to suppress star formation in massive galaxies. We investigate the most direct form of AGN feedback - galactic outflows - in the most luminous obscured AGN (L>10^45 erg/s) from the SDSS sample in the nearby universe (z<0.2). Using ALMA and Magellan observations to target molecular and ionized outflows, we find that luminous AGN can impact the dynamics and phase of the galactic medium, and confirm the complex multi-phase and multi-scaled nature of the feedback phenomenon. In particular, we found that most of these luminous AGN hosts ionized outflows. The outflow size, velocity, and energetics correlate with the AGN luminosity, and can be very extended (r > 10 kpc) and fast (v > 1000 km/s) for the most luminous ones. I end with presenting a new technique to find extended ionized outflows using broadband imaging surveys, and to characterize their occurrence rate, morphology, size distribution, and their dependence on the AGN luminosity. This technique will open a new window for feedback studies in the era of large-scale optical imaging surveys, e.g., HSC and then LSST.

  18. Effects of AGN feedback on ΛCDM galaxies

    NASA Astrophysics Data System (ADS)

    Lagos, Claudia Del P.; Cora, Sofía A.; Padilla, Nelson D.

    2008-08-01

    We study the effects of active galactic nuclei (AGN) feedback on the formation and evolution of galaxies by using a combination of a cosmological N-body simulation of the concordance Lambda cold dark matter (ΛCDM) paradigm and a semi-analytic model of galaxy formation. This model is an improved version of the one described by Cora (2006), which now considers the growth of black holes (BHs) as driven by (i) gas accretion during merger-driven starbursts and mergers with other BHs, (ii) accretion during starbursts triggered by disc instabilities and (iii) accretion of gas cooled from quasi-hydrostatic hot gas haloes. It is assumed that feedback from AGN operates in the last case. The model has been calibrated in order to reproduce observational correlations between BH mass and mass, velocity dispersion and absolute magnitudes of the galaxy bulge. AGN feedback has a strong impact on reducing or even suppressing gas cooling, an effect that becomes important at lower redshifts. This phenomenon helps to reproduce the observed galaxy luminosity function (LF) in the optical and near-infrared bands at z = 0, and the cosmic star formation rate and stellar mass functions over a wide redshift range (0 <~ z <~ 5). It also allows us to have a population of massive galaxies already in place at z >~ 1, which are mostly early-type and have older and redder stellar populations than lower mass galaxies, reproducing the observed bimodality in the galaxy colour distribution, and the morphological fractions. The evolution of the optical QSO LF is also reproduced, provided that the presence of a significant fraction of obscured QSOs is assumed. We explore the effects of AGN feedback during starbursts finding that, in order to obtain a good agreement with observations, these need to be strong enough to expel the reheated gas away from the galaxy halo. We also test new, recent prescriptions for dynamical friction time-scales, and find that they produce an earlier formation of elliptical

  19. The Horizon-AGN Simulation: Morphological Diversity of Galaxies ,Promoted by AGN Feedback

    NASA Astrophysics Data System (ADS)

    Dubois, Yohan; Peirani, Sébastien; Pichon, Christophe; Devriendt, Julien; Gavazzi, Raphaël; Welker, Charlotte; Volonteri, Marta

    2016-09-01

    The interplay between cosmic gas accretion onto galaxies and galaxy mergers drives the observed morphological diversity of galaxies. By comparing the state-of-the-art hydrodynamical cosmological simulations HORIZON-AGN and HORIZON-NOAGN, we unambiguously identify the critical role of Active Galactic Nuclei (AGN) in setting up the correct galaxy morphology for the massive end of the population. With AGN feedback, typical kinematic and morpho-metric properties of galaxy populations as well as the galaxy-halo mass relation are in much better agreement with observations. Only AGN feedback allows massive galaxies at the center of groups and clusters to become ellipticals, while without AGN feedback those galaxies reform discs. It is the merger-enhanced AGN activity that is able to freeze the morphological type of the post-merger remnant by durably quenching its quiescent star formation. Hence morphology is shown not to be purely driven by mass but also by the nature of cosmic accretion: at constant galaxy mass, ellipticals are galaxies that are mainly assembled through mergers, while discs are preferentially built from the in situ star formation fed by smooth cosmic gas infall.

  20. Effects of AGN feedback in galaxy groups and Intergalactic Medium

    NASA Astrophysics Data System (ADS)

    Lagos, C.; Padilla, N.; Cora, S.

    2009-05-01

    The combination of Cosmological numerical simulations and semi-analytical models of galaxy formation is a very appropriate method to study how different phenomena influence the galaxy and galaxy cluster formation. The main advantage of this combination consists in the fact that N-body simulations do not need to be rerun every time a change in the assumptions about baryonic processes is made since these are included in the semi-analytical models which run on the final N-Body simulation output. The Semi-analytic model takes into account radiative cooling of gas, stellar formation and different types of SN contribution, which eject energy and metals to the interstellar medium, allowing the chemical enrichment of the intergalactic medium. In this project we use the semi-analytic hybrid model by Cora (2006, MNRAS, 368, 1540) and implement the AGN feedback, in two modes, the QSO mode (which takes into account mergers and galactic disk instabilities), and the Radio mode, which modifies the cooling in the galaxies These two processes allow to suppress the super flows in the hybrid model, and allows the study of QSOs in galaxy groups. This new implementation opens different possibles studies including the QSO luminosity function, the anti-hierarchical evolution of Mass Function, the BH mass and bulge mass relation, Color-Magnitude diagrams, TF relation, the galaxy luminosity function, the effects of AGN in neighbor galaxies and the behavior of QSOs in the sub-millimeter window.

  1. Satellites of radio AGN in SDSS: Insights into agn triggering and feedback

    SciTech Connect

    Pace, Cameron; Salim, Samir E-mail: salims@indiana.edu

    2014-04-10

    We study the effects of radio jets on galaxies in their vicinity (satellites) and the role of satellites in triggering radio-loud active galactic nuclei (AGNs). The study compares the aggregate properties of satellites of a sample of 7220 radio AGNs at z < 0.3 (identified by Best and Heckman from the SDSS and NVSS+FIRST surveys) to the satellites of a control sample of radio-quiet galaxies, which are matched in redshift, color, luminosity, and axis ratio, as well as by environment type: field galaxies, cluster members, and brightest cluster galaxies (BCGs). Remarkably, we find that radio AGNs exhibit on average a 50% excess (17σ significance) in the number of satellites within 100 kpc even though the cluster membership was controlled (e.g., radio BCGs have more satellites than radio-quiet BCGs, etc.). Satellite excess is not confirmed for high-excitation sources, which are only 2% of radio AGN. Extra satellites may be responsible for raising the probability for hot gas AGN accretion via tidal effects or may otherwise enhance the intensity or duration of the radio-emitting phase. Furthermore, we find that the incidence of radio AGNs among potential hosts (massive ellipticals) is similar for field galaxies and for non-BCG cluster members, suggesting that AGN fueling depends primarily on conditions in the host halo rather than the parent, cluster halo. Regarding feedback, we find that radio AGNs, either high or low excitation, have no detectable effect on star formation in their satellites, as neither induced star formation nor star formation quenching is present in more than ∼1% of radio AGN.

  2. The effects of AGN feedback and SPH formulation on black hole growth in galaxies

    NASA Astrophysics Data System (ADS)

    Liu, MaoSheng; Di Matteo, Tiziana; Feng, Yu

    2016-05-01

    We perform simulations of isolated galaxies and major mergers to investigate the effects on black hole (BH) growth due to variations in active galactic nuclei (AGN) feedback models and different smooth particle hydrodynamic (SPH) solvers. In particular we examine density-SPH versus newer pressure-SPH formulation and their significance relative to minor changes in subgrid AGN feedback prescriptions. The aim is to use these idealized simulations to understand the impact of these effects for large cosmological volume simulations where these models are often adopted. In both isolated galaxies and galaxy mergers, we find that star formation histories are largely insensitive to the choice of SPH schemes whilst BH accretion rate can change. This can result in a factor of 2-3 difference in final BH mass for the two hydrodynamic formulations. However, the differences are much smaller than those obtained even with small changes in the subgrid AGN feedback prescription. In particular, depending on the size of the region and the manner in which the AGN energy is deposited, the star formation rate is suppressed by a factor of 2 in isolated galaxies and the star burst completely quenched during the coalescence of two galaxies. The final BH mass differs by over an order of magnitude by changes in AGN feedback model. Our results indicated that any change in the hydrodynamic formulation is likely subdominant to the effects of changing subgrid physics around the BH, although thermodynamic state and morphology of the gas remnant are also sensitive to the change in hydrodynamic solver.

  3. AGN host galaxy mass function in COSMOS. Is AGN feedback responsible for the mass-quenching of galaxies?

    NASA Astrophysics Data System (ADS)

    Bongiorno, A.; Schulze, A.; Merloni, A.; Zamorani, G.; Ilbert, O.; La Franca, F.; Peng, Y.; Piconcelli, E.; Mainieri, V.; Silverman, J. D.; Brusa, M.; Fiore, F.; Salvato, M.; Scoville, N.

    2016-04-01

    We investigate the role of supermassive black holes in the global context of galaxy evolution by measuring the host galaxy stellar mass function (HGMF) and the specific accretion rate, that is, λSAR, the distribution function (SARDF), up to z ~ 2.5 with ~1000 X-ray selected AGN from XMM-COSMOS. Using a maximum likelihood approach, we jointly fit the stellar mass function and specific accretion rate distribution function, with the X-ray luminosity function as an additional constraint. Our best-fit model characterizes the SARDF as a double power-law with mass-dependent but redshift-independent break, whose low λSAR slope flattens with increasing redshift while the normalization increases. This implies that for a given stellar mass, higher λSAR objects have a peak in their space density at earlier epoch than the lower λSAR objects, following and mimicking the well-known AGN cosmic downsizing as observed in the AGN luminosity function. The mass function of active galaxies is described by a Schechter function with an almost constant M∗⋆ and a low-mass slope α that flattens with redshift. Compared to the stellar mass function, we find that the HGMF has a similar shape and that up to log (M⋆/M⊙) ~ 11.5, the ratio of AGN host galaxies to star-forming galaxies is basically constant (~10%). Finally, the comparison of the AGN HGMF for different luminosity and specific accretion rate subclasses with a previously published phenomenological model prediction for the "transient" population, which are galaxies in the process of being mass-quenched, reveals that low-luminosity AGN do not appear to be able to contribute significantly to the quenching and that at least at high masses, that is, M⋆ > 1010.7 M⊙, feedback from luminous AGN (log Lbol ≳ 46 [erg/s]) may be responsible for the quenching of star formation in the host galaxy.

  4. Galaxy-scale AGN feedback - theory

    NASA Astrophysics Data System (ADS)

    Wagner, A. Y.; Bicknell, G. V.; Umemura, M.; Sutherland, R. S.; Silk, J.

    2016-02-01

    Powerful relativistic jets in radio galaxies are capable of driving strong outflows but also inducing star-formation by pressure-triggering collapse of dense clouds. We review theoretical work on negative and positive active galactic nuclei feedback, discussing insights gained from recent hydrodynamical simulations of jet-driven feedback on galaxy scales that are applicable to compact radio sources. The simulations show that the efficiency of feedback and the relative importance of negative and positive feedback depend strongly on interstellar medium properties, especially the column depth and spatial distribution of clouds. Negative feedback is most effective if clouds are distributed spherically and individual clouds have small column depths, while positive feedback is most effective if clouds are predominantly in a disc-like configuration.

  5. AGN and the necessity of feedback.

    PubMed

    Benson, Andrew J

    2005-03-15

    There is now good observational evidence that some type of feedback process must operate within galaxies. Such a process has long been thought to exist on the basis of theoretical studies of galaxy formation. This feedback is responsible for regulating the rate of star formation and thereby preventing the formation of an overabundance of low-mass galaxies. There is gathering evidence that this feedback process must somehow involve the supermassive black holes thought to dwell in the centres of galaxies. PMID:15681287

  6. The impact of mechanical AGN feedback on the formation of massive early-type galaxies

    NASA Astrophysics Data System (ADS)

    Choi, Ena; Ostriker, Jeremiah P.; Naab, Thorsten; Oser, Ludwig; Moster, Benjamin P.

    2015-06-01

    We employ cosmological hydrodynamical simulations to investigate the effects of AGN feedback on the formation of massive galaxies with present-day stellar masses of M_stel= 8.8 × 10^{10}-6.0 × 10^{11} M_{⊙}. Using smoothed particle hydrodynamics simulations with a pressure-entropy formulation that allows an improved treatment of contact discontinuities and fluid mixing, we run three sets of simulations of 20 haloes with different AGN feedback models: (1) no feedback, (2) thermal feedback, and (3) mechanical and radiation feedback. We assume that seed black holes are present at early cosmic epochs at the centre of emerging dark matter haloes and trace their mass growth via gas accretion and mergers with other black holes. Both feedback models successfully recover the observed MBH-σ relation and black hole-to-stellar mass ratio for simulated central early-type galaxies. The baryonic conversion efficiencies are reduced by a factor of 2 compared to models without any AGN feedback at all halo masses. However, massive galaxies simulated with thermal AGN feedback show a factor of ˜10-100 higher X-ray luminosities than observed. The mechanical/radiation feedback model reproduces the observed correlation between X-ray luminosities and velocity dispersion, e.g. for galaxies with σ = 200 km s- 1, the X-ray luminosity is reduced from 1042 erg s- 1 to 1040 erg s- 1. It also efficiently suppresses late-time star formation, reducing the specific star formation rate from 10-10.5 yr- 1 to 10-14 yr- 1 on average and resulting in quiescent galaxies since z = 2, whereas the thermal feedback model shows higher late-time in situ star formation rates than observed.

  7. A simple way to improve AGN feedback prescription in SPH simulations

    NASA Astrophysics Data System (ADS)

    Zubovas, Kastytis; Bourne, Martin A.; Nayakshin, Sergei

    2016-03-01

    Active galactic nuclei (AGN) feedback is an important ingredient in galaxy evolution, however its treatment in numerical simulations is necessarily approximate, requiring subgrid prescriptions due to the dynamical range involved in the calculations. We present a suite of smoothed particle hydrodynamics simulations designed to showcase the importance of the choice of a particular subgrid prescription for AGN feedback. We concentrate on two approaches to treating wide-angle AGN outflows: thermal feedback, where thermal and kinetic energy is injected into the gas surrounding the supermassive black hole (SMBH) particle, and virtual particle feedback, where energy is carried by tracer particles radially away from the AGN. We show that the latter model produces a far more complex structure around the SMBH, which we argue is a more physically correct outcome. We suggest a simple improvement to the thermal feedback model - injecting the energy into a cone, rather than spherically symmetrically - and show that this markedly improves the agreement between the two prescriptions, without requiring any noticeable increase in the computational cost of the simulation.

  8. Quenching histories of galaxies and the role of AGN feedback

    NASA Astrophysics Data System (ADS)

    Smethurst, Rebecca Jane; Lintott, Chris; Simmons, Brooke; Galaxy Zoo Team

    2016-01-01

    Two open issues in modern astrophysics are: (i) how do galaxies fully quench their star formation and (ii) how is this affected - or not - by AGN feedback? I present the results of a new Bayesian-MCMC analysis of the star formation histories of over 126,000 galaxies across the colour magnitude diagram showing that diverse quenching mechanisms are instrumental in the formation of the present day red sequence. Using classifications from Galaxy Zoo we show that the rate at which quenching can occur is morphologically dependent in each of the blue cloud, green valley and red sequence. We discuss the nature of these possible quenching mechanisms, considering the influence of secular evolution, galaxy interactions and mergers, both with and without black hole activity. We focus particularly on the relationship between these quenched star formation histories and the presence of an AGN by using this new Bayesian method to show a population of type 2 AGN host galaxies have recently (within 2 Gyr) undergone a rapid (τ < 1 Gyr) drop in their star formation rate. With this result we therefore present the first statistically supported observational evidence that AGN feedback is an important mechanism for the cessation of star formation in this population of galaxies. The diversity of this new method also highlights that such rapid quenching histories cannot account fully for all the quenching across the current AGN host population. We demonstrate that slower (τ > 2 Gyr) quenching rates dominate for high stellar mass (log10[M*/M⊙] > 10.75) hosts of AGN with both early- and late-type morphology. We discuss how these results show that both merger-driven and non-merger processes are contributing to the co-evolution of galaxies and supermassive black holes across the entirety of the colour magnitude diagram.

  9. The effect of AGN feedback on the X-ray morphologies of clusters: Simulations vs. observations

    NASA Astrophysics Data System (ADS)

    Chon, Gayoung; Puchwein, Ewald; Böhringer, Hans

    2016-07-01

    Clusters of galaxies probe the large-scale distribution of matter and are a useful tool to test the cosmological models by constraining cosmic structure growth and the expansion of the Universe. It is the scaling relations between mass observables and the true mass of a cluster through which we obtain the cosmological constraints by comparing to theoretical cluster mass functions. These scaling relations are, however, heavily influenced by cluster morphology. The presence of the slight tension in recent cosmological constraints on Ωm and σ8 based on the CMB and clusters has boosted the interests in looking for possible sources for the discrepancy. Therefore we study here the effect of active galactic nucleus (AGN) feedback as one of the major mechanisms modifying the cluster morphology influencing scaling relations. It is known that AGN feedback injects energies up to 1062 erg into the intracluster medium, controls the heating and cooling of a cluster, and re-distributes cold gas from the centre to outer radii. We have also learned that cluster simulations with AGN feedback can reproduce observed cluster properties, for example, the X-ray luminosity, temperature, and cooling rate at the centre better than without the AGN feedback. In this paper using cosmological hydrodynamical simulations we investigate how the AGN feedback changes the X-ray morphology of the simulated systems, and compare this to the observed Representative XMM-Newton Cluster Structure Survey (REXCESS) clusters. We apply two substructure measures, centre shifts (w) and power ratios (e.g. P3/P0), to characterise the cluster morphology, and find that our simulated clusters are more substructured than the observed clusters based on the values of w and P3/P0. We also show that the degree of this discrepancy is affected by the inclusion of AGN feedback. While the clusters simulated with the AGN feedback are in much better agreement with the REXCESS LX-T relation, they are also more substructured

  10. Neutral hydrogen in galaxy clusters: impact of AGN feedback and implications for intensity mapping

    NASA Astrophysics Data System (ADS)

    Villaescusa-Navarro, Francisco; Planelles, Susana; Borgani, Stefano; Viel, Matteo; Rasia, Elena; Murante, Giuseppe; Dolag, Klaus; Steinborn, Lisa K.; Biffi, Veronica; Beck, Alexander M.; Ragone-Figueroa, Cinthia

    2016-03-01

    By means of zoom-in hydrodynamic simulations, we quantify the amount of neutral hydrogen (H I) hosted by groups and clusters of galaxies. Our simulations, which are based on an improved formulation of smoothed particle hydrodynamics, include radiative cooling, star formation, metal enrichment and supernova feedback, and can be split into two different groups, depending on whether feedback from active galactic nuclei (AGN) is turned on or off. Simulations are analysed to account for H I self-shielding and the presence of molecular hydrogen. We find that the mass in neutral hydrogen of dark matter haloes monotonically increases with the halo mass and can be well described by a power law of the form M_{H I}(M,z)∝ M^{3/4}. Our results point out that AGN feedback reduces both the total halo mass and its H I mass, although it is more efficient in removing H I. We conclude that AGN feedback reduces the neutral hydrogen mass of a given halo by ˜50 per cent, with a weak dependence on halo mass and redshift. The spatial distribution of neutral hydrogen within haloes is also affected by AGN feedback, whose effect is to decrease the fraction of H I that resides in the halo inner regions. By extrapolating our results to haloes not resolved in our simulations, we derive astrophysical implications from the measurements of Ω _{H I}(z): haloes with circular velocities larger than ˜25 km s-1 are needed to host H I in order to reproduce observations. We find that only the model with AGN feedback is capable of reproducing the value of Ω _{H I}b_{H I} derived from available 21 cm intensity mapping observations.

  11. Connecting AGN Feedback, the Star-Forming Interstellar Medium, and Galaxy Formation

    NASA Astrophysics Data System (ADS)

    Hopkins, Philip

    The biggest shortcoming in our models of star, supermassive black hole, and galaxy formation is our poor and incomplete understanding of 'feedback' processes. In nearly all models, strong feedback from stars and black holes plays a critical role in regulating the nature of the interstellar medium (ISM) and subsequent generations of star formation and black hole growth. But our theoretical understanding of these processes has largely been restricted to either idealized cases, or simple phenomenological 'sub-grid' prescriptions. These have limited predictive power, and invoke highly uncertain assumptions for the unresolved ISM physics. As such, developing more realistic, explicit treatment of these processes is critical, and one of the primary challenges facing models of both galaxy and star formation. In this proposal, we focus on improving our understanding of AGN feedback by combining novel, high-resolution studies of both black hole growth and galaxy evolution. Critically, these will simultaneously resolve the ISM and both fueling and feedback from black holes, and include fundamentally new physics on galactic scales. Our goal is to anchor these calculations as much as possible in first principles, eliminating large uncertainties in the current models, and enable new predictions on galactic scales. Recently, we developed new numerical models to resolve star formation and feedback on scales from molecular cloud star-forming regions through galaxies. These simulations explicitly follow the energy, momentum, mass, and metal fluxes from stellar radiation pressure, photo-heating, supernovae, and stellar winds; in all cases feedback is tied directly to stellar evolution models. Unlike those previous, the models naturally produce an ISM in which molecular clouds form and disperse rapidly, with realistic phase structure and turbulence. These mechanisms simultaneously drive large galactic outflows; the galactic environment is radically different from the smooth medium of

  12. Jets and Outflows in Radio Galaxies: Implications for AGN Feedback

    NASA Astrophysics Data System (ADS)

    Torresi, Eleonora; Grandi, Paola; Costantini, Elisa; Palumbo, Giorgio G. C.

    One of the main debated astrophysical problems is the role of the AGN feedback in galaxy formation. It is known that massive black holes have a profound effect on the formation and evolution of galaxies, but how black holes and galaxies communicate is still an unsolved problem. For Radio Galaxies, feedback studies have mainly focused on jet/cavity systems in the most massive and X-ray luminous galaxy clusters. The recent high-resolution detection of warm absorbers in some Broad Line Radio Galaxies allow us to investigate the interplay between the nuclear engine and the surrounding medium from a different perspective. We report on the detection of warm absorbers in two Broad Line Radio Galaxies, 3C 382 and 3C 390.3, and discuss the physical and energetic properties of the absorbing gas. Finally, we attempt a comparison between radio-loud and radio-quiet outflows.

  13. Non-thermal AGN models

    SciTech Connect

    Band, D.L.

    1986-12-01

    The infrared, optical and x-ray continua from radio quiet active galactic nuclei (AGN) are explained by a compact non-thermal source surrounding a thermal ultraviolet emitter, presumably the accretion disk around a supermassive black hole. The ultraviolet source is observed as the ''big blue bump.'' The flat (..cap alpha.. approx. = .7) hard x-ray spectrum results from the scattering of thermal ultraviolet photons by the flat, low energy end of an electron distribution ''broken'' by Compton losses; the infrared through soft x-ray continuum is the synchrotron radiation of the steep, high energy end of the electron distribution. Quantitative fits to specific AGN result in models which satisfy the variability constraints but require electron (re)acceleration throughout the source. 11 refs., 1 fig.

  14. Studying AGN Feedback in Galaxy Clusters and Groups with Athena

    NASA Astrophysics Data System (ADS)

    Sanders, Jeremy; Athena Topical PanelAGN Feedback in Clusters; Groups

    2015-09-01

    In the centres of clusters of galaxies and groups the central active galactic nuclei are playing a vital role in preventing the rapid cooling of the surrounding hot atmosphere. Important scientific questions remain unanswered, however. These include (1) What is the mechanism by which the energy from jets is dissipated and distributed through intracluster or intragroup medium? (2) How is the AGN fuelling regulated? (3) What is the cumulative impact of powerful radio galaxies on baryons over cosmic time? With its high spectral resolution, good spatial resolution and large effective area, Athena promises to make important progress in answering these questions. For the first time it will measure both the spatially-resolved velocity distribution and thermodynamics of the cluster core region, allowing us to measure all the energetic contributions to feedback and cooling in the hot plasma. We describe how Athena will address these areas, as described in our supporting paper for the Athena mission proposal on AGN feedback in galaxy clusters and groups.

  15. Massive molecular outflows and evidence for AGN feedback from CO observations

    NASA Astrophysics Data System (ADS)

    Cicone, C.; Maiolino, R.; Sturm, E.; Graciá-Carpio, J.; Feruglio, C.; Neri, R.; Aalto, S.; Davies, R.; Fiore, F.; Fischer, J.; García-Burillo, S.; González-Alfonso, E.; Hailey-Dunsheath, S.; Piconcelli, E.; Veilleux, S.

    2014-02-01

    We study the properties of massive, galactic-scale outflows of molecular gas and investigate their impact on galaxy evolution. We present new IRAM PdBI CO(1-0) observations of local ultra-luminous infrared galaxies (ULIRGs) and quasar-hosts: a clear signature of massive and energetic molecular outflows, extending on kpc scales, is found in the CO(1-0) kinematics of four out of seven sources, with measured outflow rates of several 100 M⊙ yr-1. We combine these new observations with data from the literature, and explore the nature and origin of massive molecular outflows within an extended sample of 19 local galaxies. We find that starburst-dominated galaxies have an outflow rate comparable to their star formation rate (SFR), or even higher by a factor of ~2-4, implying that starbursts can indeed be effective in removing cold gas from galaxies. Nevertheless, our results suggest that the presence of an active galactic nucleus (AGN) can boost the outflow rate by a large factor, which is found to increase with the LAGN/Lbol ratio. The gas depletion time scales due to molecular outflows are anti-correlated with the presence and luminosity of an AGN in these galaxies, and range from a few hundred million years in starburst galaxies down to just a few million years in galaxies hosting powerful AGNs. In quasar hosts, the depletion time scales due to the outflow are much shorter than the depletion time scales due to star formation. We estimate the outflow kinetic power and find that, for galaxies hosting powerful AGNs, it corresponds to about 5% of the AGN luminosity, as expected by models of AGN feedback. Moreover, we find that momentum rates of about 20 LAGN/c are common among the AGN-dominated sources in our sample. For "pure" starburst galaxies, our data tentatively support models in which outflows are mostly momentum-driven by the radiation pressure from young stars onto dusty clouds. Overall, our results indicate that, although starbursts are effective in powering

  16. AGN and stellar feedback in star-forming galaxies at redshift 2 : outflows, mass-loading and quenching

    NASA Astrophysics Data System (ADS)

    Roos, O.

    2016-06-01

    Galactic-scale outflows are ubiquitous in observations of star-forming galaxies, up to high redshift. Such galactic outflows are mainly generated by internal sources of feedback: young stars, supernovae and active galactic nuclei (AGNs). Still, the physical origins of such outflows are not well understood, and their main driver is still debated. Up to now, most simulations take into account AGN feedback or stellar feedback but not both, because both phenomena happen on very different spatial and time scales. Most of them also still fail to reproduce all observed parameters from first principles. In this poster, we present the POGO project: Physical Origins of Galactic Outflows. With this suite of 23 simulations, we model AGN and stellar feedback simultaneously based on physical assumptions for the first time at very high resolution (6 to 1.5 pc), and investigate their impact on the outflow parameters of the host-galaxy. Here, we show that AGN and stellar feedback couple non-linearly, and that the mass-loading of the resulting outflow highly depends on the mass of the host, all the more because the coupling can either be positive (small masses) or negative (intermediate masses). Nevertheless, the main driver of the outflow remains the AGN at all masses.

  17. On the Importance of Very Light Internally Subsonic AGN Jets in Radio-mode AGN Feedback

    NASA Astrophysics Data System (ADS)

    Guo, Fulai

    2016-07-01

    Radio-mode active galactic nucleus (AGN) feedback plays a key role in the evolution of galaxy groups and clusters. Its physical origin lies in the kiloparsec-scale interaction of AGN jets with the intracluster medium. Large-scale jet simulations often initiate light internally supersonic jets with density contrast 0.01 < η < 1. Here we argue for the first time for the importance of very light (η < 0.01) internally subsonic jets. We investigated the shapes of young X-ray cavities produced in a suite of hydrodynamic simulations, and found that bottom-wide cavities are always produced by internally subsonic jets, while internally supersonic jets inflate cylindrical, center-wide, or top-wide cavities. We found examples of real cavities with shapes analogous to those inflated in our simulations by internally subsonic and internally supersonic jets, suggesting a dichotomy of AGN jets according to their internal Mach numbers. We further studied the long-term cavity evolution, and found that old cavities resulted from light jets spread along the jet direction, while those produced by very light jets are significantly elongated along the perpendicular direction. The northwestern ghost cavity in Perseus is pancake shaped, providing tentative evidence for the existence of very light jets. Our simulations show that very light internally subsonic jets decelerate faster and rise much slower in the intracluster medium than light internally supersonic jets, possibly depositing a larger fraction of jet energy to cluster cores and alleviating the problem of low coupling efficiencies found previously. The internal Mach number points to the jet’s energy content, and internally subsonic jets are energetically dominated by non-kinetic energy, such as thermal energy, cosmic rays, or magnetic fields.

  18. AGN Feedback in the X-ray Surveyor Era

    NASA Astrophysics Data System (ADS)

    Reynolds, Chris

    2015-10-01

    It is now widely recognized that the growth of supermassive black holes can have a profound influence on the evolution of their host galaxy. For example, powerful quasars resulting from the merger of gas rich galaxies can produce sub-relativistic winds that may expel cold gas from the galaxy, extinguishing continued star formation. Another form of feedback occurs in giant elliptical galaxies and galaxy clusters - relativistic jets from the central AGN appear to heat the hot interstellar/intracluster gas, preventing a cooling catastrophe that would otherwise grow the stellar mass appreciably. While current observations reveal incontrovertible signatures of these feedback processes, the underlying physical mechanisms remain very poorly understood. What drives the powerful winds in luminous quasars? How does the energy injected by relativistic jets actually become thermalized in the intracluster medium? How are the feedback loops maintained? In this talk, I will discuss these questions and the impact of future observations by Astro-H, ATHENA and the X-ray Surveyor.

  19. Mass-metallicity relations and metallicity gradients of galaxies in chemodynamical simulations with AGN feedback

    NASA Astrophysics Data System (ADS)

    Kobayashi, Chiaki

    2015-08-01

    I show metallicities of high-redshift galaxies and their time evolution in our cosmological, hydrodynamical simulations with the feedback from active galactic nuclei (AGN). We have applied a new model for the formation of black holes motivated by the first star formation, in contrast to the merging scenario of previous works. The model parameters are determined from observational constraints, namely, the cosmic star formation rate history, black hole mass-galaxy mass relation, and the size-mass relation of galaxies. We then obtain better agreement with the observed down-sizing phenomena, namely, the colour-magnitude relation, specific star formation rates, and the \\alpha enhancement of early type galaxies. In massive galaxies, AGN-driven outflows transport metals into the circumgalactic medium and the intergalactic medium, which is important for a large-scale chemical enrichment in the Universe. Smaller galaxies can get external enrichment from nearby AGN depending on their environment. Nonetheless, these metallicity changes are negligible, and the mass-metallicity relations, which are mainly generated by supernova feedback at the first star burst, are preserved. The mass-metallicity relations evolve showing a steeper slope at higher redshifts. Metallicity radial gradients dramatically evolve depending on the their merging histories, and at the present we find a weak correlation between the gradients and galaxy mass. These predictions will be tested with on-going spectral and IFU surveys.

  20. AGN Feedback in Overdense Environments at z=2.23

    NASA Astrophysics Data System (ADS)

    Lucy, Adrian B.; Lehmer, B.; Alexander, D. M.; Best, P.; Geach, J.; Harrison, C. M.; Hornschemeier, A. E.; Matsuda, Y.; Mullaney, J.; Smail, I.; Sobral, D.

    2013-01-01

    We present results from a ≈100 ks Chandra observation of the 2QZ Cluster 1004+00 galaxy overdensity at z=2.23. This 2QZ Clus structure was first identified as an overdensity of four optically-selected quasars; that sample was subsequently found to overlap with an overdensity of 22 Hα-emitting galaxies (HAEs) identified through narrow and broad band near-infrared imaging by Matsuda et al. (2011). In addition to the preselected quasars in 2QZ Clus, our Chandra observation reveals that a further three HAEs are X-ray sources, all characterized by X-ray luminosities and spectral slopes consistent with unobscured active galactic nuclei (AGN). In total, we find that ≈30% of HAEs in our observed region of 2QZ Clus are AGN. This AGN fraction is high compared to AGN fractions among HAEs in the Chandra-COSMOS field (C-COSMOS), and if this enhancement is purely a result of the quasar selection bias of our sample, we estimate that such activity is rare at this redshift. Hα is a tracer of star formation, so 2QZ Clus is well suited to the investigation of the coeval growth of supermassive black holes and their host galaxies in the precursors to rich local clusters. Moreover, we have an ideal control sample in C-COSMOS; this survey contains a large sample of HAEs classified identically using infrared imaging, but without any selection of quasars. We calculate AGN fraction as a function of galaxy overdensity in C-COSMOS, and perform stacking analyses of Chandra and 250μ Herschel SPIRE data to obtain mean black hole accretion rates dMBH/dt and star formation rates SFR. Preliminary results indicate that dMBH/dt and its ratio to SFR are significantly elevated in 2QZ Clus compared to similarly overdense regions of C-COSMOS. We discuss these relations in the context of theoretical models describing the emergence of the MBH/Mgal relation of the local Universe.

  1. Shaping the X-ray spectrum of galaxy clusters with AGN feedback and turbulence

    NASA Astrophysics Data System (ADS)

    Gaspari, M.

    2015-07-01

    The hot plasma filling galaxy clusters emits copious X-ray radiation. The classic unheated and unperturbed cooling flow model predicts dramatic cooling rates and an isobaric X-ray spectrum with constant differential luminosity distribution. The observed cores of clusters (and groups) show instead a strong deficit of soft X-ray emission: dLx/dT ∝ (T/Thot)α = 2 ± 1. Using 3D hydrodynamic simulations, we show that such deficit arises from the tight self-regulation between thermal instability condensation and AGN outflow injection: condensing clouds boost the AGN outflows, which quench cooling as they thermalize through the core. The resultant average distribution slope is α ≃ 2, oscillating within the observed 1 < α < 3. In the absence of thermal instability, the X-ray spectrum remains isothermal (α ≳ 8), while unopposed cooling drives a too shallow slope, α < 1. AGN outflows deposit their energy inside-out, releasing more heat in the inner cooler phase; radially distributed heating alone induces a declining spectrum, 1 < α < 2. Turbulence further steepens the spectrum and increases the scatter: the turbulent Mach number in the hot phase is subsonic, while it becomes transonic in the cooler phase, making perturbations to depart from the isobaric mode. Such increase in dln P/dln T leads to α ≈ 3. Self-regulated AGN outflow feedback can address the soft X-ray problem through the interplay of heating and turbulence.

  2. Radiative Transfer, Black Hole Growth, AGN Feedback in Galaxies

    NASA Astrophysics Data System (ADS)

    Novak, Gregory

    2013-01-01

    We have performed 3D hydrodynamic simulations of black hole fueling and AGN feedback using a novel method for treating the radial forces on interstellar gas due to absorption of photons by dust grains. The method provides a solution to the radiative transfer equation and hence computes forces on the gas self-consistently by first solving for the radiation field taking into account radiation sources, absorption, and scattering. The algorithm gives the correct behavior in all of the relevant limits (dominated by the central point source; dominated by the distributed isotropic source; optically thin; optically thick to UV/optical; optically thick to IR) and reasonably interpolates between the limits when necessary. The simulations allow us to study gas flows and feedback processes over length scales from ~1 pc to ~100 kpc. We find that the dynamics and final state of simulations are measurably but only moderately affected by radiative forces on dust, even when assumptions about the dust-to-gas ratio are varied from zero to a value appropriate for the Milky Way. In simulations with high gas densities designed to mimic ULIRGs with a star formation rate of several hundred solar masses per year, dust makes a more substantial contribution to the dynamics and outcome of the simulation.

  3. Cooling, AGN Feedback and Star Formation in Cool-Core Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Li, Yuan; Bryan, Greg; Ruszkowski, Mateusz

    2015-01-01

    The feedback from active galactic nuclei (AGNs) is widely considered to be the major heating source in cool-core galaxy clusters to prevent a classical cooling flow. Numerical simulations with AGN feedback have successfully suppressed radiative cooling, but generally fail to reproduce the right amount of cold gas and the expected cyclical AGN activities. We perform adaptive mesh simulations including both momentum-driven AGN feedback and star formation to study the interplay between cooling, AGN heating and star formation over ~ 6.5 Gyr time in an isolated cool-core cluster. Cold clumps first cool out of the ICM due to the non-liner perturbation driven by the AGN jets. These cold clumps feed both star formation and the supermassive black hole (SMBH), triggering an AGN outburst which increases the entropy of the ICM and reduces its cooling rate. Within 1-2 Gyr, star formation completely consumes the cold gas, which leads to a brief shutoff of the AGN. The ICM quickly cools and develops multiphase gas again, followed by another cycle of star formation/AGN outburst. Within 6.5 Gyr, we observe three such cycles. The average star formation rate is ~40 solar mass/yr. The black hole accretion rate shows a large scatter, but the average correlates well with the star formation rate and is roughly one order of magnitude lower.

  4. Stellar and quasar feedback in concert: effects on AGN accretion, obscuration, and outflows

    NASA Astrophysics Data System (ADS)

    Hopkins, Philip F.; Torrey, Paul; Faucher-Giguère, Claude-André; Quataert, Eliot; Murray, Norman

    2016-05-01

    We study the interaction of feedback from active galactic nuclei (AGN) and a multiphase interstellar medium (ISM), in simulations including explicit stellar feedback, multiphase cooling, accretion-disc winds, and Compton heating. We examine radii ˜0.1-100 pc around a black hole (BH), where the accretion rate on to the BH is determined and where AGN-powered winds and radiation couple to the ISM. We conclude: (1) the BH accretion rate is determined by exchange of angular momentum between gas and stars in gravitational instabilities. This produces accretion rates ˜0.03-1 M⊙ yr-1, sufficient to power luminous AGN. (2) The gas disc in the galactic nucleus undergoes an initial burst of star formation followed by several million years where stellar feedback suppresses the star formation rate (SFR). (3) AGN winds injected at small radii with momentum fluxes ˜LAGN/c couple efficiently to the ISM and have dramatic effects on ISM properties within ˜100 pc. AGN winds suppress the nuclear SFR by factors ˜10-30 and BH accretion rate by factors ˜3-30. They increase the outflow rate from the nucleus by factors ˜10, consistent with observational evidence for galaxy-scale AGN-driven outflows. (4) With AGN feedback, the predicted column density distribution to the BH is consistent with observations. Absent AGN feedback, the BH is isotropically obscured and there are not enough optically thin sightlines to explain type-I AGN. A `torus-like' geometry arises self-consistently as AGN feedback evacuates gas in polar regions.

  5. Kinetic AGN feedback effects on cluster cool cores simulated using SPH

    NASA Astrophysics Data System (ADS)

    Barai, Paramita; Murante, Giuseppe; Borgani, Stefano; Gaspari, Massimo; Granato, Gian Luigi; Monaco, Pierluigi; Ragone-Figueroa, Cinthia

    2016-09-01

    We implement novel numerical models of AGN feedback in the SPH code GADGET-3, where the energy from a supermassive black hole (BH) is coupled to the surrounding gas in the kinetic form. Gas particles lying inside a bi-conical volume around the BH are imparted a one-time velocity (10 000 km s-1) increment. We perform hydrodynamical simulations of isolated cluster (total mass 1014 h-1 M⊙), which is initially evolved to form a dense cool core, having central T ≤ 106 K. A BH resides at the cluster centre, and ejects energy. The feedback-driven fast wind undergoes shock with the slower moving gas, which causes the imparted kinetic energy to be thermalized. Bipolar bubble-like outflows form propagating radially outward to a distance of a few 100 kpc. The radial profiles of median gas properties are influenced by BH feedback in the inner regions (r < 20-50 kpc). BH kinetic feedback, with a large value of the feedback efficiency, depletes the inner cool gas and reduces the hot gas content, such that the initial cool core of the cluster is heated up within a time 1.9 Gyr, whereby the core median temperature rises to above 107 K, and the central entropy flattens. Our implementation of BH thermal feedback (using the same efficiency as kinetic), within the star formation model, cannot do this heating, where the cool core remains. The inclusion of cold gas accretion in the simulations produces naturally a duty cycle of the AGN with a periodicity of 100 Myr.

  6. Unravelling ICM Physics and AGN Feedback with Deep Chandra Observations of NGC 5813

    NASA Astrophysics Data System (ADS)

    Randall, Scott; Nulsen, Paul; Jones, Christine; Forman, William; Clarke, Tracy

    2015-09-01

    We present results based on very deep (650 ks) Chandra observations of the galaxy group NGC 5813. This system shows three pairs of collinear cavities, with each pair associated with an elliptical AGN outburstshock. Due to the relatively regular morphology of this system, and the unique unambiguous detection of three distinct AGN outburstshocks, it is particularly well-suited for the study of AGN feedbackand the AGN outburst history. The implied mean kinetic power is roughly the same for each outburst, demonstrating that the average AGN kinetic luminosity can remain stable over long timescales (roughly 50Myr). The two older outbursts have larger, roughly equal total energies as compared with the youngest outburst, implying that the youngest outburst is ongoing. We find that the radiative cooling rate and the mean shock heating rate of the gas are well balanced at each shock front, suggesting that AGN outburst shock heating alone is sufficient to offset cooling and establish AGN/ICM feedback within at least the central 30 kpc. This heating takes place roughly isotropically and most strongly at small radii, as is required for feedback to operate. We suggest that shock heating may play a significant role in AGN feedback at smaller radii in other systems, where weak shocks are more difficult to detect. We find non-zero shockfront widths that are too large to be explained by particle diffusion. Instead, all measured widths are consistent with shock broadening due to propagation through a turbulent ICM with a mean turbulent speed of roughly 70 km/s. Significant contributions to our understanding of AGN feedback and ICM physics, partially via studies similar to the one described here, will be one of the major achievements of the Athena mission.

  7. AGN-starburst evolutionary connection : a physical interpretation based on radiative feedback

    NASA Astrophysics Data System (ADS)

    Ishibashi, W.; Fabian, A. C.

    2016-08-01

    Observations point towards a close connection between nuclear starbursts, active galactic nuclei (AGN), and outflow phenomena. An evolutionary sequence, starting from a dust-obscured ultra-luminous infrared galaxy and eventually leading to an unobscured optical quasar, has been proposed and discussed in the literature. AGN feedback is usually invoked to expel the obscuring gas and dust in a blow-out event, but the underlying physical mechanism remains unclear. We consider AGN feedback driven by radiation pressure on dust, which directly acts on the obscuring dusty gas. We obtain that radiative feedback can potentially disrupt dense gas in the infrared-optically thick regime, and that an increase in the dust-to-gas fraction leads to an increase in the effective Eddington ratio. Thus the more dusty gas is preferentially expelled by radiative feedback, and the central AGN is prone to efficiently remove its own obscuring dust cocoon. Large amounts of dust imply heavy obscuration but also powerful feedback, suggesting a causal link between dust obscuration and blow-out. In this picture, AGN feedback and starburst phenomena are intrinsically coupled through the production of dust in supernova explosions, leading to a natural interpretation of the observed evolutionary path.

  8. Cooling, AGN Feedback, and Star Formation in Simulated Cool-core Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Li, Yuan; Bryan, Greg L.; Ruszkowski, Mateusz; Voit, G. Mark; O'Shea, Brian W.; Donahue, Megan

    2015-10-01

    Numerical simulations of active galactic nuclei (AGNs) feedback in cool-core galaxy clusters have successfully avoided classical cooling flows, but often produce too much cold gas. We perform adaptive mesh simulations that include momentum-driven AGN feedback, self-gravity, star formation, and stellar feedback, focusing on the interplay between cooling, AGN heating, and star formation in an isolated cool-core cluster. Cold clumps triggered by AGN jets and turbulence form filamentary structures tens of kpc long. This cold gas feeds both star formation and the supermassive black hole (SMBH), triggering an AGN outburst that increases the entropy of the intracluster medium (ICM) and reduces its cooling rate. Within 1-2 Gyr, star formation completely consumes the cold gas, leading to a brief shutoff of the AGN. The ICM quickly cools and redevelops multiphase gas, followed by another cycle of star formation/AGN outburst. Within 6.5 Gyr, we observe three such cycles. There is good agreement between our simulated cluster and the observations of cool-core clusters. ICM cooling is dynamically balanced by AGN heating, and a cool-core appearance is preserved. The minimum cooling time to free-fall time ratio typically varies between a few and ≳ 20. The star formation rate (SFR) covers a wide range, from 0 to a few hundred {M}⊙ {{yr}}-1, with an average of ˜ 40 {M}⊙ {{yr}}-1. The instantaneous SMBH accretion rate shows large variations on short timescales, but the average value correlates well with the SFR. Simulations without stellar feedback or self-gravity produce qualitatively similar results, but a lower SMBH feedback efficiency (0.1% compared to 1%) results in too many stars.

  9. Ultra-fast outflows (aka UFOs) in AGNs and their relevance for feedback

    NASA Astrophysics Data System (ADS)

    Cappi, Massimo; Tombesi, F.; Giustini, M.; Dadina, M.; Braito, V.; Kaastra, J.; Reeves, J.; Chartas, G.; Gaspari, M.; Vignali, C.; Gofford, J.; Lanzuisi, G.

    2012-09-01

    During the last decade, several observational evidences have been accumulated for the existence of massive, high velocity winds/outflows (aka UFOs) in nearby AGNs and, possibly, distant quasars. I will review here such evidences, present some of the latest results in this field, and discuss the relevance of UFOs for both understanding the physics of accretion/ejection flows on supermassive black holes, and for quantifying the amount of AGN feedback.

  10. Theoretical uncertainties due to AGN subgrid models in predictions of galaxy cluster observable properties

    NASA Astrophysics Data System (ADS)

    Yang, H.-Y. Karen; Sutter, P. M.; Ricker, Paul M.

    2012-12-01

    Cosmological constraints derived from galaxy clusters rely on accurate predictions of cluster observable properties, in which feedback from active galactic nuclei (AGN) is a critical component. In order to model the physical effects due to supermassive black holes (SMBH) on cosmological scales, subgrid modelling is required, and a variety of implementations have been developed in the literature. However, theoretical uncertainties due to model and parameter variations are not yet well understood, limiting the predictive power of simulations including AGN feedback. By performing a detailed parameter-sensitivity study in a single cluster using several commonly adopted AGN accretion and feedback models with FLASH, we quantify the model uncertainties in predictions of cluster integrated properties. We find that quantities that are more sensitive to gas density have larger uncertainties (˜20 per cent for Mgas and a factor of ˜2 for LX at R500), whereas TX, YSZ and YX are more robust (˜10-20 per cent at R500). To make predictions beyond this level of accuracy would require more constraints on the most relevant parameters: the accretion model, mechanical heating efficiency and size of feedback region. By studying the impact of AGN feedback on the scaling relations, we find that an anti-correlation exists between Mgas and TX, which is another reason why YSZ and YX are excellent mass proxies. This anti-correlation also implies that AGN feedback is likely to be an important source of intrinsic scatter in the Mgas-TX and LX-TX relations.

  11. The self-regulated AGN feedback loop: the role of chaotic cold accretion

    NASA Astrophysics Data System (ADS)

    Gaspari, Massimo

    2015-08-01

    Accretion and feedback tied to supermassive black holes are known to play central role in the cosmic evolution of galaxies, groups, and clusters of galaxies. The self-regulation mechanism, that is how to link feedback and accretion, is matter of intense debate.Using high-resolution 3D hydrodynamic simulations, I discuss how the AGN feedback is tightly coupled with the formation of multiphase gas and the newly probed chaotic cold accretion. In a turbulent atmosphere heated by AGN feedback, cold clouds and filaments condense out of the hot plasma via nonlinear thermal instability, up to radii of 10s kpc, and rain toward the black hole. In the inner core, the recurrent chaotic collisions between the cold clouds, filaments, and central torus promote angular momentum cancellation, boosting the accretion rate up to 100 times the Bondi rate, which is comparable to the cooling rate.Such rapid variability triggers powerful AGN outflows, which quench the cooling flow and star formation without destroying the cool core. I highlight the major imprints of mechanical AGN feedback, such as buoyant bubbles, shocks, turbulence, and uplifted gas, with a critical eye toward observational concordance. The tight self-regulation has key implications for the group/cluster scaling relations, such as Lx-Tx, in agreement with a recent X-ray stacking analysis of 250000 central galaxies.The AGN heating stifles the formation of multiphase gas, and thus accretion. Lacking the main fuel, AGN feedback subsides and the hot halo is allowed to cool again, restarting a new cycle. Ultimately, chaotic cold accretion creates a symbiotic link between the black hole and the whole host galaxy, leading to a tight self-regulated feedback loop which preserves the cores of groups and clusters in quasi thermal equilibrium throughout cosmic time.

  12. The self-regulated AGN feedback loop: the role of chaotic cold accretion

    NASA Astrophysics Data System (ADS)

    Gaspari, Massimo

    2015-08-01

    Accretion and feedback tied to supermassive black holes are known to play central role in the cosmic evolution of galaxies, groups, and clusters of galaxies. The self-regulation mechanism, that is how to link feedback and accretion, is matter of intense debate.Using high-resolution 3D hydrodynamic simulations, I discuss how the AGN feedback is tightly coupled with the formation of multiphase gas and the newly probed chaotic cold accretion. In a turbulent atmosphere heated by AGN feedback, cold clouds and filaments condense out of the hot plasma via nonlinear thermal instability, up to radii of 10s kpc, and rain toward the black hole. In the inner core, the recurrent chaotic collisions between the cold clouds, filaments, and central torus promote angular momentum cancellation, boosting the accretion rate up to 100 times the Bondi rate, which is comparable to the cooling rate.Such rapid variability triggers powerful AGN outflows, which quench the cooling flow and star formation without destroying the cool core. I highlight the major imprints of mechanical AGN feedback, such as buoyant bubbles, shocks, turbulence, and uplifted gas, with a critical eye toward observational concordance. The tight self-regulation has key implications for the scaling relations, such as Lx-Tx, and the X-ray spectrum of hot halos.The AGN heating stifles the formation of multiphase gas, and thus accretion. Lacking the main fuel, AGN feedback subsides and the hot halo is allowed to cool again, restarting a new cycle. Ultimately, chaotic cold accretion creates a symbiotic link between the black hole and the whole host galaxy, leading to a tight self-regulated feedback loop which preserves the cores of groups and clusters in quasi thermal equilibrium throughout cosmic time.

  13. The self-regulated AGN feedback loop: the role of chaotic cold accretion

    NASA Astrophysics Data System (ADS)

    Gaspari, Massimo

    2015-08-01

    Accretion and feedback tied to supermassive black holes are known to play central role in the cosmic evolution of galaxies, groups, and clusters of galaxies. The self-regulation mechanism, that is how to link feedback and accretion, is matter of intense debate.Using high-resolution 3D hydrodynamic simulations, I discuss how the AGN feedback is tightly coupled with the formation of multiphase gas and the newly probed chaotic cold accretion. In a turbulent atmosphere heated by AGN feedback, cold clouds and filaments condense out of the hot plasma via nonlinear thermal instability, up to radii of 10s kpc, and rain toward the black hole. In the inner core, the recurrent chaotic collisions between the cold clouds, filaments, and central torus promote angular momentum cancellation, boosting the accretion rate up to 100 times the Bondi rate, which is comparable to the cooling rate.Such rapid variability triggers powerful AGN outflows, which quench the cooling flow and star formation without destroying the cool core. I highlight the major imprints of mechanical AGN feedback, such as buoyant bubbles, shocks, turbulence, and uplifted gas, with a critical eye toward concordance with X-ray observations. The tight self-regulation has key implications for the group/cluster scaling relations, such as Lx-Tx, in agreement with a recent X-ray stacking analysis of 250000 central galaxies.The AGN heating stifles the formation of multiphase gas, and thus accretion. Lacking the main fuel, AGN feedback subsides and the hot halo is allowed to cool again, restarting a new cycle. Ultimately, chaotic cold accretion creates a symbiotic link between the black hole and the whole host galaxy, leading to a tight self-regulated feedback loop which preserves the cores of groups and clusters in quasi thermal equilibrium throughout cosmic time.

  14. CAN AGN FEEDBACK BREAK THE SELF-SIMILARITY OF GALAXIES, GROUPS, AND CLUSTERS?

    SciTech Connect

    Gaspari, M.; Brighenti, F.; Temi, P.

    2014-03-01

    It is commonly thought that active galactic nucleus (AGN) feedback can break the self-similar scaling relations of galaxies, groups, and clusters. Using high-resolution three-dimensional hydrodynamic simulations, we isolate the impact of AGN feedback on the L {sub x}-T {sub x} relation, testing the two archetypal and common regimes, self-regulated mechanical feedback and a quasar thermal blast. We find that AGN feedback has severe difficulty in breaking the relation in a consistent way. The similarity breaking is directly linked to the gas evacuation within R {sub 500}, while the central cooling times are inversely proportional to the core density. Breaking self-similarity thus implies breaking the cool core, morphing all systems to non-cool-core objects, which is in clear contradiction with the observed data populated by several cool-core systems. Self-regulated feedback, which quenches cooling flows and preserves cool cores, prevents dramatic evacuation and similarity breaking at any scale; the relation scatter is also limited. The impulsive thermal blast can break the core-included L {sub x}-T {sub x} at T {sub 500} ≲ 1 keV, but substantially empties and overheats the halo, generating a perennial non-cool-core group, as experienced by cosmological simulations. Even with partial evacuation, massive systems remain overheated. We show that the action of purely AGN feedback is to lower the luminosity and heat the gas, perpendicular to the fit.

  15. The Keck OSIRIS Nearby AGN (KONA) Survey: AGN Fueling and Feedback

    NASA Astrophysics Data System (ADS)

    Hicks, Erin K. S.; Müller-Sánchez, Francisco; Malkan, Matthew A.; Yu, Po-Chieh

    In an effort to better constrain the relevant physical processes dictating the co-evolution of supermassive black holes and the galaxies in which they reside we turn to local Seyfert AGN. It is only with these local AGN that we can reach the spatial resolution needed to adequately characterize the inflow and outflow mechanisms thought to be the driving forces in establishing the relationship between black holes and their host galaxies at higher redshift. We present the first results from the KONA (Keck OSIRIS Nearby AGN) survey, which takes advantage of the integral field unit OSIRIS plus laser and natural guide star adaptive optics to probe down to scales of 5-30 parsecs in a sample of 40 local Seyfert galaxies. With these K-band data we measure the two-dimensional distribution and kinematics of the nuclear stars, molecular gas, and ionized gas within the central few hundred parsecs.

  16. Kinematic signatures of AGN feedback in moderately powerful radio galaxies at z ~ 2 observed with SINFONI

    NASA Astrophysics Data System (ADS)

    Collet, C.; Nesvadba, N. P. H.; De Breuck, C.; Lehnert, M. D.; Best, P.; Bryant, J. J.; Hunstead, R.; Dicken, D.; Johnston, H.

    2016-02-01

    Most successful galaxy formation scenarios now postulate that the intense star formation in massive, high-redshift galaxies during their major growth period was truncated when powerful AGNs launched galaxy-wide outflows of gas that removed large parts of the interstellar medium. SINFONI imaging spectroscopy of the most powerful radio galaxies at z ~ 2 show clear signatures of such winds, but are too rare to be good representatives of a generic phase in the evolution of all massive galaxies at high redshift. Here we present SINFONI imaging spectroscopy of the rest-frame optical emission-line gas in 12 radio galaxies at redshifts ~2. Our sample spans a range in radio power that is intermediate between the most powerful radio galaxies with known wind signatures at these redshifts and vigorous starburst galaxies, and are about two orders of magnitude more common than the most powerful radio galaxies. Thus, if AGN feedback is a generic phase of massive galaxy evolution for reasonable values of the AGN duty cycle, these are just the sources where AGN feedback should be most important. Our sources show a diverse set of gas kinematics ranging from regular velocity gradients with amplitudes of Δv = 200-400 km s-1 consistent with rotating disks to very irregular kinematics with multiple velocity jumps of a few 100 km s-1. Line widths are generally high, typically around FWHM = 800 km s-1, more similar to the more powerful high-z radio galaxies than mass-selected samples of massive high-z galaxies without bright AGNs, and consistent with the velocity range expected from recent hydrodynamic models. A broad Hα line in one target implies a black hole mass of a few 109 M⊙. Velocity offsets of putative satellite galaxies near a few targets suggest dynamical masses of a few 1011 M⊙ for our sources, akin to the most powerful high-z radio galaxies. Ionized gas masses are 1-2 orders of magnitude lower than in the most powerful radio galaxies, and the extinction in the gas is

  17. Kiloparsec-scale outflows are prevalent among luminous AGN: outflows and feedback in the context of the overall AGN population

    NASA Astrophysics Data System (ADS)

    Harrison, C. M.; Alexander, D. M.; Mullaney, J. R.; Swinbank, A. M.

    2014-07-01

    We present integral field unit observations covering the [O III]λλ4959, 5007 and Hβ emission lines of 16 z < 0.2 type 2 active galactic nuclei (AGN). Our targets are selected from a well-constrained parent sample of ≈24 000 AGN so that we can place our observations into the context of the overall AGN population. Our targets are radio quiet with star formation rates (SFRs; ≲[10-100] M⊙ yr-1) that are consistent with normal star-forming galaxies. We decouple the kinematics of galaxy dynamics and mergers from outflows. We find high-velocity ionized gas (velocity widths ≈600-1500 km s-1; maximum velocities ≤1700 km s-1) with observed spatial extents of ≳(6-16) kpc in all targets and observe signatures of spherical outflows and bi-polar superbubbles. We show that our targets are representative of z < 0.2, luminous (i.e. L[O III] > 1041.7 erg s-1) type 2 AGN and that ionized outflows are not only common but also in ≥70 per cent (3σ confidence) of cases, they are extended over kiloparsec scales. Our study demonstrates that galaxy-wide energetic outflows are not confined to the most extreme star-forming galaxies or radio-luminous AGN; however, there may be a higher incidence of the most extreme outflow velocities in quasars hosted in ultraluminous infrared galaxies. Both star formation and AGN activity appear to be energetically viable to drive the outflows and we find no definitive evidence that favours one process over the other. Although highly uncertain, we derive mass outflow rates (typically ≈10 times the SFRs), kinetic energies (≈0.5-10 per cent of LAGN) and momentum rates (typically ≳10-20 × LAGN/c) consistent with theoretical models that predict AGN-driven outflows play a significant role in shaping the evolution of galaxies.

  18. Hot Gas and AGN Feedback in Galaxies and Nearby Groups

    NASA Astrophysics Data System (ADS)

    Jones, Christine; Forman, William; Bogdan, Akos; Randall, Scott; Kraft, Ralph; Churazov, Eugene

    2013-07-01

    Massive galaxies harbor a supermassive black hole at their centers. At high redshifts, these galaxies experienced a very active quasar phase, when, as their black holes grew by accretion, they produced enormous amounts of energy. At the present epoch, these black holes still undergo occasional outbursts, although the mode of their energy release is primarily mechanical rather than radiative. The energy from these outbursts can reheat the cooling gas in the galaxy cores and maintain the red and dead nature of the early-type galaxies. These outbursts also can have dramatic effects on the galaxy-scale hot coronae found in the more massive galaxies. We describe research in three areas related to the hot gas around galaxies and their supermassive black holes. First we present examples of galaxies with AGN outbursts that have been studied in detail. Second, we show that X-ray emitting low-luminosity AGN are present in 80% of the galaxies studied. Third, we discuss the first examples of extensive hot gas and dark matter halos in optically faint galaxies.

  19. XMM-Newton, powerful AGN winds and galaxy feedback

    NASA Astrophysics Data System (ADS)

    Pounds, K.; King, A.

    2016-06-01

    The discovery that ultra-fast ionized winds - sufficiently powerful to disrupt growth of the host galaxy - are a common feature of luminous AGN is major scientific breakthrough led by XMM-Newton. An extended observation in 2014 of the prototype UFO, PG1211+143, has revealed an unusually complex outflow, with distinct and persisting velocities detected in both hard and soft X-ray spectra. While the general properties of UFOs are consistent with being launched - at the local escape velocity - from the inner disc where the accretion rate is modestly super-Eddington (King and Pounds, Ann Rev Astron Astro- phys 2015), these more complex flows have raised questions about the outflow geometry and the importance of shocks and enhanced cooling. XMM-Newton seems likely to remain the best Observatory to study UFOs prior to Athena, and further extended observations, of PG1211+143 and other bright AGN, have the exciting potential to establish the typical wind dynamics, while providing new insights on the accretion geometry and continuum source structure. An emphasis on such large, coordinated observing programmes with XMM-Newton over the next decade will continue the successful philosophy pioneered by EXOSAT, while helping to inform the optimum planning for Athena

  20. A New Catalog of Type 1 AGNs and its Implications on the AGN Unified Model

    NASA Astrophysics Data System (ADS)

    Oh, Kyuseok; Yi, Sukyoung K.; Schawinski, Kevin; Koss, Michael; Trakhtenbrot, Benny; Soto, Kurt

    2015-07-01

    We have recently identified a substantial number of type 1 active galactic nuclei (AGNs) featuring weak broad-line regions (BLRs) at z\\lt 0.2 from detailed analysis of galaxy spectra in the Sloan Digital Sky Survey Data Release 7. These objects predominantly show a stellar continuum but also a broad Hα emission line, indicating the presence of a low-luminosity AGN oriented so that we are viewing the central engine directly without significant obscuration. These accreting black holes have previously eluded detection due to their weak nature. The newly discovered BLR AGNs have increased the number of known type 1 AGNs by 49%. Some of these new BLR AGNs were detected with the Chandra X-ray Observatory, and their X-ray properties confirm that they are indeed type 1 AGNs. Based on our new and more complete catalog of type 1 AGNs, we derived the type 1 fraction of AGNs as a function of [O iii] λ 5007 emission luminosity and explored the possible dilution effect on obscured AGNs due to star formation. The new type 1 AGN fraction shows much more complex behavior with respect to black hole mass and bolometric luminosity than has been suggested previously by the existing receding torus model. The type 1 AGN fraction is sensitive to both of these factors, and there seems to be a sweet spot (ridge) in the diagram of black hole mass and bolometric luminosity. Furthermore, we present the possibility that the Eddington ratio plays a role in determining opening angles.

  1. AGN Feedback in Galaxy Groups: A Joint GMRT/X-ray Study

    NASA Astrophysics Data System (ADS)

    Giacintucci, S.; Vrtilek, J. M.; O'Sullivan, E.; Raychaudhury, S.; David, L. P.; Venturi, T.; Athreya, R.; Gitti, M.

    2009-12-01

    We present an ongoing study of 18 nearby galaxy groups, chosen for the availability of Chandra and/or XMM-Newton data and evidence for AGN/hot intragroup gas interaction. We have obtained 235 and 610 MHz observations at the GMRT for all the groups, and 327 and 150 MHz for a few. We discuss two interesting cases-NGC 5044 and AWM 4-which exhibit different kinds of AGN/hot gas interaction. With the help of these examples we show how joining low-frequency radio data (to track the history of AGN outbursts through emission from aged electron populations) with X-ray data (to determine the state of hot gas, its disturbances, heating and cooling) can provide a unique insight into the nature of the feedback mechanism in galaxy groups.

  2. A tale of two feedbacks: Star formation in the host galaxies of radio AGNs

    SciTech Connect

    Karouzos, Marios; Im, Myungshin; Jeon, Yiseul; Kim, Ji Hoon; Trichas, Markos; Goto, Tomo; Malkan, Matt; Ruiz, Angel; Lee, Hyung Mok; Kim, Seong Jin; Oi, Nagisa; Matsuhara, Hideo; Takagi, Toshinobu; Murata, K.; Wada, Takehiko; Wada, Kensuke; Shim, Hyunjin; Hanami, Hitoshi; Serjeant, Stephen; White, Glenn J.; and others

    2014-04-01

    Several lines of argument support the existence of a link between activity at the nuclei of galaxies, in the form of an accreting supermassive black hole, and star formation activity in these galaxies. Radio jets have long been argued to be an ideal mechanism that allows active galactic nuclei (AGNs) to interact with their host galaxies and affect star formation. We use a sample of radio sources in the North Ecliptic Pole (NEP) field to study the nature of this putative link, by means of spectral energy distribution (SED) fitting. We employ the excellent spectral coverage of the AKARI infrared space telescope and the rich ancillary data available in the NEP to build SEDs extending from UV to far-IR wavelengths. We find a significant AGN component in our sample of relatively faint radio sources (AGN component and that of star formation in the host galaxy, independent of the radio luminosity. In contrast, for narrow redshift and AGN luminosity ranges, we find that increasing radio luminosity leads to a decrease in the specific star formation rate. The most radio-loud AGNs are found to lie on the main sequence of star formation for their respective redshifts. For the first time, we potentially see such a two-sided feedback process in the same sample. We discuss the possible suppression of star formation, but not total quenching, in systems with strong radio jets, that supports the maintenance nature of feedback from radio AGN jets.

  3. Multiwavelength AGN Surveys and Studies (IAU S304)

    NASA Astrophysics Data System (ADS)

    Mickaelian, Areg M.; Sanders, David B.

    2014-08-01

    1. Historical surveys: spectral and colorimetric surveys for AGN, surveys for UV-excess galaxies; 2. AGN from IR/submm surveys: 2MASS, IRAS, ISO, AKARI, SCUBA, SST, WISE, Herschel; 3. AGN from radio/mm surveys: NVSS, FIRST, ALMA, Planck, and others; 4. AGN from X-ray/gamma-ray surveys: ROSAT, ASCA, BeppoSAX, Chandra, XMM, INTEGRAL, Fermi, HESS, MAGIC, VERITAS, NuSTAR; 5. Multiwavelength AGN surveys, AGN statistics and cross-correlation of multiwavelength surveys; 6. Unification and other models of AGN, accretion modes, understanding of the structure of nearby AGN from IFUs on VLT and other telescopes; 7. AGN feedback in galaxies and clusters, AGN host galaxies and the AGN environments; 8. Binary AGN and Merging Super-Massive Black Holes; 9. Study of unique AGN, AGN variability and the Phenomena of Activity; 10. Future large projects; Author index.

  4. The host galaxies of X-ray selected AGN: feeding and feedback

    NASA Astrophysics Data System (ADS)

    Merloni, A.; Bongiorno, A.

    2014-07-01

    Using the rich multi-band photometry in the COSMOS field we explore the host galaxy properties of a large, complete, sample of X-ray and spectroscopically selected AGN. Based on a two-components fit to their Spectral Energy Distribution, we derive rest-frame magnitudes, colors, stellar masses and star formation rates up to z˜3, and we study the connection between these host galaxy properties, accretion luminosity and obscuration in galactic nuclei across more than 2/3 of the age of the Universe. Although AGN activity and star formation appear to have a common triggering mechanism, we do not find any strong evidence signaling the influence of luminous AGN on the global properties of their host galaxies. Conversely, we found that the central black hole activity have profound effects on the surrounding matter on scales comparable to the gravitational sphere of influence of the black hole. We discuss the implication of our findings for the nature of the long sough-after 'Quasar mode' feedback from AGN.

  5. Relativistic HD and MHD modelling for AGN jets

    NASA Astrophysics Data System (ADS)

    Keppens, R.; Porth, O.; Monceau-Baroux, R.; Walg, S.

    2013-12-01

    Relativistic hydro and magnetohydrodynamics (MHD) provide a continuum fluid description for plasma dynamics characterized by shock-dominated flows approaching the speed of light. Significant progress in its numerical modelling emerged in the last two decades; we highlight selected examples of modern grid-adaptive, massively parallel simulations realized by our open-source software MPI-AMRVAC (Keppens et al 2012 J. Comput. Phys. 231 718). Hydrodynamical models quantify how energy transfer from active galactic nuclei (AGN) jets to their surrounding interstellar/intergalactic medium (ISM/IGM) gets mediated through shocks and various fluid instability mechanisms (Monceau-Baroux et al 2012 Astron. Astrophys. 545 A62). With jet parameters representative for Fanaroff-Riley type-II jets with finite opening angles, we can quantify the ISM volumes affected by jet injection and distinguish the roles of mixing versus shock-heating in cocoon regions. This provides insight in energy feedback by AGN jets, usually incorporated parametrically in cosmological evolution scenarios. We discuss recent axisymmetric studies up to full 3D simulations for precessing relativistic jets, where synthetic radio maps can confront observations. While relativistic hydrodynamic models allow one to better constrain dynamical parameters like the Lorentz factor and density contrast between jets and their surroundings, the role of magnetic fields in AGN jet dynamics and propagation characteristics needs full relativistic MHD treatments. Then, we can demonstrate the collimating properties of an overal helical magnetic field backbone and study differences between poloidal versus toroidal field dominated scenarios (Keppens et al 2008 Astron. Astrophys. 486 663). Full 3D simulations allow one to consider the fate of non-axisymmetric perturbations on relativistic jet propagation from rotating magnetospheres (Porth 2013 Mon. Not. R. Astron. Soc. 429 2482). Self-stabilization mechanisms related to the detailed

  6. Feedback in the local Universe: Relation between star formation and AGN activity in early type galaxies

    NASA Astrophysics Data System (ADS)

    Vaddi, Sravani; O'Dea, Christopher; Baum, Stefi; Jones, Christine; Forman, William; Whitmore, Samantha; Ahmed, Rabeea; Pierce, Katherine; Leary, Sara

    2015-08-01

    Aim: We address the relation between star formation and AGN activity in a large sample of nearby early type (E and S0) galaxies. The redshift range of the galaxies is 0.0002Feedback from the AGN is believed to play an important role in regulating star formation and thus the process of galaxy evolution and formation. Evidence of AGN feedback is found in massive galaxies in galaxy clusters. However, how common AGN feedback is in the local universe and in small scale systems is still not evident.Methods: To answer this question, we carried out a multiple wavelength study of a sample of 231 early type galaxies which were selected to have an apparent K-band magnitude brighter than 13.5 and whose positions correlate with Chandra ACIS-I and ACIS-S sources. The galaxies in the sample are unbiased regarding their star formation and radio source properties. Using the archival observations at radio, IR and UV from VLA, WISE and GALEX respectively, we obtained the radio power, estimate FUV star formation rate (SFR) and other galaxy properties to study AGN activity and ongoing star formation.Results: The relationship between radio power and stellar mass shows that there is an upper envelope of radio power that is a steep function of stellar luminosity. This suggests that less massive galaxies have low radio power while massive galaxies are capable of hosting powerful radio sources. The Radio-MIR relation shows that galaxies with P>=1022 WHz-1 are potential candidates for being AGN. About ~ 7% of the sample show evidence of ongoing star formation with SFR ranging from 10-3 to 1 M⊙yr-1. These are also less massive and radio faint suggesting the absence of active accretion. There is nearly equal fraction of star forming galaxies in radio faint (P<1022 WHz-1) and radio bright galaxies (P>=1022 WHz-1) . Only ~ 5% of the galaxies in our sample have P>=1022 WHz-1 and most of them do not show evidence of bright accretion disks. We see a weak correlation and a dispersion of

  7. Two-phase model for black hole feeding and feedback

    NASA Astrophysics Data System (ADS)

    Nayakshin, Sergei

    2014-01-01

    We study effects of active galactic nucleus (AGN) feedback outflows on multiphase inter stellar medium (ISM) of the host galaxy. We argue that supermassive black hole (SMBH) growth is dominated by accretion of dense cold clumps and filaments. AGN feedback outflows overtake the cold medium, compress it, and trigger a powerful starburst - a positive AGN feedback. This predicts a statistical correlation between AGN luminosity and star formation rate at high luminosities. Most of the outflow's kinetic energy escapes from the bulge via low-density voids. The cold phase is pushed outward only by the ram pressure (momentum) of the outflow. The combination of the negative and positive forms of AGN feedback leads to an M-σ relation similar to the result of King. Due to porosity of cold ISM in the bulge, SMBH influence on the low density medium of the host galaxy is significant even for SMBH well below the M-σ mass. The role of SMBH feedback in our model evolves in space and time with the ISM structure. In the early gas rich phase, SMBH accelerates star formation in the bulge. During later gas poor (red-and-dead) phases, SMBH feedback is mostly negative everywhere due to scarcity of the cold ISM.

  8. Trouble for AGN Feedback? The Puzzle of the Core of the Galaxy Cluster AWM 4

    NASA Astrophysics Data System (ADS)

    Gastaldello, Fabio; Buote, David A.; Brighenti, Fabrizio; Mathews, William G.

    2008-01-01

    The core of the relaxed cluster AWM 4 is characterized by a unique combination of properties which defy a popular scenario for AGN heating of cluster cores. A flat inner temperature profile is indicative of a past, major heating episode which completely erased the cool core, as testified by the high central cooling time (gtrsim3 Gyr) and by the high central entropy level (~60 keV cm2). Yet the presence of a 1.4 GHz active central radio galaxy with extended radio lobes out to 100 kpc reveals recent feeding of the central massive black hole. A system like AWM 4 should have no radio emission at all if only feedback from the cooling hot gas regulates the AGN activity.

  9. AGN feedback in groups of galaxies: a joint X-ray/low-frequency radio study

    NASA Astrophysics Data System (ADS)

    Giacintucci, S.; O'Sullivan, E.; Vrtilek, J. M.; Raychaudhury, S.; David, L. P.; Venturi, T.; Athreya, R.; Gitti, M.

    2010-07-01

    We present an ongoing, low-frequency radio/X-ray study of 18 nearby galaxy groups, chosen for the evidence, either in the X-ray or radio images, of AGN/intragroup gas interaction. We have obtained radio observations at 235 MHz and 610 MHz with the Giant Metrewave Radio Telescope (GMRT) for all the groups, and 327 MHz and 150 MHz for a few. We present results of the recent Chandra/GMRT study of the interesting case of AWM 4, a relaxed poor cluster of galaxies with no evidence of a large cool core and no X-ray cavities associated with the central radio galaxy. Our analysis shows how joining low-frequency radio data (to track the history of AGN outbursts) with X-ray data (to determine the state of the hot gas, its disturbances, heating and cooling) can provide a unique insight into the nature of the feedback mechanism in galaxy groups.

  10. Constraining AGN Feedback in Massive Ellipticals with South Pole Telescope Measurements of the Thermal Sunyaev-Zel'dovich Effect

    NASA Astrophysics Data System (ADS)

    Spacek, Alexander; Scannapieco, Evan; Cohen, Seth; Joshi, Bhavin; Mauskopf, Philip

    2016-03-01

    Energetic feedback due to active galactic nuclei (AGNs) is likely to play an important role in the observed anti-hierarchical trend in the evolution of galaxies, and yet the energy injected into the circumgalactic medium by this process is largely unknown. One promising approach to constrain this feedback is through measurements of spectral distortions in the cosmic microwave background due to the thermal Sunyaev-Zeldovich (tSZ) effect, whose magnitude is directly proportional to the energy input by AGNs. With current instruments, making such measurements requires stacking large numbers of objects to increase signal-to-noise. While one possible target for such stacks is AGNs themselves, these are relatively scarce sources that contain contaminating emission that complicates tSZ measurements. Here we adopt an alternative approach and co-add South Pole Telescope SZ (SPT-SZ) survey data around a large set of massive quiescent elliptical galaxies at z≥slant 0.5, which are much more numerous and less contaminated than active AGNs, yet are subject to the same feedback processes from the AGNs they hosted in the past. We use data from the Blanco Cosmology Survey and VISTA Hemisphere Survey to create a large catalog of galaxies split up into two redshift bins: one with 3394 galaxies at 0.5≤slant z≤slant 1.0 and one with 924 galaxies at 1.0≤slant z≤slant 1.5, with typical stellar masses of 1.5× {10}11{M}⊙ . We then co-add the emission around these galaxies, resulting in a measured tSZ signal at 2.2σ significance for the lower redshift bin and a contaminating signal at 1.1σ for the higher redshift bin. To remove contamination due to dust emission, we use SPT-SZ source counts to model a contaminant source population in both the SPT-SZ bands and Planck high-frequency bands for a subset of 937 galaxies in the low-redshift bin and 240 galaxies in the high-redshift bin. This increases our detection to 3.6σ for low redshifts and 0.9σ for high redshifts. We find the

  11. AGN Feedback in Galaxy Groups: The Two Interesting Cases of AWM 4 and NGC 5044

    NASA Astrophysics Data System (ADS)

    Gastaldello, Fabio; Buote, David A.; Brighenti, Fabrizio; Mathews, William G.; Temi, Pasquale; Ettori, Stefano

    2009-12-01

    We present AGN feedback in the interesting cases of two groups: AWM 4 and NGC 5044. AWM 4 is characterized by a combination of properties which seems to defy the paradigm for AGN heating in cluster cores: a flat inner temperature profile indicative of a past, major heating episode which completely erased the cool core, as testified by the high central cooling time (>3 Gyrs) and by the high central entropy level (~50 keV cm2), and yet an active central radio galaxy with extended radio lobes out to 100 kpc, revealing recent feeding of the central massive black hole. A recent Chandra observation has revealed the presence of a compact cool corona associated with the BCG, solving the puzzle of the apparent lack of low entropy gas surrounding a bright radio source, but opening the question of its origin. NGC 5044 shows in the inner 10 kpc a pair of cavities together with a set of bright filaments. The cavities are consistent with a recent AGN outburst as also indicated by the extent of dust and Hα emission even though the absence of extended 1.4 GHz emission remains to be explained. The soft X-ray filaments coincident with Hα and dust emission are cooler than those which do not correlate with optical and infrared emission, suggesting that dust-aided cooling can contribute to the overall cooling. For the first time sloshing cold fronts at the scale of a galaxy group have been observed in this object.

  12. AGN feedback and delivery methods for simulations of cool-core galaxy clusters

    NASA Astrophysics Data System (ADS)

    Meece, Gregory Robert, Jr.

    Galaxy clusters are filled with a hot plasma called the intracluster medium, or ICM. In roughly half of clusters, the radiative cooling time is much shorter than the age of the cluster, meaning that the ICM should have had plenty of time to cool and form stars. Instead, observations show little cold gas in these clusters and star formation rates at least an order of magnitude below what is predicted. This dissertation explores a theory known as the Precipitation-regulated Feedback Hypothesis. As the ICM cools, thermal instability leads the formation of cold clouds that accrete onto a supermassive black hole, powering active galactic nuclei (AGN) that reheat the cluster. This feedback loop balances cooling and keeps the cluster in a rough state of thermal equilibrium.

  13. Cusp-core transformations induced by AGN feedback in the progenitors of cluster galaxies

    NASA Astrophysics Data System (ADS)

    Martizzi, Davide; Teyssier, Romain; Moore, Ben

    2013-07-01

    In a recent study, we used cosmological simulations to show that active galactic nuclei (AGN) feedback on the gas distribution in clusters of galaxies can be important in determining the spatial distribution of stars and dark matter in the central regions of these systems. The hierarchical assembly of dark matter, baryons and black holes obscures the physical mechanism behind the restructuring process. Here, we use idealized simulations to follow the response of a massive dark matter halo as we feed the central black hole with a controlled supply of cold gas. This removes most of the complexity taking place in the cosmological simulations that may have biased our previous study. We confirm our previous results: gas heated and expelled from the central regions of the halo by AGN feedback can return after cooling; repeated cycles generate gravitational potential fluctuations responsible for irreversible modifications of the dark matter mass profile. The main result is the expulsion of large amounts of baryons and dark matter from the central regions of the halo. According to the work presented here, outflow-induced fluctuations represent the only mechanism able to efficiently create dark matter cores in clusters of galaxies.

  14. Modeling IR SED of AGN with Spitzer and Herschel data

    NASA Astrophysics Data System (ADS)

    Feltre, A.

    2012-12-01

    One of the remaining open issues in the context of the analysis of Active Galactic Nuclei (AGN) is the evidence that nuclear gravitational accretion is often accompanied by a concurrent starburst (SB) activity. What is, in this picture, the role played by the obscur- ing dust around the nucleus and what do the state of the art AGN torus models have to say? Can the IR data provided by Spitzer and Herschel help us in extensively investigate both phenomena and, if so, how and with what limitations? In this paper we present our contribution to the efforts of answering these questions. We show some of the main results coming from a comparative study of various AGN SED modeling approaches, focusing mostly on the much-debated issue about the morphology of the dust distribution in the toroidal structure surrounding the AGN. We found that the properties of dust in AGN as measured by matching observations (be it broad band IR photometry or IR spectra) with models, strongly depend on the choice of the dust distribution. Then, we present the spec- tral energy distribution (SED) fitting procedure we developed, making make the best use of Spitzer and Herschel SPIRE mid- and far-IR observations, to dig into the role played by the possible presence of an AGN on the host galaxy's properties.

  15. The effect of stellar feedback on the formation and evolution of gas and dust tori in AGN

    NASA Astrophysics Data System (ADS)

    Schartmann, M.; Meisenheimer, K.; Klahr, H.; Camenzind, M.; Wolf, S.; Henning, Th.

    2009-03-01

    Recently, the existence of geometrically thick dust structures in active galactic nuclei (AGN) has been directly proven with the help of interferometric methods in the mid-infrared. The observations are consistent with a two-component model made up of a geometrically thin and warm central disc, surrounded by a colder, fluffy torus component. Within the framework of an exploratory study, we investigate one possible physical mechanism, which could produce such a structure, namely the effect of stellar feedback from a young nuclear star cluster on the interstellar medium in centres of AGN. The model is realized by numerical simulations with the help of the hydrodynamics code TRAMP. We follow the evolution of the interstellar medium by taking discrete mass-loss and energy ejection due to stellar processes, as well as optically thin radiative cooling into account. In a post-processing step, we calculate observable quantities like spectral energy distributions (SEDs) and surface brightness distributions with the help of the radiative transfer code MC3D. The interplay between injection of mass, supernova explosions and radiative cooling leads to a two-component structure made up of a cold geometrically thin, but optically thick and very turbulent disc residing in the vicinity of the angular momentum barrier, surrounded by a filamentary structure. The latter consists of cold long radial filaments flowing towards the disc and a hot tenuous medium in between, which shows both inwards and outwards directed motions. With the help of this modelling, we are able to reproduce the range of observed neutral hydrogen column densities of a sample of Seyfert galaxies as well as the relation between them and the strength of the silicate 10μm spectral feature. Despite being quite crude, our mean Seyfert galaxy model is even able to describe the SEDs of two intermediate type Seyfert galaxies observed with the Spitzer Space Telescope.

  16. Extreme Gas Kinematics in the z=2.2 Powerful Radio Galaxy MRC1138-262: Evidence for Efficient AGN Feedback in the Early Universe?

    SciTech Connect

    Nesvadba, N H; Lehnert, M D; Eisenhauer, F; Gilbert, A M; Tecza, M; Abuter, R

    2007-06-26

    To explain the properties of the most massive low-redshift galaxies and the shape of their mass function, recent models of galaxy evolution include strong AGN feedback to complement starburst-driven feedback in massive galaxies. Using the near-infrared integral-field spectrograph SPIFFI on the VLT, we searched for direct evidence for such a feedback in the optical emission line gas around the z = 2.16 powerful radio galaxy MRC1138-262, likely a massive galaxy in formation. The kpc-scale kinematics, with FWHMs and relative velocities {approx}< 2400 km s{sup -1} and nearly spherical spatial distribution, do not resemble large-scale gravitational motion or starburst-driven winds. Order-of-magnitude timescale and energy arguments favor the AGN as the only plausible candidate to accelerate the gas, with a total energy injection of {approx} few x 10{sup 60} ergs or more, necessary to power the outflow, and relatively efficient coupling between radio jet and ISM. Observed outflow properties are in gross agreement with the models, and suggest that AGN winds might have a similar, or perhaps larger, cosmological significance than starburst-driven winds, if MRC1138-262 is indeed archetypal. Moreover, the outflow has the potential to remove significant gas fractions ({approx}< 50%) from a > L* galaxy within a few 10 to 100 Myrs, fast enough to preserve the observed [{alpha}/Fe] overabundance in massive galaxies at low redshift. Using simple arguments, it appears that feedback like that observed in MRC1138-262 may have sufficient energy to inhibit material from infalling into the dark matter halo and thus regulate galaxy growth as required in some recent models of hierarchical structure formation.

  17. A Degeneracy in DRW Modelling of AGN Light Curves

    NASA Astrophysics Data System (ADS)

    Kozłowski, Szymon

    2016-04-01

    Individual light curves of active galactic nuclei (AGNs) are nowadays successfully modelled with the damped random walk (DRW) stochastic process, characterized by the power exponential covariance matrix of the signal, with the power β = 1. By Monte Carlo simulation means, we generate mock AGN light curves described by non-DRW stochastic processes (0.5 ≤ β ≤ 1.5 and β ≠ 1) and show they can be successfully and well-modelled as a single DRW process, obtaining comparable goodness of fits. A good DRW fit, in fact, may not mean that DRW is the true underlying process leading to variability and it cannot be used as a proof for it. When comparing the input (non-DRW) and measured (DRW) process parameters, the recovered time scale (amplitude) increases (decreases) with the increasing input β. In practice, this means that the recovered DRW parameters may lead to biased (or even non-existing) correlations of the variability and physical parameters of AGNs if the true AGN variability is caused by non-DRW stochastic processes. The proper way of identifying the processes leading to variability are model-independent structure functions and/or power spectral densities and then using such information on the covariance matrix of the signal in light curve modelling.

  18. A degeneracy in DRW modelling of AGN light curves

    NASA Astrophysics Data System (ADS)

    Kozłowski, Szymon

    2016-07-01

    Individual light curves of active galactic nuclei (AGNs) are nowadays successfully modelled with the damped random walk (DRW) stochastic process, characterized by the power exponential covariance matrix of the signal, with the power β = 1. By Monte Carlo simulation means, we generate mock AGN light curves described by non-DRW stochastic processes (0.5 ≤ β ≤ 1.5 and β ≠ 1) and show they can be successfully and well modelled as a single DRW process, obtaining comparable goodness of fits. A good DRW fit, in fact, may not mean that DRW is the true underlying process leading to variability and it cannot be used as a proof for it. When comparing the input (non-DRW) and measured (DRW) process parameters, the recovered time-scale (amplitude) increases (decreases) with the increasing input β. In practice, this means that the recovered DRW parameters may lead to biased (or even non-existing) correlations of the variability and physical parameters of AGNs if the true AGN variability is caused by non-DRW stochastic processes. The proper way of identifying the processes leading to variability are model-independent structure functions and/or power spectral densities and then using such information on the covariance matrix of the signal in light-curve modelling.

  19. AGN and their host galaxies

    NASA Astrophysics Data System (ADS)

    Steinborn, L. K.; Dolag, K.; Hirschmann, M.; Remus, R.-S.; Teklu, A. F.

    2016-06-01

    Large scale cosmological hydrodynamic simulations are an important tool to study the co-evolution between black holes (BHs) and their host galaxies. However, in order to model the accretion onto BHs and AGN feedback we need sub-grid models which contain several free parameters. The choice of these parameters has a significant impact on the properties of the BHs and their host galaxies. Therefore, we improve the accretion model and the AGN feedback model based on both theory and observations to eliminate most free parameters. In that way, the slope of the observed relation between BH mass and stellar mass is reproduced self-consistently. We performed a few extremely large simulation runs as part of the Magneticum Pathfinder simulation set, combining a high resolution with very large cosmological volumes, enabling us to study for example dual AGN, the role of galaxy mergers and AGN clustering properties.

  20. A Very Deep Chandra Observation of the Galaxy Group NGC 5813: AGN Shocks, Feedback, and Outburst History

    NASA Astrophysics Data System (ADS)

    Randall, S. W.; Nulsen, P. E. J.; Jones, C.; Forman, W. R.; Bulbul, E.; Clarke, T. E.; Kraft, R.; Blanton, E. L.; David, L.; Werner, N.; Sun, M.; Donahue, M.; Giacintucci, S.; Simionescu, A.

    2015-06-01

    We present results from a very deep (650 ks) Chandra X-ray observation of the galaxy group NGC 5813, the deepest Chandra observation of a galaxy group to date. This system uniquely shows three pairs of collinear cavities, with each pair associated with an unambiguous active galactic nucleus (AGN) outburst shock front. The implied mean kinetic power is roughly the same for each outburst, demonstrating that the average AGN kinetic luminosity can remain stable over long timescales (˜50 Myr). The two older outbursts have larger, roughly equal total energies as compared with the youngest outburst, implying that the youngest outburst is ongoing. We find that the gas radiative cooling rate and mean shock heating rate are well balanced at each shock front, suggesting that shock heating alone is sufficient to offset cooling and establish AGN/intracluster medium (ICM) feedback within at least the central 30 kpc. This heating takes place roughly isotropically and most strongly at small radii, as is required for feedback to operate. We suggest that shock heating may play a significant role in AGN feedback at smaller radii in other systems, where weak shocks are more difficult to detect. We find non-zero shock front widths that are too large to be explained by particle diffusion. Instead, all measured widths are consistent with shock broadening due to propagation through a turbulent ICM with a mean turbulent speed of ˜70 km s-1. Finally, we place lower limits on the temperature of any volume-filling thermal gas within the cavities that would balance the internal cavity pressure with the external ICM.

  1. AGN feedback in X-ray luminous galaxy cluster: PKS 0745-191

    NASA Astrophysics Data System (ADS)

    Sonkamble, Satish Shripati; Vagshette, Nilkanth Dattatray; Patil, Madhav Khushalrao

    2015-08-01

    We present 117 ks Chandra observation of the cooling flow cluster PKS 0745-191 providing evidence of the strong interaction between the radio source associated with the center dominant galaxy PGC 021813 and the intra-cluster gas. This system is one of the strongest cool core cluster, requiring extreme mechanical feedback from its central AGN to offset cooling of the ICM. This analysis has enabled us to detect two pairs of X-ray cavities in the central ˜ 20 kpc region. In addition to the cavities, we have also evidenced relatively cooler X-ray arc and a temperature jump due to the shock front at 92'' (184 kpc) on the western side. 2D temperature maps as well as spectral analysis of X-ray photons extracted from wedge shaped reigns revealed six different cold fronts, 3 along the eastern direction, 2 on the west direction and one in the south direction of the X-ray peak. The apparent positions of cold fronts are found to match with the spiral structure apparent in the X-ray surface brightness distribution of PKS 0745-191 that is probably due to the gas sloshing. The Mach number for this shock is found to be ˜ 1.36. Systematic study of the X-ray cavities revealed a mechanical power of ˜ 2.95 X 1045 erg s-1 and is sufficient to offset the cooling due to radiative loss. We found that the radio source associated with the center dominant galaxy of this cluster is efficient enough to carve the observed cavities. The ratio of radio luminosity to mechanical cavity power is ˜ 10-3 .

  2. Obscured accretion from AGN surveys

    NASA Astrophysics Data System (ADS)

    Vignali, Cristian

    2014-07-01

    Recent models of super-massive black hole (SMBH) and host galaxy joint evolution predict the presence of a key phase where accretion, traced by obscured Active Galactic Nuclei (AGN) emission, is coupled with powerful star formation. Then feedback processes likely self-regulate the SMBH growth and quench the star-formation activity. AGN in this important evolutionary phase have been revealed in the last decade via surveys at different wavelengths. On the one hand, moderate-to-deep X-ray surveys have allowed a systematic search for heavily obscured AGN, up to very high redshifts (z~5). On the other hand, infrared/optical surveys have been invaluable in offering complementary methods to select obscured AGN also in cases where the nuclear X-ray emission below 10 keV is largely hidden to our view. In this review I will present my personal perspective of the field of obscured accretion from AGN surveys.

  3. AGN feedback in action: a new powerful wind in 1SXPS J050819.8+172149?

    NASA Astrophysics Data System (ADS)

    Ballo, L.; Severgnini, P.; Braito, V.; Campana, S.; Della Ceca, R.; Moretti, A.; Vignali, C.

    2015-09-01

    Context. Galaxy merging is widely accepted to be a driving factor in galaxy formation and evolution, while the feedback from actively accreting nuclei is thought to regulate the black hole-bulge coevolution and the star formation process. Aims: In this context, we focused on 1SXPS J050819.8+172149, a local (z = 0.0175) Seyfert 1.9 galaxy (L bol ~ 4 × 1043 erg s-1). The source belongs to an infrared-luminous interacting pair of galaxies, characterized by a luminosity for the whole system (due to the combination of star formation and accretion) of log (L IR/L⊙) = 11.2. We present here the first detailed description of the 0.3-10 keV spectrum of 1SXPS J050819.8+172149, monitored by Swift with nine pointings performed in less than one month. Methods: The X-ray emission of 1SXPS J050819.8+172149 is analysed by combining all the Swift pointings, for a total of ~72 ks XRT net exposure. The averaged Swift-BAT spectrum from the 70-month survey is also analysed. Results: The slope of the continuum is Γ ~ 1.8, with an intrinsic column density of ~2.4 × 1022cm-2, and a de-absorbed luminosity of ~4 × 1042 erg s-1 in the 2-10 keV band. Our observations provide a tentative (2.1σ) detection of a blueshifted Fe xxvi absorption line (rest-frame E ~ 7.8 keV), thus suggesting the discovery of a new candidate powerful wind in 1SXPS J050819.8+172149. The physical properties of the outflow cannot be firmly assessed owing to the low statistics of the spectrum and to the observed energy of the line, too close to the higher boundary of the Swift-XRT bandpass. However, our analysis suggests that, if the detection is confirmed, the line could be associated with a high-velocity (v out ~ 0.1c) outflow most likely launched within 80 r S. To our knowledge this is the first detection of a previously unknown ultrafast wind with Swift. The high column density suggested by the observed equivalent width of the line (EW ~ -230 eV, although with large uncertainties) would imply a kinetic output

  4. Supermassive Black Holes, AGN Feedback, and Hot X-ray Coronae in Early Type Galaxies

    NASA Astrophysics Data System (ADS)

    Forman, William R.; Anderson, Michael E.; Churazov, Eugene; Nulsen, Paul; Jones, Christine; Kraft, Ralph P.

    2016-06-01

    We present the analysis of a sample of more than 200 nearby, early type galaxies observed with the Chandra X-ray Observatory. We exclude resolved point sources, and model the emission from both unresolved X-ray binaries and CVs and ABs to derive the residual thermal emission from the hot atmosphere around each galaxy. We compute the X-ray luminosity of the central supermassive black hole (SMBH). Using galaxy velocity dispersion (or stellar mass) as a proxy for SMBH mass, we derive the Eddington ratios for these low luminosity AGN. We present the X-ray luminosity and gas temperature of the hot coronae as a function of stellar mass (a proxy for dark matter halo mass) and central velocity dispersion to look for anomalously X-ray bright gaseous coronae and to determine the stellar (or halo) mass, below which galactic winds may be important. For hot coronae with X-ray cavities, we derive the "mechanical" power of SMBHs and compare these to their radiative luminosities.

  5. Feedback control indirect response models.

    PubMed

    Zhang, Yaping; D'Argenio, David Z

    2016-08-01

    A general framework is introduced for modeling pharmacodynamic processes that are subject to autoregulation, which combines the indirect response (IDR) model approach with methods from classical feedback control of engineered systems. The canonical IDR models are modified to incorporate linear combinations of feedback control terms related to the time course of the difference (the error signal) between the pharmacodynamic response and its basal value. Following the well-established approach of traditional engineering control theory, the proposed feedback control indirect response models incorporate terms proportional to the error signal itself, the integral of the error signal, the derivative of the error signal or combinations thereof. Simulations are presented to illustrate the types of responses produced by the proposed feedback control indirect response model framework, and to illustrate comparisons with other PK/PD modeling approaches incorporating feedback. In addition, four examples from literature are used to illustrate the implementation and applicability of the proposed feedback control framework. The examples reflect each of the four mechanisms of drug action as modeled by each of the four canonical IDR models and include: selective serotonin reuptake inhibitors and extracellular serotonin; histamine H2-receptor antagonists and gastric acid; growth hormone secretagogues and circulating growth hormone; β2-selective adrenergic agonists and potassium. The proposed feedback control indirect response approach may serve as an exploratory modeling tool and may provide a bridge for development of more mechanistic systems pharmacology models. PMID:27394724

  6. NGC 3801 caught in the act: a post-merger star-forming early-type galaxy with AGN-jet feedback

    NASA Astrophysics Data System (ADS)

    Hota, Ananda; Rey, Soo-Chang; Kang, Yongbeom; Kim, Suk; Matsushita, Satoki; Chung, Jiwon

    2012-05-01

    In the current models of galaxy formation and evolution, AGN feedback is crucial to reproduce galaxy luminosity function, colour-magnitude relation and M•-σ relation. However, whether AGN feedback can indeed expel and heat up significant amount of cool molecular gas and consequently quench star formation is yet to be demonstrated observationally. Only in four cases so far (Cen A, NGC 3801, NGC 6764 and Mrk 6), X-ray observations have found evidences of jet-driven shocks heating the ISM. We chose the least explored galaxy NGC 3801, and present the first ultraviolet imaging and stellar population analysis of this galaxy from GALEX data. We find this merger-remnant early-type galaxy to have an intriguing spiral wisp of young star-forming regions (age ranging from 100 to 500 Myr). Taking clues from dust/PAH, H I and CO emission images, we interpret NGC 3801 to have a kinematically decoupled core or an extremely warped gas disc. From the HST data, we also show evidence of ionized gas outflow similar to that observed in H I and molecular gas (CO) data, which may have caused the decline of star formation leading to the red optical colour of the galaxy. However, from these panchromatic data, we interpret that the expanding shock shells from the young (˜2.4 Myr) radio jets are yet to reach the outer gaseous regions of the galaxy. It seems we observe this galaxy at a rare stage of its evolutionary sequence where post-merger star formation has already declined and new powerful jet feedback is about to affect the gaseous star-forming outer disc within the next 10 Myr, to further transform it into a red-and-dead early-type galaxy.

  7. FEEDBACK FROM CENTRAL BLACK HOLES IN ELLIPTICAL GALAXIES. II. CAN PURELY MECHANICAL ENERGY FEEDBACK MODELS WORK?

    SciTech Connect

    Shin Minsu; Ostriker, Jeremiah P.; Ciotti, Luca

    2010-03-01

    By using high-resolution one-dimensional hydrodynamical simulations, we investigate the effects of purely mechanical feedback from super massive black holes (SMBHs) in the evolution of elliptical galaxies for a broad range of feedback efficiencies and compare the results to four major observational constraints. In particular, we focus on (1) the central black hole to stellar mass ratio of the host galaxy, (2) the lifetime of the luminous quasar phase, (3) the mass of stars formed in the host galaxy within the last Gyr, and (4) the X-ray luminosity of the hot diffuse gas. As a result, we try to pin down the most successful range of mechanical feedback efficiencies. We find that while low feedback efficiencies result in too much growth of the SMBH, high efficiencies totally blow out the hot interstellar gas, and the models are characterized by very low thermal X-ray luminosity well below the observed range. The net lifetime of the quasar phase is strongly coupled to the mass ratio between SMBH and its host galaxy, while the X-ray luminosity is generally correlated to the recent star formation within the last Gyr. When considering the popularly adopted model of the constant feedback efficiency, the feedback energy deposited into the ambient medium should be more than 0.01% of the SMBH accretion energy to be consistent with the SMBH mass to stellar mass ratio in the local universe. Yet, the X-ray luminosity of the hot gas favors about 0.005% of the accretion energy as the mechanical active galactic nucleus (AGN) feedback energy. We conclude that the purely mechanical feedback mode is unlikely to be simultaneously compatible with all four observable tests, even allowing a broad range of feedback efficiencies, and that including both radiative and mechanical feedback together may be a solution to comply with the observational constraints. In addition to the adopted observational constraints, our simulations also show that the ratio of SMBH growth rate over its current

  8. ACTIVE GALACTIC NUCLEI AS MAIN CONTRIBUTORS TO THE ULTRAVIOLET IONIZING EMISSIVITY AT HIGH REDSHIFTS: PREDICTIONS FROM A {Lambda}-CDM MODEL WITH LINKED AGN/GALAXY EVOLUTION

    SciTech Connect

    Giallongo, E.; Menci, N.; Fiore, F.; Castellano, M.; Fontana, A.; Grazian, A.; Pentericci, L.

    2012-08-20

    We have evaluated the contribution of the active galactic nuclei (AGN) population to the ionization history of the universe based on a semi-analytic model of galaxy formation and evolution in the cold dark matter cosmological scenario. The model connects the growth of black holes and of the ensuing AGN activity to galaxy interactions. In the model we have included a self-consistent physical description of the escape of ionizing UV photons; this is based on the blast-wave model for the AGN feedback we developed in a previous paper to explain the distribution of hydrogen column densities in AGNs of various redshifts and luminosities, due to absorption by the host galaxy gas. The model predicts UV luminosity functions for AGNs that are in good agreement with those derived from the observations especially at low and intermediate redshifts (z {approx} 3). At higher redshifts (z > 5), the model tends to overestimate the data at faint luminosities. Critical biases in both the data and in the model are discussed to explain such apparent discrepancies. The predicted hydrogen photoionization rate as a function of redshift is found to be consistent with that derived from the observations. All of the above suggests that we should reconsider the role of the AGNs as the main driver of the ionization history of the universe.

  9. Dust in the torus of the AGN unified model

    NASA Astrophysics Data System (ADS)

    Mason, Rachel E.

    2015-10-01

    In these proceedings I briefly summarize our current understanding of the dusty torus of the AGN unified model: its structure, composition, and ideas about its origin and evolution. The paper is based on an invited review talk at the 7th Meeting on Cosmic Dust, which covered dust-related topics in areas from comets to debris disks and high-redshift galaxies. This is therefore intended to be an accessible, introductory overview of the torus with some emphasis on the solid-state spectral features observed.

  10. Feedback under the microscope - I. Thermodynamic structure and AGN-driven shocks in M87

    NASA Astrophysics Data System (ADS)

    Million, E. T.; Werner, N.; Simionescu, A.; Allen, S. W.; Nulsen, P. E. J.; Fabian, A. C.; Böhringer, H.; Sanders, J. S.

    2010-10-01

    We present the first in a series of papers discussing the thermodynamic properties of M87 and the central regions of the Virgo Cluster in unprecedented detail. Using a deep Chandra exposure (574 ks), we present high-resolution thermodynamic maps created from the spectra of ~16000 independent regions, each with ~1000 net counts. The excellent spatial resolution of the thermodynamic maps reveals the dramatic and complex temperature, pressure, entropy and metallicity structure of the system. The `X-ray arms', driven outwards from M87 by the central active galactic nuclei (AGN), are prominent in the brightness, temperature and entropy maps. Excluding the `X-ray arms', the diffuse cluster gas at a given radius is strikingly isothermal. This suggests either that the ambient cluster gas, beyond the arms, remains relatively undisturbed by AGN uplift or that conduction in the intracluster medium (ICM) is efficient along azimuthal directions, as expected under action of the heat-flux-driven buoyancy instability (HBI). We confirm the presence of a thick (~40 arcsec or ~3kpc) ring of high-pressure gas at a radius of ~180 arcsec (~14kpc) from the central AGN. We verify that this feature is associated with a classical shock front, with an average Mach number M = 1.25. Another, younger shock-like feature is observed at a radius of ~40 arcsec (~3kpc) surrounding the central AGN, with an estimated Mach number M >~ 1.2. As shown previously, if repeated shocks occur every ~10 Myr, as suggested by these observations, then AGN-driven weak shocks could produce enough energy to offset radiative cooling of the ICM. A high significance enhancement of Fe abundance is observed at radii 350-400 arcsec (27-31kpc). This ridge is likely formed in the wake of the rising bubbles filled with radio-emitting plasma that drag cool, metal-rich gas out of the central galaxy. We estimate that at least ~1.0 × 106 solar masses of Fe has been lifted and deposited at a radius of 350-400 arcsec

  11. Constraints on Feedback in the Local Universe: The Relation Between Star Formation and AGN Activity in Early Type Galaxies

    NASA Astrophysics Data System (ADS)

    Vaddi, Sravani; O'Dea, Christopher P.; Baum, Stefi Alison

    2016-01-01

    We address the relation between star formation and AGN activity in a sample of 231 nearby (0.0002 < z < 0.0358) early type galaxies by carrying out a multi-wavelength study using archival observations in the UV, IR and radio. Our results indicate that early type galaxies in the current epoch are rarely powerful AGNs, with P < 1022 WHz-1 for a majority of the galaxies. Only massive galaxies are capable of hosting powerful radio sources while less massive galaxies are hosts to lower radio power sources. Evidence of ongoing star formation is seen in approximately 7% of the sample. The SFR of these galaxies is less than 0.1 M⊙yr-1. They also tend to be radio faint (P < 1022 WHz-1). There is a nearly equal fraction of star forming galaxies in radio faint (P < 1022 WHz-1) and radio bright galaxies (P ≥ 1022 WHz-1) suggesting that both star formation and radio mode feedback are constrained to be very low in our sample. We notice that our galaxy sample and the Brightest Cluster Galaxies (BCGs) follow similar trends in radio power versus SFR. This may be produced if both radio power and SFR are related to stellar mass.

  12. Constraints on Feedback in the Local Universe: The Relation between Star Formation and AGN Activity in Early-type Galaxies

    NASA Astrophysics Data System (ADS)

    Vaddi, Sravani; O'Dea, Christopher P.; Baum, Stefi A.; Whitmore, Samantha; Ahmed, Rabeea; Pierce, Katherine; Leary, Sara

    2016-02-01

    We address the relation between star formation and active galactic nucleus (AGN) activity in a sample of 231 nearby (0.0002 < z < 0.0358) early-type galaxies by carrying out a multi-wavelength study using archival observations in the UV, IR, and radio. Our results indicate that early-type galaxies in the current epoch are rarely powerful AGNs, with P\\lt {10}22 {{WHz}}-1 for a majority of the galaxies. Only massive galaxies are capable of hosting powerful radio sources while less massive galaxies are hosts to lower radio power sources. Evidence of ongoing star formation is seen in approximately 7% of the sample. The star formation rate (SFR) of these galaxies is less than 0.1 M⊙ yr-1. They also tend to be radio faint (P\\lt {10}22 {{WHz}}-1). There is a nearly equal fraction of star-forming galaxies in radio faint (P\\lt {10}22 {{WHz}}-1) and radio bright galaxies (P≥slant {10}22 {{WHz}}-1) suggesting that both star formation and radio mode feedback are constrained to be very low in our sample. We notice that our galaxy sample and the Brightest Cluster Galaxies follow similar trends in radio power versus SFR. This may be produced if both radio power and SFR are related to stellar mass.

  13. AGN Feedback And Evolution of Radio Sources: Discovery of An X-Ray Cluster Associated With Z=1 Quasar

    SciTech Connect

    Siemiginowska, Aneta; Cheung, C.C.; LaMassa, S.; Burke, D.; Aldcroft, T.L.; Bechtold, J.; Elvis, M.; Worrall, D.M.; /Bristol U.

    2006-01-11

    We report the first significant detection of an X-ray cluster associated with a powerful (L{sub bol} {approx} 10{sup 47} erg sec{sup -1}) radio-loud quasar at high redshift (z=1.06). Diffuse X-ray emission is detected out to {approx} 120 kpc from the CSS quasar 3C 186. A strong Fe-line emission at the z{sub rest} = 1.06 confirms its thermal nature. We find that the CSS radio source is highly overpressured with respect to the thermal cluster medium by 2-3 orders of magnitude. This provides direct observational evidence that the radio source is not thermally confined as posited in the ''frustrated'' scenario for CSS sources. Instead, the radio source may be young and at an early stage of its evolution. This source provides the first detection of the AGN in outburst in the center of a cooling flow cluster. Powerful radio sources are thought to be triggered by the cooling flows. The evidence for the AGN activity and intermittent outbursts comes from the X-ray morphology of low redshift clusters, which usually do not harbour quasars. 3C186 is a young active radio source which can supply the energy into the cluster and potentially prevent its cooling. We discuss energetics related to the quasar activity and the cluster cooling flow, and possible feedback between the evolving radio source and the cluster.

  14. THE QUASAR OUTFLOW CONTRIBUTION TO AGN FEEDBACK: VLT MEASUREMENTS OF SDSS J0318-0600

    SciTech Connect

    Dunn, Jay P.; Bautista, Manuel; Arav, Nahum; Edmonds, Doug; Moe, Max; Korista, Kirk; Costantini, Elisa; Benn, Chris; Ellison, Sara E-mail: arav@vt.ed E-mail: kirk.korista@wmich.ed E-mail: mmoe@cfa.harvard.ed

    2010-02-01

    We present high spectral resolution Very Large Telescope observations of the broad absorption line quasar SDSS J0318 - 0600. This high-quality data set allows us to extract accurate ionic column densities and determine an electron number density of n{sub e} = 10{sup 3.3+}-{sup 0.2} cm{sup -3} for the main outflow absorption component. The heavily reddened spectrum of SDSS J0318-0600 requires purely silicate dust with a reddening curve characteristic of predominately large grains, from which we estimate the bolometric luminosity. We carry out photoionization modeling to determine the total column density, ionization parameter, and distance of the gas and find that the photoionization models suggest abundances greater than solar. Due to the uncertainty in the location of the dust extinction, we arrive at two viable distances for the main ouflow component from the central source, 6 and 17 kpc, where we consider the 6 kpc location as somewhat more physically plausible. Assuming the canonical global covering of 20% for the outflow and a distance of 6 kpc, our analysis yields a mass flux of 120 M{sub sun} yr{sup -1} and a kinetic luminosity that is approx0.1% of the bolometric luminosity of the object. Should the dust be part of the outflow, then these values are approx4x larger. The large mass flux and kinetic luminosity make this outflow a significant contributor to active galactic nucleus feedback processes.

  15. A Model for Type 2 Coronal Line Forest (CLiF) AGNs

    NASA Astrophysics Data System (ADS)

    Glidden, Ana; Rose, Marvin; Elvis, Martin; McDowell, Jonathan

    2016-06-01

    We present a model for the classification of Coronal Line Forest Active Galactic Nuclei (CLiF AGNs). CLiF AGNs are of special interest due to their remarkably large number of emission lines, especially forbidden high-ionization lines (FHILs). Rose et al. suggest that their emission is dominated by reflection from the inner wall of the obscuring region rather than direct emission from the accretion disk. This makes CLiF AGNs laboratories to test AGN-torus models. Modeling an AGN as an accreting supermassive black hole surrounded by a cylinder of dust and gas, we show a relationship between the viewing angle and the revealed area of the inner wall. From the revealed area, we can determine the amount of FHIL emission at various angles. We calculate the strength of [Fe vii]λ6087 emission for a number of intermediate angles (30°, 40°, and 50°) and compare the results with the luminosity of the observed emission line from six known CLiF AGNs. We find that there is good agreement between our model and the observational results. The model also enables us to determine the relationship between the type 2:type 1 AGN fraction vs the ratio of torus height to radius, h/r.

  16. Linking X-ray AGN with dark matter halos: a model compatible with AGN luminosity function and large-scale clustering properties

    NASA Astrophysics Data System (ADS)

    Hütsi, Gert; Gilfanov, Marat; Sunyaev, Rashid

    2014-01-01

    Aims: Our goal is to find a minimalistic model that describes the luminosity function and large-scale clustering bias of X-ray-selected active galactic nuclei in the general framework of the concordance ΛCDM model. Methods: We assume that a simple population-averaged scaling relation between the AGN X-ray luminosity LX and the host dark matter halo mass Mh exists. With such a relation, the AGN X-ray luminosity function can be computed from the halo mass function. Using the concordance ΛCDM halo mass function for the latter, we obtain the Mh - LX relation required to match the redshift-dependent AGN X-ray luminosity function known from X-ray observations. Results: We find that with a simple power-law-scaling Mh ∝ LΓ(z), our model can successfully reproduce the observed X-ray luminosity function. Furthermore, we automatically obtain predictions for the large-scale AGN clustering amplitudes and their dependence on the luminosity and redshift, which seem to be compatible with AGN clustering measurements. Our model also includes the redshift-dependent AGN duty cycle, which peaks at the redshift z ≃ 1, and its peak value is consistent with unity, suggesting that on average there is no more than one AGN per dark matter halo. For a typical X-ray-selected AGN at z ~ 1, our best-fit Mh - LX scaling implies low Eddington ratio LX/LEdd ~ 10-4 - 10-3 (2-10 keV band, no bolometric correction applied) and correspondingly high mass-growth e-folding times, suggesting that typical X-ray AGN are dominantly fueled via relatively inefficient "hot-halo" accretion mode.

  17. The Vertical Structure of Nuclear Starburst Disks: Testing a Model of AGN Obscuration

    NASA Astrophysics Data System (ADS)

    Ballantyne, David R.; Gohil, Raj

    2016-04-01

    Nuclear starburst disks are Eddington-limited, radiation pressure supported disks that may be active in the nuclear environment of active galaxies (ULIRGS and AGNs). Earlier analytical models suggested that, under certain conditions, these disks may be geometrically thick on pc-scales, and thus could be a viable source for AGN obscuration, partcularly at z≤1, when gas factions in galaxies are still significant. Here, we present early results from numerical 2D models of nuclear starburst disks where the vertical structure is calculated explicitly from solving the hydrostatic balance and radiative transfer equations. We quantitatively assess under which conditions the starburst disk may present substantial obscuring columns for AGN observations.

  18. X-ray selected AGN in a Merging Cluster Environment

    NASA Astrophysics Data System (ADS)

    Norman, Dara; Coldwell, Georgina; Soechting, Ilona

    2010-08-01

    Although a general understanding of the overall AGN population is being addressed by optical large area surveys, a complete picture of cluster AGN is hampered by survey biases and a lack of information about AGN environments where we can trace cluster interactions. Optically selected AGN are under-represented in cluster environments due to color selection criteria insensitive to red and dusty sources. X-ray selection of AGN can overcome this bias. Hierarchical simulations suggest the gravitational processes which govern the evolution of clusters also have a role in AGN triggering, and AGN feedback is critically important to galaxy evolution. Confirmation of models requires comparisons not just of the cluster galaxy population, but also of the distributions of AGN in clusters especially forming clusters, which are not fully identified in surveys. Weak lensing cluster selection can overcome this bias. We propose to obtain GMOS-S spectra for a sample of 23 X-ray selected , optically faint (20 with R>20.3) AGN cluster candidates in an X-ray cluster discovered by its weak lensing shear signal. This cluster is unique in the large number of 1) X-ray AGN candidates identified in its environment and 2) X-ray sub-clusters identified. We require redshift data to identify AGN cluster members.

  19. Intracluster medium cooling, AGN feedback, and brightest cluster galaxy properties of galaxy groups. Five properties where groups differ from clusters

    NASA Astrophysics Data System (ADS)

    Bharadwaj, V.; Reiprich, T. H.; Schellenberger, G.; Eckmiller, H. J.; Mittal, R.; Israel, H.

    2014-12-01

    Aims: We aim to investigate cool-core and non-cool-core properties of galaxy groups through X-ray data and compare them to the AGN radio output to understand the network of intracluster medium (ICM) cooling and feedback by supermassive black holes. We also aim to investigate the brightest cluster galaxies (BCGs) to see how they are affected by cooling and heating processes, and compare the properties of groups to those of clusters. Methods: Using Chandra data for a sample of 26 galaxy groups, we constrained the central cooling times (CCTs) of the ICM and classified the groups as strong cool-core (SCC), weak cool-core (WCC), and non-cool-core (NCC) based on their CCTs. The total radio luminosity of the BCG was obtained using radio catalogue data and/or literature, which in turn was compared to the cooling time of the ICM to understand the link between gas cooling and radio output. We determined K-band luminosities of the BCG with 2MASS data, and used a scaling relation to constrain the masses of the supermassive black holes, which were then compared to the radio output. We also tested for correlations between the BCG luminosity and the overall X-ray luminosity and mass of the group. The results obtained for the group sample were also compared to previous results for clusters. Results: The observed cool-core/non-cool-core fractions for groups are comparable to those of clusters. However, notable differences are seen: 1) for clusters, all SCCs have a central temperature drop, but for groups this is not the case as some have centrally rising temperature profiles despite very short cooling times; 2) while for the cluster sample, all SCC clusters have a central radio source as opposed to only 45% of the NCCs, for the group sample, all NCC groups have a central radio source as opposed to 77% of the SCC groups; 3) for clusters, there are indications of an anticorrelation trend between radio luminosity and CCT. However, for groups this trend is absent; 4) the indication of

  20. Feeding versus feedback in AGN from near-infrared IFU observations XI: NGC 2110

    NASA Astrophysics Data System (ADS)

    Diniz, Marlon R.; Riffel, Rogemar A.; Storchi-Bergmann, Thaisa; Winge, Claudia

    2015-10-01

    We present a two-dimensional mapping of the gas flux distributions, as well as of the gas and stellar kinematics in the inner 220 pc of the Seyfert galaxy NGC 2110, using K-band integral field spectroscopy obtained with the Gemini Near-infrared Integral Field Spectrograph at a spatial resolution of ≈24 pc and spectral resolution of ≈40 km s- 1. The H2 λ2.1218 μm emission extends over the whole field of view and is attributed to heating by X-rays from the AGN and/or by shocks, while the Brγ emission is restricted to a bipolar region extending along the south-east-north-west direction. The masses of the warm molecular gas and of the ionized gas are M_H_2≈ 1.4× 10^3 {M_{{⊙}}} and M_{H II}≈ 1.8× 10^6 {M_{{⊙}}}, respectively. The stellar kinematics present velocity dispersions reaching 250 km s-1 and a rotation pattern reaching an amplitude of 200 km s-1. The gas velocity fields present a similar rotation pattern but also additional components that we attribute to inflows and outflows most clearly observed in the molecular gas emission. The inflows are observed beyond the inner 70 pc and are associated with a spiral arm seen in blueshift to the north-east and another in redshift to the south-west. We have estimated a mass inflow rate in warm molecular gas of ≈4.6 × 10-4 M⊙ yr-1. Within the inner 70 pc, another kinematic component is observed in the H2 emission that can be interpreted as due to a bipolar nuclear outflow oriented along the east-west direction, with a mass outflow rate of ≈4.3 × 10-4 M⊙ yr-1 in warm H2.

  1. Probabilistic models for feedback systems.

    SciTech Connect

    Grace, Matthew D.; Boggs, Paul T.

    2011-02-01

    In previous work, we developed a Bayesian-based methodology to analyze the reliability of hierarchical systems. The output of the procedure is a statistical distribution of the reliability, thus allowing many questions to be answered. The principal advantage of the approach is that along with an estimate of the reliability, we also can provide statements of confidence in the results. The model is quite general in that it allows general representations of all of the distributions involved, it incorporates prior knowledge into the models, it allows errors in the 'engineered' nodes of a system to be determined by the data, and leads to the ability to determine optimal testing strategies. In this report, we provide the preliminary steps necessary to extend this approach to systems with feedback. Feedback is an essential component of 'complexity' and provides interesting challenges in modeling the time-dependent action of a feedback loop. We provide a mechanism for doing this and analyze a simple case. We then consider some extensions to more interesting examples with local control affecting the entire system. Finally, a discussion of the status of the research is also included.

  2. AGN coronal emission models - I. The predicted radio emission

    NASA Astrophysics Data System (ADS)

    Raginski, I.; Laor, Ari

    2016-06-01

    Accretion discs in active galactic nucleus (AGN) may be associated with coronal gas, as suggested by their X-ray emission. Stellar coronal emission includes radio emission, and AGN corona may also be a significant source for radio emission in radio quiet (RQ) AGN. We calculate the coronal properties required to produce the observed radio emission in RQ AGN, either from synchrotron emission of power-law (PL) electrons, or from cyclosynchrotron emission of hot mildly relativistic thermal electrons. We find that a flat spectrum, as observed in about half of RQ AGN, can be produced by corona with a disc or a spherical configuration, which extends from the innermost regions out to a pc scale. A spectral break to an optically thin power-law emission is expected around 300-1000 GHz, as the innermost corona becomes optically thin. In the case of thermal electrons, a sharp spectral cut-off is expected above the break. The position of the break can be measured with very long baseline interferometry observations, which exclude the cold dust emission, and it can be used to probe the properties of the innermost corona. Assuming equipartition of the coronal thermal energy density, the PL electrons energy density, and the magnetic field, we find that the energy density in a disc corona should scale as ˜R-1.3, to get a flat spectrum. In the spherical case the energy density scales as ˜R-2, and is ˜4 × 10-4 of the AGN radiation energy density. In Paper II we derive additional constraints on the coronal parameters from the Gudel-Benz relation, Lradio/LX-ray ˜ 10- 5, which RQ AGN follow.

  3. Physical properties of simulated galaxy populations at z = 2 - I. Effect of metal-line cooling and feedback from star formation and AGN

    NASA Astrophysics Data System (ADS)

    Haas, Marcel R.; Schaye, Joop; Booth, C. M.; Dalla Vecchia, Claudio; Springel, Volker; Theuns, Tom; Wiersma, Robert P. C.

    2013-11-01

    We use hydrodynamical simulations from the OverWhelmingly Large Simulations (OWLS) project to investigate the dependence of the physical properties of galaxy populations at redshift 2 on metal-line cooling and feedback from star formation and active galactic nuclei (AGN). We find that if the sub-grid feedback from star formation is implemented kinetically, the feedback is only efficient if the initial wind velocity exceeds a critical value. This critical velocity increases with galaxy mass and also if metal-line cooling is included. This suggests that radiative losses quench the winds if their initial velocity is too low. If the feedback is efficient, then the star formation rate is inversely proportional to the amount of energy injected per unit stellar mass formed (which is proportional to the initial mass loading for a fixed wind velocity). This can be understood if the star formation is self-regulating, i.e. if the star formation rate (and thus the gas fraction) increases until the outflow rate balances the inflow rate. Feedback from AGN is efficient at high masses, while increasing the initial wind velocity with gas pressure or halo mass allows one to generate galaxy-wide outflows at all masses. Matching the observed galaxy mass function requires efficient feedback. In particular, the predicted faint-end slope is too steep unless we resort to highly mass loaded winds for low-mass objects. Such efficient feedback from low-mass galaxies (M* ≪ 1010 M⊙) also reduces the discrepancy with the observed specific star formation rates, which are higher than predicted unless the feedback transitions from highly efficient to inefficient just below M* ˜ 5 × 109 M⊙.

  4. OT1_ppapadop_1: Strong AGN feedback onto the ISM and its effects: A SPIRE FTS view of the molecular gas in 3C293

    NASA Astrophysics Data System (ADS)

    Papadopoulos, P.

    2010-07-01

    We propose to use the SPIRE FTS to study the large molecular gas reservoir of the powerful radio galaxy 3C293, the scene of a very strong AGN jet-gas interaction, and the first known case of shock-powered luminous mid-J/high-J CO lines. These were discovered during our large ground-based CO line survey of Luminous Infrared Galaxies (LIRGs) and AGN hosts, and set this object apart as that with the most excited molecular gas of the entire survey, yet with its large gas reservoir (~2x10^9Msol) surprisingly idle in terms of star formation rate (SFR~4Msol/yr). A deep SPIRE FTS spectrum will complete our ground-based CO Spectral Line Energy Distribution (SLED) of this remarkable system and allow excellent constraints to be placed on the thermal state of its molecular gas reservoir and possible suppressing effects of the AGN on star formation in the host galaxy. It will also be the first opportunity to study, locally, powerful AGN mechanical feedback onto the interstellar medium of host galaxies, which will occur frequently in the Early Universe during galaxy formation in the deep gravitational wells of proto-clusters marked by such powerful radio galaxies.

  5. MAJOR CONTRIBUTOR TO AGN FEEDBACK: VLT X-SHOOTER OBSERVATIONS OF S IV BALQSO OUTFLOWS

    SciTech Connect

    Borguet, Benoit C. J.; Arav, Nahum; Edmonds, Doug; Chamberlain, Carter; Benn, Chris

    2013-01-01

    We present the most energetic BALQSO outflow measured to date, with a kinetic luminosity of at least 10{sup 46} erg s{sup -1}, which is 5% of the bolometric luminosity of this high Eddington ratio quasar. The associated mass-flow rate is 400 solar masses per year. Such kinetic luminosity and mass-flow rate should provide strong active galactic nucleus feedback effects. The outflow is located at about 300 pc from the quasar and has a velocity of roughly 8000 km s{sup -1}. Our distance and energetic measurements are based in large part on the identification and measurement of S IV and S IV* broad absorption lines (BALs). The use of this high-ionization species allows us to generalize the result to the majority of high-ionization BALQSOs that are identified by their C IV absorption. We also report the energetics of two other outflows seen in another object using the same technique. The distances of all three outflows from the central source (100-2000 pc) suggest that we observe BAL troughs much farther away from the central source than the assumed acceleration region of these outflows (0.01-0.1 pc).

  6. Major Contributor to AGN Feedback: VLT X-shooter Observations of S IV BALQSO Outflows

    NASA Astrophysics Data System (ADS)

    Borguet, Benoit C. J.; Arav, Nahum; Edmonds, Doug; Chamberlain, Carter; Benn, Chris

    2013-01-01

    We present the most energetic BALQSO outflow measured to date, with a kinetic luminosity of at least 1046 erg s-1, which is 5% of the bolometric luminosity of this high Eddington ratio quasar. The associated mass-flow rate is 400 solar masses per year. Such kinetic luminosity and mass-flow rate should provide strong active galactic nucleus feedback effects. The outflow is located at about 300 pc from the quasar and has a velocity of roughly 8000 km s-1. Our distance and energetic measurements are based in large part on the identification and measurement of S IV and S IV* broad absorption lines (BALs). The use of this high-ionization species allows us to generalize the result to the majority of high-ionization BALQSOs that are identified by their C IV absorption. We also report the energetics of two other outflows seen in another object using the same technique. The distances of all three outflows from the central source (100-2000 pc) suggest that we observe BAL troughs much farther away from the central source than the assumed acceleration region of these outflows (0.01-0.1 pc). Based on observations collected at the European Southern Observatory, Chile, PID: 87.B-0229.

  7. Modelling galaxy and AGN evolution in the infrared: black hole accretion versus star formation activity

    NASA Astrophysics Data System (ADS)

    Gruppioni, C.; Pozzi, F.; Zamorani, G.; Vignali, C.

    2011-09-01

    We present a new backward evolution model for galaxies and active galactic nuclei (AGNs) in the infrared (IR). What is new in this model is the separate study of the evolutionary properties of different IR populations (i.e. spiral galaxies, starburst galaxies, low-luminosity AGNs, 'unobscured' type 1 AGNs and 'obscured' type 2 AGNs) defined through a detailed analysis of the spectral energy distributions (SEDs) of large samples of IR-selected sources. The evolutionary parameters have been constrained by means of all the available observables from surveys in the mid- and far-IR (source counts, redshift and luminosity distributions, luminosity functions). By decomposing the SEDs representative of the three AGN classes into three distinct components (a stellar component emitting most of its power in the optical/near-IR, an AGN component due to the hot dust heated by the central black hole peaking in the mid-IR, and a starburst component dominating the far-IR spectrum), we have disentangled the AGN contribution to the monochromatic and total IR luminosity emitted by different populations considered in our model from that due to star formation activity. We have then obtained an estimate of the total IR luminosity density [and star formation density (SFD) produced by IR galaxies] and the first ever estimate of the black hole mass accretion density (BHAR) from the IR. The derived evolution of the BHAR is in agreement with estimates from X-rays, though the BHAR values we derive from the IR are slightly higher than the X-ray ones. Finally, we have simulated source counts, redshift distributions, and SFD and BHAR that we expect to obtain with the future cosmological surveys in the mid-/far-IR that will be performed with the JWST-MIRI and SPICA-SAFARI. Outputs of the model are available online.1

  8. Modeling optical and UV polarization of AGNs. III. From uniform-density to clumpy regions

    NASA Astrophysics Data System (ADS)

    Marin, F.; Goosmann, R. W.; Gaskell, C. M.

    2015-05-01

    Context. A growing body of evidence suggests that some, if not all, scattering regions of active galactic nuclei (AGNs) are clumpy. The inner AGN components cannot be spatially resolved with current instruments and must be studied by numerical simulations of observed spectroscopy and polarization data. Aims: We run radiative transfer models in the optical/UV for a variety of AGN reprocessing regions with different distributions of clumpy scattering media. We obtain geometry-sensitive polarization spectra and images to improve our previous AGN models and their comparison with the observations. Methods: We use the latest public version 1.2 of the Monte Carlo code stokes presented in the first two papers of this series to model AGN reprocessing regions of increasing morphological complexity. We replace previously uniform-density media with up to thousands of constant-density clumps. We couple a continuum source to fragmented equatorial scattering regions, polar outflows, and toroidal obscuring dust regions and investigate a wide range of geometries. We also consider different levels of fragmentation in each scattering region to evaluate the importance of fragmentation for the net polarization of the AGN. Results: In comparison with uniform-density models, equatorial distributions of gas and dust clouds result in grayer spectra and show a decrease in the net polarization percentage at all lines of sight. The resulting polarization position angle depends on the morphology of the clumpy structure, with extended tori favoring parallel polarization while compact tori produce orthogonal polarization position angles. In the case of polar scattering regions, fragmentation increases the net polarization unless the cloud filling factor is small. A complete AGN model constructed from the individual, fragmented regions can produce low polarization percentages (<2%), with a parallel polarization angle for observer inclinations up to 70° for a torus half opening angle of 60°. For

  9. Photoionization modeling of GRO 1655-40: A scaled down AGN Warm Absrobers!

    NASA Astrophysics Data System (ADS)

    Kazanas, Demosthenes; Fukumura, Keigo; Shrader, Chris R.; Behar, Ehud; Tombesi, Francesco

    2016-04-01

    We present photoinization models of the absorption features Galactic X-ray Binary (XRB) by implementing the MHD accretion disk wind models employed to account for the ionization properties of the AGN Warm Absorbers (WA)(Fukumura et a. 2010). The implementation of the same models rests on the fact that the radial density profiles of these winds, n(r)~1/r, guarantees the correct values of the hydrogen equivalent column NH of the most important ionic species at the correct values of their ionization parameter ξ and velocity v. The similarity of the winds' ionization properties is broken only by the peak frequency of the ionizing SED, which is in the UV in AGN and in X-rays in XRBs. This difference implies that the inner regions of the XRB winds are far more ionized than those of AGN, resulting in much smaller velocities for the same ionic species (e.g. Fe XXV) in XRB (v~1,000 km/s) than in AGN (v~10,000 km/s), in agreement with observation. Estimates of the wind mass flux deduced from our photonization modeling, imply that the latter is much larger than that needed to power the observed X-ray emission, a property that appears to be generic from the Galactic to the AGN black hole mass range suggesting a common underlying structure.

  10. Modeling AGN outbursts from supermassive black hole binaries

    NASA Astrophysics Data System (ADS)

    Tanaka, T.

    2012-12-01

    When galaxies merge to assemble more massive galaxies, their nuclear supermassive black holes (SMBHs) should form bound binaries. As these interact with their stellar and gaseous environments, they will become increasingly compact, culminating in inspiral and coalescence through the emission of gravitational radiation. Because galaxy mergers and interactions are also thought to fuel star formation and nuclear black hole activity, it is plausible that such binaries would lie in gas-rich environments and power active galactic nuclei (AGN). The primary difference is that these binaries have gravitational potentials that vary - through their orbital motion as well as their orbital evolution - on humanly tractable timescales, and are thus excellent candidates to give rise to coherent AGN variability in the form of outbursts and recurrent transients. Although such electromagnetic signatures would be ideally observed concomitantly with the binary's gravitational-wave signatures, they are also likely to be discovered serendipitously in wide-field, high-cadence surveys; some may even be confused for stellar tidal disruption events. I discuss several types of possible "smoking gun" AGN signatures caused by the peculiar geometry predicted for accretion disks around SMBH binaries.

  11. Linking ULIRGS and Quasars: Looking for Predicted Morphological Signatures of AGN Feedback

    NASA Astrophysics Data System (ADS)

    Steward, Nicole; Hicks, E. K. S.; Davies, R. I.

    2012-01-01

    Current leading theories propose a galactic evolutionary tract linking ultra-luminous infrared galaxies (ULIRGS) with quasars via a `blowout’ stage, during which the energy output resulting from accretion of material onto the central black hole expels the gas obscuring the central quasar. However, this phase would be short-lived and therefore difficult to directly observe, meaning evidence that this is indeed how galaxies evolve is scare. We obtained 2-D K-band integral field data with SINFONI on the VLT for a sample of six quasars that are divided into 'pre-' and 'post-blowout' by comparing their ratios of infrared luminosity to the luminosity of the optical 'big blue bump'. By measuring the spatial distribution and column density of the warm molecular gas on scales down to less than 1 kpc we determine if a correlation exists between these quantities and the `pre-’ an `post-blowout’ subsamples as predicted by evolutionary models.

  12. Compton Thick AGN in the COSMOS field

    NASA Astrophysics Data System (ADS)

    Lanzuisi, Giorgio; Cosmos Collaboration

    2015-09-01

    I will present the results we published in a couple of recent papers (Lanzuisi et al. 2015, A&A 573A 137, Lanzuisi et al. 2015, arXiv 1505.01153) on the properties of X-ray selected Compton Thick (CT, NH>10^24 cm^-2) AGN, in the COSMOS survey. We exploited the rich multi-wavelength dataset available in this field, to show that CT AGN tend to harbor smaller, rapidly growing SMBH with respect to unobscured AGN, and have a higher chance of being hosted by star-forming, merging and post-merger systems.We also demonstrated the detectability of even more heavily obscured AGN (NH>10^25 cm^-2), thanks to a truly multi-wavelength approach in the same field. The extreme source detected in this way shows strong evidences of ongoing powerful AGN feedback, detected as blue-shifted wings of high ionization optical emission lines such as [NeV] and [FeVII], as well as of the [OIII] emission line.The results obtained from these works point toward a scenario in which highly obscured AGN occupy a peculiar place in the galaxy-AGN co-evolution process, in which both the host and the SMBH rapidly evolve toward the local relations.We will also present estimates on the detectability of such extreme sources up to redshift ~6-7 with Athena. Combining the most up to date models for the Luminosity Function of CT AGN at high z, aggressive data analysis techniques on faint sources, and the current Athena survey design, we demonstrate that we will detect, and recognize as such, a small (few to ten) but incredibly valuable sample of CT AGN at such high redshift.

  13. AGN Obscuration Through Dusty Infrared Dominated Flows. II. Multidimensional, Radiation-Hydrodynamics Modeling

    NASA Technical Reports Server (NTRS)

    Dorodnitsyn, Anton; Kallman, Tim; Bisno\\vatyiI-Kogan, Gennadyi

    2011-01-01

    We explore a detailed model in which the active galactic nucleus (AGN) obscuration results from the extinction of AGN radiation in a global ow driven by the pressure of infrared radiation on dust grains. We assume that external illumination by UV and soft X-rays of the dusty gas located at approximately 1pc away from the supermassive black hole is followed by a conversion of such radiation into IR. Using 2.5D, time-dependent radiation hydrodynamics simulations in a ux-limited di usion approximation we nd that the external illumination can support a geometrically thick obscuration via out ows driven by infrared radiation pressure in AGN with luminosities greater than 0:05 L(sub edd) and Compton optical depth, Tau(sub T) approx > & 1.

  14. Modeling active galactic nucleus feedback in cool-core clusters: The balance between heating and cooling

    SciTech Connect

    Li, Yuan; Bryan, Greg L.

    2014-07-01

    We study the long-term evolution of an idealized cool-core galaxy cluster under the influence of momentum-driven active galactic nucleus (AGN) feedback using three-dimensional high-resolution (60 pc) adaptive mesh refinement simulations. The feedback is modeled with a pair of precessing jets whose power is calculated based on the accretion rate of the cold gas surrounding the supermassive black hole (SMBH). The intracluster medium first cools into clumps along the propagation direction of the jets. As the jet power increases, gas condensation occurs isotropically, forming spatially extended structures that resemble the observed Hα filaments in Perseus and many other cool-core clusters. Jet heating elevates the gas entropy, halting clump formation. The cold gas that is not accreted onto the SMBH settles into a rotating disk of ∼10{sup 11} M {sub ☉}. The hot gas cools directly onto the disk while the SMBH accretes from its innermost region, powering the AGN that maintains a thermally balanced state for a few Gyr. The mass cooling rate averaged over 7 Gyr is ∼30 M {sub ☉} yr{sup –1}, an order of magnitude lower than the classic cooling flow value. Medium resolution simulations produce similar results, while in low resolution runs, the cluster experiences cycles of gas condensation and AGN outbursts. Owing to its self-regulating mechanism, AGN feedback can successfully balance cooling with a wide range of model parameters. Our model also produces cold structures in early stages that are in good agreement with the observations. However, the long-lived massive cold disk is unrealistic, suggesting that additional physical processes are still needed.

  15. Testing the AGN unification model in the infrared. First results with GTC/CanariCam

    NASA Astrophysics Data System (ADS)

    Ramos Almeida, C.

    2015-05-01

    The unified model for Active Galactic Nuclei (AGN) accounts for a variety of observational differences in terms of viewing geometry alone. However, from the fitting of high spatial resolution infrared (IR) data with clumpy torus models, it has been hinted that the immediate dusty surroundings of Type-1 and 2 Seyfert nuclei might be intrinsically different in terms of covering factor (torus width and number of clouds). Moreover, these torus covering factors also showed variations among objects belonging to the same type, in contradiction with simple unification. Interestingly, these intrinsic differences in Seyfert tori could explain, for example, the lack of broad optical lines in the polarized spectra of about half of the brightest Seyfert 2 galaxies. On the other hand, recent IR interferometry studies have revealed that, in at least four Seyfert galaxies, the mid-IR emission is elongated in the polar direction. These results are difficult to reconcile with unified models, which claim that the bulk of the mid-IR emission comes from the torus. In this invited contribution I summarize the latest results on high angular resolution IR studies of AGN, which constitute a crucial test for AGN unification. These results include those from the mid-infrared instrument CanariCam on the 10.4 m Gran Telescopio CANARIAS (GTC), which are starting to be published by the CanariCam AGN team, Los Piratas (https://sites.google.com/site/piratasrelatedpublications).

  16. The Prevalence of Gas Outflows in Type 2 AGNs. II. 3D Biconical Outflow Models

    NASA Astrophysics Data System (ADS)

    Bae, Hyun-Jin; Woo, Jong-Hak

    2016-09-01

    We present 3D models of biconical outflows combined with a thin dust plane for investigating the physical properties of the ionized gas outflows and their effect on the observed gas kinematics in type 2 active galactic nuclei (AGNs). Using a set of input parameters, we construct a number of models in 3D and calculate the spatially integrated velocity and velocity dispersion for each model. We find that three primary parameters, i.e., intrinsic velocity, bicone inclination, and the amount of dust extinction, mainly determine the simulated velocity and velocity dispersion. Velocity dispersion increases as the intrinsic velocity or the bicone inclination increases, while velocity (i.e., velocity shifts with respect to systemic velocity) increases as the amount of dust extinction increases. Simulated emission-line profiles well reproduce the observed [O iii] line profiles, e.g., narrow core and broad wing components. By comparing model grids and Monte Carlo simulations with the observed [O iii] velocity–velocity dispersion distribution of ∼39,000 type 2 AGNs, we constrain the intrinsic velocity of gas outflows ranging from ∼500 to ∼1000 km s‑1 for the majority of AGNs, and up to ∼1500–2000 km s‑1 for extreme cases. The Monte Carlo simulations show that the number ratio of AGNs with negative [O iii] velocity to AGNs with positive [O iii] velocity correlates with the outflow opening angle, suggesting that outflows with higher intrinsic velocity tend to have wider opening angles. These results demonstrate the potential of our 3D models for studying the physical properties of gas outflows, applicable to various observations, including spatially integrated and resolved gas kinematics.

  17. First systematic search for oxygen-line blobs at high redshift: Uncovering AGN feedback and star formation quenching

    SciTech Connect

    Yuma, Suraphong; Ouchi, Masami; Ono, Yoshiaki; Momose, Rieko; Drake, Alyssa B.; Simpson, Chris; Shimasaku, Kazuhiro; Nakajima, Kimihiko; Akiyama, Masayuki; Mori, Masao; Umemura, Masayuki

    2013-12-10

    We present the first systematic search for extended metal-line [O II] λλ3726, 3729 nebulae, or [O II] blobs (O IIBs), at z = 1.2 using deep narrowband imaging with a survey volume of 1.9 × 10{sup 5} Mpc{sup 3} on the 0.62 deg{sup 2} sky of Subaru-XMM Deep Survey (SXDS) field. We discover a giant O IIB, called 'O IIB 1', with a spatial extent over ∼75 kpc at a spectroscopic redshift of z = 1.18, and also identify a total of 12 O IIBs with a size of >30 kpc. Our optical spectrum of O IIB 1 presents [Ne V] λ3426 line at the 6σ level, indicating that this object harbors an obscured type-2 active galactic nucleus (AGN). The presence of gas outflows in this object is suggested by two marginal detections of Fe II λ2587 absorption and Fe II* λ2613 emission lines both of which are blueshifted at as large as 500-600 km s{sup –1}, indicating that the heating source of O IIB 1 is AGN or associated shock excitation rather than supernovae produced by starbursts. The number density of O IIB 1-type giant blobs is estimated to be ∼5 × 10{sup –6} Mpc{sup –3} at z ∼ 1.2, which is comparable with that of AGNs driving outflow at a similar redshift, suggesting that giant O IIBs are produced only by AGN activity. On the other hand, the number density of small O IIBs, 6 × 10{sup –5} Mpc{sup –3}, compared to that of z ∼ 1 galaxies in the blue cloud in the same M{sub B} range, may imply that 3% of star-forming galaxies at z ∼ 1 are quenching star formation through outflows involving extended [O II] emission.

  18. Active Galactic Nuclei flicker on a characteristic timescale of 105 years: implications for black hole growth and AGN feedback

    NASA Astrophysics Data System (ADS)

    Schawinski, Kevin; Koss, Michael; Sartori, Lia F.; Berney, Simon

    2016-01-01

    The total duration of quasar phases has been estimated to be on the order of 100 Myr to 1 Gyr. However, black hole accretion may not be a smooth process and a long-lasting growth phase may actually be composed of maby brief 105 year accretion bursts, interspersed by low-Eddington phases and even quiescence. I present an observational argument for the 105 year timescale, discuss its implications as well as current observational efforts to map out the entire AGN lifecycle.

  19. Distinguishing Feedback Mechanisms in Clock Models

    NASA Astrophysics Data System (ADS)

    Golden, Alexander; Lubensky, David

    Biological oscillators are very diverse but can be classified based on dynamical motifs such as type of feedback. The S. Elongatus circadian oscillator is a novel circadian oscillator that can operate at constant protein number by modifying covalent states. It can be reproduced in vitro with only 3 different purified proteins: KaiA, KaiB, and KaiC. We use computational and analytic techniques to compare models of the S. Elongatus post-translational oscillator that rely on positive feedback with models that rely on negative feedback. We show that introducing a protein that binds competitively with KaiA to the KaiB-KaiC complex can distinguish between positive and negative feedback as the primary driver of the rhythm, which has so far been difficult to address experimentally. NSF Grant DMR-1056456.

  20. NuSTAR Survey of Swift/BAT AGN as a Probe of the Unified Model

    NASA Astrophysics Data System (ADS)

    Balokovic, M.

    2015-09-01

    NuSTAR has enabled studies of the local AGN to extend into the spectral window above 10 keV with unprecedented spatial resolution and two orders of magnitude better sensitivity than any other instrument operating in that energy range. As a part of its long-term extragalactic program NuSTAR is surveying the nearby population of AGN detected at hard X-ray energies by the Swift/BAT instrument. We present results based on observations of ~100 Swift/BAT-selected Type-2 Seyferts surveyed in the first three years of NuSTAR operation. This large sample forms an atlas of the highest quality hard X-ray spectra available to date. Assuming a range of hard X-ray spectral models, phenomenological as well as physically motivated, we constrain the main spectral parameters for each source individually and test the applicability of the models on a large sample for the first time. This analysis allows us to determine distributions of the main spectral parameters related to the torus, such as the absorption column, reflection strength, and iron line equivalent width, in a well-defined population of nearby obscured AGN. More advanced models for the AGN torus allow us to investigate differences between various subsamples and interpret them within the unified model paradigm. We will discuss the implications for the structure of the torus in the local population of Type-2 Seyferts and present a comprehensive comparison of constraints derived from X-ray data and constraints from observations at other wavelengths for a relatively large sample.

  1. Cold-gas outflows in typical low-redshift galaxies are driven by star formation, not AGN

    NASA Astrophysics Data System (ADS)

    Sarzi, Marc; Kaviraj, Sugata; Nedelchev, Borislav; Tiffany, Joshua; Shabala, Stanislav S.; Deller, Adam T.; Middelberg, Enno

    2016-02-01

    Energetic feedback from active galactic nuclei (AGN) is an important ingredient for regulating the star formation history of galaxies in models of galaxy formation, which makes it important to study how AGN feedback actually occurs in practice. In order to catch AGNs in the act of quenching star formation, we have used the interstellar Na I λλ5890, 5895(NaD) absorption lines to look for cold-gas outflows in a sample of 456 nearby galaxies for which we could unambiguously ascertain the presence of radio-AGN activity, thanks to radio imaging at milli-arcsecond scales. While compact radio emission indicating a radio AGN was found in 103 galaxies (23 per cent of the sample), and 23 objects (5 per cent) exhibited NaD absorption-line kinematics suggestive of cold-gas outflows, not one object showed evidence of a radio AGN and of a cold-gas outflow simultaneously. Radio-AGN activity was found predominantly in early-type galaxies, while cold-gas outflows were mainly seen in spiral galaxies with central star formation or composite star formation/AGN activity. Optical AGNs also do not seem capable of driving galactic winds in our sample. Our work adds to a picture of the low-redshift Universe, where cold-gas outflows in massive galaxies are generally driven by star formation and where radio-AGN activity occurs most often in systems in which the gas reservoir has already been significantly depleted.

  2. Finite Feedback Cycling in Structural Equation Models

    ERIC Educational Resources Information Center

    Hayduk, Leslie A.

    2009-01-01

    In models containing reciprocal effects, or longer causal loops, the usual effect estimates assume that any effect touching a loop initiates an infinite cycling of effects around that loop. The real world, in contrast, might permit only finite feedback cycles. I use a simple hypothetical model to demonstrate that if the world permits only a few…

  3. Modeling heart rate variability by stochastic feedback

    NASA Technical Reports Server (NTRS)

    Amaral, L. A.; Goldberger, A. L.; Stanley, H. E.

    1999-01-01

    We consider the question of how the cardiac rhythm spontaneously self-regulates and propose a new mechanism as a possible answer. We model the neuroautonomic regulation of the heart rate as a stochastic feedback system and find that the model successfully accounts for key characteristics of cardiac variability, including the 1/f power spectrum, the functional form and scaling of the distribution of variations of the interbeat intervals, and the correlations in the Fourier phases which indicate nonlinear dynamics.

  4. Support for an Evolutionary Model of AGN Nuclei

    NASA Astrophysics Data System (ADS)

    Dultzin, D.

    2015-09-01

    I will present our recent results (2013-2015) on the role of the environment in the nuclear activity of interacting Galaxies, all of which support an evolutionary sequence in the nuclear activity. We studied close galactic pairs of similar mass in the local Universe. We analyzed 385 spectra of S S, E E, and E S pairs, and try to disentangle the role of morphology on induced activity . We compare with our own sample of bona fide isolated galaxies containing a statistically significant number of all morphological types. Our main results are in conflict with the simplest version of the so called Unified Model (UM), and suggest that high accretion rates are essential to form the Broad Line Region in active galaxies. We also investigated the structure of the dusty torus surrounding Syfert 1 and 2 nuclei, both in pairs and isolated. The results also lead to a disagreement with the UM. Finally, we present our results on the Nuclear Activity in the context of the evolution of Compact Groups of galaxies over the past 3 Gyrs. Our analysis is based on the largest multiwavelength compact group sample to-date, and the results are also in conflict with an orientation obscuration effect alone.

  5. Nonsmooth feedback controls of nonlocal dispersal models

    NASA Astrophysics Data System (ADS)

    Malaguti, Luisa; Rubbioni, Paola

    2016-03-01

    The paper deals with a nonlocal diffusion equation which is a model for biological invasion and disease spread. A nonsmooth feedback control term is included and the existence of controlled dynamics is proved, satisfying different kinds of nonlocal condition. Jump discontinuities appear in the process. The existence of optimal control strategies is also shown, under suitably regular control functionals. The investigation makes use of techniques of multivalued analysis and is based on the degree theory for condensing operators in Hilbert spaces.

  6. Obscured AGN

    NASA Astrophysics Data System (ADS)

    Barger, Amy

    2014-07-01

    Obscured AGN may correspond to a substantial fraction of the supermassive black hole growth rate. I will present new surveys with the SCUBA-2 instrument on the James Clerk Maxwell Telescope of the Chandra Deep Fields and discuss whether we can distinguish obscured AGN in hard X-ray and radio selected samples using submillimeter observations.

  7. The Close AGN Reference Survey (CARS)

    NASA Astrophysics Data System (ADS)

    Rothberg, Barry; Husemann, Bernd; Busch, Gerold; Dierkes, Jens; Eckart, Andreas; Krajnovic, Davor; Scharwaechter, Julia; Tremblay, Grant R.; Urrutia, Tanya

    2015-08-01

    We present the first science results from the Close AGN Reference Survey (CARS). This program is a snapshot survey of 39 local type 1 AGN (0.01 < z <0.06) designed to address the issue of AGN-driven star formation quenching by characterizing the condition for star formation in AGN host galaxies. The primary sample was observed with Multi Unit Spectrscopic Explorer (MUSE), an optical wavelength integral field unit (IFU) with a 1'x1' field of view on the VLT. The optical 3D spectroscopy complements existing sub-mm CO(1-0) data and near-IR imaging to establish a unique dataset combining molecular and stellar masses with star formation rates, gas, stellar kinematics and AGN properties. The primary goals of CARS are to:1) investigate if the star formation efficiency and gas depletion time scales are suppressed as a consequence of AGN feedback; 2) identify AGN-driven outflows and their relation to the molecular gas reservoir of the host galaxy; 3) investigate the the balance of AGN feeding and feedback through the ratio of the gas reservoir to the AGN luminosity; and 4) provide the community with a reference survey of local AGN with a high legacy value. Future work will incorporate near-infrared IFU observations to present a complete spatially resolved picture of the interplay among AGN, star-formation, stellar populations, and the ISM.

  8. Ribosome flow model with positive feedback

    PubMed Central

    Margaliot, Michael; Tuller, Tamir

    2013-01-01

    Eukaryotic mRNAs usually form a circular structure; thus, ribosomes that terminatae translation at the 3′ end can diffuse with increased probability to the 5′ end of the transcript, initiating another cycle of translation. This phenomenon describes ribosomal flow with positive feedback—an increase in the flow of ribosomes terminating translating the open reading frame increases the ribosomal initiation rate. The aim of this paper is to model and rigorously analyse translation with feedback. We suggest a modified version of the ribosome flow model, called the ribosome flow model with input and output. In this model, the input is the initiation rate and the output is the translation rate. We analyse this model after closing the loop with a positive linear feedback. We show that the closed-loop system admits a unique globally asymptotically stable equilibrium point. From a biophysical point of view, this means that there exists a unique steady state of ribosome distributions along the mRNA, and thus a unique steady-state translation rate. The solution from any initial distribution will converge to this steady state. The steady-state distribution demonstrates a decrease in ribosome density along the coding sequence. For the case of constant elongation rates, we obtain expressions relating the model parameters to the equilibrium point. These results may perhaps be used to re-engineer the biological system in order to obtain a desired translation rate. PMID:23720534

  9. Model feedback in Bayesian propensity score estimation.

    PubMed

    Zigler, Corwin M; Watts, Krista; Yeh, Robert W; Wang, Yun; Coull, Brent A; Dominici, Francesca

    2013-03-01

    Methods based on the propensity score comprise one set of valuable tools for comparative effectiveness research and for estimating causal effects more generally. These methods typically consist of two distinct stages: (1) a propensity score stage where a model is fit to predict the propensity to receive treatment (the propensity score), and (2) an outcome stage where responses are compared in treated and untreated units having similar values of the estimated propensity score. Traditional techniques conduct estimation in these two stages separately; estimates from the first stage are treated as fixed and known for use in the second stage. Bayesian methods have natural appeal in these settings because separate likelihoods for the two stages can be combined into a single joint likelihood, with estimation of the two stages carried out simultaneously. One key feature of joint estimation in this context is "feedback" between the outcome stage and the propensity score stage, meaning that quantities in a model for the outcome contribute information to posterior distributions of quantities in the model for the propensity score. We provide a rigorous assessment of Bayesian propensity score estimation to show that model feedback can produce poor estimates of causal effects absent strategies that augment propensity score adjustment with adjustment for individual covariates. We illustrate this phenomenon with a simulation study and with a comparative effectiveness investigation of carotid artery stenting versus carotid endarterectomy among 123,286 Medicare beneficiaries hospitlized for stroke in 2006 and 2007. PMID:23379793

  10. The cosmic evolution of massive black holes in the Horizon-AGN simulation

    NASA Astrophysics Data System (ADS)

    Volonteri, M.; Dubois, Y.; Pichon, C.; Devriendt, J.

    2016-08-01

    We analyse the demographics of black holes (BHs) in the large-volume cosmological hydrodynamical simulation Horizon-AGN. This simulation statistically models how much gas is accreted on to BHs, traces the energy deposited into their environment and, consequently, the back-reaction of the ambient medium on BH growth. The synthetic BHs reproduce a variety of observational constraints such as the redshift evolution of the BH mass density and the mass function. Strong self-regulation via AGN feedback, weak supernova feedback, and unresolved internal processes result in a tight BH-galaxy mass correlation. Starting at z ˜ 2, tidal stripping creates a small population of BHs over-massive with respect to the halo. The fraction of galaxies hosting a central BH or an AGN increases with stellar mass. The AGN fraction agrees better with multi-wavelength studies, than single-wavelength ones, unless obscuration is taken into account. The most massive haloes present BH multiplicity, with additional BHs gained by ongoing or past mergers. In some cases, both a central and an off-centre AGN shine concurrently, producing a dual AGN. This dual AGN population dwindles with decreasing redshift, as found in observations. Specific accretion rate and Eddington ratio distributions are in good agreement with observational estimates. The BH population is dominated in turn by fast, slow, and very slow accretors, with transitions occurring at z = 3 and z = 2, respectively.

  11. The cosmic evolution of massive black holes in the Horizon-AGN simulation

    NASA Astrophysics Data System (ADS)

    Volonteri, M.; Dubois, Y.; Pichon, C.; Devriendt, J.

    2016-08-01

    We analyse the demographics of black holes (BHs) in the large-volume cosmological hydrodynamical simulation Horizon-AGN. This simulation statistically models how much gas is accreted onto BHs, traces the energy deposited into their environment and, consequently, the back-reaction of the ambient medium on BH growth. The synthetic BHs reproduce a variety of observational constraints such as the redshift evolution of the BH mass density and the mass function. Strong self-regulation via AGN feedback, weak supernova feedback, and unresolved internal processes result in a tight BH-galaxy mass correlation. Starting at z~2, tidal stripping creates a small population of BHs over-massive with respect to the halo. The fraction of galaxies hosting a central BH or an AGN increases with stellar mass. The AGN fraction agrees better with multi-wavelength studies, than single-wavelength ones, unless obscuration is taken into account. The most massive halos present BH multiplicity, with additional BHs gained by ongoing or past mergers. In some cases, both a central and an off-centre AGN shine concurrently, producing a dual AGN. This dual AGN population dwindles with decreasing redshift, as found in observations. Specific accretion rate and Eddington ratio distributions are in good agreement with observational estimates. The BH population is dominated in turn by fast, slow, and very slow accretors, with transitions occurring at z=3 and z=2 respectively.

  12. Cloud Feedback in Atmospheric General Circulation Models: An Update

    NASA Technical Reports Server (NTRS)

    Cess, R. D.; Zhang, M. H.; Ingram, W. J.; Potter, G. L.; Alekseev, V.; Barker, H. W.; Cohen-Solal, E.; Colman, R. A.; Dazlich, D. A.; DelGenio, A. D.; Dix, M. R.; Dymnikov, V.; Esch, M.; Fowler, L. D.; Fraser, J. R.; Galin, V.; Gates, W. L.; Hack, J. J.; Kiehl, J. T.; LeTreut, H.

    1996-01-01

    Six years ago, we compared the climate sensitivity of 19 atmospheric general circulation models and found a roughly threefold variation among the models; most of this variation was attributed to differences in the models' depictions of cloud feedback. In an update of this comparison, current models showed considerably smaller differences in net cloud feedback, with most producing modest values. There are, however, substantial differences in the feedback components, indicating that the models still have physical disagreements.

  13. The universal spectrum of AGNs and QSOs

    NASA Technical Reports Server (NTRS)

    Kazanas, D.

    1985-01-01

    The effects of the feedback of e(+)-e(-) pair reinjection in a plasma due to photon photon absorption of its own radiation are examined. A mechanism is presented which can produce an electron distribution function that can account for the overall spectral distribution of radiation of AGNs and QSOs and the specific slopes observed in the IR to UV and 2-50 keV bands. It is interesting to note that the necessary condition for this mechanism to work (i.e., most of energy injected at e(M sub e)(C sup 2) is realized in the accretion shock model of Kazanas and Ellison. This mechanism involves only one free parameter the compactness of the sources, L/R, whose mean value can also account for the diffuse gamma ray background in terms of AGNs.

  14. Evidence for Ultra-Fast Outflows in Radio-Quiet AGNs. 2; Detailed Photoionization Modeling of Fe K-Shell Absorption Lines

    NASA Technical Reports Server (NTRS)

    Tombesi, Francesco; Clapp, M.; Reeves, J. N.; Palumbo, G. G. C.; Braito, V.; Dadina, M.

    2011-01-01

    X-ray absorption line spectroscopy has recently shown evidence for previously unknown Ultra-fast Outflows (UFOs) in radio-quiet AGNs. In the previous paper of this series we defined UFOs as those absorbers with an outflow velocity higher than 10,000km/s and assessed the statistical significance of the associated blue shifted FeK absorption lines in a large sample of 42 local radio-quiet AGNs observed with XMM-Newton. In the present paper we report a detailed curve of growth analysis and directly model the FeK absorbers with the Xstar photo-ionization code. We confirm that the frequency of sources in the radio-quiet sample showing UFOs is >35%. The outflow velocity distribution spans from \\sim10,000km/s (\\sim0.03c) up to \\siml00,000kmis (\\sim0.3c), with a peak and mean value of\\sim42,000km/s (\\sim0.14c). The ionization parameter is very high and in the range log\\xi 3-6 erg s/cm, with a mean value of log\\xi 4.2 erg s/cm. The associated column densities are also large, in the range N_H\\siml0(exp 22)-10(exp 24)/sq cm, with a mean value of N_H\\siml0(exp23)/sq cm. We discuss and estimate how selection effects, such as those related to the limited instrumental sensitivity at energies above 7keV, may hamper the detection of even higher velocities and higher ionization absorbers. We argue that, overall, these results point to the presence of extremely ionized and possibly almost Compton thick outflowing material in the innermost regions of AGNs. This also suggests that UFOs may potentially play a significant role in the expected cosmological feedback from AGNs and their study can provide important clues on the connection between accretion disks, winds and jets.

  15. Accretion disk winds in active galactic nuclei: X-ray observations, models, and feedback

    NASA Astrophysics Data System (ADS)

    Tombesi, F.

    2016-05-01

    Powerful winds driven by active galactic nuclei (AGN) are often invoked to play a fundamental role in the evolution of both supermassive black holes (SMBHs) and their host galaxies, quenching star formation and explaining the tight SMBH-galaxy relations. A strong support of this ``quasar mode'' feedback came from the recent X-ray observation of a mildly relativistic accretion disk wind in a ultraluminous infrared galaxy (ULIRG) and its connection with a large-scale molecular outflow, providing a direct link between the SMBH and the gas out of which stars form. Spectroscopic observations, especially in the X-ray band, show that such accretion disk winds may be common in local AGN and quasars. However, their origin and characteristics are still not fully understood. Detailed theoretical models and simulations focused on radiation, magnetohydrodynamic (MHD) or a combination of these two processes to investigate the possible acceleration mechanisms and the dynamics of these winds. Some of these models have been directly compared to X-ray spectra, providing important insights into the wind physics. However, fundamental improvements on these studies will come only from the unprecedented energy resolution and sensitivity of the upcoming X-ray observatories, namely ASTRO-H (launch date early 2016) and Athena (2028).

  16. The resolution bias: low-resolution feedback simulations are better at destroying galaxies

    NASA Astrophysics Data System (ADS)

    Bourne, Martin A.; Zubovas, Kastytis; Nayakshin, Sergei

    2015-10-01

    Feedback from supermassive black holes is thought to play a key role in regulating the growth of host galaxies. Cosmological and galaxy formation simulations using smoothed particle hydrodynamics (SPH), which usually use a fixed mass for SPH particles, often employ the same sub-grid active galactic nuclei (AGN) feedback prescription across a range of resolutions. It is thus important to ask how the impact of the simulated AGN feedback on a galaxy changes when only the numerical resolution (the SPH particle mass) changes. We present a suite of simulations modelling the interaction of an AGN outflow with the ambient turbulent and clumpy interstellar medium in the inner part of the host galaxy at a range of mass resolutions. We find that, with other things being equal, degrading the resolution leads to feedback becoming more efficient at clearing out all gas in its path. For the simulations presented here, the difference in the mass of the gas ejected by AGN feedback varies by more than a factor of 10 between our highest and lowest resolution simulations. This happens because feedback-resistant high-density clumps are washed out at low effective resolutions. We also find that changes in numerical resolution lead to undesirable artefacts in how the AGN feedback affects the AGN immediate environment.

  17. A Comprehensive Model for Compton-thick and Compton-thin X-ray Reprocessing in AGN

    NASA Astrophysics Data System (ADS)

    Yaqoob, Tahir

    2009-09-01

    X-ray reprocessing is common in AGN, yet current modeling practices invoke ad hoc components, some of which may be inappropriate in the Compton-thick regime. This results in derived parameters that do not have obvious physical meaning. Our results so far indicate that the universal use of a disk geometry and interpretation of the so-called "reflection fraction" as a solid angle, can be wrong by a factor of ~5 compared to a torus geometry. We propose to compute a comprehensive set of models that improve upon previous work in several critical ways, yielding transmitted, reflected, and fluorescent line spectra that are self-consistent. The models will be suitable for many applications including Chandra grating spectroscopy and studies of AGN populations found in deep surveys, up to z~10.

  18. Delayed Feedback Model of Axonal Length Sensing

    PubMed Central

    Karamched, Bhargav R.; Bressloff, Paul C.

    2015-01-01

    A fundamental question in cell biology is how the sizes of cells and organelles are regulated at various stages of development. Size homeostasis is particularly challenging for neurons, whose axons can extend from hundreds of microns to meters (in humans). Recently, a molecular-motor-based mechanism for axonal length sensing has been proposed, in which axonal length is encoded by the frequency of an oscillating retrograde signal. In this article, we develop a mathematical model of this length-sensing mechanism in which advection-diffusion equations for bidirectional motor transport are coupled to a chemical signaling network. We show that chemical oscillations emerge due to delayed negative feedback via a Hopf bifurcation, resulting in a frequency that is a monotonically decreasing function of axonal length. Knockdown of either kinesin or dynein causes an increase in the oscillation frequency, suggesting that the length-sensing mechanism would produce longer axons, which is consistent with experimental findings. One major prediction of the model is that fluctuations in the transport of molecular motors lead to a reduction in the reliability of the frequency-encoding mechanism for long axons. PMID:25954897

  19. An exceptionally powerful AGN outburst in the low-luminosity non-cool-core group

    NASA Astrophysics Data System (ADS)

    O'Sullivan, Ewan

    2013-10-01

    The shallow potentials of galaxy groups make them vulnerable to heating and gas loss caused by powerful AGN outbursts. Theoretical models suggest that feedback at z~2 must have ejected gas from groups, reducing their baryon content, but a lack of identified nearby non-cool-core (NCC) groups makes it difficult to determine whether AGN continue to have such a significant impact on the structure of the intra-group medium (IGM). We propose a deep observation of HCG 15, a disturbed non-cool-core group which appears to have undergone an exceptionally powerful AGN outburst ~190-330 Myr ago. We will search for cavities, make a more accurate estimate of the outburst power, examine the IGM for evidence of outward gas transport, and determine whether the AGN has disrupted the group core.

  20. VizieR Online Data Catalog: AGN torus models. SED library (Siebenmorgen+, 2015)

    NASA Astrophysics Data System (ADS)

    Siebenmorgen, R.; Heymann, F.; Efstathiou, A.

    2015-08-01

    There are 3600 ASCII tables files in two columns format. The first is the wavelength in microns, the second column is the flux in Jy. SEDs are computed for AGNs at a distance of 50Mpc and a luminosity of 1011L⊙. The file names include the five basic model parameters: a) th: The viewing angle corresponding to bins at 86, 80, 73, 67, 60, 52, 43, 33, and 19 degree measured from the pole (z-axis). thx= th1 ,.., th9 b) R : The inner radius of the dusty torus. R= 300, 514, 772, 1000, 1545 in units: (10^15 cm) c) Vc: The cloud volume filling factor. Vc= 1.5, 7.7, 38.5, 77.7 (%). d) Ac: The optical depth (in V) of the individual clouds. Ac= 0, 4.5, 13.5, 45. e) Ad: The optical depth (in V) of the disk midplane. Ad= 0, 30, 100, 300, 1000. Example: File notation. RxxxxVcxxxAcxxxx_Adxxxx.thx R1545Vc777Ac0135_Ad1000.th9 (2 data files).

  1. Do stars contribute to AGN fuelling?

    NASA Astrophysics Data System (ADS)

    Davies, Richard

    2011-11-01

    While the existence of a starburst-AGN connection is undisputed, there is no consensus on whether AGN fuelling is synchronous with star formation or follows it during a post-starburst phase. I begin by presenting an overview of some of the observational evidence and theoretical models favouring each perspective. I then focus on recent high resolution observations that are able to probe the central tens of parsecs where star formation might influence AGN activity. I show that both the starburst phase and the physical state of the dense molecular gas imply that stellar feedback plays a critical role in first hindering and then helping accretion. I argue that it is only after the early turbulent phases of a starburst that gas from slow stellar winds can accrete efficiently to smaller scales. And I outline other contexts where similar processes appear to be at work. I finish by showing how the properties of the obscuring torus are directly coupled to this star formation, and that we should be thinking of the torus as a complex dynamical entity.

  2. HIGHER EDUCATION--A POPULATION FLOW FEEDBACK MODEL.

    ERIC Educational Resources Information Center

    REISMAN, ARNOLD

    A MATHEMATICAL MODEL IS DEVELOPED TO STUDY THE PRODUCTION OF DOCTORAL, MASTER'S, AND BACHELOR'S DEGREES AND THEIR FEEDBACK INTO HIGHER EDUCATION. FEEDBACK IS DETERMINED BY A SET OF "BASIC BALANCE EQUATIONS" WHICH STATE THAT THE TOTAL RATE OF FLOW INTO A CATEGORY LESS THE RATE OF OUTFLOW IS EQUAL TO THE RATE OF ACCUMULATION OR GROWTH IN A GIVEN…

  3. Deep Chandra , HST-COS, and megacam observations of the Phoenix cluster: Extreme star formation and AGN feedback on hundred kiloparsec scales

    DOE PAGESBeta

    McDonald, Michael; McNamara, Brian R.; Perimeter Institute for Theoretical Physics, Waterloo; van Weeren, Reinout J.; Applegate, Douglas E.; Bayliss, Matthew; Harvard Univ., Cambridge, MA; Bautz, Marshall W.; Benson, Bradford A.; Univ. of Chicago, Chicago, IL; et al

    2015-09-28

    In this study, we present new ultraviolet, optical, and X-ray data on the Phoenix galaxy cluster (SPT-CLJ2344-4243). Deep optical imaging reveals previously undetected filaments of star formation, extending to radii of ~50–100 kpc in multiple directions. Combined UV-optical spectroscopy of the central galaxy reveals a massive (2 × 109 M⊙), young (~4.5 Myr) population of stars, consistent with a time-averaged star formation rate of 610 ± 50 M⊙ yr–1. We report a strong detection of O vi λλ1032,1038, which appears to originate primarily in shock-heated gas, but may contain a substantial contribution (>1000 M⊙ yr–1) from the cooling intracluster mediummore » (ICM). We confirm the presence of deep X-ray cavities in the inner ~10 kpc, which are among the most extreme examples of radio-mode feedback detected to date, implying jet powers of 2 – 7 × 1045 erg s–1. We provide evidence that the active galactic nucleus inflating these cavities may have only recently transitioned from "quasar-mode" to "radio-mode," and may currently be insufficient to completely offset cooling. A model-subtracted residual X-ray image reveals evidence for prior episodes of strong radio-mode feedback at radii of ~100 kpc, with extended "ghost" cavities indicating a prior epoch of feedback roughly 100 Myr ago. This residual image also exhibits significant asymmetry in the inner ~200 kpc (0.15R500), reminiscent of infalling cool clouds, either due to minor mergers or fragmentation of the cooling ICM. Taken together, these data reveal a rapidly evolving cool core which is rich with structure (both spatially and in temperature), is subject to a variety of highly energetic processes, and yet is cooling rapidly and forming stars along thin, narrow filaments.« less

  4. Deep Chandra, HST-COS, and Megacam Observations of the Phoenix Cluster: Extreme Star Formation and AGN Feedback on Hundred Kiloparsec Scales

    NASA Astrophysics Data System (ADS)

    McDonald, Michael; McNamara, Brian R.; van Weeren, Reinout J.; Applegate, Douglas E.; Bayliss, Matthew; Bautz, Marshall W.; Benson, Bradford A.; Carlstrom, John E.; Bleem, Lindsey E.; Chatzikos, Marios; Edge, Alastair C.; Fabian, Andrew C.; Garmire, Gordon P.; Hlavacek-Larrondo, Julie; Jones-Forman, Christine; Mantz, Adam B.; Miller, Eric D.; Stalder, Brian; Veilleux, Sylvain; ZuHone, John A.

    2015-10-01

    We present new ultraviolet, optical, and X-ray data on the Phoenix galaxy cluster (SPT-CLJ2344-4243). Deep optical imaging reveals previously undetected filaments of star formation, extending to radii of ˜50-100 kpc in multiple directions. Combined UV-optical spectroscopy of the central galaxy reveals a massive (2 × 109 M⊙), young (˜4.5 Myr) population of stars, consistent with a time-averaged star formation rate of 610 ± 50 M⊙ yr-1. We report a strong detection of O vi λλ1032,1038, which appears to originate primarily in shock-heated gas, but may contain a substantial contribution (>1000 M⊙ yr-1) from the cooling intracluster medium (ICM). We confirm the presence of deep X-ray cavities in the inner ˜10 kpc, which are among the most extreme examples of radio-mode feedback detected to date, implying jet powers of 2-7 × 1045 erg s-1. We provide evidence that the active galactic nucleus inflating these cavities may have only recently transitioned from “quasar-mode” to “radio-mode,” and may currently be insufficient to completely offset cooling. A model-subtracted residual X-ray image reveals evidence for prior episodes of strong radio-mode feedback at radii of ˜100 kpc, with extended “ghost” cavities indicating a prior epoch of feedback roughly 100 Myr ago. This residual image also exhibits significant asymmetry in the inner ˜200 kpc (0.15R500), reminiscent of infalling cool clouds, either due to minor mergers or fragmentation of the cooling ICM. Taken together, these data reveal a rapidly evolving cool core which is rich with structure (both spatially and in temperature), is subject to a variety of highly energetic processes, and yet is cooling rapidly and forming stars along thin, narrow filaments.

  5. Atmospheric convergence feedback in a simple model for El Nino

    NASA Technical Reports Server (NTRS)

    Zebiak, S. E.

    1986-01-01

    A parameterization is developed for the feedback between dynamics and heating associated with moisture convergence in the tropical atmospheric boundary layer. The feedback improves the ability of a simple model to simulate observed anomalies of the tropical atmosphere during El Nino events. In particular, two features of the observations are reproduced by including the feedback process: the smaller scale of atmospheric anomalies as compared to SST anomalies, and the focusing of the anomalies in the vicinity of the mean convergence zones. The principal remaining shortcomings of the model are discussed.

  6. Cybernetics: A Model for Feedback in the ESL Classroom.

    ERIC Educational Resources Information Center

    Zamel, Vivian

    1981-01-01

    Examines cybernetics as a model which provides framework with which to view communicators and the communications in the ESL classroom because it implies the kind of feedback the learner can assimilate and act upon. (Author/BK)

  7. Feedbacks, climate sensitivity, and the limits of linear models

    NASA Astrophysics Data System (ADS)

    Rugenstein, M.; Knutti, R.

    2015-12-01

    The term "feedback" is used ubiquitously in climate research, but implies varied meanings in different contexts. From a specific process that locally affects a quantity, to a formal framework that attempts to determine a global response to a forcing, researchers use this term to separate, simplify, and quantify parts of the complex Earth system. We combine large (>120 member) ensemble GCM and EMIC step forcing simulations over a broad range of forcing levels with a historical and educational perspective to organize existing ideas around feedbacks and linear forcing-feedback models. With a new method overcoming internal variability and initial condition problems we quantify the non-constancy of the climate feedback parameter. Our results suggest a strong state- and forcing-dependency of feedbacks, which is not considered appropriately in many studies. A non-constant feedback factor likely explains some of the differences in estimates of equilibrium climate sensitivity from different methods and types of data. We discuss implications for the definition of the forcing term and its various adjustments. Clarifying the value and applicability of the linear forcing feedback framework and a better quantification of feedbacks on various timescales and spatial scales remains a high priority in order to better understand past and predict future changes in the climate system.

  8. Relativistic X-ray reverberation modelling of the combined time-averaged and lag-energy spectra in AGN

    NASA Astrophysics Data System (ADS)

    Chainakun, P.; Young, A. J.; Kara, E.

    2016-08-01

    General relativistic ray tracing simulations of the time-averaged spectrum and energy-dependent time delays in active galactic nuclei (AGN) are presented. We model the lamp-post geometry in which the accreting gas is illuminated by an X-ray source located on the rotation axis of the black hole. The spectroscopic features imprinted in the reflection component are modelled using REFLIONX. The associated time delays after the direct continuum, known as reverberation lags, are computed including the full effects of dilution and ionization gradients on the disc. We perform, for the first time, simultaneous fitting of the time-averaged and lag-energy spectra in three AGN: Mrk 335, IRAS 13224-3809 and Ark 564 observed with XMM-Newton. The best-fitting source height and central mass of each AGN partly agree with those previously reported. We find that including the ionization gradient in the model naturally explains lag-energy observations in which the 3 keV and 7-10 keV bands precede other bands. To obtain the clear 3 keV and 7-10 keV dips in the lag-energy profile, the model requires either a source height >5 rg, or a disc that is highly ionized at small radii and is colder further out. We also show that fitting the lag or the mean spectra alone can lead to different results and interpretations. This is therefore important to combine the spectral and timing data in order to find the plausible but self-consistent fits which are achievable with our model.

  9. Relativistic X-ray reverberation modelling of the combined time-averaged and lag-energy spectra in AGN

    NASA Astrophysics Data System (ADS)

    Chainakun, P.; Young, A. J.; Kara, E.

    2016-08-01

    General relativistic ray tracing simulations of the time-averaged spectrum and energy-dependent time delays in AGN are presented. We model the lamp-post geometry in which the accreting gas is illuminated by an X-ray source located on the rotation axis of the black hole. The spectroscopic features imprinted in the reflection component are modelled using REFLIONX. The associated time delays after the direct continuum, known as reverberation lags, are computed including the full effects of dilution and ionization gradients on the disc. We perform, for the first time, simultaneous fitting of the time-averaged and lag-energy spectra in three AGN: Mrk 335, IRAS 13224-3809 and Ark 564 observed with XMM-Newton. The best fitting source height and central mass of each AGN partly agree with those previously reported. We find that including the ionization gradient in the model naturally explains lag-energy observations in which the 3 keV and 7-10 keV bands precede other bands. To obtain the clear 3 keV and 7-10 keV dips in the lag-energy profile, the model requires either a source height > 5$r_g$, or a disc that is highly ionized at small radii and is colder further out. We also show that fitting the lag or the mean spectra alone can lead to different results and interpretations. This is therefore important to combine the spectral and timing data in order to find the plausible but self-consistent fits which is achievable with our model.

  10. Deep Chandra , HST-COS, and megacam observations of the Phoenix cluster: Extreme star formation and AGN feedback on hundred kiloparsec scales

    SciTech Connect

    McDonald, Michael; McNamara, Brian R.; van Weeren, Reinout J.; Applegate, Douglas E.; Bayliss, Matthew; Bautz, Marshall W.; Benson, Bradford A.; Carlstrom, John E.; Bleem, Lindsey E.; Chatzikos, Marios; Edge, Alastair C.; Fabian, Andrew C.; Garmire, Gordon P.; Hlavacek-Larrondo, Julie; Jones-Forman, Christine; Mantz, Adam B.; Miller, Eric D.; Stalder, Brian; Veilleux, Sylvain; ZuHone, John A.

    2015-09-28

    In this study, we present new ultraviolet, optical, and X-ray data on the Phoenix galaxy cluster (SPT-CLJ2344-4243). Deep optical imaging reveals previously undetected filaments of star formation, extending to radii of ~50–100 kpc in multiple directions. Combined UV-optical spectroscopy of the central galaxy reveals a massive (2 × 109 M), young (~4.5 Myr) population of stars, consistent with a time-averaged star formation rate of 610 ± 50 M yr–1. We report a strong detection of O vi λλ1032,1038, which appears to originate primarily in shock-heated gas, but may contain a substantial contribution (>1000 M yr–1) from the cooling intracluster medium (ICM). We confirm the presence of deep X-ray cavities in the inner ~10 kpc, which are among the most extreme examples of radio-mode feedback detected to date, implying jet powers of 2 – 7 × 1045 erg s–1. We provide evidence that the active galactic nucleus inflating these cavities may have only recently transitioned from "quasar-mode" to "radio-mode," and may currently be insufficient to completely offset cooling. A model-subtracted residual X-ray image reveals evidence for prior episodes of strong radio-mode feedback at radii of ~100 kpc, with extended "ghost" cavities indicating a prior epoch of feedback roughly 100 Myr ago. This residual image also exhibits significant asymmetry in the inner ~200 kpc (0.15R500), reminiscent of infalling cool clouds, either due to minor mergers or fragmentation of the cooling ICM. Taken together, these data reveal a rapidly evolving cool core which is rich with structure (both spatially and in temperature), is subject to a variety of highly energetic processes, and yet is cooling rapidly and forming stars along thin, narrow filaments.

  11. Photoionization Models of the H_2 Emission of the Narrow Line Region of AGNs

    NASA Astrophysics Data System (ADS)

    Aleman, I.; Gruenwald, R.

    2011-05-01

    The excitation mechanism of the narrow line region (NLR) of AGNs is still an open question. Excitation by UV radiation from O and B stars, x-rays from the central black hole, shock from supernovae or jets, or a combination of these mechanisms have been suggested. In the present work, we use photoionization models to study the excitation mechanisms of the H_2 infrared emission lines in the NLR. In the literature, analyzes of the H_2 emission have been done assuming that the molecules is present only in neutral regions (photodissociation regions, x-ray-dominated regions, or shocks; Veilleux et al. 1997, Krabbe et al. 2000, Rigopoulou et al. 2002, Rodriguez-Ardila et al. 2004, 2005, and Davies et al. 2005). However, they are not conclusive. In previous work (Aleman & Gruenwald 2004, 2011), we show that the H_2 emission from the ionized region of PNe can be significant for planetary nebulae (PNe) with hot central stars (T⋆ > 150000 K). Such stars produce copious amounts of high energy photons, which create an extended partially ionized region that favors the H_2 survival. The conditions in the NLR are similar to those in PNe with hot central stars, so we can expect that the H_2 emission might also be important. We obtain and analyze a grid of photoionization models for different NRL parameters. We study the resulting H_2 density and emission, as well as, the formation, destruction, excitation, and de-excitation mechanisms. The higher values observed for the H_2 1-0 S(1)/Brγ ratio cannot be reproduced by our models. The calculated ratios are between 10^-8 and 10^-1, while the observational ration can be as high as 10. The calculated ratio is strongly anti-correlated with the ionization parameter (U) and only models with U<10-3 result in ratios inside the observational range. We show that the NLR is an environment more hostile to the H_2 molecule than the ionized region of PNe. Another interesting result of our calculations is that the H_2 formation on grain surfaces

  12. Accretion Timescales from Kepler AGN

    NASA Astrophysics Data System (ADS)

    Kasliwal, Vishal P.; Vogeley, Michael S.; Richards, Gordon T.

    2015-01-01

    We constrain AGN accretion disk variability mechanisms using the optical light curves of AGN observed by Kepler. AGN optical fluxes are known to exhibit stochastic variations on timescales of hours, days, months and years. The excellent sampling properties of the original Kepler mission - high S/N ratio (105), short sampling interval (30 minutes), and long sampling duration (~ 3.5 years) - allow for a detailed examination of the differences between the variability processes present in various sub-types of AGN such as Type I and II Seyferts, QSOs, and Blazars. We model the flux data using the Auto-Regressive Moving Average (ARMA) representation from the field of time series analysis. We use the Kalman filter to determine optimal mode parameters and use the Akaike Information Criteria (AIC) to select the optimal model. We find that optical light curves from Kepler AGN cannot be fit by low order statistical models such as the popular AR(1) process or damped random walk. Kepler light curves exhibit complicated power spectra and are better modeled by higher order ARMA processes. We find that Kepler AGN typically exhibit power spectra that change from a bending power law (PSD ~ 1/fa) to a flat power spectrum on timescales in the range of ~ 5 - 100 days consistent with the orbital and thermal timescales of a typical 107 solar mass black hole.

  13. Warm Absorber Diagnostics of AGN Dynamics

    NASA Astrophysics Data System (ADS)

    Kallman, Timothy

    Warm absorbers and related phenomena are observable manifestations of outflows or winds from active galactic nuclei (AGN) that have great potential value. Understanding AGN outflows is important for explaining the mass budgets of the central accreting black hole, and also for understanding feedback and the apparent co-evolution of black holes and their host galaxies. In the X-ray band warm absorbers are observed as photoelectric absorption and resonance line scattering features in the 0.5-10 keV energy band; the UV band also shows resonance line absorption. Warm absorbers are common in low luminosity AGN and they have been extensively studied observationally. They may play an important role in AGN feedback, regulating the net accretion onto the black hole and providing mechanical energy to the surroundings. However, fundamental properties of the warm absorbers are not known: What is the mechanism which drives the outflow?; what is the gas density in the flow and the geometrical distribution of the outflow?; what is the explanation for the apparent relation between warm absorbers and the surprising quasi-relativistic 'ultrafast outflows' (UFOs)? We propose a focused set of model calculations that are aimed at synthesizing observable properties of warm absorber flows and associated quantities. These will be used to explore various scenarios for warm absorber dynamics in order to answer the questions in the previous paragraph. The guiding principle will be to examine as wide a range as possible of warm absorber driving mechanisms, geometry and other properties, but with as careful consideration as possible to physical consistency. We will build on our previous work, which was a systematic campaign for testing important class of scenarios for driving the outflows. We have developed a set of tools that are unique and well suited for dynamical calculations including radiation in this context. We also have state-of-the-art tools for generating synthetic spectra, which are

  14. Hot Flow Model for Low Luminosity AGNs and Black Hole Binaries: the Role and Origin of Non-thermal Electrons

    NASA Astrophysics Data System (ADS)

    Niedzwiecki, Andrzej; Xie, Fu-Guo; Stepnik, Agnieszka

    2014-08-01

    Optically thin, two-temperature accretion flows are widely considered as a relevant accretion mode below ~0.01 LEdd in AGNs as well as in X-ray binaries. We study spectral formation in such flows using a refined model with a fully general relativistic description of both the radiative (leptonic and hadronic) and hydrodynamic processes, and with an exact treatment of global Comptonization. We point out that basic properties of two-temperature flows determine the relative strengths of the synchrotron radiation of thermal electrons and non-thermal electrons from charged-pion decay, in a manner consistent with observations. In AGNs, the non-thermal synchrotron dominates the seed photon input down to ~10-5 LEdd and it allows to explain the X-ray spectral index-Eddington ratio relation as well as the cut-off energies measured in the best-studied AGNs; the (standard) model with the thermal synchrotron being the main source of seed photons does not agree with these observations. For stellar-mass black holes, non-thermal electrons from hadronic processes become important only above ~0.01 LEdd (and may be relevant for the non-thermal tails observed in luminous hard states of Cyg X-1 and GX 339-4) and we find that the thermal synchrotron provides a sufficient seed photon flux to explain observations of black hole transients below ~0.01 LEdd. We also note that non-thermal acceleration processes in hot flows are constrained by comparisons of the predicted gamma-ray fluxes (from neutral pion decay) with Fermi-LAT upper limits. For NGC 4151, it limits the energy content in the non-thermal component of proton distribution to at most 1 per cent.

  15. Ionized Absorbers in AGN

    NASA Astrophysics Data System (ADS)

    Mathur, S.

    1999-08-01

    As a part of this program, we observed three AGN:PKS2251 + 113, PG0043 = 039 and PLH909. Two objects show signatures of absorbtion in their UV spectra. Based on our earlier modeling of X-ray warm absorbents, we expected to observe X-ray observation in these objects. The third, PLH909, is known to have soft excess in EINSTEIN data. Attachment: "Exploratory ASCA observation of broad absorption line quasi-stellar objects".

  16. Ionized Absorbers in AGN

    NASA Technical Reports Server (NTRS)

    Mathur, S.

    1999-01-01

    As a part of this program, we observed three AGN:PKS2251 + 113, PG0043 = 039 and PLH909. Two objects show signatures of absorbtion in their UV spectra. Based on our earlier modeling of X-ray warm absorbents, we expected to observe X-ray observation in these objects. The third, PLH909, is known to have soft excess in EINSTEIN data. Attachment: "Exploratory ASCA observation of broad absorption line quasi-stellar objects".

  17. Microscale Heat Conduction Models and Doppler Feedback

    SciTech Connect

    Hawari, Ayman I.; Ougouag, Abderrafi

    2015-01-22

    The objective of this project is to establish an approach for providing the fundamental input that is needed to estimate the magnitude and time-dependence of the Doppler feedback mechanism in Very High Temperature reactors. This mechanism is the foremost contributor to the passive safety of gas-cooled, graphite-moderated high temperature reactors that use fuel based on Tristructural-Isotropic (TRISO) coated particles. Therefore, its correct prediction is essential to the conduct of safety analyses for these reactors. Since the effect is directly dependent on the actual temperature reached by the fuel during transients, the underlying phenomena of heat deposition, heat transfer and temperature rise must be correctly predicted. To achieve the above objective, this project will explore an approach that accounts for lattice effects as well as local temperature variations and the correct definition of temperature and related local effects.

  18. Ultra-fast outflows (aka UFOs) from AGNs and QSOs

    NASA Astrophysics Data System (ADS)

    Cappi, M.; Tombesi, F.; Giustini, M.

    During the last decade, strong observational evidence has been accumulated for the existence of massive, high velocity winds/outflows (aka Ultra Fast Outflows, UFOs) in nearby AGNs and in more distant quasars. Here we briefly review some of the most recent developments in this field and discuss the relevance of UFOs for both understanding the physics of accretion disk winds in AGNs, and for quantifying the global amount of AGN feedback on the surrounding medium.

  19. Feedbacks, climate sensitivity and the limits of linear models.

    PubMed

    Knutti, Reto; Rugenstein, Maria A A

    2015-11-13

    The term 'feedback' is used ubiquitously in climate research, but implies varied meanings in different contexts. From a specific process that locally affects a quantity, to a formal framework that attempts to determine a global response to a forcing, researchers use this term to separate, simplify and quantify parts of the complex Earth system. We combine new model results with a historical and educational perspective to organize existing ideas around feedbacks and linear models. Our results suggest that the state- and forcing-dependency of feedbacks are probably not appreciated enough, and not considered appropriately in many studies. A non-constant feedback parameter likely explains some of the differences in estimates of equilibrium climate sensitivity from different methods and types of data. Clarifying the value and applicability of the linear forcing feedback framework and a better quantification of feedbacks on various timescales and spatial scales remains a high priority in order to better understand past and predict future changes in the climate system. PMID:26438287

  20. Climatic Feedbacks and Desertification: The Mediterranean Model.

    NASA Astrophysics Data System (ADS)

    Millán, M. M.; Estrela, M. J.; Sanz, M. J.; Mantilla, E.; Martín, M.; Pastor, F.; Salvador, R.; Vallejo, R.; Alonso, L.; Gangoiti, G.; Ilardia, J. L.; Navazo, M.; Albizuri, A.; Artíñano, B.; Ciccioli, P.; Kallos, G.; Carvalho, R. A.; Andrés, D.; Hoff, A.; Werhahn, J.; Seufert, G.; Versino, B.

    2005-03-01

    Mesometeorological information obtained in several research projects in southern Europe has been used to analyze perceived changes in the western Mediterranean summer storm regime. A procedure was developed to disaggregate daily precipitation data into three main components: frontal precipitation, summer storms, and Mediterranean cyclogenesis. Working hypotheses were derived on the likely processes involved. The results indicate that the precipitation regime in this Mediterranean region is very sensitive to variations in surface airmass temperature and moisture. Land-use perturbations that accumulated over historical time and greatly accelerated in the last 30 yr may have induced changes from an open, monsoon-type regime with frequent summer storms over the mountains inland to one dominated by closed vertical recirculations where feedback mechanisms favor the loss of storms over the coastal mountains and additional heating of the sea surface temperature during summer. This, in turn, favors Mediterranean cyclogenesis and torrential rains in autumn-winter. Because these intense rains and floods can occur anywhere in the basin, perturbations to the hydrological cycle in any part of the basin can propagate to the whole basin and adjacent regions. Furthermore, present levels of air pollutants can produce greenhouse heating, amplifying the perturbations and pushing the system over critical threshold levels. The questions raised are relevant for the new European Union (EU) water policies in southern Europe and for other regions dominated by monsoon-type weather systems.

  1. An Alternative Feedback/Evaluation Model for Outdoor Wilderness Programs.

    ERIC Educational Resources Information Center

    Dawson, R.

    Project D.A.R.E. (Development through Adventure, Responsibility and Education), an adventure-based outdoor program, uses a feedback/evaluation model, combining a learning component with a two-part participant observational model. The first phase focuses on evaluation of the child and progress made while he is in the program (stages one to four);…

  2. A biopsychosocial model based on negative feedback and control

    PubMed Central

    Carey, Timothy A.; Mansell, Warren; Tai, Sara J.

    2014-01-01

    Although the biopsychosocial model has been a popular topic of discussion for over four decades it has not had the traction in fields of research that might be expected of such an intuitively appealing idea. One reason for this might be the absence of an identified mechanism or a functional architecture that is authentically biopsychosocial. What is needed is a robust mechanism that is equally important to biochemical processes as it is to psychological and social processes. Negative feedback may be the mechanism that is required. Negative feedback has been implicated in the regulation of neurotransmitters as well as important psychological and social processes such as emotional regulation and the relationship between a psychotherapist and a client. Moreover, negative feedback is purported to also govern the activity of all other organisms as well as humans. Perceptual Control Theory (PCT) describes the way in which negative feedback establishes control at increasing levels of perceptual complexity. Thus, PCT may be the first biopsychosocial model to be articulated in functional terms. In this paper we outline the working model of PCT and explain how PCT provides an embodied hierarchical neural architecture that utilizes negative feedback to control physiological, psychological, and social variables. PCT has major implications for both research and practice and, importantly, provides a guide by which fields of research that are currently separated may be integrated to bring about substantial progress in understanding the way in which the brain alters, and is altered by, its behavioral and environmental context. PMID:24616685

  3. Low Order Empirical Galerkin Models for Feedback Flow Control

    NASA Astrophysics Data System (ADS)

    Tadmor, Gilead; Noack, Bernd

    2005-11-01

    Model-based feedback control restrictions on model order and complexity stem from several generic considerations: real time computation, the ability to either measure or reliably estimate the state in real time and avoiding sensitivity to noise, uncertainty and numerical ill-conditioning are high on that list. Empirical POD Galerkin models are attractive in the sense that they are simple and (optimally) efficient, but are notoriously fragile, and commonly fail to capture transients and control effects. In this talk we review recent efforts to enhance empirical Galerkin models and make them suitable for feedback design. Enablers include `subgrid' estimation of turbulence and pressure representations, tunable models using modes from multiple operating points, and actuation models. An invariant manifold defines the model's dynamic envelope. It must be respected and can be exploited in observer and control design. These ideas are benchmarked in the cylinder wake system and validated by a systematic DNS investigation of a 3-dimensional Galerkin model of the controlled wake.

  4. AGN identification and host galaxies properties in the MOSDEF survey

    NASA Astrophysics Data System (ADS)

    Azadi, Mojegan; Coil, Alison L.; MOSDEF team

    2016-06-01

    We present new results on the identification and host galaxy properties of X-ray, IR and optically-selected AGN at 1.4 < z < 3.8, using spectroscopic data from the on-going MOSDEF survey, which is obtaining rest-frame optical spectra of ~1,500 galaxies and AGN using the new Keck/MOSFIRE instrument. We find clear selection effects when identifying AGN at different wavelengths, in that optically-selected AGN are more likely to be found in galaxies with low SFR, while IR AGN are typically found in galaxies with higher SFR. There is also a bias against finding AGN at any wavelength in low mass galaxies. We find that optical AGN selection identifies less powerful AGN that may be obscured at other wavelengths. Combining the AGN we identify at different wavelengths, we find that AGN host galaxies have similar stellar age and dust content as inactive galaxies of the same stellar mass. Finally, we do not find a significant correlation between either SFR or stellar mass and L[OIII], which argues against the presence of strong AGN feedback.

  5. A Lumped Parameter Model for Feedback Studies in Tokamaks

    NASA Astrophysics Data System (ADS)

    Chance, M. S.; Chu, M. S.; Okabayashi, M.; Glasser, A. H.

    2004-11-01

    A lumped circuit model of the feedback stabilization studies in tokamaks is calculated. This work parallels the formulation by Boozer^a, is analogous to the studies done on axisymmetric modes^b, and generalizes the cylindrical model^c. The lumped circuit parameters are derived from the DCON derived eigenfunctions of the plasma, the resistive shell and the feedback coils. The inductances are calculated using the VACUUM code which is designed to calculate the responses between the various elements in the feedback system. The results are compared with the normal mode^d and the system identification^e approaches. ^aA.H. Boozer, Phys. Plasmas 5, 3350 (1998). ^b E.A. Lazarus et al., Nucl. Fusion 30, 111 (1990). ^c M. Okabayashi et al., Nucl. Fusion 38, 1607 (1998). ^dM.S. Chu et al., Nucl. Fusion 43, 441 (2003). ^eY.Q. Liu et al., Phys. Plasmas 7, 3681 (2000).

  6. An integrative model linking feedback environment and organizational citizenship behavior.

    PubMed

    Peng, Jei-Chen; Chiu, Su-Fen

    2010-01-01

    Past empirical evidence has suggested that a positive supervisor feedback environment may enhance employees' organizational citizenship behavior (OCB). In this study, we aim to extend previous research by proposing and testing an integrative model that examines the mediating processes underlying the relationship between supervisor feedback environment and employee OCB. Data were collected from 259 subordinate-supervisor dyads across a variety of organizations in Taiwan. We used structural equation modeling to test our hypotheses. The results demonstrated that supervisor feedback environment influenced employees' OCB indirectly through (1) both positive affective-cognition and positive attitude (i.e., person-organization fit and organizational commitment), and (2) both negative affective-cognition and negative attitude (i.e., role stressors and job burnout). Theoretical and practical implications are discussed. PMID:21166326

  7. The Role of Turbulence in AGN Self-Regulation in Galaxy Clusters

    SciTech Connect

    Scannapieco, Evan; Brueggen, Marcus

    2009-12-18

    Cool cores of galaxy clusters are thought to be heated by low-power active galactic nuclei (AGN), whose accretion is regulated by feedback. However, the interaction between the hot gas ejected by the AGN and the ambient intracluster medium is extremely difficult to simulate, as it involves a wide range of spatial scales and gas that is Rayleigh-Taylor (RT) unstable. Here we use a subgrid model for RT-driven turbulence to overcome these problems and present the first observationally-consistent hydrodynamical simulations of AGN self-regulation in galaxy clusters. For a wide range of parameter choices the cluster in our three-dimensional simulations regulates itself for at least several 10{sup 9} years. Heating balances cooling through a string of outbreaks with a typical recurrence time of {approx_equal}80 Myrs, a timescale that depends only on the global cluster properties.

  8. An Emerging Model for Student Feedback: Electronic Distributed Evaluation

    ERIC Educational Resources Information Center

    Brunk-Chavez, Beth; Arrigucci, Annette

    2012-01-01

    In this article we address several issues and challenges that the evaluation of writing presents individual instructors and composition programs as a whole. We present electronic distributed evaluation, or EDE, as an emerging model for feedback on student writing and describe how it was integrated into our program's course redesign. Because the…

  9. Implementing Relevance Feedback in the Bayesian Network Retrieval Model.

    ERIC Educational Resources Information Center

    de Campos, Luis M.; Fernandez-Luna, Juan M.; Huete, Juan F.

    2003-01-01

    Discussion of relevance feedback in information retrieval focuses on a proposal for the Bayesian Network Retrieval Model. Bases the proposal on the propagation of partial evidences in the Bayesian network, representing new information obtained from the user's relevance judgments to compute the posterior relevance probabilities of the documents…

  10. γ-Ray Generation in Microquasars: the link with AGN

    NASA Astrophysics Data System (ADS)

    Latham, I. J.; Aye, K.-M.; Brown, A. M.; Chadwick, P. M.; Hadjichristidis, C. N.; Le Gallou, R.; McComb, T. J. L.; Nolan, S. J.; Orford, K. J.; Osborne, J. L.; Noutsos, A.; Rayner, S. M.

    2005-02-01

    The link between the physical processes responsible for high energy emission from relativistic jets in AGN and microquasars is investigated. A Fortran code based on an existing inhomogeneous, synchrotron self-Compton (SSC) model, for AGN is presented. The code is then applied to the AGN 3C 279 and the microquasar LS5039. Spectral energy distributions (SED's) are presented.

  11. Modeling terrestrial gamma ray flashes produced by relativistic feedback discharges

    NASA Astrophysics Data System (ADS)

    Liu, Ningyu; Dwyer, Joseph R.

    2013-05-01

    This paper reports a modeling study of terrestrial gamma ray flashes (TGFs) produced by relativistic feedback discharges. Terrestrial gamma ray flashes are intense energetic radiation originating from the Earth's atmosphere that has been observed by spacecraft. They are produced by bremsstrahlung interactions of energetic electrons, known as runaway electrons, with air atoms. An efficient physical mechanism for producing large fluxes of the runaway electrons to make the TGFs is the relativistic feedback discharge, where seed runaway electrons are generated by positrons and X-rays, products of the discharge itself. Once the relativistic feedback discharge becomes self-sustaining, an exponentially increasing number of relativistic electron avalanches propagate through the same high-field region inside the thundercloud until the electric field is partially discharged by the ionization created by the discharge. The modeling results indicate that the durations of the TGF pulses produced by the relativistic feedback discharge vary from tens of microseconds to several milliseconds, encompassing all durations of the TGFs observed so far. In addition, when a sufficiently large potential difference is available in thunderclouds, a self-propagating discharge known as the relativistic feedback streamer can be formed, which propagates like a conventional positive streamer. For the relativistic feedback streamer, the positive feedback mechanism of runaway electron production by the positrons and X-rays plays a similar role as the photoionization for the conventional positive streamer. The simulation results of the relativistic feedback streamer show that a sequence of TGF pulses with varying durations can be produced by the streamer. The relativistic streamer may initially propagate with a pulsed manner and turn into a continuous propagation mode at a later stage. Milliseconds long TGF pulses can be produced by the feedback streamer during its continuous propagation. However

  12. Effects of Active galactic nuclei feedback in galaxy population

    NASA Astrophysics Data System (ADS)

    Lagos, C.; Cora, S.; Padilla, N.

    We analyze the effects of feedback from Active Galactic Nuclei (AGN) on the formation and evolution of galaxies, which is assumed to quench cooling flows in massive halos. With this aim we use an hybrid model that combines a cosmological Lambda CDM simulation with a semi-analytic model of galaxy formation. We consider the semi-analytic model described by Cora (2006) (SAMC06) which has been improved by including AGNs, which are associated with the presence of supermassive black holes (BHs). Modellization of BH includes gas accretion during merger-driven starbursts and black hole mergers (Malbon et al., 2006), accretion during starbursts triggered by disk instabilities (Bower et al. 2006), and accretion of cooling gas from quasi-hydrostatically cooling haloes (Croton et al. 2006); Eddington limit is applied in all accretion processes. It is assumed that feedback from AGNs operates in the later case. We show that this new model can simultaneously explain: (i) the bright-end of the galaxy luminosity function (LF); (ii) the observed older population of stars in massive galaxies, thus reproducing the stellar mass function (SMF); (iii) a star formation rate (SFR) seemingly showing an anti-hierarchical galaxy growth. The success of our model is mainly due to the ability of AGN feedback to suppress further cooling and SF in the most massive structures.

  13. A model for reverberating circuits with controlled feedback

    NASA Astrophysics Data System (ADS)

    Rodrigues, Vanessa de Freitas; de Castro, Maria Clícia Stelling; Wedemann, Roseli Suzi; Cortez, Celia Martins

    2015-12-01

    We studied the behavior of a mathematic-computational model for a reverberating neuronal circuit with controlled feedback, verifying the output pattern of the circuit, by means simulations using a program in language C++. Using values obtained from surveying the literature from animal experiments, we observed that the model was able to reproduce the polissynaptic activity of a neuron group of a vigil rat, with looping time of three neurons of the order of magnitude of 102 ms.

  14. The relativistic feedback discharge model of terrestrial gamma ray flashes

    NASA Astrophysics Data System (ADS)

    Dwyer, Joseph R.

    2012-02-01

    As thunderclouds charge, the large-scale fields may approach the relativistic feedback threshold, above which the production of relativistic runaway electron avalanches becomes self-sustaining through the generation of backward propagating runaway positrons and backscattered X-rays. Positive intracloud (IC) lightning may force the large-scale electric fields inside thunderclouds above the relativistic feedback threshold, causing the number of runaway electrons, and the resulting X-ray and gamma ray emission, to grow exponentially, producing very large fluxes of energetic radiation. As the flux of runaway electrons increases, ionization eventually causes the electric field to discharge, bringing the field below the relativistic feedback threshold again and reducing the flux of runaway electrons. These processes are investigated with a new model that includes the production, propagation, diffusion, and avalanche multiplication of runaway electrons; the production and propagation of X-rays and gamma rays; and the production, propagation, and annihilation of runaway positrons. In this model, referred to as the relativistic feedback discharge model, the large-scale electric fields are calculated self-consistently from the charge motion of the drifting low-energy electrons and ions, produced from the ionization of air by the runaway electrons, including two- and three-body attachment and recombination. Simulation results show that when relativistic feedback is considered, bright gamma ray flashes are a natural consequence of upward +IC lightning propagating in large-scale thundercloud fields. Furthermore, these flashes have the same time structures, including both single and multiple pulses, intensities, angular distributions, current moments, and energy spectra as terrestrial gamma ray flashes, and produce large current moments that should be observable in radio waves.

  15. An energy balance climate model with cloud feedbacks

    NASA Technical Reports Server (NTRS)

    Roads, J. O.; Vallis, G. K.

    1984-01-01

    The present two-level global climate model, which is based on the atmosphere-surface energy balance, includes physically based parameterizations for the exchange of heat and moisture across latitude belts and between the surface and the atmosphere, precipitation and cloud formation, and solar and IR radiation. The model field predictions obtained encompass surface and atmospheric temperature, precipitation, relative humidity, and cloudiness. In the model integrations presented, it is noted that cloudiness is generally constant with changing temperature at low latitudes. High altitude cloudiness increases with temperature, although the cloud feedback effect on the radiation field remains small because of compensating effects on thermal and solar radiation. The net global feedback by the cloud field is negative, but small.

  16. Feeding and feeback: The impact of AGN on the circumgalactic medium.

    NASA Astrophysics Data System (ADS)

    Ellison, Sara

    2014-10-01

    A galaxy's history is shaped by the fuelling and feedback of gas both from and into the circumgalactic medium (CGM). The importance of the CGM in low z galaxies has been unequivocally demonstrated in recent years, thanks to the availability of COS and a coupling with large galaxy surveys. These studies have traced the HI and metals out to several hundred kpc, revealing a rich and extended medium around star-forming galaxies. However, the impact of AGN on this CGM is almost completely unknown. We propose to observe the CGM probed by background QSOs at impact parameters up to 175 kpc around 10 moderately high luminosity AGN-dominated galaxies selected from the SDSS. By comparing with an archival sample of non-AGN in the same stellar mass, redshift and impact parameter regime we will investigate 1) the extent of the halo, its velocity structure and its metal enrichment and 2) the ionization structure and physical properties of the AGN galaxies' CGM. These objectives are both scientifically timely and yet only recently achievable, thanks to the combination of COS's high sensitivity, the compilation of large numbers of local AGN, and the development of sophisticated ionization models by our team.

  17. Modelling feedback and magnetic fields in radio galaxy evolution

    NASA Astrophysics Data System (ADS)

    Huarte-Espinosa, Martin

    2012-08-01

    The intra-cluster medium (ICM) in galaxy clusters contains magnetic fields on Mpc scales. The main probe of these cluster magnetic fields (CMFs) is the Faraday rotation of the polarized emission from radio sources that are either embedded in, or behind the ICM. Several questions are open concerning the structure and evolution of the magnetic fields in both the ICM and the radio sources. We present three-dimensional magnetohydrodynamical numerical simulations to study randomly tangled magnetic fields in the core of a cluster under the effects of light and hypersonic AGN jets. We investigate the power of the jets and carry out synthetic observations to explore the observational signatures of our model radio sources. Our polarization maps agree with the observations, and show that the magnetic structure inside the sources is shaped by the backflow of the jets. Filaments in the synthetic synchrotron emissivity maps suggest that turbulence develops in evolved sources. The polarimetry statistics correlate with time, with the viewing angle and with the jet-to-ambient density contrast. As the sources expand, the linear polarization fraction decreases and the magnetic structure inside thin sources seems more uniform than inside fat ones. Moreover, we see that the jets distort and amplify the CMFs especially at the head of the jets and that this effect correlates with the power and evolution of the jets. We find good agreement with the RM fluctuations of Hydra A. One of the most important results is that the jet-produced RM enhancements may lead to an overestimate of the strength of the CMFs by a factor of about 70%. The physics of radio source expansion may explain the flattening of the RM structure functions at large scales. The advection of metals from a central active galaxy to the ICM in a cool-core cluster is also investigated with an additional suite of hydrodynamical simulations. These metals provide information about the ICM dynamical history and of the CMFs as well

  18. X-Ray Cavities in a Sample of 83 SPT-selected Clusters of Galaxies: Tracing the Evolution of AGN Feedback in Clusters of Galaxies out to z=1.2

    NASA Astrophysics Data System (ADS)

    Hlavacek-Larrondo, J.; McDonald, M.; Benson, B. A.; Forman, W. R.; Allen, S. W.; Bleem, L. E.; Ashby, M. L. N.; Bocquet, S.; Brodwin, M.; Dietrich, J. P.; Jones, C.; Liu, J.; Reichardt, C. L.; Saliwanchik, B. R.; Saro, A.; Schrabback, T.; Song, J.; Stalder, B.; Vikhlinin, A.; Zenteno, A.

    2015-05-01

    X-ray cavities are key tracers of mechanical (or radio mode) heating arising from the active galactic nuclei (AGNs) in brightest cluster galaxies (BCGs). We report on a survey for X-ray cavities in 83 massive, high-redshift (0.4\\lt z\\lt 1.2) clusters of galaxies selected by their Sunyaev-Zel’dovich signature in the South Pole Telescope data. Based on Chandra X-ray images, we find a total of six clusters having symmetric pairs of surface brightness depressions consistent with the picture of radio jets inflating X-ray cavities in the intracluster medium (ICM). The majority of these detections are of relatively low significance and require deeper follow-up data in order to be confirmed. Further, this search will miss small (<10 kpc) X-ray cavities that are unresolved by Chandra at high (z≳ 0.5) redshift. Despite these limitations, our results suggest that the power generated by AGN feedback in BCGs has remained unchanged for over half of the age of the universe (\\gt 7 Gyr at z˜ 0.8). On average, the detected X-ray cavities have powers of (0.8-5)× {{10}45} erg {{s}-1}, enthalpies of (3-6)× {{10}59} erg, and radii of ˜17 kpc. Integrating over 7 Gyr, we find that the supermassive black holes in BCGs may have accreted 108 to several {{10}9} {{M}⊙ } of material to power these outflows. This level of accretion indicates that significant supermassive black hole growth may occur not only at early times, in the quasar era, but at late times as well. We also find that X-ray cavities at high redshift may inject an excess heat of 0.1-1.0 keV per particle into the hot ICM above and beyond the energy needed to offset cooling. Although this result needs to be confirmed, we note that the magnitude of excess heating is similar to the energy needed to preheat clusters, break self-similarity, and explain the excess entropy in hot atmospheres.

  19. Complex dynamics in the Oregonator model with linear delayed feedback

    NASA Astrophysics Data System (ADS)

    Sriram, K.; Bernard, S.

    2008-06-01

    The Belousov-Zhabotinsky (BZ) reaction can display a rich dynamics when a delayed feedback is applied. We used the Oregonator model of the oscillating BZ reaction to explore the dynamics brought about by a linear delayed feedback. The time-delayed feedback can generate a succession of complex dynamics: period-doubling bifurcation route to chaos; amplitude death; fat, wrinkled, fractal, and broken tori; and mixed-mode oscillations. We observed that this dynamics arises due to a delay-driven transition, or toggling of the system between large and small amplitude oscillations, through a canard bifurcation. We used a combination of numerical bifurcation continuation techniques and other numerical methods to explore the dynamics in the strength of feedback-delay space. We observed that the period-doubling and quasiperiodic route to chaos span a low-dimensional subspace, perhaps due to the trapping of the trajectories in the small amplitude regime near the canard; and the trapped chaotic trajectories get ejected from the small amplitude regime due to a crowding effect to generate chaotic-excitable spikes. We also qualitatively explained the observed dynamics by projecting a three-dimensional phase portrait of the delayed dynamics on the two-dimensional nullclines. This is the first instance in which it is shown that the interaction of delay and canard can bring about complex dynamics.

  20. An Axisymmetric Hydrodynamical Model for the Torus Wind in AGN. 2; X-ray Excited Funnel Flow

    NASA Technical Reports Server (NTRS)

    Dorodnitsyn, A.; Kallman, T.; Proga, D.

    2008-01-01

    We have calculated a series of models of outflows from the obscuring torus in active galactic nuclei (AGN). Our modeling assumes that the inner face of a rotationally supported torus is illuminated and heated by the intense X-rays from the inner accretion disk and black hole. As a result of such heating a strong biconical outflow is observed in our simulations. We calculate 3-dimensional hydrodynamical models, assuming axial symmetry, and including the effects of X-ray heating, ionization, and radiation pressure. We discuss the behavior of a large family of these models, their velocity fields, mass fluxes and temperature, as functions of the torus properties and X-ray flux. Synthetic warm absorber spectra are calculated, assuming pure absorption, for sample models at various inclination angles and observing times. We show that these models have mass fluxes and flow speeds which are comparable to those which have been inferred from observations of Seyfert 1 warm absorbers, and that they can produce rich absorption line spectra.

  1. AGN Obscuration Through Dusty Infrared Dominated Flows. 1; Radiation-Hydrodynamics Solution for the Wind

    NASA Technical Reports Server (NTRS)

    Dorodnitsyn, A.; Bisnovatyi-Kogan. G. S.; Kallman, T.

    2011-01-01

    We construct a radiation-hydrodynamics model for the obscuring toroidal structure in active galactic nuclei. In this model the obscuration is produced at parsec scale by a dense, dusty wind which is supported by infrared radiation pressure on dust grains. To find the distribution of radiation pressure, we numerically solve the 2D radiation transfer problem in a flux limited diffusion approximation. We iteratively couple the solution with calculations of stationary 1D models for the wind, and obtain the z-component of the velocity. Our results demonstrate that for AGN luminosities greater than 0.1 L(sub edd) external illumination can support a geometrically thick obscuration via outflows driven by infrared radiation pressure. The terminal velocity of marginally Compton-thin models (0.2 < tau(sub T) < 0.6), is comparable to or greater than the escape velocity. In Compton thick models the maximum value of the vertical component of the velocity is lower than the escape velocity, suggesting that a significant part of our torus is in the form of failed wind. The results demonstrate that obscuration via normal or failed infrared-driven winds is a viable option for the AGN torus problem and AGN unification models. Such winds can also provide an important channel for AGN feedback.

  2. Introduction of the aerosol feedback process in the model BOLCHEM

    NASA Astrophysics Data System (ADS)

    Russo, Felicita; Maurizi, Alberto; D'Isidoro, Massimo; Tampieri, Francesco

    2010-05-01

    The effect of aerosols on the climate is still one of the least understood processes in the atmospheric science. The use of models to simulate the interaction between aerosols and climate can help understanding the physical processes that rule this interaction and hopefully predicting the future effects of anthropogenic aerosols on climate. In particular regional models can help study the effect of aerosols on the atmospheric dynamics on a local scale. In the work performed here we studied the feedback of aerosols in the radiative transfer calculation using the regional model BOLCHEM. The coupled meteorology-chemistry model BOLCHEM is based on the BOLAM meteorological model. The BOLAM dynamics is based on hydrostatic primitive equations, with wind components u and v, potential temperature ?, specific humidity q, surface pressure ps, as dependent variables. The vertical coordinate σ is terrain-following with variables distributed on a non-uniformly spaced staggered Lorentz grid. In the standard configuration of the model a collection of climatological aerosol optical depth values for each aerosol species is used for the radiative transfer calculation. In the feedback exercise presented here the aerosol optical depth was calculated starting from the modeled aerosol concentrations using an approximate Mie formulation described by Evans and Fournier (Evans, B.T.N. and G.R. Fournier, Applied Optics, 29, 1990). The calculation was done separately for each species and aerosol size distribution. The refractive indexes for the different species were taken from P. Stier's work (P. Stier et al., Atmos. Chem. Phys., 5, 2005) and the aerosol extinction obtained by Mie calculation were compared with the results reported by OPAC (M. Hess et al., Bull. Am. Met. Soc., 79, 1998). Two model runs, with and without the aerosol feedback, were performed to study the effects of the feedback on meteorological parameters. As a first setup of the model runs we selected a domain over the

  3. Modeling distributed feedback GaAs-based lasers in dentistry

    NASA Astrophysics Data System (ADS)

    Shih, Meng-Mu

    2012-01-01

    Distributed-feedback gallium-arsenide-based lasers with metal-gratings can generate stable wavelength at 980nm for applications in dentistry. This model uses the periodic optical waveguide method to calculate the coupling coefficient, which is a key parameter of laser performance. This model shows how the optical, geometrical, and material parameters depending on each other and how they affect the coupling coefficients in the laser waveguides. Numerical results compare the coupling coefficients of 980 nm lasers with those of 810 nm lasers. The modeling processes, including results, discussions, and physical interpretations, help to design and analyze lasers for more clinical and research applications in dentistry.

  4. THERMAL AND RADIATIVE ACTIVE GALACTIC NUCLEUS FEEDBACK HAVE A LIMITED IMPACT ON STAR FORMATION IN HIGH-REDSHIFT GALAXIES

    SciTech Connect

    Roos, Orianne; Juneau, Stéphanie; Bournaud, Frédéric; Gabor, Jared M.

    2015-02-10

    The effects of active galactic nuclei (AGNs) on their host galaxies depend on the coupling between the injected energy and the interstellar medium (ISM). Here, we model and quantify the impact of long-range AGN ionizing radiation—in addition to the often considered small-scale energy deposition—on the physical state of the multi-phase ISM of the host galaxy and on its total star formation rate (SFR). We formulate an AGN spectral energy distribution matched with observations, which we use with the radiative transfer (RT) code Cloudy to compute AGN ionization in a simulated high-redshift disk galaxy. We use a high-resolution (∼6 pc) simulation including standard thermal AGN feedback and calculate RT in post-processing. Surprisingly, while these models produce significant AGN-driven outflows, we find that AGN ionizing radiation and heating reduce the SFR by a few percent at most for a quasar luminosity (L {sub bol} = 10{sup 46.5} erg s{sup –1}). Although the circumgalactic gaseous halo can be kept almost entirely ionized by the AGN, most star-forming clouds (n ≳ 10{sup 2} {sup –} {sup 3} cm{sup –3}) and even the reservoirs of cool atomic gas (n ∼ 0.3-10 cm{sup –3})—which are the sites of future star formation (SF; 100-200 Myr), are generally too dense to be significantly affected. Our analysis ignores any absorption from a putative torus, making our results upper limits on the effects of ionizing radiation. Therefore, while the AGN-driven outflows can remove substantial amounts of gas in the long term, the impact of AGN feedback on the SF efficiency in the interstellar gas in high-redshift galaxies is marginal, even when long-range radiative effects are accounted for.

  5. Quantifying and Reducing Climate-Carbon Cycle Feedback Uncertainties: Analysis of CMIP5 Earth System Model Feedbacks

    NASA Astrophysics Data System (ADS)

    Hoffman, F. M.; Randerson, J. T.

    2011-12-01

    Increasing atmospheric carbon dioxide (CO2) concentrations, resulting from anthropogenic perturbation of the global carbon cycle, are altering the Earth's climate. Climate change is expected to induce feedbacks on future CO2 concentrations and on the climate system itself. These feedbacks are highly uncertain, potentially large, and difficult to predict using Earth System Models (ESMs). In order to reduce the range of uncertainty in climate predictions, model representation of feedbacks must be improved through comparisons with contemporary observations. In this study, we quantify the terrestrial and ocean carbon storage sensitivity to climate and atmospheric CO2 concentration of ESMs participating in the Climate Model Intercomparison Project Phase 5 (CMIP5) following the methodology of Friedlingstein et al. (2006). In order to evaluate the models' abilities to capture the 21st century carbon cycle and to offer possible constraints on the modeled feedback strengths, comparisons with contemporary observations will be made over three different time scales: seasonal to annual, interannual to decadal, and decadal to centennial. A conceptual framework for evaluating climate-carbon cycle feedbacks in global models--employing best-available observational data--will be presented, along with results from application of this framework to CMIP5 model output. Included in the analysis will be prototype model evaluation benchmarks of the carbon cycle being designed for the International Land Model Benchmarking (ILAMB) Project.

  6. Modeling mutual feedback between users and recommender systems

    NASA Astrophysics Data System (ADS)

    Zeng, An; Yeung, Chi Ho; Medo, Matúš; Zhang, Yi-Cheng

    2015-07-01

    Recommender systems daily influence our decisions on the Internet. While considerable attention has been given to issues such as recommendation accuracy and user privacy, the long-term mutual feedback between a recommender system and the decisions of its users has been neglected so far. We propose here a model of network evolution which allows us to study the complex dynamics induced by this feedback, including the hysteresis effect which is typical for systems with non-linear dynamics. Despite the popular belief that recommendation helps users to discover new things, we find that the long-term use of recommendation can contribute to the rise of extremely popular items and thus ultimately narrow the user choice. These results are supported by measurements of the time evolution of item popularity inequality in real systems. We show that this adverse effect of recommendation can be tamed by sacrificing part of short-term recommendation accuracy.

  7. Modelling human balance using switched systems with linear feedback control.

    PubMed

    Kowalczyk, Piotr; Glendinning, Paul; Brown, Martin; Medrano-Cerda, Gustavo; Dallali, Houman; Shapiro, Jonathan

    2012-02-01

    We are interested in understanding the mechanisms behind and the character of the sway motion of healthy human subjects during quiet standing. We assume that a human body can be modelled as a single-link inverted pendulum, and the balance is achieved using linear feedback control. Using these assumptions, we derive a switched model which we then investigate. Stable periodic motions (limit cycles) about an upright position are found. The existence of these limit cycles is studied as a function of system parameters. The exploration of the parameter space leads to the detection of multi-stability and homoclinic bifurcations. PMID:21697168

  8. THE EFFECTS OF X-RAY FEEDBACK FROM ACTIVE GALACTIC NUCLEI ON HOST GALAXY EVOLUTION

    SciTech Connect

    Hambrick, D. Clay; Ostriker, Jeremiah P.; Naab, Thorsten; Johansson, Peter H.

    2011-09-01

    Hydrodynamic simulations of galaxies with active galactic nuclei (AGNs) have typically employed feedback that is purely local, i.e., an injection of energy to the immediate neighborhood of the black hole (BH). We perform GADGET-2 simulations of massive elliptical galaxies with an additional feedback component: an observationally calibrated X-ray radiation field which emanates from the BH and heats gas out to large radii from the galaxy center. We find that including the heating and radiation pressure associated with this X-ray flux in our simulations enhances the effects which are commonly reported from AGN feedback. This new feedback model is twice as effective as traditional feedback at suppressing star formation, produces three times less star formation in the last 6 Gyr, and modestly lowers the final BH mass (30%). It is also significantly more effective than an X-ray background in reducing the number of satellite galaxies.

  9. XMM tests galaxy evolutions models

    NASA Astrophysics Data System (ADS)

    Miniati, Francesco

    2011-10-01

    Current models of galaxy evolution rely critically on feedback supernova and AGN feedback processes. The energy released by past star formation and AGN activity imprints a fossil record on the thermodynamic properties of the intra-group-medium (IGM). This can be decoded by studying the X-ray emission. for an unbiased sample of groups with known galaxy and AGN properties. Therefore we propose an X-ray survey with XMM-Newton for 255 ksec to observe 17 galaxy groups with Msim10(13) M_odot selected from our Zurich ENvironmental Survey that host >8 members.

  10. On the physical origin of AGN outflow driving mechanisms

    NASA Astrophysics Data System (ADS)

    Ishibashi, Wako

    2016-07-01

    Super-massive black holes in active galactic nuclei (AGN) respond to the accretion process by feeding back energy and momentum into the surrounding environment. Galaxy-scale outflows are thought to provide the physical link connecting the small scales of the central black hole to the large scales of the host galaxy. Such powerful outflows are now starting to be commonly observed, and have been considered as a proof of AGN feedback in action. However, the physical origin of the mechanism driving the observed outflows is still unclear, and whether it is due to energy-driving or radiation-driving is a source of much debate in the literature. We consider AGN feedback driven by radiation pressure on dust, and show that AGN radiative feedback is capable of driving powerful outflows on galactic scales. In particular, we can obtain outflowing shells with high velocity and large momentum flux, by properly taking into account the effects of radiation trapping. Alternatively, the observed outflow characteristics may be significantly biased by AGN variability. I will discuss the resulting implications in the global context of black hole accretion-AGN feedback coupling.

  11. Modeling energy intake by adding homeostatic feedback and drug intervention.

    PubMed

    Gennemark, Peter; Hjorth, Stephan; Gabrielsson, Johan

    2015-02-01

    Energy intake (EI) is a pivotal biomarker used in quantification approaches to metabolic disease processes such as obesity, diabetes, and growth disorders. Eating behavior is however under both short-term and long-term control. This control system manifests itself as tolerance and rebound phenomena in EI, when challenged by drug treatment or diet restriction. The paper describes a model with the capability to capture physiological counter-regulatory feedback actions triggered by energy imbalances. This feedback is general as it handles tolerance to both increases and decreases in EI, and works in both acute and chronic settings. A drug mechanism function inhibits (or stimulates) EI. The deviation of EI relative to a reference level (set-point) serves as input to a non-linear appetite control signal which in turn impacts EI in parallel to the drug intervention. Three examples demonstrate the potential usefulness of the model in both acute and chronic dosing situations. The model shifts the predicted concentration-response relationship rightwardly at lower concentrations, in contrast to models that do not handle functional adaptation. A fourth example further shows that the model may qualitatively explain differences in rate and extent of adaptation in observed EI and its concomitants in both rodents and humans. PMID:25388764

  12. Modeling active galactic nucleus feedback in cool-core clusters: The formation of cold clumps

    SciTech Connect

    Li, Yuan; Bryan, Greg L.

    2014-07-10

    We perform high-resolution (15-30 pc) adaptive mesh simulations to study the impact of momentum-driven active galactic nucleus (AGN) feedback in cool-core clusters, focusing in this paper on the formation of cold clumps. The feedback is jet-driven with an energy determined by the amount of cold gas within 500 pc of the super-massive black hole. When the intracluster medium in the core of the cluster becomes marginally stable to radiative cooling, with the thermal instability to the free-fall timescale ratio t{sub TI}/t{sub ff} < 3-10, cold clumps of gas start to form along the propagation direction of the AGN jets. By tracing the particles in the simulations, we find that these cold clumps originate from low entropy (but still hot) gas that is accelerated by the jet to outward radial velocities of a few hundred km s{sup –1}. This gas is out of hydrostatic equilibrium and so can cool. The clumps then grow larger as they decelerate and fall toward the center of the cluster, eventually being accreted onto the super-massive black hole. The general morphology, spatial distribution, and estimated Hα morphology of the clumps are in reasonable agreement with observations, although we do not fully replicate the filamentary morphology of the clumps seen in the observations, probably due to missing physics.

  13. Modeling Channelization in Coastal Wetlands with Ecological Feedbacks

    NASA Astrophysics Data System (ADS)

    Hughes, Z. J.; Mahadevan, A.; Pennings, S.; FitzGerald, D.

    2014-12-01

    In coastal wetlands in Georgia and South Carolina, dendritic channel networks are actively incising headward at the rate of nearly 2 m/yr. The future geomorphic evolution of these marshes remains in question as rates of relative sea-level rise increase. Our objective is to understand the mechanisms that lead to the evolution of these channel networks through field observations and modeling. We model the geomorphological evolution of tidal creeks by viewing the wetland as a permeable medium. The porosity of the medium affects its hydraulic conductivity, which in turn is altered by erosion. Our multiphase model spontaneously generates channelization and branching networks through flow and erosion. In our field studies, we find that crabs play an active role in grazing vegetation and in the bioturbation of sediments. These effects are incorporated in our model based on field and laboratory observations of crab behavior and its effects on the marsh. We find the erosional patterns and channelization are significantly altered by the faunal feedback. Crabs enhance the growth of channels, inducing the headward erosion of creeks where flow-induced stresses are weakest. They are instrumental in generating high rates of creek extension, which channelize the marsh more effectively in response to sea-level rise. This indicates that the evolution of coastal wetlands is responding to interactions between physics and ecology and highlights the importance of the faunal contribution to these feedbacks.

  14. Neuromechanical models for insect locomotion: Stability, maneuverability, and proprioceptive feedback

    NASA Astrophysics Data System (ADS)

    Kukillaya, R.; Proctor, J.; Holmes, P.

    2009-06-01

    We describe a hierarchy of models for legged locomotion, emphasizing relationships among feedforward (preflexive) stability, maneuverability, and reflexive feedback. We focus on a hexapedal geometry representative of insect locomotion in the ground plane that includes a neural central pattern generator circuit, nonlinear muscles, and a representative proprioceptive sensory pathway. Although these components of the model are rather complex, neglect of leg mass yields a neuromechanical system with only three degrees of freedom, and numerical simulations coupled with a Poincaré map analysis shows that the feedforward dynamics is strongly stable, apart from one relatively slow mode and a neutral mode in body yaw angle. These modes moderate high frequency perturbations, producing slow heading changes that can be corrected by a stride-to-stride steering strategy. We show that the model's response to a lateral impulsive perturbation closely matches that of a cockroach subject to a similar impulse. We also describe preliminary studies of proprioceptive leg force feedback, showing how a reflexive pathway can reinforce the preflexive stability inherent in the system.

  15. The origin of UV-optical variability in AGN and test of disc models: XMM-Newton and ground-based observations of NGC 4395

    NASA Astrophysics Data System (ADS)

    McHardy, I. M.; Connolly, S. D.; Peterson, B. M.; Bieryla, A.; Chand, H.; Elvis, M. S.; Emmanoulopoulos, D.; Falco, E.; Gandhi, P.; Kaspi, S.; Latham, D.; Lira, P.; McCully, C.; Netzer, H.; Uemura, M.

    2016-05-01

    The origin of short timescale (weeks/months) variability of AGN, whether due to intrinsic disc variations or reprocessing of X-ray emission by a surrounding accretion disc, has been a puzzle for many years. However recently a number of observational programmes, particularly of NGC 5548 with Swift, have shown that the UV/optical variations lag behind the X-ray variations in a manner strongly supportive of X-ray reprocessing. Somewhat surprisingly, the implied size of the accretion disc is ∼3 times greater than expected from a standard, smooth, Shakura-Sunyaev thin disc model. Although the difference may be explained by a clumpy accretion disc, it is not clear whether the difference will occur in all AGN or whether it may change as, eg, a function of black hole mass, accretion rate, or disc temperature. Measurements of interband lags for most AGN require long timescale monitoring, which is hard to arrange. However for low mass (< 106 M⊙) AGN, the combination of XMM-Newton EPIC (X-rays) with the optical monitor in fast readout mode allows an X-ray/UV-optical lag to be measured within a single long observation. Here we summarise previous related observations and report on XMM-Newton observations of NGC 4395 (mass 100 times lower, accretion rate ∼20 times lower than for NGC 5548). We find that the UVW1 lags the X-rays by ∼ 470 s. Simultaneous observations at 6 different ground based observatories also allowed the g-band lag (∼ 800s) to be measured. These observations are in agreement with X-ray reprocessing but initial analysis suggests that, for NGC 4395, they do not differ markedly from the predictions of the standard thin disc model.

  16. The Cosmological Impact of AGN Outflows: Measuring Absolute Abundances and Kinetic Luminosities

    NASA Astrophysics Data System (ADS)

    Arav, Nahum

    2009-07-01

    AGN outflows are increasingly invoked as a major contributor to the formation and evolution of supermassive black holes, their host galaxies, the surrounding IGM, and cluster cooling flows. Our HST/COS proposal will determine reliable absolute chemical abundances in six AGN outflows, which influences several of the processes mentioned above. To date there is only one such determination, done by our team on Mrk 279 using 16 HST/STIS orbits and 100 ksec of FUSE time. The advent of COS and its high sensitivity allows us to choose among fainter objects at redshifts high enough to preclude the need for FUSE. This will allow us to determine the absolute abundances for six AGN {all fainter than Mrk 279} using only 40 HST COS orbits. This will put abundances studies in AGN on a firm footing, an elusive goal for the past four decades. In addition, prior FUSE observations of four of these targets indicate that it is probable that the COS observations will detect troughs from excited levels of C III. These will allow us to measure the distances of the outflows and thereby determine their kinetic luminosity, a major goal in AGN feedback research. We will use our state of the art column density extraction methods and velocity-dependent photoionization models to determine the abundances and kinetic luminosity. Previous AGN outflow projects suffered from the constraints of deciding what science we could do using ONE of the handful of bright targets that were observable. With COS we can choose the best sample for our experiment. As an added bonus, most of the spectral range of our targets has not been observed previously, greatly increasing the discovery phase space.

  17. Tidal Downsizing model - IV. Destructive feedback in planets

    NASA Astrophysics Data System (ADS)

    Nayakshin, Sergei

    2016-09-01

    The role of negative feedback from a massive solid core on its massive gas envelope in the Tidal Downsizing scenario of planet formation is investigated via one-dimensional planet evolution models followed by population synthesis calculations. It is shown that cores more massive than ˜10 M⊕ release enough energy to reverse contraction of their parent gas envelopes, culminating in their destruction. This process may help to explain why observed gas giant planets are so rare, why massive cores are so ubiquitous, and why there is a sharp rollover in the core mass function above ˜20 M⊕. Additionally, the short time-scales with which these massive cores are assembled in TD may help explain formation route of Uranus, Neptune and the suspected HL Tau planets. Given the negative role of cores in assembly of gas giants in the model, an antimony is found between massive cores and gas giants: cores in survived gas giant planets are on average less massive than cores free of massive envelopes. In rare circumstances when core feedback self-regulates, extremely metal-rich gas giants, such as CoRoT-20b, a gas giant made of heavy elements by up to ˜50 per cent, can be made.

  18. Decreased specific star formation rates in AGN host galaxies

    NASA Astrophysics Data System (ADS)

    Shimizu, T. Taro; Mushotzky, Richard F.; Meléndez, Marcio; Koss, Michael; Rosario, David J.

    2015-09-01

    We investigate the location of an ultra-hard X-ray selected sample of active galactic nuclei (AGN) from the Swift Burst Alert Telescope (BAT) catalogue with respect to the main sequence (MS) of star-forming galaxies using Herschel-based measurements of the star formation rate (SFR) and M*'s from Sloan Digital Sky Survey photometry where the AGN contribution has been carefully removed. We construct the MS with galaxies from the Herschel Reference Survey and Herschel Stripe 82 Survey using the exact same methods to measure the SFR and M* as the Swift/BAT AGN. We find that a large fraction of the Swift/BAT AGN lie below the MS indicating decreased specific SFR (sSFR) compared to non-AGN galaxies. The Swift/BAT AGN are then compared to a high-mass galaxy sample (CO Legacy Database for GALEX Arecibo SDSS Survey, COLD GASS), where we find a similarity between the AGN in COLD GASS and the Swift/BAT AGN. Both samples of AGN lie firmly between star-forming galaxies on the MS and quiescent galaxies far below the MS. However, we find no relationship between the X-ray luminosity and distance from the MS. While the morphological distribution of the BAT AGN is more similar to star-forming galaxies, the sSFR of each morphology is more similar to the COLD GASS AGN. The merger fraction in the BAT AGN is much higher than the COLD GASS AGN and star-forming galaxies and is related to distance from the MS. These results support a model in which bright AGN tend to be in high-mass star-forming galaxies in the process of quenching which eventually starves the supermassive black hole itself.

  19. Model reduction and feedback control of transitional channel flow

    NASA Astrophysics Data System (ADS)

    Ilak, Milos

    This dissertation examines the use of reduced-order models for design of linear feedback controllers for fluid flows. The focus is on transitional channel flow, a canonical shear flow case with a simple geometry yet complex dynamics. Reduced-order models of the linearized Navier-Stokes equations, which describe the evolution of perturbations in transitional channel flow, are computed using two methods for snapshot-based balanced truncation, Balanced Proper Orthogonal Decomposition (BPOD) and Eigensystem Realization Algorithm (ERA). The performance of these models in feedback control is evaluated in both linearized and nonlinear Direct Numerical Simulations (DNS) of channel flow. The first part of the dissertation describes the application of BPOD to very large systems, and the detailed evaluation of the resulting reduced-order models. Exact balanced truncation, a standard method from control theory, is not computationally tractable for very large systems, such as those typically encountered in fluid flow simulations. The BPOD method, introduced by Rowley (2005), provides a close approximation. We first show that the approximation is indeed close by applying the method to a 1-D linear perturbation to channel flow at a single spatial wavenumber pair, for which exact balanced truncation is tractable. Next, as the first application of BPOD to a very high-dimensional linear system, we show that reduced-order BPOD models of a localized 3-D perturbation capture the dynamics very well. Moreover, the BPOD models significantly outperform standard Proper Orthogonal Decomposition (POD) models, as illustrated by a striking example where models using the POD modes that capture most of the perturbation energy fail to capture the perturbation dynamics. Next, reduced-order models of a complete control system for linearized channel flow are obtained using ERA, a computationally efficient method that results in the same reduced-order models as BPOD. Linear Quadratic Gaussian (LQG

  20. THE LICK AGN MONITORING PROJECT 2011: DYNAMICAL MODELING OF THE BROAD-LINE REGION IN Mrk 50

    SciTech Connect

    Pancoast, Anna; Brewer, Brendon J.; Treu, Tommaso; Bennert, Vardha N.; Sand, David J.; Barth, Aaron J.; Cooper, Michael C.; Canalizo, Gabriela; Filippenko, Alexei V.; Li, Weidong; Cenko, S. Bradley; Clubb, Kelsey I.; Gates, Elinor L.; Greene, Jenny E.; Malkan, Matthew A.; Stern, Daniel; Assef, Roberto J.; Woo, Jong-Hak; Bae, Hyun-Jin; Buehler, Tabitha; and others

    2012-07-20

    We present dynamical modeling of the broad-line region (BLR) in the Seyfert 1 galaxy Mrk 50 using reverberation mapping data taken as part of the Lick AGN Monitoring Project (LAMP) 2011. We model the reverberation mapping data directly, constraining the geometry and kinematics of the BLR, as well as deriving a black hole mass estimate that does not depend on a normalizing factor or virial coefficient. We find that the geometry of the BLR in Mrk 50 is a nearly face-on thick disk, with a mean radius of 9.6{sup +1.2}{sub -0.9} light days, a width of the BLR of 6.9{sup +1.2}{sub -1.1} light days, and a disk opening angle of 25 {+-} 10 deg above the plane. We also constrain the inclination angle to be 9{sup +7}{sub -5} deg, close to face-on. Finally, the black hole mass of Mrk 50 is inferred to be log{sub 10}(M{sub BH}/M{sub Sun }) = 7.57{sup +0.44}{sub -0.27}. By comparison to the virial black hole mass estimate from traditional reverberation mapping analysis, we find the normalizing constant (virial coefficient) to be log{sub 10} f = 0.78{sup +0.44}{sub -0.27}, consistent with the commonly adopted mean value of 0.74 based on aligning the M{sub BH}-{sigma}* relation for active galactic nuclei and quiescent galaxies. While our dynamical model includes the possibility of a net inflow or outflow in the BLR, we cannot distinguish between these two scenarios.

  1. Feedbacks Between Numerical and Analytical Models in Hydrogeology

    NASA Astrophysics Data System (ADS)

    Zlotnik, V. A.; Cardenas, M. B.; Toundykov, D.; Cohn, S.

    2012-12-01

    Hydrogeology is a relatively young discipline which combines elements of Earth science and engineering. Mature fundamental disciplines (e.g., physics, chemistry, fluid mechanics) have centuries-long history of mathematical modeling even prior to discovery of Darcy's law. Thus, in hydrogeology, relatively few classic analytical models (such those by Theis, Polubarinova-Kochina, Philip, Toth, Henry, Dagan, Neuman) were developed by the early 1970's. The advent of computers and practical demands refocused mathematical models towards numerical techniques. With more diverse but less mathematically-oriented training, most hydrogeologists shifted from analytical methods to use of standardized computational software. Spatial variability in internal properties and external boundary conditions and geometry, and the added complexity of chemical and biological processes will remain major challenges for analytical modeling. Possibly, analytical techniques will play a subordinate role to numerical approaches in many applications. On the other hand, the rise of analytical element modeling of groundwater flow is a strong alternative to numerical models when data demand and computational efficiency is considered. The hallmark of analytical models - transparency and accuracy - will remain indispensable for scientific exploration of complex phenomena and for benchmarking numerical models. Therefore, there will always be feedbacks and complementarities between numerical and analytical techniques, as well as a certain ideological schism among various views to modeling. We illustrate the idea of feedbacks by reviewing evolution of Joszef Toth's analytical model of gravity driven flow systems. Toth's (1963) approach was to reduce the flow domain to a rectangle which allowed for closed-form solution of the governing equations. Succeeding numerical finite-element models by Freeze and Witherspoon (1966-1968) explored the effects of geometry and heterogeneity on regional groundwater flow

  2. The Starburst-AGN Connection under the Multiwavelength Limelight

    NASA Astrophysics Data System (ADS)

    Guainazzi, Matteo

    2011-11-01

    Since the discovery of a tight relation between supermassive black hole masses, the bulge luminosity, and the stellar velocity dispersion in the local universe galaxies, mounting experimental evidence has been collected pointing to a connection between nuclear activity and star formation over a wide range of redshifts. Although a growing number of galaxies from different samples exhibit simultaneous starburst and AGN phenomenology, it is still a matter of debate whether this is the smoking gun of a causal relation between them, and, if so, with which trend. Basic issues in modern astrophysics, such as the evolution of galaxies and supermassive black holes, AGN feeding and feedback to the interstellar and intergalactic medium, as well as the role played by the environment on the star formation history are related to this "Starburst-AGN Connection". This Workshop aims at gathering observational and theoretical astronomers so as to answer the following questions: * The "Starburst-AGN Connection": A causal relation? * "Starburst-AGN Connection" at low and high redshift: any evidence for evolution? * Is there a connection between AGN obscuration and star formation? * In which way are the star formation and AGN phenomena affected by the environment? * Do stars contribute to AGN fueling? Multiwavelength observations in the last decade have given a paramount contribution to improve our understanding in this field. The Workshop will build on this panoptic view, and aims at contributing to the scientific case of future ground-based and space large observatories.

  3. Computational Modeling of Morphogenesis Regulated by Mechanical Feedback

    PubMed Central

    Ramasubramanian, Ashok; Taber, Larry A.

    2008-01-01

    Mechanical forces cause changes in form during embryogenesis and likely play a role in regulating these changes. This paper explores the idea that changes in homeostatic tissue stress (target stress), possibly modulated by genes, drive some morphogenetic processes. Computational models are presented to illustrate how regional variations in target stress can cause a range of complex behaviors involving the bending of epithelia. These models include growth and cytoskeletal contraction regulated by stress-based mechanical feedback. All simulations were carried out using the commercial finite element code ABAQUS, with growth and contraction included by modifying the zero-stress state in the material constitutive relations. Results presented for bending of bilayered beams and invagination of cylindrical and spherical shells provide insight into some of the mechanical aspects that must be considered in studying morphogenetic mechanisms. PMID:17318485

  4. Modeling and sensory feedback control for space manipulators

    NASA Technical Reports Server (NTRS)

    Masutani, Yasuhiro; Miyazaki, Fumio; Arimoto, Suguru

    1989-01-01

    The positioning control problem of the endtip of space manipulators whose base are uncontrolled is examined. In such a case, the conventional control method for industrial robots based on a local feedback at each joint is not applicable, because a solution of the joint displacements that satisfies a given position and orientation of the endtip is not decided uniquely. A sensory feedback control scheme for space manipulators based on an artificial potential defined in a task-oriented coordinates is proposed. Using this scheme, the controller can easily determine the input torque of each joint from the data of an external sensor such as a visual device. Since the external sensor is mounted on the unfixed base, the manipulator must track the moving image of the target in sensor coordinates. Moreover the dynamics of the base and the manipulator are interactive. However, the endtip is proven to asymptotically approach the stationary target in an inertial coordinate frame by the Liapunov's method. Finally results of computer simulation for a 6-link space manipulator model show the effectiveness of the proposed scheme.

  5. A feedback model for the source of auroral kilometric radiation

    NASA Technical Reports Server (NTRS)

    Calvert, W.

    1982-01-01

    It is noted that in order to compensate for the wave refraction inside the source, the boundary reflection surfaces must converge with altitude, and this implies that the most likely auroral kilometric radiation source would be a thin, local density enhancement, since the refractive index contours at its boundaries would be expected to slope inward. The ISEE observations of multiple spectral components, which are attributed to separate oscillations at different altitudes in the same enhancement, indicate a source thickness as small as 25 km and an internal wave growth threshold of roughly 40 dB, rather than the 70-120 dB previously believed necessary to account for auroral kilometric radiation without feedback. What is considered more significant is that the feedback model accounts for numerous aspects of the auroral kilometric radiation behavior, predicts emission at the wave growth saturation level, and leads to the conclusion that auroral kilometric radiation originates at many compact sites, each emitting a nearly monochromatic wave.

  6. The Angular Clustering of WISE-Selected AGN: Different Haloes for Obscured and Unobscured AGN

    NASA Astrophysics Data System (ADS)

    Yan, Lin

    2015-08-01

    We calculate the angular correlation function for a sample of 170,000 AGN extracted from the Wide-field Infrared Survey Explorer (WISE) catalog, selected to have red mid-IR colors (W1 - W2 > 0.8) and 4.6 micron flux densities brighter than 0.14 mJy). The sample is expected to be >90% reliable at identifying AGN, and to have a mean redshift of z=1.1. In total, the angular clustering of WISE-AGN is roughly similar to that of optical AGN. We cross-match these objects with the photometric SDSS catalog and distinguish obscured sources with (r - W2) > 6 from bluer, unobscured AGN. Obscured sources present a higher clustering signal than unobscured sources. Since the host galaxy morphologies of obscured AGN are not typical red sequence elliptical galaxies and show disks in many cases, it is unlikely that the increased clustering strength of the obscured population is driven by a host galaxy segregation bias. By using relatively complete redshift distributions from the COSMOS survey, we find obscured sources at mean redshift z=0.9 have a bias of b = 2.9 \\pm 0.6 and are hosted in dark matter halos with a typical mass of log(M/M_odot)~13.5. In contrast, unobscured AGN at z~1.1 have a bias of b = 1.6 \\pm 0.6 and inhabit halos of log(M/M_odot)~12.4. These findings suggest that obscured AGN inhabit denser environments than unobscured AGN, and are difficult to reconcile with the simplest AGN unification models, where obscuration is driven solely by orientation.

  7. Neutrinos from AGN

    NASA Technical Reports Server (NTRS)

    Kazanas, Demosthenes; White, Nicholas E. (Technical Monitor)

    2000-01-01

    The great penetrating power of neutrinos makes them ideal probe of astrophysical sites and conditions inaccessible to other forms of radiation. These are the centers of stars (collapsing or not) and the centers of Active Galactic Nuclei (AGN). It has been suggested that AGN presented a very promising source of high energy neutrinos, possibly detectable by underwater neutrino detectors. This paper reviews the evolution of ideas concerning the emission of neutrinos from AGN in view of the more recent developments in gamma-ray astronomy and their implications for the neutrino emission from these class of objects.

  8. Cell cultures as models of cardiac mechanoelectric feedback

    PubMed Central

    Zhang, Yibing; Sekar, Rajesh B.; McCulloch, Andrew D.; Tung, Leslie

    2008-01-01

    Although stretch-activated currents have been extensively studied in isolated cells and intact hearts in the context of mechanoelectric feedback (MEF) in the heart, quantitative data regarding other mechanical parameters such as pressure, shear, bending, etc, are still lacking at the multicellular level. Cultured cardiac cell monolayers have been used increasingly in the past decade as an in vitro model for the studies of fundamental mechanisms that underlie normal and pathological electrophysiology at the tissue level. Optical mapping makes possible multisite recording and analysis of action potentials and wavefront propagation, suitable for monitoring the electrophysiological activity of the cardiac cell monolayer under a wide variety of controlled mechanical conditions. In this paper, we review methodologies that have been developed or could be used to mechanically perturb cell monolayers, and present some new results on the acute effects of pressure, shear stress and anisotropic strain on cultured neonatal rat ventricular myocyte (NRVM) monolayers. PMID:18384846

  9. Spectral Energy Distributions of Type 1 AGNs

    NASA Astrophysics Data System (ADS)

    Hao, Heng

    The spectral energy distributions (SEDs) of active galactic nuclei (AGNs) are essential to understand the physics of supermassive black holes (SMBHs) and their host galaxies. This thesis present a detailed study of AGN SED shapes in the optical-near infrared bands (0.3--3microm) for 413 X-ray selected Type 1 AGNs from the XMM-COSMOS Survey. We define a useful near-IR/optical index-index ('color-color') diagram to investigate the mixture of AGN continuum, host galaxy and reddening contributions. We found that ˜90% of the AGNs lie on mixing curves between the Elvis et al. (1994) mean AGN SED (E94) and a host galaxy, with only the modest reddening [E(B-V)=0.1--0.2] expected in type 1 AGNs. Lower luminosity and Eddington ratio objects have more host galaxy, as expected. The E94 template is remarkably good in describing the SED shape in the 0.3--3microrn decade of the spectrum over a range of 3.2 dex in LOPT, 2.7 dex in L/LEdd, and for redshifts up to 3. The AGN phenomenon is thus insensitive to absolute or relative accretion rate and to cosmic time. However, 10% of the AGNs are inconsistent with any AGN+host+reddening mix. These AGNs have weak or non-existent near-IR bumps, suggesting a lack of the hot dust characteristic of AGNs. The fraction of these hot-dust-poor AGNs evolves with redshift from 6% at low redshift (z < 2) to 20% at moderately high redshift (2 < z < 3.5). A similar fraction of HDP quasars are found in the Elvis et al. 1994 (BQS) and Richards et al. 2006 (SDSS) samples. The 1--3microm emission of the HDP quasars is a factor 2--4 smaller than the typical E94 AGN SED. The implied torus covering factor is 2%--29%, well below the 75% required by unified models. The weak hot dust emission seems to expose an extension of the accretion disk continuum in some of AGNs. For these, we estimate the outer edge of their accretion disks to lie at ˜104 Schwarzschild radii, more than ten times the gravitational stability radii. Either the host-dust is destroyed

  10. Feedback control by online learning an inverse model.

    PubMed

    Waegeman, Tim; Wyffels, Francis; Schrauwen, Francis

    2012-10-01

    A model, predictor, or error estimator is often used by a feedback controller to control a plant. Creating such a model is difficult when the plant exhibits nonlinear behavior. In this paper, a novel online learning control framework is proposed that does not require explicit knowledge about the plant. This framework uses two learning modules, one for creating an inverse model, and the other for actually controlling the plant. Except for their inputs, they are identical. The inverse model learns by the exploration performed by the not yet fully trained controller, while the actual controller is based on the currently learned model. The proposed framework allows fast online learning of an accurate controller. The controller can be applied on a broad range of tasks with different dynamic characteristics. We validate this claim by applying our control framework on several control tasks: 1) the heating tank problem (slow nonlinear dynamics); 2) flight pitch control (slow linear dynamics); and 3) the balancing problem of a double inverted pendulum (fast linear and nonlinear dynamics). The results of these experiments show that fast learning and accurate control can be achieved. Furthermore, a comparison is made with some classical control approaches, and observations concerning convergence and stability are made. PMID:24808008

  11. Steps Toward Unveiling the True Population of AGN: Photometric Selection of Broad-Line AGN

    NASA Astrophysics Data System (ADS)

    Schneider, Evan; Impey, C.

    2012-01-01

    We present an AGN selection technique that enables identification of broad-line AGN using only photometric data. An extension of infrared selection techniques, our method involves fitting a given spectral energy distribution with a model consisting of three physically motivated components: infrared power law emission, optical accretion disk emission, and host galaxy emission. Each component can be varied in intensity, and a reduced chi-square minimization routine is used to determine the optimum parameters for each object. Using this model, both broad- and narrow-line AGN are seen to fall within discrete ranges of parameter space that have plausible bounds, allowing physical trends with luminosity and redshift to be determined. Based on a fiducial sample of AGN from the catalog of Trump et al. (2009), we find the region occupied by broad-line AGN to be distinct from that of quiescent or star-bursting galaxies. Because this technique relies only on photometry, it will allow us to find AGN at fainter magnitudes than are accessible in spectroscopic surveys, and thus probe a population of less luminous and/or higher redshift objects. With the vast availability of photometric data in large surveys, this technique should have broad applicability and result in large samples that will complement X-ray AGN catalogs.

  12. A feedback model of magnetron sputtering plasmas in HIPIMS

    NASA Astrophysics Data System (ADS)

    Ross, A. E.; Ganesan, R.; Bilek, M. M. M.; McKenzie, D. R.

    2015-04-01

    We present a 1D feedback model that captures the essential elements of plasma pulse initiation and is useful for control and diagnostics of sputtering plasmas. Our model falls into the class of single-species population models with recruitment and time delay, which show no oscillatory behaviour. The model can reproduce essential features of published time-current traces from plasma discharges and is useful to determine the key parameters affecting the evolution of the discharge. We include the external circuit and we focus on the time evolution of the current as a function of the applied voltage and the plasma parameters. We find the necessity of a nonlinear loss term in the time-dependent plasma ion population to ensure a stable discharge, and we show that a higher secondary electron emission coefficient reduces the time delay for current initiation. We report that I-V characteristics in the plateau region, where it exists, fit a power curve of the form I = kVn, where n is influenced most strongly by the nonlinear loss term.

  13. Evidence for Ultra-Fast Outflows in Radio-Quiet AGNs: III - Location and Energetics

    NASA Technical Reports Server (NTRS)

    Tombesi, F.; Cappi, M.; Reeves, J. N.; Braito, V.

    2012-01-01

    Using the results of a previous X-ray photo-ionization modelling of blue-shifted Fe K absorption lines on a sample of 42 local radio-quiet AGNs observed with XMM-Newton, in this letter we estimate the location and energetics of the associated ultrafast outflows (UFOs). Due to significant uncertainties, we are essentially able to place only lower/upper limits. On average, their location is in the interval approx.0.0003-0.03pc (approx.10(exp 2)-10(exp 4)tau(sub s) from the central black hole, consistent with what is expected for accretion disk winds/outflows. The mass outflow rates are constrained between approx.0.01- 1 Stellar Mass/y, corresponding to approx. or >5-10% of the accretion rates. The average lower-upper limits on the mechanical power are logE(sub K) approx. or = 42.6-44.6 erg/s. However, the minimum possible value of the ratio between the mechanical power and bolometric luminosity is constrained to be comparable or higher than the minimum required by simulations of feedback induced by winds/outflows. Therefore, this work demonstrates that UFOs are indeed capable to provide a significant contribution to the AGN r.osmological feedback, in agreement with theoretical expectations and the recent observation of interactions between AGN outflows and the interstellar medium in several Seyferts galaxies .

  14. Evidence for ultrafast outflows in radio-quiet AGNs - III. Location and energetics

    NASA Astrophysics Data System (ADS)

    Tombesi, F.; Cappi, M.; Reeves, J. N.; Braito, V.

    2012-05-01

    Using the results of a previous X-ray photoionization modelling of blueshifted Fe K absorption lines on a sample of 42 local radio-quiet AGNs observed with XMM-Newton, in this Letter we estimate the location and energetics of the associated ultrafast outflows (UFOs). Due to significant uncertainties, we are essentially able to place only lower/upper limits. On average, their location is in the interval ˜0.0003-0.03 pc (˜ 102-104rs) from the central black hole, consistent with what is expected for accretion disc winds/outflows. The mass outflow rates are constrained between ˜0.01 and 1 M⊙ yr-1, corresponding to >rsim5-10 per cent of the accretion rates. The average lower/upper limits on the mechanical power are log? 42.6-44.6 erg s-1. However, the minimum possible value of the ratio between the mechanical power and bolometric luminosity is constrained to be comparable or higher than the minimum required by simulations of feedback induced by winds/outflows. Therefore, this work demonstrates that UFOs are indeed capable to provide a significant contribution to the AGN cosmological feedback, in agreement with theoretical expectations and the recent observation of interactions between AGN outflows and the interstellar medium in several Seyfert galaxies.

  15. First X-ray Statistical Tests for Clumpy-Torus Models: Constraints from RXTEmonitoring of Seyfert AGN

    NASA Astrophysics Data System (ADS)

    Markowitz, Alex; Krumpe, Mirko; Nikutta, R.

    2016-06-01

    In two papers (Markowitz, Krumpe, & Nikutta 2014, and Nikutta et al., in prep.), we derive the first X-ray statistical constraints for clumpy-torus models in Seyfert AGN by quantifying multi-timescale variability in line of-sight X-ray absorbing gas as a function of optical classification.We systematically search for discrete absorption events in the vast archive of RXTE monitoring of 55 nearby type Is and Compton-thin type IIs. We are sensitive to discrete absorption events due to clouds of full-covering, neutral/mildly ionized gas transiting the line of sight. Our results apply to both dusty and non-dusty clumpy media, and probe model parameter space complementary to that for eclipses observed with XMM-Newton, Suzaku, and Chandra.We detect twelve eclipse events in eight Seyferts, roughly tripling the number previously published from this archive. Event durations span hours to years. Most of our detected clouds are Compton-thin, and most clouds' distances from the black hole are inferred to be commensurate with the outer portions of the BLR or the inner regions of infrared-emitting dusty tori.We present the density profiles of the highest-quality eclipse events; the column density profile for an eclipsing cloud in NGC 3783 is doubly spiked, possibly indicating a cloud that is being tidallysheared. We discuss implications for cloud distributions in the context of clumpy-torus models. We calculate eclipse probabilities for orientation-dependent Type I/II unification schemes.We present constraints on cloud sizes, stability, and radial distribution. We infer that clouds' small angular sizes as seen from the SMBH imply 107 clouds required across the BLR + torus. Cloud size is roughly proportional to distance from the black hole, hinting at the formation processes (e.g., disk fragmentation). All observed clouds are sub-critical with respect to tidal disruption; self-gravity alone cannot contain them. External forces, such as magnetic fields or ambient pressure, are

  16. Modeling X-ray Absorbers in AGNs with MHD-Driven Accretion-Disk Winds

    NASA Astrophysics Data System (ADS)

    Fukumura, Keigo; Kazanas, D.; Shrader, C. R.; Tombesi, F.; Contopoulos, J.; Behar, E.

    2013-04-01

    We have proposed a systematic view of the observed X-ray absorbers, namely warm absorbers (WAs) in soft X-ray and highly-ionized ultra-fast outflows (UFOs), in the context of magnetically-driven accretion-disk wind models. While potentially complicated by variability and thermal instability in these energetic outflows, in this simplistic model we have calculated 2D kinematic field as well as density and ionization structure of the wind with density profile of 1/r corresponding to a constant column distribution per decade of ionization parameter. In particular we show semi-analytically that the inner layer of the disk-wind manifests itself as the strongly-ionized fast outflows while the outer layer is identified as the moderately-ionized absorbers. The computed characteristics of these two apparently distinct absorbers are consistent with X-ray data (i.e. a factor of ~100 difference in column and ionization parameters as well as low wind velocity vs. near-relativistic flow). With the predicted contour curves for these wind parameters one can constrain allowed regions for the presence of WAs and UFOs.The model further implies that the UFO's gas pressure is comparable to that of the observed radio jet in 3C111 suggesting that the magnetized disk-wind with density profile of 1/r is a viable agent to help sustain such a self-collimated jet at small radii.

  17. The Alpine snow-albedo feedback in regional climate models

    NASA Astrophysics Data System (ADS)

    Winter, Kevin J.-P. M.; Kotlarski, Sven; Scherrer, Simon C.; Schär, Christoph

    2016-04-01

    The effect of the snow-albedo feedback (SAF) on 2m temperatures and their future changes in the European Alps is investigated in the ENSEMBLES regional climate models (RCMs) with a focus on the spring season. A total of 14 re-analysis-driven RCM experiments covering the period 1961-2000 and 10 GCM-driven transient climate change projections for 1950-2099 are analysed. A positive springtime SAF is found in all RCMs, but the range of the diagnosed SAF is large. Results are compared against an observation-based SAF estimate. For some RCMs, values very close to this estimate are found; other models show a considerable overestimation of the SAF. Net shortwave radiation has the largest influence of all components of the energy balance on the diagnosed SAF and can partly explain its spatial variability. Model deficiencies in reproducing 2m temperatures above snow and ice and associated cold temperature biases at high elevations seem to contribute to a SAF overestimation in several RCMs. The diagnosed SAF in the observational period strongly influences the estimated SAF contribution to twenty first century temperature changes in the European Alps. This contribution is subject to a clear elevation dependency that is governed by the elevation-dependent change in the number of snow days. Elevations of maximum SAF contribution range from 1500 to 2000 m in spring and are found above 2000 m in summer. Here, a SAF contribution to the total simulated temperature change between 0 and 0.5 °C until 2099 (multi-model mean in spring: 0.26 °C) or 0 and 14 % (multi-model mean in spring: 8 %) is obtained for models showing a realistic SAF. These numbers represent a well-funded but only approximate estimate of the SAF contribution to future warming, and a remaining contribution of model-specific SAF misrepresentations cannot be ruled out.

  18. AGN Winds and Blazar Phenomenology

    NASA Technical Reports Server (NTRS)

    Kazanas, Demos

    2012-01-01

    The launch of {\\em Fermi} produced a significant number of AGN detections to allow statistical treatment of their properties. One of the first such systematics was the "Blazar Divide" in FSRQs and BL Lacs according to their gamma-ray spectral index and luminosity. Further data accumulation indicated this separation to be less clear than thought before. An MHD wind model which can model successfully the Seyfert X-ray absorber properties provides the vestiges of an account of the observed blazar classification. We propose to employ this model to model in detail the broad band blazar spectra and their statistical properties in terms of the physical parameters of these MHD winds.

  19. Modeling Feedbacks Between Water and Vegetation in the Climate System

    NASA Technical Reports Server (NTRS)

    Miller, James R.; Russell, Gary L.; Hansen, James E. (Technical Monitor)

    2001-01-01

    Not only is water essential for life on earth, but life itself affects the global hydrologic cycle and consequently the climate of the planet. Whether the global feedbacks between life and the hydrologic cycle tend to stabilize the climate system about some equilibrium level is difficult to assess. We use a global climate model to examine how the presence of vegetation can affect the hydrologic cycle in a particular region. A control for the present climate is compared with a model experiment in which the Sahara Desert is replaced by vegetation in the form of trees and shrubs common to the Sahel region. A second model experiment is designed to identify the separate roles of two different effects of vegetation, namely the modified albedo and the presence of roots that can extract moisture from deeper soil layers. The results show that the presence of vegetation leads to increases in precipitation and soil moisture in western Sahara. In eastern Sahara, the changes are less clear. The increase in soil moisture is greater when the desert albedo is replaced by the vegetation albedo than when both the vegetation albedo and roots are added. The effect of roots is to withdraw water from deeper layers during the dry season. One implication of this study is that the insertion of vegetation into the Sahara modifies the hydrologic cycle so that the vegetation is more likely to persist than initially.

  20. Sensory feedback in a bump attractor model of path integration.

    PubMed

    Poll, Daniel B; Nguyen, Khanh; Kilpatrick, Zachary P

    2016-04-01

    Mammalian spatial navigation systems utilize several different sensory information channels. This information is converted into a neural code that represents the animal's current position in space by engaging place cell, grid cell, and head direction cell networks. In particular, sensory landmark (allothetic) cues can be utilized in concert with an animal's knowledge of its own velocity (idiothetic) cues to generate a more accurate representation of position than path integration provides on its own (Battaglia et al. The Journal of Neuroscience 24(19):4541-4550 (2004)). We develop a computational model that merges path integration with feedback from external sensory cues that provide a reliable representation of spatial position along an annular track. Starting with a continuous bump attractor model, we explore the impact of synaptic spatial asymmetry and heterogeneity, which disrupt the position code of the path integration process. We use asymptotic analysis to reduce the bump attractor model to a single scalar equation whose potential represents the impact of asymmetry and heterogeneity. Such imperfections cause errors to build up when the network performs path integration, but these errors can be corrected by an external control signal representing the effects of sensory cues. We demonstrate that there is an optimal strength and decay rate of the control signal when cues appear either periodically or randomly. A similar analysis is performed when errors in path integration arise from dynamic noise fluctuations. Again, there is an optimal strength and decay of discrete control that minimizes the path integration error. PMID:26754972

  1. A Disk-Corona Model for Optical-to-Hard X-ray spectrum of AGN

    NASA Astrophysics Data System (ADS)

    Kawaguchi, T.; Shimura, T.; Mineshige, S.

    We construct a disk-corona model to account for the optical-to-X-ray spectral energy distributions of Seyfert nuclei and QSOs. We study the emission spectrum emerging from a vertical disk-corona structure composed of two-temperature plasma by solving hydrostatic equilibrium and radiative transfer self-consistently. A fraction f of viscous heating is assumed to be dissipated in a corona where advective cooling is also included, and the remaining fraction, 1-f, within the main body of the disk. The model exhibits different photon indices in X-ray (Γ ~ 2.5 below 2 keV and ~ 1.5 above, where Fν ∝ ν(1 - Γ)) as the result of different emission mechanisms and different sites; the former slope is due to unsaturated Comptonization from the innermost zone and the latter is due to a combination of Comptonization and bremsstrahlung from the entire corona (<= 300 RSch). Because of the shorter dynamical time-scale at inner region than that at outer region, the emission from the inner radii is likely to be more variable than radiation from the outer parts. Then, the X-ray spectrum is expected to be softer in brighter phase, as observed in many Broad-Line Seyfert 1 nuclei.

  2. Feedback and sensitivity in an electrical circuit: An analog for climate models

    SciTech Connect

    Schwartz, S.E.

    2010-07-27

    Earth's climate sensitivity is often interpreted in terms of feedbacks that can alter the sensitivity from that of a no-feedback Stefan-Boltzmann radiator, with the feedback concept and algebra introduced by analogy to the use of this concept in the electronics literature. This analogy is quite valuable in interpreting the sensitivity of the climate system, but usage of this algebra and terminology in the climate literature is often inconsistent, with resultant potential for confusion and loss of physical insight. Here a simple and readily understood electrical resistance circuit is examined in terms of feedback theory to introduce and define the terminology that is used to quantify feedbacks. This formalism is applied to the feedbacks in an energy-balance model of Earth's climate and used to interpret the magnitude of feedback in the climate system that corresponds to present estimates of Earth's climate sensitivity.

  3. Towards modelling X-ray reverberation in AGN: piecing together the extended corona

    NASA Astrophysics Data System (ADS)

    Wilkins, D. R.; Cackett, E. M.; Fabian, A. C.; Reynolds, C. S.

    2016-05-01

    Models of X-ray reverberation from extended coronae are developed from general relativistic ray tracing simulations. Reverberation lags between correlated variability in the directly observed continuum emission and that reflected from the accretion disc arise due to the additional light travel time between the corona and reflecting disc. X-ray reverberation is detected from an increasing sample of Seyfert galaxies and a number of common properties are observed, including a transition from the characteristic reverberation signature at high frequencies to a hard lag within the continuum component at low frequencies, as well as a pronounced dip in the reverberation lag at 3 keV. These features are not trivially explained by the reverberation of X-rays originating from simple point sources. We therefore model reverberation from coronae extended both over the surface of the disc and vertically. Causal propagation through its extent for both the simple case of constant velocity propagation and propagation linked to the viscous time-scale in the underlying accretion disc is included as well as stochastic variability arising due to turbulence locally on the disc. We find that the observed features of X-ray reverberation in Seyfert galaxies can be explained if the long time-scale variability is dominated by the viscous propagation of fluctuations through the corona. The corona extends radially at low height over the surface of the disc but with a bright central region in which fluctuations propagate up the black hole rotation axis driven by more rapid variability arising from the innermost regions of the accretion flow.

  4. Computer modelling of bunch-by-bunch feedback for the SLAC B-factory design

    SciTech Connect

    Briggs, D.; Fox, J.D.; Hosseini, W.; Klaisner, L.; Morton, P.; Pellegrin, J.L.; Thompson, K.A. ); Lambertson, G. )

    1991-05-01

    The SLAC B-factory design, with over 1600 high current bunches circulating in each ring, will require a feedback system to avoid coupled-bunch instabilities. A computer model of the storage ring, including the RF system, wave fields, synchrotron radiation loss, and the bunch-by-bunch feedback system is presented. The feedback system model represents the performance of a fast phase detector front end (including system noise and imperfections), a digital filter used to generate a correction voltage, and a power amplifier and beam kicker system. The combined ring-feedback system model is used to study the feedback system performance required to suppress instabilities and to quantify the dynamics of the system. Results are presented which show the time development of coupled bunch instabilities and the damping action of the feedback system. 3 refs., 5 figs., 2 tabs.

  5. An accurate halo model for fitting non-linear cosmological power spectra and baryonic feedback models

    NASA Astrophysics Data System (ADS)

    Mead, A. J.; Peacock, J. A.; Heymans, C.; Joudaki, S.; Heavens, A. F.

    2015-12-01

    We present an optimized variant of the halo model, designed to produce accurate matter power spectra well into the non-linear regime for a wide range of cosmological models. To do this, we introduce physically motivated free parameters into the halo-model formalism and fit these to data from high-resolution N-body simulations. For a variety of Λ cold dark matter (ΛCDM) and wCDM models, the halo-model power is accurate to ≃ 5 per cent for k ≤ 10h Mpc-1 and z ≤ 2. An advantage of our new halo model is that it can be adapted to account for the effects of baryonic feedback on the power spectrum. We demonstrate this by fitting the halo model to power spectra from the OWLS (OverWhelmingly Large Simulations) hydrodynamical simulation suite via parameters that govern halo internal structure. We are able to fit all feedback models investigated at the 5 per cent level using only two free parameters, and we place limits on the range of these halo parameters for feedback models investigated by the OWLS simulations. Accurate predictions to high k are vital for weak-lensing surveys, and these halo parameters could be considered nuisance parameters to marginalize over in future analyses to mitigate uncertainty regarding the details of feedback. Finally, we investigate how lensing observables predicted by our model compare to those from simulations and from HALOFIT for a range of k-cuts and feedback models and quantify the angular scales at which these effects become important. Code to calculate power spectra from the model presented in this paper can be found at https://github.com/alexander-mead/hmcode.

  6. Compton Thick AGN in the XMM-COSMOS field

    NASA Astrophysics Data System (ADS)

    Lanzuisi, G.; Perna, M.; Delvecchio, I.; Berta, S.; Brusa, M.; Gruppioni, C.; Comastri, A.

    2016-06-01

    I will present results we published in two recent papers (Lanzuisi et al. 2015, A&A 573A 137, Lanzuisi et al. 2015, A&A 578A 120) on the properties of X-ray selected Compton Thick (CT, NH>10^{24} cm^{-2}) AGN, in the XMM-COSMOS survey. We exploited the rich multi-wavelength dataset available in this field, to show that CT AGN tend to harbor smaller, rapidly growing SMBH with respect to unobscured AGN, and have a higher chance of being hosted by star-forming, merging and post-merger systems. We also demonstrated the detectability of even more heavily obscured AGN (NH>10^{25} cm^{-2}), thanks to a truly multi-wavelength approach in the same field, and to the unrivaled XMM sensitivity. The extreme source detected in this way shows strong evidences of ongoing powerful AGN feedback, detected as blue-shifted wings of high ionization optical emission lines such as [NeV] and [FeVII], as well as of the [OIII] emission line. The results obtained from these works point toward a scenario in which highly obscured AGN occupy a peculiar place in the galaxy-AGN co-evolution process, in which both the host and the SMBH rapidly evolve toward the local relations.

  7. Compton Thick AGN in the XMM-COSMOS field

    NASA Astrophysics Data System (ADS)

    Lanzuisi, G.; Perna, M.; Delvecchio, I.; Berta, S.; Brusa, M.; Gruppioni, C.; Comastri, A.

    2016-06-01

    I will present results we published in two recent papers (Lanzuisi et al. 2015, A&A 573A 137, Lanzuisi et al. 2015, A≈A 578A 120) on the properties of X-ray selected Compton Thick (CT, NH>10^{24} cm^{-2}) AGN, in the XMM-COSMOS survey. We exploited the rich multi-wavelength dataset available in this field, to show that CT AGN tend to harbor smaller, rapidly growing SMBH with respect to unobscured AGN, and have a higher chance of being hosted by star-forming, merging and post-merger systems. We also demonstrated the detectability of even more heavily obscured AGN (NH>10^{25} cm^{-2}), thanks to a truly multi-wavelength approach in the same field, and to the unrivaled XMM sensitivity. The extreme source detected in this way shows strong evidences of ongoing powerful AGN feedback, detected as blue-shifted wings of high ionization optical emission lines such as [NeV] and [FeVII], as well as of the [OIII] emission line. The results obtained from these works point toward a scenario in which highly obscured AGN occupy a peculiar place in the galaxy-AGN co-evolution process, in which both the host and the SMBH rapidly evolve toward the local relations.

  8. Obscured AGN Accretion Across Cosmic Time

    NASA Astrophysics Data System (ADS)

    Coil, Alison

    for the unified model of AGN. Our X-ray absorption study will accurately determine the distribution of AGN absorption column densities. We will measure the dependence of this absorption distribution on both luminosity and redshift to z~3, resolving outstanding discrepancies in the literature. We propose to develop and implement a new Bayesian X-ray spectral fitting technique to obtain unbiased measurements of absorption column densities and their associated uncertainties. By compiling large samples of X-ray sources over a wide range of redshifts and depths and fully propagating the errors in individual measurements of column densities and X-ray luminosities, we will robustly measure the joint evolution of AGN accretion activity and absorption properties. In all of these projects we will adopt advanced methodologies to quantify and correct for selection effects, incompleteness, and biases, which severely hamper such studies if not fully accounted for. Our proposed work will allow us to place strong constraints on the prominence of obscured AGN activity and reveal the true evolution of AGN accretion over the history of the Universe. To ensure the legacy and impact of our findings, we commit to publicly release major, high-level data products. This will build on the substantial archive of public data available from the AEGIS and DEEP survey teams and the forthcoming release from PRIMUS. We will release catalogs providing accurate measurements of X-ray luminosities, column densities, and photometric redshifts with robust error estimates for our large samples of X-ray sources, covering the most prominent extragalactic survey fields.

  9. A Moral Experience Feedback Loop: Modeling a System of Moral Self-Cultivation in Everyday Life

    ERIC Educational Resources Information Center

    Sherblom, Stephen A.

    2015-01-01

    This "systems thinking" model illustrates a common feedback loop by which people engage the moral world and continually reshape their moral sensibility. The model highlights seven processes that collectively form this feedback loop: beginning with (1) one's current moral sensibility which shapes processes of (2) perception, (3)…

  10. Observational evidence for thin AGN disks

    NASA Technical Reports Server (NTRS)

    Netzer, Hagai

    1992-01-01

    AGN spectrum and spectral features, polarization, inclination, and X-ray line and continuum reflection features are discussed in a critical way in order to determine the ones that are the least model-dependent. The sign and strength of absorption and emission edges are found to be model-dependent, and relativistic broadening and shifting makes them hard to detect. The presence or absence of the predicted Lyman edge polarization feature may be used as a decisive test for thin, bare AGN disks. Other good model-independent tests are several inclination-related line and continuum correlations in big AGN samples. It is shown that electron temperature near the surface of the disk can greatly exceed the disk equilibrium temperature, which causes deviations from LTE. This effect must be incorporated into realistic disk models.

  11. A speed feedback control strategy for car-following model

    NASA Astrophysics Data System (ADS)

    Zhu, Wen-Xing; Zhang, Li-Dong

    2014-11-01

    A speed feedback control mechanism was introduced into the system to improve the dynamical performance of the traffic flow. The modern control theory was used to analyze the stability of the system. It is found that the stability region varies with the feedback coefficient proportionally. In addition, the unit step responses in time domain and phase-frequency curves in frequency domain were given with different feedback coefficients in step response diagram and Bode diagram respectively. The overshoot and phase margins are inversely proportional to the speed feedback coefficients in an underdamped condition. The simulations were conducted to verify the validity of the improvement. The conclusion can be drawn that the analytical result and the simulation result are in good agreement with each other.

  12. Does Changing Atmospheric Model Resolution Affect Atmospheric Feedbacks?

    NASA Astrophysics Data System (ADS)

    Tett, S. F.; Wehner, M. F.; Stone, D. A.

    2014-12-01

    Simulations of the Community Atmosphere Model version 5.1 (CAM5.1) at horizontal resolutions of approximately 2, 1 and 0.25 degrees driven with climatological sea surface temperatures (SST) and 1990 forcings were carried out. The 1 and 2 degree CAM5.1 configurations used the default parameter values with the 0.25 degree CAM5.1 using the 1 degree configuration except the physics timestep being halved. Perturbed experiments, using CAM5.1, in which either SST is uniformly increased by 2K or CO2 doubled werealso carried out using the same configurations. A ``Cess'' type feedback analysis (twice change in 2xCO2/change in 2K simulations) was used to diagnose a ``Cess'' sensitivity. This sensitivity increased slightly with resolution due to changes in both the response to the uniform SST increase and to doubling CO2. This appears to arise from differing changes in tropical cloudsas resolution increases. Our results suggest that uncertainty in climate sensitivity is not strongly impacted by changing horizontal resolution up to 25 km. Thus, uncertainty in parameterisation likely remain the leading source of uncertainty in climate sensitivity.

  13. The impact of AGN on their host galaxies

    NASA Astrophysics Data System (ADS)

    Harrison, C. M.

    2014-07-01

    In these proceedings I briefly: (1) review the impact (or ``feedback'') that active galactic nuclei (AGN) are predicted to have on their host galaxies and larger scale environment, (2) review the observational evidence for or against these predictions and (3) present new results on ionised outflows in AGN. The observational support for the ``maintenance mode'' of feedback is strong (caveat the details); AGN at the centre of massive halos appear to be regulating the cooling of hot gas, which could in turn control the levels of future star formation (SF) and black hole growth. In contrast, direct observational support for more rapid forms of feedback, which dramatically impact on SF (i.e., the ``quasar mode''), remains elusive. From a systematic study of the spectra of ~24 000 AGN we find that extreme ionised gas kinematics are common, and are most prevalent in radio bright AGN (L 1.4 GHz > 103 W Hz-1). Follow-up IFU observations have shown that these extreme gas kinematics are extended over kilo-parsec scales. However, the co-existence of high-levels of SF, luminous AGN activity and radio jets raises interesting questions on the primary drivers and impact of these outflows. Galaxy-wide, high-mass outflows are being observed in an increasing number of AGN and are a plausible mechanism for the depletion of gas; however, there is still much work to be done to determine the physical processes that drive these outflows and to measure the level of impact that they have on their host galaxies.

  14. Mid-IR Observations of AGN

    NASA Astrophysics Data System (ADS)

    Packham, Christopher C.; Alonso Herrero, Almudena; Levenson, Nancy A.; Piratas AGN Group

    2016-01-01

    We present new observations of AGN, predominantly from the 10.4m GranTeCan. These observations are modeled and interpreted within the context of the clumpy torus models. In this poster we present our recent results and interpretation of the model outputs.

  15. Active galactic nucleus feedback in an isolated elliptical galaxy: The effect of strong radiative feedback in the kinetic mode

    SciTech Connect

    Gan, Zhaoming; Yuan, Feng; Ostriker, Jeremiah P.; Ciotti, Luca; Novak, Gregory S.

    2014-07-10

    Based on two-dimensional high-resolution hydrodynamic numerical simulation, we study the mechanical and radiative feedback effects from the central active galactic nucleus (AGN) on the cosmological evolution of an isolated elliptical galaxy. The inner boundary of the simulation domain is carefully chosen so that the fiducial Bondi radius is resolved and the accretion rate of the black hole is determined self-consistently. It is well known that when the accretion rates are high and low, the central AGNs will be in cold and hot accretion modes, which correspond to the radiative and kinetic feedback modes, respectively. The emitted spectrum from the hot accretion flows is harder than that from the cold accretion flows, which could result in a higher Compton temperature accompanied by a more efficient radiative heating, according to previous theoretical works. Such a difference of the Compton temperature between the two feedback modes, the focus of this study, has been neglected in previous works. Significant differences in the kinetic feedback mode are found as a result of the stronger Compton heating. More importantly, if we constrain models to correctly predict black hole growth and AGN duty cycle after cosmological evolution, we find that the favored model parameters are constrained: mechanical feedback efficiency diminishes with decreasing luminosity (the maximum efficiency being ≅ 10{sup –3.5}), and X-ray Compton temperature increases with decreasing luminosity, although models with fixed mechanical efficiency and Compton temperature can be found that are satisfactory as well. We conclude that radiative feedback in the kinetic mode is much more important than previously thought.

  16. Reduced-order model based feedback control of the modified Hasegawa-Wakatani model

    NASA Astrophysics Data System (ADS)

    Goumiri, I. R.; Rowley, C. W.; Ma, Z.; Gates, D. A.; Krommes, J. A.; Parker, J. B.

    2013-04-01

    In this work, the development of model-based feedback control that stabilizes an unstable equilibrium is obtained for the Modified Hasegawa-Wakatani (MHW) equations, a classic model in plasma turbulence. First, a balanced truncation (a model reduction technique that has proven successful in flow control design problems) is applied to obtain a low dimensional model of the linearized MHW equation. Then, a model-based feedback controller is designed for the reduced order model using linear quadratic regulators. Finally, a linear quadratic Gaussian controller which is more resistant to disturbances is deduced. The controller is applied on the non-reduced, nonlinear MHW equations to stabilize the equilibrium and suppress the transition to drift-wave induced turbulence.

  17. Reduced-order model based feedback control of the modified Hasegawa-Wakatani model

    SciTech Connect

    Goumiri, I. R.; Rowley, C. W.; Ma, Z.; Gates, D. A.; Krommes, J. A.; Parker, J. B.

    2013-04-15

    In this work, the development of model-based feedback control that stabilizes an unstable equilibrium is obtained for the Modified Hasegawa-Wakatani (MHW) equations, a classic model in plasma turbulence. First, a balanced truncation (a model reduction technique that has proven successful in flow control design problems) is applied to obtain a low dimensional model of the linearized MHW equation. Then, a model-based feedback controller is designed for the reduced order model using linear quadratic regulators. Finally, a linear quadratic Gaussian controller which is more resistant to disturbances is deduced. The controller is applied on the non-reduced, nonlinear MHW equations to stabilize the equilibrium and suppress the transition to drift-wave induced turbulence.

  18. Radio AGN in the local universe: unification, triggering and evolution

    NASA Astrophysics Data System (ADS)

    Tadhunter, Clive

    2016-06-01

    Associated with one of the most important forms of active galactic nucleus (AGN) feedback, and showing a strong preference for giant elliptical host galaxies, radio AGN (L_{1.4 GHz} > 10^{24} W Hz^{-1}) are a key sub-class of the overall AGN population. Recently their study has benefitted dramatically from the availability of high-quality data covering the X-ray to far-IR wavelength range obtained with the current generation of ground- and space-based telescope facilities. Reflecting this progress, here I review our current state of understanding of the population of radio AGN at low and intermediate redshifts (z < 0.7), concentrating on their nuclear AGN and host galaxy properties, and covering three interlocking themes: the classification of radio AGN and its interpretation; the triggering and fuelling of the jet and AGN activity; and the evolution of the host galaxies. I show that much of the observed diversity in the AGN properties of radio AGN can be explained in terms of a combination of orientation/anisotropy, mass accretion rate, and variability effects. The detailed morphologies of the host galaxies are consistent with the triggering of strong-line radio galaxies (SLRG) in galaxy mergers. However, the star formation properties and cool ISM contents suggest that the triggering mergers are relatively minor in terms of their gas masses in most cases, and would not lead to major growth of the supermassive black holes and stellar bulges; therefore, apart from a minority (<20 %) that show evidence for higher star formation rates and more massive cool ISM reservoirs, the SLRG represent late-time re-triggering of activity in mature giant elliptical galaxies. In contrast, the host and environmental properties of weak-line radio galaxies (WLRG) with Fanaroff-Riley class I radio morphologies are consistent with more gradual fuelling of the activity via gas accretion at low rates onto the supermassive black holes.

  19. Feedback Mechanisms in a Mechanical Model of Cell Polarization

    PubMed Central

    Wang, Xinxin; Carlsson, Anders E.

    2014-01-01

    Directed cell migration requires a spatially polarized distribution of polymerized actin. We develop and treat a mechanical model of cell polarization based on polymerization and depolymerization of actin filaments at the two ends of a cell, modulated by forces at either end that are coupled by the cell membrane. We solve this model using both a simulation approach that treats filament nucleation, polymerization, and depolymerization stochastically, and a rate-equation approach based on key properties such as the number of filaments N and the number of polymerized subunits F at either end of the cell. The rate-equation approach agrees closely with the stochastic approach at steady state and, when appropriately generalized, also predicts the dynamic behavior accurately. The calculated transitions from symmetric to polarized states show that polarization is enhanced by a high free-actin concentration, a large pointed-end off-rate, a small barbed-end off-rate, and a small spontaneous nucleation rate. The rate-equation approach allows us to perform a linear-stability analysis to pin down the key interactions that drive the polarization. The polarization is driven by a positive-feedback loop having two interactions. First, an increase in F at one side of the cell lengthens the filaments and thus reduces the decay rate of N (increasing N); second, increasing N enhances F because the force per growing filament tip is reduced. We find that the transitions induced by changing system properties result from supercritical pitchfork bifurcations. The filament lifetime depends strongly on the average filament length, and this effect is crucial for obtaining polarization correctly. PMID:25313164

  20. Reduced-Order Model Based Feedback Control For Modified Hasegawa-Wakatani Model

    SciTech Connect

    Goumiri, I. R.; Rowley, C. W.; Ma, Z.; Gates, D. A.; Krommes, J. A.; Parker, J. B.

    2013-01-28

    In this work, the development of model-based feedback control that stabilizes an unstable equilibrium is obtained for the Modi ed Hasegawa-Wakatani (MHW) equations, a classic model in plasma turbulence. First, a balanced truncation (a model reduction technique that has proven successful in ow control design problems) is applied to obtain a low dimensional model of the linearized MHW equation. Then a modelbased feedback controller is designed for the reduced order model using linear quadratic regulators (LQR). Finally, a linear quadratic gaussian (LQG) controller, which is more resistant to disturbances is deduced. The controller is applied on the non-reduced, nonlinear MHW equations to stabilize the equilibrium and suppress the transition to drift-wave induced turbulence.

  1. Long Timescale Variability of AGN with RXTE

    NASA Astrophysics Data System (ADS)

    McHardy, I. M.; Uttley, P.; Taylor, R. D.; Seymour, N.

    2004-07-01

    In this paper we review the very large contribution made by RXTE to our understanding of Active Galaxies (AGN). We discuss the relationship between AGN and Galactic Black Hole X-ray binary systems (GBHs) and show, by comparison of their powerspectral densities (PSDs) that some AGN are the equivalent of GBHs in their `high' state, rather than in their `low' state as has previously been assumed. We plot the timescale at which the PSD slope steepens from -1 to -2 against the black hole mass for a sample of AGN, and for Cyg X-1 in its high and low states. We find it is not possible to fit all AGN to the same linear scaling of break timescale with black hole mass. However broad line AGN are consistent with a linear scaling of break timescale with mass from Cyg X-1 in its low state and NLS1 galaxies scale better with Cyg X-1 in its high state, although there is an exception, NGC3227. We suggest that the relationship between black hole mass and break timescale is a function of another underlying parameter which may be accretion rate or black hole spin or, probably, both. We examine X-ray spectral variability and show how simple `flux-flux' plots can distinguish between `two-component' and `spectral pivoting' models. We also examine the relationship between the X-ray emission and that in other wavebands. In the case of X-ray/optical variability we show how cooler discs in AGN with larger mass black holes lead to greater proximity of the X-ray and optical emission regions and hence to more highly correlated variability. The very large amplitude of optical variability then rules out reprocessing as the origin of the optical emission. We show how the radio emission in NGC 4051 is strongly correlated with the X-ray emission, implying some contribution to the X-ray emission from a jet for which there is some evidence in radio images. We point out, however, that we have only studied in detail the X-ray variability of a handful of AGN. There is a strong requirement to extend such

  2. On the influence of poleward jet shift on shortwave cloud feedback in global climate models

    NASA Astrophysics Data System (ADS)

    Wall, Casey J.; Hartmann, Dennis L.

    2015-12-01

    Experiments designed to separate the effect of atmospheric warming from the effect of shifts of the eddy-driven jet on shortwave (SW) cloud feedback are performed with three global climate models (GCMs). In each model a warming simulation produces a robust SW cloud feedback dipole, with a negative (positive) feedback in the high-latitudes (subtropics). The cloud brightening in high-latitudes that characterizes warming simulations is not produced by jet shifts alone in any of the models, but is highly sensitive to perturbations of freezing temperature seen by the cloud microphysics scheme, indicating that thermodynamic mechanisms involving the phase of cloud condensate dominate the SW feedback at high-latitudes. In one of the models a poleward jet shift causes significant cloud dimming throughout the midlatitudes, but in two models it does not. Differences in cloud response to jet shifts in two of the models are attributed to differences in the shallow convection parameterizations.

  3. SWIFT Observations AGN

    NASA Technical Reports Server (NTRS)

    Mushotzky, Richard

    2008-01-01

    I will present results from the x-ray and optical follow-up observations of the Swift Burst Alert Telescope (BAT) Active Galactic Nuclei (AGN) survey. I will discuss the nature of obscuration in these objects, the relationship to optical properties and the change of properties with luminosity and galaxy type.

  4. AGN-2979, an inhibitor of tryptophan hydroxylase activation, does not affect serotonin synthesis in Flinders Sensitive Line rats, a rat model of depression, but produces a significant effect in Flinders Resistant Line rats

    PubMed Central

    Kanemaru, Kazuya; Nishi, Kyoko; Diksic, Mirko

    2009-01-01

    The neurotransmitter, serotonin, is involved in several brain functions, including both normal, physiological functions, and pathophysiological functions. Alterations in any of the normal parameters of serotonergic neurotransmission can produce several different psychiatric disorders, including major depression. In many instances, brain neurochemical variables are not able to be studied properly in humans, thus making the use of good animal models extremely valuable. One of these animal models is the Flinders Sensitive Line (FSL) of rats, which has face, predictive and constructive validities in relation to human depression. The objective of this study was to quantify the effect of the tryptophan hydroxylase (TPH) activation inhibitor, AGN-2979, on the FSL rats (rats with depression-like behaviour), and compare it to the effect on the Flinders Resistant Line (FRL) of rats used as the control rats. The effect was evaluated by measuring changes in regional serotonin synthesis in the vehicle treated rats (FSL-VEH and FRL-VEH) relative to those measured in the AGN-2979 treated rats (FSL-AGN and FRL-AGN). Regional serotonin synthesis was measured autoradiographically in more than thirty brain regions. The measurements were performed using α-[14C]methyl-L-tryptophan as the tracer. The results indicate that AGN-2979 did not produce a significant reduction of TPH activity in the AGN-2979 group relative to the vehicle group (a reduction would have been observed if there had been an activation of TPH by the experimental set up) in the FSL rats. On the other hand, there was a highly significant reduction of synthesis in the FRL rats treated by AGN-2979, relative to the vehicle group. Together, the results demonstrate that in the FSL rats, AGN-2979 does not affect serotonin synthesis. This suggests that there was no activation of TPH in the FSL rats during the experimental procedure, but such activation did occur in the FRL rats. Because of this finding, it could be

  5. Stabilizing PID controllers for a single-link biomechanical model with position, velocity, and force feedback.

    PubMed

    Iqbal, Kamran; Roy, Anindo

    2004-12-01

    In this paper we address the problem of PID stabilization of a single-link inverted pendulum-based biomechanical model with force feedback, two levels of position and velocity feedback, and with delays in all the feedback loops. The novelty of the proposed model lies in its physiological relevance, whereby both small and medium latency sensory feedbacks from muscle spindle (MS), and force feedback from Golgi tendon organ (GTO) are included in the formulation. The biomechanical model also includes active and passive viscoelastic feedback from Hill-type muscle model and a second-order low-pass function for muscle activation. The central nervous system (CNS) regulation of postural movement is represented by a proportional-integral-derivative (PID) controller. Padé approximation of delay terms is employed to arrive at an overall rational transfer function of the biomechanical model. The Hermite-Biehler theorem is then used to derive stability results, leading to the existence of stabilizing PID controllers. An algorithm for selection of stabilizing feedback gains is developed using the linear matrix inequality (LMI) approach. PMID:15796343

  6. Young AGN Outburst Running over Older X-Ray Cavities

    NASA Astrophysics Data System (ADS)

    Bogdan, Akos; van Weeren, Reinout Johannes; Kraft, Ralph; Forman, William; Scott, Randall; Giacintucci, Simona; Churazov, Eugene; O'Dea, Christopher; Baum, Stefi; Noell-Storr, Jacob; Jones, Christine

    2015-08-01

    Although the energetic feedback from active galactic nuclei (AGNs) is believed to have a profound effect on the evolution of galaxies and clusters of galaxies, details of AGN heating remain elusive. Here, we study NGC 193 -- a nearby lenticular galaxy in a group -- based on X-ray and radio observations. These data reveal the complex AGN outburst history of the galaxy: we detect a pair of inner X-ray cavities, an outer X-ray cavity, a shock front, and radio lobes extending beyond the inner cavities. We suggest that the inner cavities were produced about 78 Myr ago by a weaker AGN outburst, while the outer cavity, the radio lobes, and the shock front are due to a younger (13-26 Myr) and 4-8 times more powerful outburst. Combining this with the observed morphology of NGC 193, we conclude that NGC 193 likely represents the first example of a second, more powerful, AGN outburst overrunning an older, weaker outburst. These results help us to understand how the outburst energy is dissipated uniformly in the core of galaxies, and therefore may play a crucial role in resolving how AGN outbursts suppress the formation of large cooling flows at cluster centers.

  7. YOUNG AGN OUTBURST RUNNING OVER OLDER X-RAY CAVITIES

    SciTech Connect

    Bogdán, Ákos; Van Weeren, Reinout J.; Kraft, Ralph P.; Forman, William R.; Randall, Scott; Jones, Christine; Giacintucci, Simona; Churazov, Eugene; O'Dea, Christopher P.; Baum, Stefi A.; Noell-Storr, Jacob

    2014-02-20

    Although the energetic feedback from active galactic nuclei (AGNs) is believed to have a profound effect on the evolution of galaxies and clusters of galaxies, details of AGN heating remain elusive. Here, we study NGC 193—a nearby lenticular galaxy—based on X-ray (Chandra) and radio (Very Large Array and Giant Meter-wave Radio Telescope) observations. These data reveal the complex AGN outburst history of the galaxy: we detect a pair of inner X-ray cavities, an outer X-ray cavity, a shock front, and radio lobes extending beyond the inner cavities. We suggest that the inner cavities were produced ∼78 Myr ago by a weaker AGN outburst, while the outer cavity, the radio lobes, and the shock front are due to a younger (13-26 Myr) and 4-8 times more powerful outburst. Combining this with the observed morphology of NGC 193, we conclude that NGC 193 likely represents the first example of a second, more powerful, AGN outburst overrunning an older, weaker outburst. These results help us to understand how the outburst energy is dissipated uniformly in the core of galaxies, and therefore may play a crucial role in resolving how AGN outbursts suppress the formation of large cooling flows at cluster centers.

  8. A UV to mid-IR study of AGN selection

    SciTech Connect

    Chung, Sun Mi; Kochanek, Christopher S.; Assef, Roberto; Brown, Michael J. I.; Stern, Daniel; Jannuzi, Buell T.; Gonzalez, Anthony H.; Hickox, Ryan C.; Moustakas, John

    2014-07-20

    We classify the spectral energy distributions (SEDs) of 431,038 sources in the 9 deg{sup 2} Boötes field of the NOAO Deep Wide-Field Survey (NDWFS). There are up to 17 bands of data available per source, including ultraviolet (GALEX), optical (NDWFS), near-IR (NEWFIRM), and mid-infrared (IRAC and MIPS) data, as well as spectroscopic redshifts for ∼20,000 objects, primarily from the AGN and Galaxy Evolution Survey. We fit galaxy, active galactic nucleus (AGN), stellar, and brown dwarf templates to the observed SEDs, which yield spectral classes for the Galactic sources and photometric redshifts and galaxy/AGN luminosities for the extragalactic sources. The photometric redshift precision of the galaxy and AGN samples are σ/(1 + z) = 0.040 and σ/(1 + z) = 0.169, respectively, with the worst 5% outliers excluded. On the basis of the χ{sub ν}{sup 2} of the SED fit for each SED model, we are able to distinguish between Galactic and extragalactic sources for sources brighter than I = 23.5 mag. We compare the SED fits for a galaxy-only model and a galaxy-AGN model. Using known X-ray and spectroscopic AGN samples, we confirm that SED fitting can be successfully used as a method to identify large populations of AGNs, including spatially resolved AGNs with significant contributions from the host galaxy and objects with the emission line ratios of 'composite' spectra. We also use our results to compare with the X-ray, mid-IR, optical color, and emission line ratio selection techniques. For an F-ratio threshold of F > 10, we find 16,266 AGN candidates brighter than I = 23.5 mag and a surface density of ∼1900 AGN deg{sup –2}.

  9. Theoretical modelling of the feedback stabilization of external MHD modes in toroidal geometry

    NASA Astrophysics Data System (ADS)

    Chance, M. S.; Chu, M. S.; Okabayashi, M.; Turnbull, A. D.

    2002-03-01

    A theoretical framework for understanding the feedback mechanism for stabilization of external MHD modes has been formulated. Efficient computational tools - the GATO stability code coupled with a substantially modified VACUUM code - have been developed to effectively design viable feedback systems against these modes. The analysis assumed a thin resistive shell and a feedback coil structure accurately modelled in θ and phi, albeit with only a single harmonic variation in phi. Time constants and induced currents in the enclosing resistive shell are calculated. An optimized configuration based on an idealized model has been computed for the DIII-D device. Up to 90% of the effectiveness of an ideal wall can be achieved.

  10. Introducing Subrid-scale Cloud Feedbacks to Radiation for Regional Meteorological and Cllimate Modeling

    EPA Science Inventory

    Convection systems and associated cloudiness directly influence regional and local radiation budgets, and dynamics and thermodynamics through feedbacks. However, most subgrid-scale convective parameterizations in regional weather and climate models do not consider cumulus cloud ...

  11. Structure Function Analysis of AGN Variability using Kepler

    NASA Astrophysics Data System (ADS)

    Kasliwal, Vishal P.; Vogeley, Michael S.; Richards, Gordon T.

    2014-06-01

    We study the variability properties of AGN light-curves observed by the Kepler satellite. AGN optical fluxes are known to exhibit stochastic variations on time-scales of hours, days, months and years. Previous efforts to characterize the stochastic nature of this variability have been hampered by the lack of high-precision space-based measurements of AGN fluxes with regular cadence. Kepler provides light-curves with a S/N ratio of 10-5 for 87 AGN observed over a period of ~ 3 years with a cadence of once every 30 minutes allowing for a detailed examination of the variability process. We probe AGN variability using the Structure Functions of the light-curves of the Kepler AGN. Monte-Carlo simulations of the structure function are used to fit the observed light-curve to models for the Power Spectral Density. We test various models for the form of the PSD including the damped random walk and the powered exponential models. We show that on the shorter time-scales probed by Kepler data, the damped random walk model fails to adequately characterize AGN variability. We find that the PSD may be better modelled by combination of a steep power law of the form 1/f3 on shorter time-scales, and a more shallow power law of the form 1/f2 on the longer time-scales traditionally probed by ground-based variability studies.

  12. Knowing and acting in the clinical workplace: trainees' perspectives on modelling and feedback.

    PubMed

    Stegeman, J H; Schoten, E J; Terpstra, O T

    2013-10-01

    In this article we discuss clinical workplace learning using a dual approach: a theoretical one and an empirical one. Drawing on the philosophical work of Aristotle, Polanyi and Schön we posit that the 'knowing and acting' underpinning day-to-day medical practice is personal and embraces by nature a tacit dimension. Consequently, imparting and acquiring this knowledge type necessitates personal interaction between trainer and trainee. The tacit dimension particularly influences modelling and feedback. In our empirical exploration we explore these educational routes in two disparate disciplines: surgery and paediatrics. We use a longitudinal design with in-depth interviewing. Our conclusion on modelling is: modelling is a dynamic and fragmented process reflecting discipline bound characteristics and working styles. On feedback it is: 'feedback' serves as vehicle for three distinctive forms of commenting on performance, each holding a specific power of expression for learning. We propose to view clinical workplace learning as: an interactive master-apprenticeship model encompassing modelling and feedback as natural educational routes. We conceptualise modelling and feedback as 'function' of interaction (developing grounded theory). Modelling function and feedback function may serve to study these routes as didactical components of ongoing interaction between trainer and trainee rather than an educator-driven series of unrelated events. PMID:22895867

  13. Detecting vegetation-precipitation feedbacks in mid-Holocene North Africa from two climate models

    SciTech Connect

    Wang, Yi; Notaro, Michael; Liu, Zhengyu; Gallimore, Robert; Levis, Samuel; Kutzbach, John E.

    2008-03-31

    Using two climate-vegetation model simulations from the Fast Ocean Atmosphere Model (FOAM) and the Community Climate System Model (CCSM, version 2), we investigate vegetation-precipitation feedbacks across North Africa during the mid-Holocene. From mid-Holocene snapshot runs of FOAM and CCSM2, we detect a negative feedback at the annual timescale with our statistical analysis. Using the Monte- Carlo bootstrap method, the annual negative feedback is further confirmed to be significant in both simulations. Additional analysis shows that this negative interaction is partially caused by the competition between evaporation and transpiration in North African grasslands. Furthermore, we find the feedbacks decrease with increasing timescales, and change signs from positive to negative at increasing timescales in FOAM. The proposed mechanism for this sign switch is associated with the different persistent timescales of upper and lower soil water contents, and their interactions with vegetation and atmospheric precipitation.

  14. A Dynamic Feedback Model for High Repetition Rate LINAC-Driven FELS

    SciTech Connect

    Mellado Munoz, M.; Doolittle, L.; Emma, P.; Huang, G.; Ratti, A.; Serrano, C.; Byrd, J. M.

    2012-05-20

    One of the concepts for the next generation of linacdriven FELs is a CW superconducting linac driving an electron beam with MHz repetition rates. One of the challenges for next generation FELs is improve the stability of the xray pulses by improving the shot-to-shot stability of the energy, charge, peak current, and timing jitter of the electron beam. A high repetition rate FEL with a CW linac presents an opportunity to use a variety of broadband feedbacks to stabilize the beam parameters. To understand the performance of such a feedback system, we are developing a dynamic model of the machine with a focus on the longitudinal beam properties. The model is being developed as an extension of the LITrack code and includes the dynamics of the beam-cavity interaction, RF feedback, beam-based feedback, and multibunch effects. In this paper, we present a detailed description of this model.

  15. A new switching parameter varying optoelectronic delayed feedback model with computer simulation

    PubMed Central

    Liu, Lingfeng; Miao, Suoxia; Cheng, Mengfan; Gao, Xiaojing

    2016-01-01

    In this paper, a new switching parameter varying optoelectronic delayed feedback model is proposed and analyzed by computer simulation. This model is switching between two parameter varying optoelectronic delayed feedback models based on chaotic pseudorandom sequences. Complexity performance results show that this model has a high complexity compared to the original model. Furthermore, this model can conceal the time delay effectively against the auto-correlation function, delayed mutual information and permutation information analysis methods, and can extent the key space, which greatly improve its security. PMID:26923101

  16. A new switching parameter varying optoelectronic delayed feedback model with computer simulation

    NASA Astrophysics Data System (ADS)

    Liu, Lingfeng; Miao, Suoxia; Cheng, Mengfan; Gao, Xiaojing

    2016-02-01

    In this paper, a new switching parameter varying optoelectronic delayed feedback model is proposed and analyzed by computer simulation. This model is switching between two parameter varying optoelectronic delayed feedback models based on chaotic pseudorandom sequences. Complexity performance results show that this model has a high complexity compared to the original model. Furthermore, this model can conceal the time delay effectively against the auto-correlation function, delayed mutual information and permutation information analysis methods, and can extent the key space, which greatly improve its security.

  17. A new switching parameter varying optoelectronic delayed feedback model with computer simulation.

    PubMed

    Liu, Lingfeng; Miao, Suoxia; Cheng, Mengfan; Gao, Xiaojing

    2016-01-01

    In this paper, a new switching parameter varying optoelectronic delayed feedback model is proposed and analyzed by computer simulation. This model is switching between two parameter varying optoelectronic delayed feedback models based on chaotic pseudorandom sequences. Complexity performance results show that this model has a high complexity compared to the original model. Furthermore, this model can conceal the time delay effectively against the auto-correlation function, delayed mutual information and permutation information analysis methods, and can extent the key space, which greatly improve its security. PMID:26923101

  18. Does the obscured AGN fraction really depend on luminosity?

    NASA Astrophysics Data System (ADS)

    Sazonov, S.; Churazov, E.; Krivonos, R.

    2015-12-01

    We use a sample of 151 local non-blazar active galactic nuclei (AGN) selected from the INTEGRAL all-sky hard X-ray survey to investigate if the observed declining trend of the fraction of obscured (i.e. showing X-ray absorption) AGN with increasing luminosity is mostly an intrinsic or selection effect. Using a torus-obscuration model, we demonstrate that in addition to negative bias, due to absorption in the torus, in finding obscured AGN in hard X-ray flux-limited surveys, there is also positive bias in finding unobscured AGN, due to Compton reflection in the torus. These biases can be even stronger taking into account plausible intrinsic collimation of hard X-ray emission along the axis of the obscuring torus. Given the AGN luminosity function, which steepens at high luminosities, these observational biases lead to a decreasing observed fraction of obscured AGN with increasing luminosity even if this fraction has no intrinsic luminosity dependence. We find that if the central hard X-ray source in AGN is isotropic, the intrinsic (i.e. corrected for biases) obscured AGN fraction still shows a declining trend with luminosity, although the intrinsic obscured fraction is significantly larger than the observed one: the actual fraction is larger than ˜85 per cent at L ≲ 1042.5 erg s-1 (17-60 keV), and decreases to ≲60 per cent at L ≳ 1044 erg s-1. In terms of the half-opening angle θ of an obscuring torus, this implies that θ ≲ 30° in lower luminosity AGN, and θ ≳ 45° in higher luminosity ones. If, however, the emission from the central supermassive black hole is collimated as dL/dΩ ∝ cos α, the intrinsic dependence of the obscured AGN fraction is consistent with a luminosity-independent torus half-opening angle θ ˜ 30°.

  19. Theoretical modeling of the dynamics of a semiconductor laser subject to double-reflector optical feedback

    NASA Astrophysics Data System (ADS)

    Bakry, A.; Abdulrhmann, S.; Ahmed, M.

    2016-06-01

    We theoretically model the dynamics of semiconductor lasers subject to the double-reflector feedback. The proposed model is a new modification of the time-delay rate equations of semiconductor lasers under the optical feedback to account for this type of the double-reflector feedback. We examine the influence of adding the second reflector to dynamical states induced by the single-reflector feedback: periodic oscillations, period doubling, and chaos. Regimes of both short and long external cavities are considered. The present analyses are done using the bifurcation diagram, temporal trajectory, phase portrait, and fast Fourier transform of the laser intensity. We show that adding the second reflector attracts the periodic and perioddoubling oscillations, and chaos induced by the first reflector to a route-to-continuous-wave operation. During this operation, the periodic-oscillation frequency increases with strengthening the optical feedback. We show that the chaos induced by the double-reflector feedback is more irregular than that induced by the single-reflector feedback. The power spectrum of this chaos state does not reflect information on the geometry of the optical system, which then has potential for use in chaotic (secure) optical data encryption.

  20. Cadence Requirements for AGN Accretion Studies with LSST

    NASA Astrophysics Data System (ADS)

    Moreno, Jackeline; Vogeley, Michael S.; Richards, Gordon T.; Kasliwal, Vishal P.

    2016-01-01

    We test various samplings of mock AGN lightcurves to determine minimum cadence requirements for future technologies like the Large Synoptic Survey Telescope (LSST). AGN lightcurves exhibit stochastic behavior, with variability seen in ground-based optical surveys on timescales from days to years. Significant variability structure on timescales up to a few days was revealed by the high time resolution (~30 minutes) of Kepler Satellite. Now it is apparent that under-sampling by ground based instruments may be leaving out a big chunk of the AGN accretion picture. To probe Kepler AGN, recent studies have investigated the suitability of sophisticated models like CARMA processes to better understand dominant mechanisms driving observed variability across these timescales. By testing models against AGN photometry, we gain insights about accretion physics, intrinsic differences between AGN sub-types, and physical scales pertaining to orbits or casually connected matter flows. We investigate cadence, time window, and regularity requirements that accurately recover parameters of our model lightcurves constructed with a CARMA process and observations such that ground based telescopes can optimally collect data for AGN science.

  1. Signal-Response Modeling of Partial Hormone Feedback Networks

    PubMed Central

    Johnson, Michael L.; Veldhuis, Paula P.; Evans, William S.

    2009-01-01

    Background Endocrine feedback control networks are typically complex and contain multiple hormones, pools, and compartments. The hormones themselves commonly interact via multiple pathways and targets within the networks, and a complete description of such relationships may involve hundreds of parameters. In addition, it is often difficult, if not impossible, to collect experimental data pertaining to every component within the network. Therefore, the complete simultaneous analysis of such networks is challenging. Nevertheless, an understanding of these networks is critical for furthering our knowledge of hormonal regulation in both physiologic and pathophysiologic conditions. Methods We propose a novel approach for the analysis of dose-response relationships of subsets of hormonal feedback networks. The algorithm and signal-response quantification (SRQuant) software is based on convolution integrals, and tests whether several discretely measured input signals can be individually delayed, spread in time, transformed, combined, and discretely convolved with an elimination function to predict the time course of the concentration of an output hormone. Signal-response quantification is applied to examples from the endocrine literature to demonstrate its applicability to the analysis of the different endocrine networks. Results In one example, SRQuant determines the dose-response relationship by which one hormone regulates another, highlighting its advantages over other traditional methods. In a second example, for the first time (to the best of our knowledge), we show that the secretion of glucagon may be jointly controlled by the β and the δ cells. Conclusion We have developed a novel convolution integral-based approach, algorithm, and software (SRQuant) for the analysis of dose-response relationships within subsets of complex endocrine feedback control networks. PMID:20046649

  2. Relativistic feedback models of terrestrial gamma-ray flashes and gamma-ray glows

    NASA Astrophysics Data System (ADS)

    Dwyer, J. R.

    2015-12-01

    Relativistic feedback discharges, also known as dark lightning, are capable of explaining many of the observed properties of terrestrial gamma-ray flashes (TGFs) and gamma-ray glows, both created within thunderstorms. During relativistic feedback discharges, the generation of energetic electrons is self-sustained via the production of backward propagating positrons and back-scattered x-rays, resulting in very larges fluxes of energetic radiation. In addition, ionization produces large electric currents that generate LF/VLF radio emissions and eventually discharge the electric field, terminating the gamma-ray production. In this presentation, new relativistic feedback model results will be presented and compared to recent observations.

  3. Insights into low-latitude cloud feedbacks from high-resolution models.

    PubMed

    Bretherton, Christopher S

    2015-11-13

    Cloud feedbacks are a leading source of uncertainty in the climate sensitivity simulated by global climate models (GCMs). Low-latitude boundary-layer and cumulus cloud regimes are particularly problematic, because they are sustained by tight interactions between clouds and unresolved turbulent circulations. Turbulence-resolving models better simulate such cloud regimes and support the GCM consensus that they contribute to positive global cloud feedbacks. Large-eddy simulations using sub-100 m grid spacings over small computational domains elucidate marine boundary-layer cloud response to greenhouse warming. Four observationally supported mechanisms contribute: 'thermodynamic' cloudiness reduction from warming of the atmosphere-ocean column, 'radiative' cloudiness reduction from CO2- and H2O-induced increase in atmospheric emissivity aloft, 'stability-induced' cloud increase from increased lower tropospheric stratification, and 'dynamical' cloudiness increase from reduced subsidence. The cloudiness reduction mechanisms typically dominate, giving positive shortwave cloud feedback. Cloud-resolving models with horizontal grid spacings of a few kilometres illuminate how cumulonimbus cloud systems affect climate feedbacks. Limited-area simulations and superparameterized GCMs show upward shift and slight reduction of cloud cover in a warmer climate, implying positive cloud feedbacks. A global cloud-resolving model suggests tropical cirrus increases in a warmer climate, producing positive longwave cloud feedback, but results are sensitive to subgrid turbulence and ice microphysics schemes. PMID:26438280

  4. Spontaneous oscillations in a nonlinear delayed-feedback shunting model of the pupil light reflex

    NASA Astrophysics Data System (ADS)

    Bressloff, P. C.; Wood, C. V.

    1998-09-01

    We analyze spontaneous oscillations in a second-order delayed-feedback shunting model of the pupil light reflex. This model describes in a simple fashion the nonlinear effects of both the iris and retinal parts of the reflex pathway. In the case of smooth negative feedback, linear stability analysis is used to determine the conditions for a Hopf bifurcation in the pupil area as a function of various neurophysiological parameters of the system such as the time delay and the strength of neural connections. We also investigate oscillation onset in the case of piecewise negative feedback and obtain an analytical expression for the period of oscillations. Finally, complex periodic behavior is shown to arise in the presence of mixed feedback.

  5. Simulating Cortical Feedback Modulation as Changes in Excitation and Inhibition in a Cortical Circuit Model

    PubMed Central

    Murray, John D.; McCormick, David A.

    2016-01-01

    Abstract Cortical feedback pathways are hypothesized to distribute context-dependent signals during flexible behavior. Recent experimental work has attempted to understand the mechanisms by which cortical feedback inputs modulate their target regions. Within the mouse whisker sensorimotor system, cortical feedback stimulation modulates spontaneous activity and sensory responsiveness, leading to enhanced sensory representations. However, the cellular mechanisms underlying these effects are currently unknown. In this study we use a simplified neural circuit model, which includes two recurrent excitatory populations and global inhibition, to simulate cortical modulation. First, we demonstrate how changes in the strengths of excitation and inhibition alter the input–output processing responses of our model. Second, we compare these responses with experimental findings from cortical feedback stimulation. Our analyses predict that enhanced inhibition underlies the changes in spontaneous and sensory evoked activity observed experimentally. More generally, these analyses provide a framework for relating cellular and synaptic properties to emergent circuit function and dynamic modulation. PMID:27595137

  6. Simulating Cortical Feedback Modulation as Changes in Excitation and Inhibition in a Cortical Circuit Model.

    PubMed

    Zagha, Edward; Murray, John D; McCormick, David A

    2016-01-01

    Cortical feedback pathways are hypothesized to distribute context-dependent signals during flexible behavior. Recent experimental work has attempted to understand the mechanisms by which cortical feedback inputs modulate their target regions. Within the mouse whisker sensorimotor system, cortical feedback stimulation modulates spontaneous activity and sensory responsiveness, leading to enhanced sensory representations. However, the cellular mechanisms underlying these effects are currently unknown. In this study we use a simplified neural circuit model, which includes two recurrent excitatory populations and global inhibition, to simulate cortical modulation. First, we demonstrate how changes in the strengths of excitation and inhibition alter the input-output processing responses of our model. Second, we compare these responses with experimental findings from cortical feedback stimulation. Our analyses predict that enhanced inhibition underlies the changes in spontaneous and sensory evoked activity observed experimentally. More generally, these analyses provide a framework for relating cellular and synaptic properties to emergent circuit function and dynamic modulation. PMID:27595137

  7. Starburst or AGN dominance in submm-luminous candidate AGN

    NASA Astrophysics Data System (ADS)

    Coppin, Kristen; Alexander, Dave; Aretxaga, Itziar; Blain, Andrew; Chapman, Scott; Clements, Dave; Dunlop, James; Dunne, Loretta; Dye, Simon; Farrah, Duncan; Hughes, David; Ivison, Rob; Kim, Sungeun; Menendez-Delmestre, Karin; Oliver, Sebastian; Page, Mat; Pope, Alexandra; Rowan-Robinson, Michael; Scott, Douglas; Smail, Ian; Swinbank, Mark; Vaccari, Mattia; van Kampen, Eelco

    2008-03-01

    It is widely believed that starbursts/ULIRGs and AGN activity are triggered by galaxy interactions and merging; and sub-mm selected galaxies (SMGs) seem to be simply high redshift ULIRGs, observed near the peak of activity. In this evolutionary picture every SMG would host an AGN, which would eventually grow a black hole strong enough to blow off all of the gas and dust leaving an optically luminous QSO. In order to probe this evolutionary sequence, a crucial sub-sample to focus on would be the 'missing link' sources, which demonstrate both strong starburst and AGN signatures and to determine if the starburst is the main power source even in SMGs when we have evidence that an AGN is present. The best way to determine if a dominant AGN is present is to look in the mid-IR for their signatures, since often even deep X-ray observations miss identifying the presence of AGN in heavily dust-obscured SMGs. We have selected a sample of SMGs which are good candidates for harboring powerful AGN on the basis of their IRAC colours (S8um/S4.5um>2). Once we confirm these SMGs are AGN-dominated, we can then perform an audit of the energy balance between star-formation and AGN within this special sub-population of SMGs where the BH has grown appreciably to begin heating the dust emission. The proposed observations with IRS will probe the physics of how SMGs evolve from a cold-dust starburst-dominated ULIRG to an AGN/QSO by measuring the level of the mid-IR continuum, PAH luminosity, and Si absorption in these intermediate `transitory' AGN/SMGs.

  8. Ultra-Fast Outflows in Radio-Loud AGN: New Constraints on Jet-Disk Connection

    NASA Astrophysics Data System (ADS)

    Sambruna, Rita

    There is strong observational and theoretical evidence that outflows/jets are coupled to accretion disks in black hole accreting systems, from Galactic to extragalactic sizes. While in radio-quiet AGN there is ample evidence for the presence of Ultra-Fast Outflows (UFOs) from the presence of blue-shifted absorption features in their 4-10~keV spectra, sub-relativistic winds are expected on theoretical basis in radio-loud AGN but have not been observed until now. Our recent Suzaku observations of 5 bright Broad- Line Radio Galaxies (BLRGs, the radio-loud counterparts of Seyferts) has started to change this picture. We found strong evidence for UFOs in 3 out of 5 BLRGs, with ionization parameters, column densities, and velocities of the absorber similar to Seyferts. Moreover, the outflows in BLRGs are likely to be energetically very significant: from the Suzaku data of the three sources, outflow masses similar to the accretion masses and kinetic energies of the wind similar to the X-ray luminosity and radio power of the jet are inferred. Clearly, UFOs in radio-loud AGN represent a new key ingredient to understand their central engines and in particular, the jet-disk linkage. Our discovery of UFOs in a handful of BLRGs raises the questions of how common disk winds are in radio-loud AGN, what the absorber physical and dynamical characteristics are, and what is the outflow role in broader picture of galaxy-black hole connection for radio sources, i.e., for large-scale feedback models. To address these and other issues, we propose to use archival XMM-Newton and Suzaku spectra to search for Ultra-Fast Outflows in a large number of radio sources. Over a period of two years, we will conduct a systematic, uniform analysis of the archival X-ray data, building on our extensive experience with a similar previous project for Seyferts, and using robust analysis and statistical methodologies. As an important side product, we will also obtain accurate, self- consistent measurements

  9. Using visual cues to enhance haptic feedback for palpation on virtual model of soft tissue.

    PubMed

    Li, Min; Konstantinova, Jelizaveta; Secco, Emanuele L; Jiang, Allen; Liu, Hongbin; Nanayakkara, Thrishantha; Seneviratne, Lakmal D; Dasgupta, Prokar; Althoefer, Kaspar; Wurdemann, Helge A

    2015-11-01

    This paper explores methods that make use of visual cues aimed at generating actual haptic sensation to the user, namely pseudo-haptics. We propose a new pseudo-haptic feedback-based method capable of conveying 3D haptic information and combining visual haptics with force feedback to enhance the user's haptic experience. We focused on an application related to tumor identification during palpation and evaluated the proposed method in an experimental study where users interacted with a haptic device and graphical interface while exploring a virtual model of soft tissue, which represented stiffness distribution of a silicone phantom tissue with embedded hard inclusions. The performance of hard inclusion detection using force feedback only, pseudo-haptic feedback only, and the combination of the two feedbacks was compared with the direct hand touch. The combination method and direct hand touch had no significant difference in the detection results. Compared with the force feedback alone, our method increased the sensitivity by 5%, the positive predictive value by 4%, and decreased detection time by 48.7%. The proposed methodology has great potential for robot-assisted minimally invasive surgery and in all applications where remote haptic feedback is needed. PMID:26018755

  10. Dimethylsulphide, clouds, and phytoplankton: Insights from a simple plankton ecosystem feedback model

    NASA Astrophysics Data System (ADS)

    Cropp, Roger; Norbury, John; Braddock, Roger

    2007-06-01

    The hypothesis that marine plankton ecosystems may effectively regulate climate by the production of dimethylsulphide (DMS) has attracted substantial research effort over recent years. This hypothesis suggests that DMS produced by marine ecosystems can affect cloud properties and hence the averaged irradiance experienced by the phytoplankton that produce DMS's precursor dimethylsulphoniopropionate (DMSP). This paper describes the use of a simple model to examine the effects of such a biogenic feedback on the ecosystem that initiates it. We compare the responses to perturbation of a simple marine nitrogen-phytoplankton-zooplankton (NPZ) ecosystem model with and without biogenic feedback. Our analysis of this heuristic model reveals that the addition of the feedback can increase the model's resilience to perturbation and hence stabilize the model ecosystem. This result suggests the hypothesis that DMS may play a role in stabilizing marine plankton ecosystem dynamics through its effect on the atmosphere.

  11. Observational and model evidence for positive low-level cloud feedback.

    PubMed

    Clement, Amy C; Burgman, Robert; Norris, Joel R

    2009-07-24

    Feedbacks involving low-level clouds remain a primary cause of uncertainty in global climate model projections. This issue was addressed by examining changes in low-level clouds over the Northeast Pacific in observations and climate models. Decadal fluctuations were identified in multiple, independent cloud data sets, and changes in cloud cover appeared to be linked to changes in both local temperature structure and large-scale circulation. This observational analysis further indicated that clouds act as a positive feedback in this region on decadal time scales. The observed relationships between cloud cover and regional meteorological conditions provide a more complete way of testing the realism of the cloud simulation in current-generation climate models. The only model that passed this test simulated a reduction in cloud cover over much of the Pacific when greenhouse gases were increased, providing modeling evidence for a positive low-level cloud feedback. PMID:19628865

  12. A Global Picture of AGN Winds

    NASA Technical Reports Server (NTRS)

    Kazanas, D.; Fukumura, K.

    2011-01-01

    We present a unified structure for accretion powered sources across their entire luminosity range from accreting galactic black holes to the most luminous quasars, with emphasis on AGN and their phenomenology. Central to this end is the notion of MHD winds launched from the accretion disks that power these objects. This work similar in spirit to that of Elvis of more that a decade ago, provides, on one hand, only the broadest characteristics of these objects, but on the other, also scaling laws that allow one to make contact with objects of different luminosity. The conclusion of this work is that AGN phenomenology can be accounted for in terms of dot(m), the wind mass flux in units of the Eddington value, the observer's inclination angle theta and alpha_OX the logarithmic slope between UV and X-ray flares. However given the well known correlation between alpha(sub ox) and UV Luminosity, we conclude that the AGN structure depends on only two parameters. The small number of model parameters hence suggests that an understanding of the global AGN properties maybe within reach.

  13. Computer modeling of endovascular patch welding using temperature feedback

    SciTech Connect

    Glinsky, M.E.; London, R.A.; Zimmerman, G.B.; Jacques, S.L.; Ols, J.D.

    1995-11-01

    A new computer program, LATIS, being developed at Lawrence Livermore National Laboratory is used to study the effect of pulsed laser irradiation with temperature feedback on endovascular patch welding. Various physical and biophysical effects are included in these simulations: laser light scattering and absorption, tissue heating and heat conduction, vascular cooling, and tissue thermal damage. The geometry of a patch being held against the inner vessel wall (500 {mu}m inner diameter) by a balloon is considered. The system is exposed to light pulsed from an optical fiber inside the balloon. The laser power is adjusted during the course of a pulse. This is done automatically in the simulation by temperature feedback. A minimum in the depth of damage into the vessel wall is found. The minimum damage zone is about the thickness of the patch material that is heated by the laser. The more ordered the tissue the thinner the minimum zone of damage. The pulse length which minimizes the zone of damage is found to be the time for energy to diffuse across the layer. The delay time between the pulses is determined by the time for the heated layer to cool down. An optimal pulse length exists which minimizes the total time needed to weld the patch to the wall while keeping the thickness of the damaged tissue to less than 100 {mu}m. For the case that is considered, a patch dyed with light absorbing ICG on the side next to the vessel (thickness of the dyed layer is 60 {mu}m), the best protocol is found to be 33-600 ms pulses applied over 1.6 min.

  14. Toward a Unified AGN Structure

    NASA Technical Reports Server (NTRS)

    Kazanas, Demosthenes; Fukumura, Keigo; Shrader, Chris; Behar, Ehud; Contopoulosa, Ioannis

    2012-01-01

    We present a unified model for the structure and appearance of accretion powered sources across their entire luminosity range from galactic X-ray binaries (XRB) to luminous quasars, with emphasis on AG N and their phenomenology. Central to this model is the notion of MHD winds launched by the accretion disks that power these objects. These winds provide the matter that manifests as blueshifted absorption features in the UV and X-ray spectra of a large fraction of these sources; furthermore, their density distribution in the poloidal plane determines their "appearance" (i.e. the column and velocity structure of these absorption features and the obscuration of the continuum source) as a function of the observer inclination angle (a feature to which INTEGRAL has made significant contributions). This work focuses on just the broadest characteristics of these objects; nonetheless, it provides scaling laws that allow one to reproduce within this model the properties of objects extending in luminosity from luminous quasars to XRBs. Our general conclusion is that the AGN phenomenology can be accounted for in terms of three parameters: The wind maSS flux in units of the Eddington value, m(dot), the observers' inclination angle Theta and the logarithmic slope between the 0/UV and X-ray fluxes alpha(sub ox); however because of a correlation between alpha(sub ox) and UV luminosity the number of significant parameters is two. The AGN correlations implied by this model appear to extend to and consistent with the XRB phenomenology, suggesting the presence of a truly unified underlying structure for accretion powered sources.

  15. Disentangling AGN and Star Formation in Soft X-Rays

    NASA Technical Reports Server (NTRS)

    LaMassa, Stephanie M.; Heckman, T. M.; Ptak, A.

    2012-01-01

    We have explored the interplay of star formation and active galactic nucleus (AGN) activity in soft X-rays (0.5-2 keV) in two samples of Seyfert 2 galaxies (Sy2s). Using a combination of low-resolution CCD spectra from Chandra and XMM-Newton, we modeled the soft emission of 34 Sy2s using power-law and thermal models. For the 11 sources with high signal-to-noise Chandra imaging of the diffuse host galaxy emission, we estimate the luminosity due to star formation by removing the AGN, fitting the residual emission. The AGN and star formation contributions to the soft X-ray luminosity (i.e., L(sub x,AGN) and L(sub x,SF)) for the remaining 24 Sy2s were estimated from the power-law and thermal luminosities derived from spectral fitting. These luminosities were scaled based on a template derived from XSINGS analysis of normal star-forming galaxies. To account for errors in the luminosities derived from spectral fitting and the spread in the scaling factor, we estimated L(sub x,AGN) and L(sub x,SF))from Monte Carlo simulations. These simulated luminosities agree with L(sub x,AGN) and L(sub x,SF) derived from Chandra imaging analysis within a 3sigma confidence level. Using the infrared [Ne ii]12.8 micron and [O iv]26 micron lines as a proxy of star formation and AGN activity, respectively, we independently disentangle the contributions of these two processes to the total soft X-ray emission. This decomposition generally agrees with L(sub x,SF) and L(sub x,AGN) at the 3 sigma level. In the absence of resolvable nuclear emission, our decomposition method provides a reasonable estimate of emission due to star formation in galaxies hosting type 2 AGNs.

  16. DISENTANGLING AGN AND STAR FORMATION IN SOFT X-RAYS

    SciTech Connect

    LaMassa, Stephanie M.; Heckman, T. M.; Ptak, A.

    2012-10-20

    We have explored the interplay of star formation and active galactic nucleus (AGN) activity in soft X-rays (0.5-2 keV) in two samples of Seyfert 2 galaxies (Sy2s). Using a combination of low-resolution CCD spectra from Chandra and XMM-Newton, we modeled the soft emission of 34 Sy2s using power-law and thermal models. For the 11 sources with high signal-to-noise Chandra imaging of the diffuse host galaxy emission, we estimate the luminosity due to star formation by removing the AGN, fitting the residual emission. The AGN and star formation contributions to the soft X-ray luminosity (i.e., L{sub x,AGN} and L{sub x,SF}) for the remaining 24 Sy2s were estimated from the power-law and thermal luminosities derived from spectral fitting. These luminosities were scaled based on a template derived from XSINGS analysis of normal star-forming galaxies. To account for errors in the luminosities derived from spectral fitting and the spread in the scaling factor, we estimated L{sub x,AGN} and L{sub x,SF} from Monte Carlo simulations. These simulated luminosities agree with L{sub x,AGN} and L{sub x,SF} derived from Chandra imaging analysis within a 3{sigma} confidence level. Using the infrared [Ne II]12.8 {mu}m and [O IV]26 {mu}m lines as a proxy of star formation and AGN activity, respectively, we independently disentangle the contributions of these two processes to the total soft X-ray emission. This decomposition generally agrees with L{sub x,SF} and L{sub x,AGN} at the 3{sigma} level. In the absence of resolvable nuclear emission, our decomposition method provides a reasonable estimate of emission due to star formation in galaxies hosting type 2 AGNs.

  17. Optical-feedback cavity-enhanced absorption spectroscopy in a linear cavity: model and experiments

    NASA Astrophysics Data System (ADS)

    Manfred, Katherine M.; Ciaffoni, Luca; Ritchie, Grant A. D.

    2015-08-01

    Optical-feedback cavity-enhanced absorption spectroscopy is a highly sensitive trace gas sensing technique that relies on feedback from a resonant intracavity field to successively lock the laser to the cavity as the wavelength is scanned across a molecular absorption with a comb of resonant frequencies. V-shaped optical cavities have been favoured in the past in order to avoid additional feedback fields from non-resonant reflections that potentially suppress the locking to the resonant cavity frequency. A model of the laser-cavity coupling demonstrates, however, that the laser can stably lock to a resonant linear cavity, within certain constraints on the relative intensity of the two feedback sources. By mode mismatching the field into the linear cavity, we have shown that it is theoretically and practically possible to spatially filter out the unwanted non-resonant component in order for the resonant field to dominate the feedback competition at the laser. A 5.3 cw quantum cascade laser scanning across a absorption feature demonstrated stable locking to achieve a minimum detectable absorption coefficient of for 1-s averaging. Detailed investigations of feedback effects on the laser output verified the validity of our theoretical models.

  18. Regular network model for the sea ice-albedo feedback in the Arctic.

    PubMed

    Müller-Stoffels, Marc; Wackerbauer, Renate

    2011-03-01

    The Arctic Ocean and sea ice form a feedback system that plays an important role in the global climate. The complexity of highly parameterized global circulation (climate) models makes it very difficult to assess feedback processes in climate without the concurrent use of simple models where the physics is understood. We introduce a two-dimensional energy-based regular network model to investigate feedback processes in an Arctic ice-ocean layer. The model includes the nonlinear aspect of the ice-water phase transition, a nonlinear diffusive energy transport within a heterogeneous ice-ocean lattice, and spatiotemporal atmospheric and oceanic forcing at the surfaces. First results for a horizontally homogeneous ice-ocean layer show bistability and related hysteresis between perennial ice and perennial open water for varying atmospheric heat influx. Seasonal ice cover exists as a transient phenomenon. We also find that ocean heat fluxes are more efficient than atmospheric heat fluxes to melt Arctic sea ice. PMID:21456825

  19. Thermocline and Direct Windstress Feedbacks In A Stochastically Driven Linear Enso Model

    NASA Astrophysics Data System (ADS)

    Burgers, G.; van Oldenborgh, G. J.

    El Niño ­ Southern Oscillation (ENSO) simulations with a linear model improve markedly if zonal advection effects are included as a direct windstress feedback on SST, both in forced and in coupled runs. First, runs forced by observed monthly windstresses are studied with a linear 1.5-layer reduced gravity model and a linear SST equation with a thermocline feedback and a direct windstress feedback. With only the thermocline feedback, the model is only able to simulate SST in the NINO3 area. The region where SST agrees with observa- tions extends much more to the west if the windstress feedback is added (r=0.83 for the NINO3 index and r=0.84 for the NINO4 index over 1968-1999). In addition the correlation between the NINO3 and the NINO4 index, which is of the order of 0.75, can only be properly simulated if the windstress feedback is included. Next a simple statistical atmosphere is added that is based on a regression of observed winds to the NINO3 and NINO4 indices. The coupled system is driven by noise in the coefficients of the two regression patterns that is inferred from the scatter in the regression. The resulting system displays irregular oscillations with a period of the order of 3-4 years if both feedbacks are included, with episodes of eastward as well as westward propagating SST anomalies. Also in the coupled system, the observed correlation between the NINO3 and the NINO4 can be reproduced if, and only if, the windstress feedback is included. The amplitude of the oscillations is much enhanced by including the windstress feedback, and the period increased. Also the characteris- tics of the noise have an influence on the nature of the ENSO cycle. The system of a linear shallow water model with two linear SST feedbacks and a two-pattern statisti- cal atmosphere forms a convenient framework for discussing the influence of climate change on ENSO.

  20. The Spitzer Mid-infrared AGN Survey. II. The Demographics and Cosmic Evolution of the AGN Population

    NASA Astrophysics Data System (ADS)

    Lacy, M.; Ridgway, S. E.; Sajina, A.; Petric, A. O.; Gates, E. L.; Urrutia, T.; Storrie-Lombardi, L. J.

    2015-04-01

    We present luminosity functions derived from a spectroscopic survey of active galactic nuclei (AGNs) selected from Spitzer Space Telescope imaging surveys. Selection in the mid-infrared is significantly less affected by dust obscuration. We can thus compare the luminosity functions of obscured and unobscured AGNs in a more reliable fashion than by using optical or X-ray data alone. We find that the AGN luminosity function can be well described by a broken power-law model in which the break luminosity decreases with redshift. At high redshifts (z\\gt 1.6), we find significantly more AGNs at a given bolometric luminosity than found by either optical quasar surveys or hard X-ray surveys. The fraction of obscured AGNs decreases rapidly with increasing AGN luminosity, but, at least at high redshifts, appears to remain at ≈ 50% even at bolometric luminosities ˜ {{10}14} {{L}⊙ }. The data support a picture in which the obscured and unobscured populations evolve differently, with some evidence that high luminosity obscured quasars peak in space density at a higher redshift than their unobscured counterparts. The amount of accretion energy in the universe estimated from this work suggests that AGNs contribute about 12% to the total radiation intensity of the universe, and a high radiative accretion efficiency ≈ 0.18-0.07+0.12 is required to match current estimates of the local mass density in black holes.

  1. Host Galaxy Properties of the Swift BAT Ultra Hard X-Ray Selected AGN

    NASA Technical Reports Server (NTRS)

    Koss, Michael; Mushotzky, Richard; Veilleux, Sylvain; Winter, Lisa M.; Baumgartner, Wayne; Tueller, Jack; Gehrels, Neil; Valencic, Lynne

    2011-01-01

    We have assembled the largest sample of ultra hard X-ray selected (14-195 keV) AGN with host galaxy optical data to date, with 185 nearby (z<0.05), moderate luminosity AGN from the Swift Burst Alert Telescope (BAT) sample. The BAT AGN host galaxies have intermediate optical colors (u -- r and g -- r) that are bluer than a comparison sample of inactive galaxies and optically selected AGN from the Sloan Digital Sky Survey (SDSS) which are chosen to have the same stellar mass. Based on morphological classifications from the RC3 and the Galaxy Zoo, the bluer colors of BAT AGN are mainly due to a higher fraction of mergers and massive spirals than in the comparison samples. BAT AGN in massive galaxies (log Stellar Mass >10.5) have a 5 to 10 times higher rate of spiral morphologies than in SDSS AGN or inactive galaxies. We also see enhanced far-IR emission in BAT AGN suggestive of higher levels of star formation compared to the comparison samples. BAT AGN are preferentially found in the most massive host galaxies with high concentration indexes indicative of large bulge-to-disk ratios and large supermassive black holes. The narrow-line (NL) BAT AGN have similar intrinsic luminosities as the SDSS NL Seyferts based on measurements of [O III] Lambda 5007. There is also a correlation between the stellar mass and X-ray emission. The BAT AGN in mergers have bluer colors and greater ultra hard X-ray emission compared to the BAT sample as whole. In agreement with the Unified Model of AGN, and the relatively unbiased nature of the BAT sources, the host galaxy colors and morphologies are independent of measures of obscuration such as X-ray column density or Seyfert type. The high fraction of massive spiral galaxies and galaxy mergers in BAT AGN suggest that host galaxy morphology is related to the activation and fueling of local AGN.

  2. A model of a flexible anguilliform swimmer driven by a central pattern generator with proprioceptive feedback

    NASA Astrophysics Data System (ADS)

    Hamlet, Christina; Tytell, Eric; Hoffman, Kathleen; Fauci, Lisa

    2015-11-01

    The swimming of a simple vertebrate, the lamprey, can shed light on how a flexible body can couple with a fluid environment to swim rapidly and efficiently. Animals use proprioceptive sensory information to sense how their bodies are bending, and then adjust the neural signals to their muscles to improve performance. We will present recent progress in the development of a computational model of a lamprey swimming in a Navier-Stokes fluid where a simple central pattern generator model, based on phase oscillators, is coupled to the evolving body dynamics of the swimmer through curvature and curvature derivative feedback. Such feedback can be positive (frequency decreasing), negative (frequency increasing), or mixed (positive to one side of the body and negative to the other, or vice versa). We will examine how the emergent swimming behavior and cost of transport depends upon these functional forms of proprioceptive feedback chosen in the model.

  3. Design of a Model-based Controller with Temperature Feedback for Laser Cladding

    NASA Astrophysics Data System (ADS)

    Devesse, Wim; De Baere, Dieter; Guillaume, Patrick

    Laser cladding, also known as direct metal deposition, is an additive manufacturing technique for the production of freeform metallic parts. High quality parts can be created with the use of feedback control systems which stabilize the melt pool during the cladding process. Current laser cladding control systems are based on low order, empirical models of the process, which have low dynamic accuracy and limit the performance that can be achieved. In this paper, a control system based on a physical heat conduction model of the melt pool dynamics is presented. The control structure consists of a static linear state feedback control law designed using pole placement and combined with a PI controller. The controller is able to regulate the melt pool size by modulating the laser power using a number of surface temperature measurements as the feedback signal. Simulation results using a detailed finite element model show that the controller has good tracking behavior and disturbance rejection properties.

  4. Approximation techniques for parameter estimation and feedback control for distributed models of large flexible structures

    NASA Technical Reports Server (NTRS)

    Banks, H. T.; Rosen, I. G.

    1984-01-01

    Approximation ideas are discussed that can be used in parameter estimation and feedback control for Euler-Bernoulli models of elastic systems. Focusing on parameter estimation problems, ways by which one can obtain convergence results for cubic spline based schemes for hybrid models involving an elastic cantilevered beam with tip mass and base acceleration are outlined. Sample numerical findings are also presented.

  5. Cloud radiation forcings and feedbacks: General circulation model tests and observational validation

    SciTech Connect

    Lee, Wan-Ho; Iacobellis, S.F.; Somerville, R.C.J.

    1997-10-01

    Using an atmospheric general circulation model (the National Center for Atmospheric Research Community Climate Model: CCM2), the effects on climate sensitivity of several different cloud radiation parameterizations have been investigated. In addition to the original cloud radiation scheme of CCM2, four parameterizations incorporating prognostic cloud water were tested: one version with prescribed cloud radiative properties and three other versions with interactive cloud radiative properties. The authors` numerical experiments employ perpetual July integrations driven by globally constant sea surface temperature forcings of two degrees, both positive and negative. A diagnostic radiation calculation has been applied to investigate the partial contributions of high, middle, and low cloud to the total cloud radiative forcing, as well as the contributions of water vapor, temperature, and cloud to the net climate feedback. The high cloud net radiative forcing is positive, and the middle and low cloud net radiative forcings are negative. The total net cloud forcing is negative in all of the model versions. The effect of interactive cloud radiative properties on global climate sensitivity is significant. The net cloud radiative feedbacks consist of quite different shortwave and longwave components between the schemes with interactive cloud radiative properties and the schemes with specified properties. The increase in cloud water content in the warmer climate leads to optically thicker middle- and low-level clouds and in turn to negative shortwave feedbacks for the interactive radiative schemes, while the decrease in cloud amount simply produces a positive shortwave feedback for the schemes with a specified cloud water path. For the longwave feedbacks, the decrease in high effective cloudiness for the schemes without interactive radiative properties leads to a negative feedback, while for the other cases, the longwave feedback is positive. 29 refs., 18 figs., 6 tabs.

  6. The Robust Software Feedback Model: An Effective Waterfall Model Tailoring for Space SW

    NASA Astrophysics Data System (ADS)

    Tipaldi, Massimo; Gotz, Christoph; Ferraguto, Massimo; Troiano, Luigi; Bruenjes, Bernhard

    2013-08-01

    The selection of the most suitable software life cycle process is of paramount importance in any space SW project. Despite being the preferred choice, the waterfall model is often exposed to some criticism. As matter of fact, its main assumption of moving to a phase only when the preceding one is completed and perfected (and under the demanding SW schedule constraints) is not easily attainable. In this paper, a tailoring of the software waterfall model (named “Robust Software Feedback Model”) is presented. The proposed methodology sorts out these issues by combining a SW waterfall model with a SW prototyping approach. The former is aligned with the SW main production line and is based on the full ECSS-E-ST-40C life-cycle reviews, whereas the latter is carried out in advance versus the main SW streamline (so as to inject its lessons learnt into the main streamline) and is based on a lightweight approach.

  7. Forcing and feedback in the MPI-ESM-LR coupled model under abruptly quadrupled CO2

    NASA Astrophysics Data System (ADS)

    Block, K.; Mauritsen, T.

    2013-12-01

    Radiative feedback mechanisms associated with temperature, water vapor, cloud, and surface albedo change determine climate sensitivity to radiative forcing. Here we use the linearized radiative kernel-technique in combination with a Gregory analysis to determine the strength and structure of feedbacks, as well as direct and adjusted CO2 forcings in the coupled Max Planck Institute Earth System Model at base resolution (MPI-ESM-LR). We show that the combined Kernel-Gregory approach yields an elegant separation of surface temperature-dependent feedbacks from contributions to radiative forcing by fast adjustments. MPI-ESM-LR exhibits a relatively large cloud adjustment of nearly 2 W m-2 in direct response to quadrupled CO2, with positive cloud adjustment evident throughout the tropics, subtropics and over most landmasses whereas midlatitude storm tracks contribute negatively. The model features a nonlinear regression of radiation imbalance to global mean surface temperature change, resulting in a significantly increasing effective climate sensitivity after about 20 years which is approximately at temperatures 4-5 K above preindustrial. This feature is not uncommon among climate models and is relevant for future climate projections. We analyze the contribution of the individual feedback processes to this behavior and discuss possible origins such as differential ocean warming patterns associated with deep-ocean heat uptake or state dependencies of the feedback processes.

  8. Starburst or AGN Dominance in Submillimetre-Luminous Candidate AGN?

    NASA Astrophysics Data System (ADS)

    Coppin, Kristen; Pope, Alexandra; Menéndez-Delmestre, Karín; Alexander, David M.; Dunlop, James

    2010-06-01

    It is widely believed that ultraluminous infrared (IR) galaxies and active galactic nuclei (AGN) activity are triggered by galaxy interactions and merging, with the peak of activity occurring at z~2, where submillimetre galaxies are thousands of times more numerous than local ULIRGs. In this evolutionary picture, submillimetre galaxies (SMGs) would host an AGN, which would eventually grow a black hole (BH) strong enough to blow off all of the gas and dust leaving an optically luminous QSO. To probe this evolutionary sequence we have focussed on the `missing link' sources, which demonstrate both strong starburst (SB) and AGN signatures, in order to determine if the SB is the main power source even in SMGs when we have evidence that an AGN is present from their IRAC colours. The best way to determine if a dominant AGN is present is to look for their signatures in the mid-infrared with the Spitzer IRS, since often even deep X-ray observations miss identifying the presence of AGN in heavily dust-obscured SMGs. We present the results of our audit of the energy balance between star-formation and AGN within this special sub-population of SMGs-where the BH has grown appreciably to begin heating the dust emission.

  9. The bulge-disc decomposition of AGN host galaxies

    NASA Astrophysics Data System (ADS)

    Bruce, V. A.; Dunlop, J. S.; Mortlock, A.; Kocevski, D. D.; McGrath, E. J.; Rosario, D. J.

    2016-05-01

    We present the results from a study of the morphologies of moderate luminosity X-ray-selected active galactic nuclei (AGN) host galaxies in comparison to a carefully mass-matched control sample at 0.5 < z < 3 in the CANDELS GOODS-S field. We apply a multiwavelength morphological decomposition analysis to these two samples and report on the differences between the morphologies as fitted from single Sérsic and multiple Sérsic models, and models which include an additional nuclear point-source component. Thus, we are able to compare the widely adopted single Sérsic fits from previous studies to the results from a full morphological decomposition, and address the issue of how biased the inferred properties of AGN hosts are by a potential nuclear contribution from the AGN itself. We find that the AGN hosts are indistinguishable from the general galaxy population except that beyond z ≃ 1.5 they have significantly higher bulge fractions. Even including nuclear sources in our modelling, the probability of this result arising by chance is ˜1 × 10-5, alleviating concerns that previous, purely single Sérsic, analyses of AGN hosts could have been spuriously biased towards higher bulge fractions. This data set also allows us to further probe the physical nature of these point-source components; we find no strong correlation between the point-source component and AGN activity. Our analysis of the bulge and disc fractions of these AGN hosts in comparison to a mass-matched control sample reveals a similar morphological evolutionary track for both the active and non-active populations, providing further evidence in favour of a model where AGN activity is triggered by secular processes.

  10. Dose-response-time modelling: Second-generation turnover model with integral feedback control.

    PubMed

    Andersson, Robert; Jirstrand, Mats; Peletier, Lambertus; Chappell, Michael J; Evans, Neil D; Gabrielsson, Johan

    2016-01-01

    This study presents a dose-response-time (DRT) analysis based on a large preclinical biomarker dataset on the interaction between nicotinic acid (NiAc) and free fatty acids (FFA). Data were collected from studies that examined different rates, routes, and modes of NiAc provocations on the FFA time course. All information regarding the exposure to NiAc was excluded in order to demonstrate the utility of a DRT model. Special emphasis was placed on the selection process of the biophase model. An inhibitory Imax-model, driven by the biophase amount, acted on the turnover rate of FFA. A second generation NiAc/FFA model, which encompasses integral (slow buildup of tolerance - an extension of the previously used NiAc/FFA turnover models) and moderator (rapid and oscillatory) feedback control, was simultaneously fitted to all time courses in normal rats. The integral feedback control managed to capture an observed 90% adaptation (i.e., almost a full return to baseline) when 10 days constant-rate infusion protocols of NiAc were used. The half-life of the adaptation process had a 90% prediction interval between 3.5-12 in the present population. The pharmacodynamic parameter estimates were highly consistent when compared to an exposure-driven analysis, partly validating the DRT modelling approach and suggesting the potential of DRT analysis in areas where exposure data are not attainable. Finally, new numerical algorithms, which rely on sensitivity equations to robustly and efficiently compute the gradients in the parameter optimization, were successfully used for the mixed-effects approach in the parameter estimation. PMID:26529383

  11. TORUS2015: The AGN unification scheme after 30 years

    NASA Astrophysics Data System (ADS)

    Gandhi, P.; Hoenig, S. F.

    2015-09-01

    The torus paradigm has proved to be remarkably successful at unifying the observed zoo of active galaxy (AGN) classes, despite having many manifest holes. The field is still data-driven with novel observational results at multiple wavelengths emerging rapidly. We are only now beginning to map out the structure of dusty gas feeding and obscuring AGN, and to model its evolution in galaxy growth. But these have also brought out several apparently contradictory results which must hold the key to future progress. As we celebrate 30 years of the paradigm, this is the perfect time to draw together our current knowledge and reassess the state of the field. This will be an international workshop at the University of Southampton, UK, with the objective of laying out the major challenges to the field and paving future research directions. Our hope is to facilitate plenty of informal discussions between multiwavelength observers and theorists, addressing some key issues: * What is the main driver in the unification scheme? What are the roles of orientation, mass accretion rate and feedback? * What is the nature and structure of gas and dust in the torus? Do we have a self-consistent picture across multiple wavelengths? * How critical is the role of the torus as an interface between small nuclear scales and large galactic scales? Does galaxy evolution necessarily require tori? * How close are we to self-consistently simulating nuclear activity including AGN feeding and nuclear star-formation? Workshop Rationale The three themes of accretion, orientation, and evolution will be covered through invited and solicited contributions. Different to other conferences, we are building each session around some key papers that have shaped the field or those with great future potential to do so. We specifically pit competing ideas against each other to help painting a realistic picture of the state-of-the-art. Each session will end with discussion rounds delving into important future

  12. Vegetation controls on northern high latitude snow-albedo feedback: observations and CMIP5 model simulations.

    PubMed

    Loranty, Michael M; Berner, Logan T; Goetz, Scott J; Jin, Yufang; Randerson, James T

    2014-02-01

    The snow-masking effect of vegetation exerts strong control on albedo in northern high latitude ecosystems. Large-scale changes in the distribution and stature of vegetation in this region will thus have important feedbacks to climate. The snow-albedo feedback is controlled largely by the contrast between snow-covered and snow-free albedo (Δα), which influences predictions of future warming in coupled climate models, despite being poorly constrained at seasonal and century time scales. Here, we compare satellite observations and coupled climate model representations of albedo and tree cover for the boreal and Arctic region. Our analyses reveal consistent declines in albedo with increasing tree cover, occurring south of latitudinal tree line, that are poorly represented in coupled climate models. Observed relationships between albedo and tree cover differ substantially between snow-covered and snow-free periods, and among plant functional type. Tree cover in models varies widely but surprisingly does not correlate well with model albedo. Furthermore, our results demonstrate a relationship between tree cover and snow-albedo feedback that may be used to accurately constrain high latitude albedo feedbacks in coupled climate models under current and future vegetation distributions. PMID:24039000

  13. Stabilization of traffic flow in optimal velocity model via delayed-feedback control

    NASA Astrophysics Data System (ADS)

    Jin, Yanfei; Hu, Haiyan

    2013-04-01

    Traffic jams may occur due to various reasons, such as traffic accidents, lane reductions and on-ramps. In order to suppress the traffic congestion in an optimal velocity traffic model without any driver's delay taken into account, a delayed-feedback control of both displacement and velocity differences is proposed in this study. By using the delay-independent stability criteria and the H∞-norm, the delayed-feedback control can be determined to stabilize the unstable traffic flow and suppress the traffic jam. The numerical case studies are given to demonstrate and verify the new control method. Furthermore, a comparison is made between the new control method and the method proposed by Konishi et al. [K. Konishi, M. Hirai, H. Kokame, Decentralized delayed-feedback control of an optimal velocity traffic model, Eur. Phys. J. B 15 (2000) 715-722]. The results show that the new control method makes the traffic flow more stable and improves the control performance.

  14. Delayed feedback control via minimum entropy strategy in an economic model

    NASA Astrophysics Data System (ADS)

    Salarieh, Hassan; Alasty, Aria

    2008-02-01

    In this paper minimum entropy (ME) algorithm for controlling chaos, is applied to the Behrens-Feichtinger model, as a discrete-time dynamic system which models a drug market. The ME control is implemented through delayed feedback. It is assumed that the dynamic equations of the system are not known, so the proper feedback gain cannot be obtained analytically from the system equations. In the ME approach the feedback gain is obtained and adapted in such a way that the entropy of the system converges to zero, hence a fixed point of the system will be stabilized. Application of the proposed method with different economic control strategies is numerically investigated. Simulation results show the effectiveness of the ME method to control chaos in economic systems with unknown dynamic equations.

  15. Development of the force-feedback model for an epidural needle insertion simulator.

    PubMed

    Hiemenz, L; Stredney, D; Schmalbrock, P

    1998-01-01

    The Ohio Supercomputer Center and the Department of Anesthesiology at the OSU Medical Center have developed a computer-based simulation system for use in training anesthesiology residents in the technique of placing a needle for an epidural block. Although the simulator has been well regarded, the fidelity of the haptic feedback is limited because it is based on subjective expert-user evaluation and not on objective model-based or data-based empirical methods. Only a single degree of freedom for force-feedback is required. However, the simulation must be able to accurately portray the force required to puncture each layer of tissue in order to feel realistic. The purpose of the research described in this paper was to devise a methodology for creating empirically based realistic force-feedback models for the epidural needle insertion procedure using MRI data and biomechanical data from materials testing. PMID:10180553

  16. The KMOS AGN Survey at High Redshift (KASHz)

    NASA Astrophysics Data System (ADS)

    Harrison, C.; Alexander, D.; Mullaney, J.; Stott, J.; Swinbank, M.; Arumugam, V.; Bauer, F.; Bower, R.; Bunker, A.; Sharples, R.

    2016-03-01

    The KMOS AGN Survey at High Redshift (KASHz) is an extensive observational programme to obtain spatially resolved spectroscopy of distant galaxies that host rapidly growing supermassive black holes (i.e., active galactic nuclei [AGN]). By exploiting the unique capabilities of KMOS we will spatially resolve the ionised gas kinematics in around 200 such galaxies. A fundamental prediction of galaxy formation models is that AGN inject considerable energy into their host galaxies and ultimately destroy or remove star-forming material via outflows. However, until now, observational constraints of this prediction have been limited to only a small number of distant galaxies. KASHz will provide the strongest constraints to date on the prevalence, properties and impact of ionised outflows in the host galaxies of distant AGN. The survey is described and our first results presented.

  17. Simulations of cosmic-ray feedback by active galactic nuclei in galaxy clusters

    NASA Astrophysics Data System (ADS)

    Sijacki, Debora; Pfrommer, Christoph; Springel, Volker; Enßlin, Torsten A.

    2008-07-01

    Feedback processes by active galactic nuclei (AGN) appear to be a key for understanding the nature of the very X-ray luminous cool cores found in many clusters of galaxies. We investigate a numerical model for AGN feedback where for the first time a relativistic particle population in AGN-inflated bubbles is followed within a full cosmological context. In our high-resolution simulations of galaxy cluster formation, we assume that black hole accretion is accompanied by energy feedback that occurs in two different modes, depending on the accretion rate itself. At high accretion rates, a small fraction of the radiated energy is coupled thermally to the gas surrounding the quasar, while in a low-accretion state, mechanically efficient feedback in the form of hot, buoyant bubbles that are inflated by radio activity is considered. Unlike previous work, we inject a non-thermal particle population of relativistic protons into the AGN bubbles, instead of adopting a purely thermal heating. We then follow the subsequent evolution of the cosmic-ray (CR) plasma inside the bubbles, considering both its hydrodynamical interactions and dissipation processes relevant to the CR population. This permits us to analyse the impact of CR bubbles on the surrounding intracluster medium, and in particular, how this contrasts with the purely thermal case. Due to the different buoyancy of relativistic plasma and the comparatively long CR dissipation time-scale, we find substantial changes in the evolution of clusters as a result of CR feedback. In particular, the non-thermal population can provide significant pressure support in central cluster regions at low thermal temperatures, providing a natural explanation for the decreasing temperature profiles found in cool core clusters. At the same time, the morphologies of the bubbles and of the induced X-ray cavities show a striking similarity to observational findings. AGN feedback with CRs also proves efficient in regulating cluster cooling

  18. AGN from HeII: AGN host galaxy properties & demographics

    NASA Astrophysics Data System (ADS)

    Baer, Rudolf E.; Schawinski, Kevin; Weigel, Anna

    2016-01-01

    We present an analysis of HeII emitting objects classified as AGN. In a sample of 81'192 galaxies taken from the seventh data release (DR7) of the Sloan Digital Sky Survey in the redshift interval 0.02 < z < 0.05 and with r < 17 AB mag, the Baldwin, Philips & Terlevitsch 1981 method (BPT) identifies 1029 objects as active galactic nuclei. By applying an analysis using HeII λ 4686 emission lines, based on Shirazi & Binchmann 2012, we have identified an additional 283 active galactic nuclei, which were missed by the BPT method. This represents an increase of over 25 %. The characteristics of the HeII selected AGN are different from the AGN found through the PBT; the colour - mass diagram and the colour histogram both show that HeII selected AGN are bluer. This new selection technique can help inform galaxy black hole coevolution scenarios.

  19. Galaxy Zoo: AGN may be fueled by stellar bars in the local Universe

    NASA Astrophysics Data System (ADS)

    Galloway, Melanie; Willett, Kyle; Fortson, Lucy; Galaxy Zoo Science Team

    2015-01-01

    Bars are a mechanism that have been proposed to explain how gas in the outer regions of a galaxy can be channeled inward and fuel AGN. Multiple observational studies have reported a significantly higher bar fraction in AGN than non-AGN. To accurately probe whether an excess of bars in AGN host galaxies exists because the galaxies host a bar, it is necessary to compare bar and AGN fractions at fixed mass and color, because the presence of bars strongly correlates with both. Thus, a sufficiently large sample is necessary to maintain adequate numbers in subsets of fixed mass and color. We have created a large, volume-limited sample of 19,765 disc galaxies using data from the Sloan Digital Sky Survey. By using morphological classifications from the Galaxy Zoo 2 project, we identify stellar bars in 51.8% of AGN hosts and 37.1% of star-forming disk galaxies. Once mass and color are fixed, there remains a statistically significant increase in the fraction of barred AGN over their unbarred counterparts. Using the L[O III]/MBH ratio as a measure of accretion efficiency, we also show that barred AGN do not exhibit stronger accretion than unbarred AGN at fixed mass or color. The data are consistent with a model in which bar-driven fueling does contribute to the probability of an actively growing black hole, but in which other dynamical mechanisms must contribute to AGN fueling via smaller, non-axisymmetric perturbations.

  20. Reduced-order-model based feedback control of the Modified Hasegawa-Wakatani equations

    NASA Astrophysics Data System (ADS)

    Goumiri, Imene; Rowley, Clarence; Ma, Zhanhua; Gates, David; Parker, Jeffrey; Krommes, John

    2012-10-01

    In this study, we demonstrate the development of model-based feedback control for stabilization of an unstable equilibrium obtained in the Modified Hasegawa-Wakatani (MHW) equations, a classic model in plasma turbulence. First, a balanced truncation is applied; a model reduction technique that has been proved successful in flow control design problems, to obtain a low dimensional model of the linearized MHW equation. A model-based feedback controller is then designed for the reduced order model using linear quadratic regulators (LQR) then a linear quadratic gaussian (LQG) control. The controllers are then applied on the original linearized and nonlinear MHW equations to stabilize the equilibrium and suppress the transition to drift-wave induced turbulences.

  1. AGN Science: The Past, The Present, The Future . AGN Science

    NASA Astrophysics Data System (ADS)

    Boller, Th.

    I review some basic results on AGN science by concentrating on the Fe K and Fe L line observations and on the Narrow-Line Seyfert 1 physics. This paper is based on a talk given at the Vulcano workshop, 'The multifrequency behavior of high energy cosmic sources` in 2009. Given the length of the talk and the number of pages the review on AGN science cannot be complete and is biased towards two science topics and my personal view.

  2. Nonlinear feedback model attitude control using CCD in magnetic suspension system

    NASA Technical Reports Server (NTRS)

    Lin, CHIN-E.; Hou, Ann-San

    1994-01-01

    A model attitude control system for a CCD camera magnetic suspension system is studied in this paper. In a recent work, a position and attitude sensing method was proposed. From this result, model position and attitude of a magnetic suspension system can be detected by generating digital outputs. Based on this achievement, a control system design using nonlinear feedback techniques for magnetic suspended model attitude control is proposed.

  3. Frequency modulated cutaneous orientation feedback from artificial arms. [dynamic control model of human arm

    NASA Technical Reports Server (NTRS)

    Solomonow, M.; Freedy, A.; Lyman, J.

    1975-01-01

    A model of the human arm, emphasizing the neuromuscular mechanisms of feedback control, has been constructed. The various parameters and functions of physiological receptors in the feedback section have been classified into an automated category that can be incorporated in the prosthesis servo loop, and into a sensory category that should be communicated to the operator if control and dynamic performance are to be optimized. A scheme for simultaneous display of two such sensory parameters, i.e., fingertip pressure and elbow position, has been developed, implemented and evaluated. The neurophysiological mechanism of such displays, and the feasibility of sensory transformation, is discussed in this paper.

  4. An epidemic spreading model on adaptive scale-free networks with feedback mechanism

    NASA Astrophysics Data System (ADS)

    Li, Tao; Liu, Xiongding; Wu, Jie; Wan, Chen; Guan, Zhi-Hong; Wang, Yuanmei

    2016-05-01

    A SIRS epidemic model with feedback mechanism on adaptive scale-free networks is presented. Using the mean field theory the spreading dynamics of the epidemic is studied in detail. The basic reproductive number and equilibriums are derived. Theoretical results indicate that the basic reproductive number is significantly dependent on the topology of the underlying networks. The existence of equilibriums is determined by the basic reproductive number. The global stability of disease-free equilibrium and the epidemic permanence are proved in detail. The feedback mechanism cannot change the basic reproductive number, but it can reduce the endemic level and weaken the epidemic spreading. Numerical simulations confirmed the analytical results.

  5. The Effects of Verbal Instruction, Modeling, Rehearsal, and Feedback on Correct Posture during Flute Playing

    ERIC Educational Resources Information Center

    Dib, Nancy Ellen; Sturmey, Peter

    2007-01-01

    A behavioral skills training package, including verbal instruction, modeling, rehearsal, and feedback, was used to teach children correct posture, defined as keeping feet on the floor, legs parallel to each other, and the back and neck perpendicular to the floor, during flute lessons. Three typically developing girls aged 8 to 9 years…

  6. Immediate Feedback and Opportunity to Revise Answers: Application of a Graded Response IRT Model

    ERIC Educational Resources Information Center

    Attali, Yigal

    2011-01-01

    Recently, Attali and Powers investigated the usefulness of providing immediate feedback on the correctness of answers to constructed response questions and the opportunity to revise incorrect answers. This article introduces an item response theory (IRT) model for scoring revised responses to questions when several attempts are allowed. The model…

  7. Learning to Swim Using Video Modelling and Video Feedback within a Self-Management Program

    ERIC Educational Resources Information Center

    Lao, So-An; Furlonger, Brett E.; Moore, Dennis W.; Busacca, Margherita

    2016-01-01

    Although many adults who cannot swim are primarily interested in learning by direct coaching there are options that have a focus on self-directed learning. As an alternative a self-management program combined with video modelling, video feedback and high quality and affordable video technology was used to assess its effectiveness to assisting an…

  8. Video Modeling by Experts with Video Feedback to Enhance Gymnastics Skills

    ERIC Educational Resources Information Center

    Boyer, Eva; Miltenberger, Raymond G.; Batsche, Catherine; Fogel, Victoria

    2009-01-01

    The effects of combining video modeling by experts with video feedback were analyzed with 4 female competitive gymnasts (7 to 10 years old) in a multiple baseline design across behaviors. During the intervention, after the gymnast performed a specific gymnastics skill, she viewed a video segment showing an expert gymnast performing the same skill…

  9. Preschoolers' Use of Feedback for Flexible Behavior: Insights from a Computational Model

    ERIC Educational Resources Information Center

    Chevalier, Nicolas; Dauvier, Bruno; Blaye, Agnes

    2009-01-01

    This study addressed preschoolers' cognitive flexibility in an inductive task requiring response feedback processing to infer relevant task goals. A total of 63 4- to 6-year-olds were tested on a perceptual matching task in which they needed to switch attention among three colors. A computational model was designed to track down how responses to…

  10. A computational model of the temporal dynamics of plasticity in procedural learning: sensitivity to feedback timing

    PubMed Central

    Valentin, Vivian V.; Maddox, W. Todd; Ashby, F. Gregory

    2014-01-01

    The evidence is now good that different memory systems mediate the learning of different types of category structures. In particular, declarative memory dominates rule-based (RB) category learning and procedural memory dominates information-integration (II) category learning. For example, several studies have reported that feedback timing is critical for II category learning, but not for RB category learning—results that have broad support within the memory systems literature. Specifically, II category learning has been shown to be best with feedback delays of 500 ms compared to delays of 0 and 1000 ms, and highly impaired with delays of 2.5 s or longer. In contrast, RB learning is unaffected by any feedback delay up to 10 s. We propose a neurobiologically detailed theory of procedural learning that is sensitive to different feedback delays. The theory assumes that procedural learning is mediated by plasticity at cortical-striatal synapses that are modified by dopamine-mediated reinforcement learning. The model captures the time-course of the biochemical events in the striatum that cause synaptic plasticity, and thereby accounts for the empirical effects of various feedback delays on II category learning. PMID:25071629

  11. Using Video Modeling with Voiceover Instruction Plus Feedback to Train Staff to Implement Direct Teaching Procedures.

    PubMed

    Giannakakos, Antonia R; Vladescu, Jason C; Kisamore, April N; Reeve, Sharon A

    2016-06-01

    Direct teaching procedures are often an important part of early intensive behavioral intervention for consumers with autism spectrum disorder. In the present study, a video model with voiceover (VMVO) instruction plus feedback was evaluated to train three staff trainees to implement a most-to-least direct (MTL) teaching procedure. Probes for generalization were conducted with untrained direct teaching procedures (i.e., least-to-most, prompt delay) and with an actual consumer. The results indicated that VMVO plus feedback was effective in training the staff trainees to implement the MTL procedure. Although additional feedback was required for the staff trainees to show mastery of the untrained direct teaching procedures (i.e., least-to-most and prompt delay) and with an actual consumer, moderate to high levels of generalization were observed. PMID:27606244

  12. Thermal Modeling and Feedback Requirements for LIFE Neutronic Simulations

    SciTech Connect

    Seifried, J E

    2009-07-15

    An initial study is performed to determine how temperature considerations affect LIFE neutronic simulations. Among other figures of merit, the isotopic mass accumulation, thermal power, tritium breeding, and criticality are analyzed. Possible fidelities of thermal modeling and degrees of coupling are explored. Lessons learned from switching and modifying nuclear datasets is communicated.

  13. Models as Feedback: Developing Representational Competence in Chemistry

    ERIC Educational Resources Information Center

    Padalkar, Shamin; Hegarty, Mary

    2015-01-01

    Spatial information in science is often expressed through representations such as diagrams and models. Learning the strengths and limitations of these representations and how to relate them are important aspects of developing scientific understanding, referred to as "representational competence." Diagram translation is particularly…

  14. Modeling of bovine spongiform encephalopathy in a two-species feedback loop.

    PubMed

    Barnes, Richard; Lehman, Clarence

    2013-06-01

    Bovine spongiform encephalopathy, otherwise known as mad cow disease, can spread when an individual cow consumes feed containing the infected tissues of another individual, forming a one-species feedback loop. Such feedback is the primary means of transmission for BSE during epidemic conditions. Following outbreaks in the European Union and elsewhere, many governments enacted legislation designed to limit the spread of such diseases via elimination or reduction of one-species feedback loops in agricultural systems. However, two-species feedback loops-those in which infectious material from one-species is consumed by a secondary species whose tissue is then consumed by the first species-were not universally prohibited and have not been studied before. Here we present a basic ecological disease model which examines the rôle feedback loops may play in the spread of BSE and related diseases. Our model shows that there are critical thresholds between the infection's expansion and decrease related to the lifespan of the hosts, the growth rate of the prions, and the amount of prions circulating between hosts. The ecological disease dynamics can be intrinsically oscillatory, having outbreaks as well as refractory periods which can make it appear that the disease is under control while it is still increasing. We show that non-susceptible species that have been intentionally inserted into a feedback loop to stop the spread of disease do not, strictly by themselves, guarantee its control, though they may give that appearance by increasing the refractory period of an epidemic's oscillations. We suggest ways in which age-related dynamics and cross-species coupling should be considered in continuing evaluations aimed at maintaining a safe food supply. PMID:23746801

  15. Synthetic Feedback Loop Model for Increasing Microbial Biofuel Production Using a Biosensor

    PubMed Central

    Harrison, Mary E.; Dunlop, Mary J.

    2012-01-01

    Current biofuel production methods use engineered bacteria to break down cellulose and convert it to biofuel. A major challenge in microbial fuel production is that increasing biofuel yields can be limited by the toxicity of the biofuel to the organism that is producing it. Previous research has demonstrated that efflux pumps are effective at increasing tolerance to various biofuels. However, when overexpressed, efflux pumps burden cells, which hinders growth and slows biofuel production. Therefore, the toxicity of the biofuel must be balanced with the toxicity of pump overexpression. We have developed a mathematical model for cell growth and biofuel production that implements a synthetic feedback loop using a biosensor to control efflux pump expression. In this way, the production rate will be maximal when the concentration of biofuel is low because the cell does not expend energy expressing efflux pumps when they are not needed. Additionally, the microbe is able to adapt to toxic conditions by triggering the expression of efflux pumps, which allow it to continue biofuel production. Sensitivity analysis indicates that the feedback sensor model is insensitive to many system parameters, but a few key parameters can influence growth and production. In comparison to systems that express efflux pumps at a constant level, the feedback sensor increases overall biofuel production by delaying pump expression until it is needed. This result is more pronounced when model parameters are variable because the system can use feedback to adjust to the actual rate of biofuel production. PMID:23112794

  16. Modeling Discontinuous Phase Transitions in Gel Membranes: Focus on Hysteresis and Feedback Mechanisms

    NASA Astrophysics Data System (ADS)

    Kuksenok, Olga

    Feedback mechanisms are vital in a number of processes in biological systems. For example, feedback loops play an essential role during a limb development in mammals and are responsible for the asymmetric cell division to constrain the growth in plants to the specific regions. An integration of well-controlled feedback loops into the fully synthetic materials is an important step in designing a range of biomimetic functionalities. Herein, we focus on hydrogels functionalized with light-sensitive trisodium salt of copper chlorophyllin and study discontinuous phase transitions in these systems. Prior experimental studies had shown that illumination of these functionalized gels results in their heating and in discontinuous, first order phase transition upon the variation in temperature. Herein, we develop the first computational model for these gels; the framework of the model is based on the gel Lattice Spring Model, in this work we account for the gel heating under the illumination. The results of our simulations are in a good agreement with prior experimental studies. We focus on pattern development during the volume phase transitions in membranes of various thicknesses and show that one can effectively utilize light intensity to remotely control feedback loops in these systems.

  17. Exact Distributions for Stochastic Gene Expression Models with Bursting and Feedback

    NASA Astrophysics Data System (ADS)

    Kumar, Niraj; Platini, Thierry; Kulkarni, Rahul V.

    2014-12-01

    Stochasticity in gene expression can give rise to fluctuations in protein levels and lead to phenotypic variation across a population of genetically identical cells. Recent experiments indicate that bursting and feedback mechanisms play important roles in controlling noise in gene expression and phenotypic variation. A quantitative understanding of the impact of these factors requires analysis of the corresponding stochastic models. However, for stochastic models of gene expression with feedback and bursting, exact analytical results for protein distributions have not been obtained so far. Here, we analyze a model of gene expression with bursting and feedback regulation and obtain exact results for the corresponding protein steady-state distribution. The results obtained provide new insights into the role of bursting and feedback in noise regulation and optimization. Furthermore, for a specific choice of parameters, the system studied maps on to a two-state biochemical switch driven by a bursty input noise source. The analytical results derived provide quantitative insights into diverse cellular processes involving noise in gene expression and biochemical switching.

  18. Modeling jet and outflow feedback during star cluster formation

    SciTech Connect

    Federrath, Christoph; Schrön, Martin; Banerjee, Robi; Klessen, Ralf S.

    2014-08-01

    Powerful jets and outflows are launched from the protostellar disks around newborn stars. These outflows carry enough mass and momentum to transform the structure of their parent molecular cloud and to potentially control star formation itself. Despite their importance, we have not been able to fully quantify the impact of jets and outflows during the formation of a star cluster. The main problem lies in limited computing power. We would have to resolve the magnetic jet-launching mechanism close to the protostar and at the same time follow the evolution of a parsec-size cloud for a million years. Current computer power and codes fall orders of magnitude short of achieving this. In order to overcome this problem, we implement a subgrid-scale (SGS) model for launching jets and outflows, which demonstrably converges and reproduces the mass, linear and angular momentum transfer, and the speed of real jets, with ∼1000 times lower resolution than would be required without the SGS model. We apply the new SGS model to turbulent, magnetized star cluster formation and show that jets and outflows (1) eject about one-fourth of their parent molecular clump in high-speed jets, quickly reaching distances of more than a parsec, (2) reduce the star formation rate by about a factor of two, and (3) lead to the formation of ∼1.5 times as many stars compared to the no-outflow case. Most importantly, we find that jets and outflows reduce the average star mass by a factor of ∼ three and may thus be essential for understanding the characteristic mass of the stellar initial mass function.

  19. X-Ray Absorption, Nuclear Infrared Emission, and Dust Covering Factors of AGNs: Testing Unification Schemes

    NASA Astrophysics Data System (ADS)

    Mateos, S.; Carrera, F. J.; Alonso-Herrero, A.; Hernán-Caballero, A.; Barcons, X.; Asensio Ramos, A.; Watson, M. G.; Blain, A.; Caccianiga, A.; Ballo, L.; Braito, V.; Ramos Almeida, C.

    2016-03-01

    We present the distributions of the geometrical covering factors of the dusty tori (f2) of active galactic nuclei (AGNs) using an X-ray selected complete sample of 227 AGNs drawn from the Bright Ultra-hard XMM-Newton Survey. The AGNs have z from 0.05 to 1.7, 2-10 keV luminosities between 1042 and 1046 erg s-1, and Compton-thin X-ray absorption. Employing data from UKIDSS, 2MASS, and the Wide-field Infrared Survey Explorer in a previous work, we determined the rest-frame 1-20 μm continuum emission from the torus, which we model here with the clumpy torus models of Nenkova et al. Optically classified type 1 and type 2 AGNs are intrinsically different, with type 2 AGNs having, on average, tori with higher f2 than type 1 AGNs. Nevertheless, ˜20% of type 1 AGNs have tori with large covering factors, while ˜23%-28% of type 2 AGNs have tori with small covering factors. Low f2 are preferred at high AGN luminosities, as postulated by simple receding torus models, although for type 2 AGNs the effect is certainly small. f2 increases with the X-ray column density, which implies that dust extinction and X-ray absorption take place in material that share an overall geometry and most likely belong to the same structure, the putative torus. Based on our results, the viewing angle, AGN luminosity, and also f2 determine the optical appearance of an AGN and control the shape of the rest-frame ˜1-20 μm nuclear continuum emission. Thus, the torus geometrical covering factor is a key ingredient of unification schemes.

  20. Clustering of ROSAT All-Sky Survey AGNs Through Cross-Correlation Functions

    NASA Astrophysics Data System (ADS)

    Krumpe, Mirko; Miyaji, Takamitsu; Coil, Alison

    2010-07-01

    We investigate the clustering propertiesof ~1550 low-redshift broad-line AGNs detected in the ROSAT All-Sky Survey (RASS) through a cross-correlation function (CCF) with ~46000 Luminous Red Galaxies (LRGs) in the Sloan Digital Sky Survey (SDSS). Using this approach, we avoid small-number statistics and systematic errors caused by the variation of the Galactic absorption compared to a direct measurement of the AGN auto-correlation function (ACF). We compute the ACF of low-z RASS-AGN based on the CCF for the total X-ray sample ( = 0.25) and found a correlation length of r0 = 4.3-0.4+0.4 h-1 Mpc. Furthermore, we discovered an X-ray luminosity dependence of the clustering signal, i.e. high luminosity AGN cluster stronger than low luminosity AGN. We have also applied a Halo Occupation Distribution (HOD) model directly to our AGN-LRG CCF.

  1. Terrestrial Feedbacks Incorporated in Global Vegetation Models through Observed Trait-Environment Responses

    NASA Astrophysics Data System (ADS)

    Bodegom, P. V.

    2015-12-01

    Most global vegetation models used to evaluate climate change impacts rely on plant functional types to describe vegetation responses to environmental stresses. In a traditional set-up in which vegetation characteristics are considered constant within a vegetation type, the possibility to implement and infer feedback mechanisms are limited as feedback mechanisms will likely involve a changing expression of community trait values. Based on community assembly concepts, we implemented functional trait-environment relationships into a global dynamic vegetation model to quantitatively assess this feature. For the current climate, a different global vegetation distribution was calculated with and without the inclusion of trait variation, emphasizing the importance of feedbacks -in interaction with competitive processes- for the prevailing global patterns. These trait-environmental responses do, however, not necessarily imply adaptive responses of vegetation to changing conditions and may locally lead to a faster turnover in vegetation upon climate change. Indeed, when running climate projections, simulations with trait variation did not yield a more stable or resilient vegetation than those without. Through the different feedback expressions, global and regional carbon and water fluxes were -however- strongly altered. At a global scale, model projections suggest an increased productivity and hence an increased carbon sink in the next decades to come, when including trait variation. However, by the end of the century, a reduced carbon sink is projected. This effect is due to a downregulation of photosynthesis rates, particularly in the tropical regions, even when accounting for CO2-fertilization effects. Altogether, the various global model simulations suggest the critical importance of including vegetation functional responses to changing environmental conditions to grasp terrestrial feedback mechanisms at global scales in the light of climate change.

  2. The nature and energetics of AGN-driven perturbations in the hot gas in the Perseus Cluster

    DOE PAGESBeta

    Zhuravleva, I.; Churazov, E.; Arevalo, P.; Schekochihin, A. A.; Forman, W. R.; Allen, S. W.; Simionescu, A.; Sunyaev, R.; Vikhlinin, A.; Werner, N.

    2016-03-07

    In this paper, cores of relaxed galaxy clusters are often disturbed by AGN. Their Chandra observations revealed a wealth of structures induced by shocks, subsonic gas motions, bubbles of relativistic plasma, etc. In this paper, we determine the nature and energy content of gas fluctuations in the Perseus core by probing statistical properties of emissivity fluctuations imprinted in the soft- and hard-band X-ray images. About 80 per cent of the total variance of perturbations on ~8–70 kpc scales in the core have an isobaric nature, i.e. are consistent with subsonic displacements of the gas in pressure equilibrium with the ambientmore » medium. The observed variance translates to the ratio of energy in perturbations to thermal energy of ~13 per cent. In the region dominated by weak ‘ripples’, about half of the total variance is associated with isobaric perturbations on scales of a few tens of kpc. If these isobaric perturbations are induced by buoyantly rising bubbles, then these results suggest that most of the AGN-injected energy should first go into bubbles rather than into shocks. Using simulations of a shock propagating through the Perseus atmosphere, we found that models reproducing the observed features of a central shock have more than 50 per cent of the AGN-injected energy associated with the bubble enthalpy and only about 20 per cent is carried away with the shock. Such energy partition is consistent with the AGN-feedback model, mediated by bubbles of relativistic plasma, and supports the importance of turbulence in the cooling–heating balance.« less

  3. The nature and energetics of AGN-driven perturbations in the hot gas in the Perseus Cluster

    NASA Astrophysics Data System (ADS)

    Zhuravleva, I.; Churazov, E.; Arévalo, P.; Schekochihin, A. A.; Forman, W. R.; Allen, S. W.; Simionescu, A.; Sunyaev, R.; Vikhlinin, A.; Werner, N.

    2016-05-01

    Cores of relaxed galaxy clusters are often disturbed by AGN. Their Chandra observations revealed a wealth of structures induced by shocks, subsonic gas motions, bubbles of relativistic plasma, etc. In this paper, we determine the nature and energy content of gas fluctuations in the Perseus core by probing statistical properties of emissivity fluctuations imprinted in the soft- and hard-band X-ray images. About 80 per cent of the total variance of perturbations on ˜8-70 kpc scales in the core have an isobaric nature, i.e. are consistent with subsonic displacements of the gas in pressure equilibrium with the ambient medium. The observed variance translates to the ratio of energy in perturbations to thermal energy of ˜13 per cent. In the region dominated by weak `ripples', about half of the total variance is associated with isobaric perturbations on scales of a few tens of kpc. If these isobaric perturbations are induced by buoyantly rising bubbles, then these results suggest that most of the AGN-injected energy should first go into bubbles rather than into shocks. Using simulations of a shock propagating through the Perseus atmosphere, we found that models reproducing the observed features of a central shock have more than 50 per cent of the AGN-injected energy associated with the bubble enthalpy and only about 20 per cent is carried away with the shock. Such energy partition is consistent with the AGN-feedback model, mediated by bubbles of relativistic plasma, and supports the importance of turbulence in the cooling-heating balance.

  4. Incorporation of surface albedo-temperature feedback in a one-dimensional radiative-connective climate model

    NASA Technical Reports Server (NTRS)

    Wang, W. C.; Stone, P. H.

    1979-01-01

    The feedback between ice snow albedo and temperature is included in a one dimensional radiative convective climate model. The effect of this feedback on sensitivity to changes in solar constant is studied for the current values of the solar constant and cloud characteristics. The ice snow albedo feedback amplifies global climate sensitivity by 33% and 50%, respectively, for assumptions of constant cloud altitude and constant cloud temperature.

  5. Effects of noise variance model on optimal feedback design and actuator placement

    NASA Technical Reports Server (NTRS)

    Ruan, Mifang; Choudhury, Ajit K.

    1994-01-01

    In optimal placement of actuators for stochastic systems, it is commonly assumed that the actuator noise variances are not related to the feedback matrix and the actuator locations. In this paper, we will discuss the limitation of that assumption and develop a more practical noise variance model. Various properties associated with optimal actuator placement under the assumption of this noise variance model are discovered through the analytical study of a second order system.

  6. Optimal velocity model with consideration of the lateral effect and its feedback control research

    NASA Astrophysics Data System (ADS)

    Zheng, Y. Z.; Ge, H. X.

    2016-06-01

    In this paper, a car-following model with the consideration of lateral effect is constructed. An improved control signal with considering more comprehensive information is introduced according to the feedback control theory. The stability conditions with control signal or not are derived. Numerical simulations are carried out to illustrate the advantage of the modified model with and without the control signal, and the results are consistent with the analytical ones.

  7. Cloud Radiation Forcings and Feedbacks: General Circulation Model Tests and Observational Validation

    NASA Technical Reports Server (NTRS)

    Lee,Wan-Ho; Iacobellis, Sam F.; Somerville, Richard C. J.

    1997-01-01

    Using an atmospheric general circulation model (the National Center for Atmospheric Research Community Climate Model: CCM2), the effects on climate sensitivity of several different cloud radiation parameterizations have been investigated. In addition to the original cloud radiation scheme of CCM2, four parameterizations incorporating prognostic cloud water were tested: one version with prescribed cloud radiative properties and three other versions with interactive cloud radiative properties. The authors' numerical experiments employ perpetual July integrations driven by globally constant sea surface temperature forcings of two degrees, both positive and negative. A diagnostic radiation calculation has been applied to investigate the partial contributions of high, middle, and low cloud to the total cloud radiative forcing, as well as the contributions of water vapor, temperature, and cloud to the net climate feedback. The high cloud net radiative forcing is positive, and the middle and low cloud net radiative forcings are negative. The total net cloud forcing is negative in all of the model versions. The effect of interactive cloud radiative properties on global climate sensitivity is significant. The net cloud radiative feedbacks consist of quite different shortwave and longwave components between the schemes with interactive cloud radiative properties and the schemes with specified properties. The increase in cloud water content in the warmer climate leads to optically thicker middle- and low-level clouds and in turn to negative shortwave feedbacks for the interactive radiative schemes, while the decrease in cloud amount simply produces a positive shortwave feedback for the schemes with a specified cloud water path. For the longwave feedbacks, the decrease in high effective cloudiness for the schemes without interactive radiative properties leads to a negative feedback, while for the other cases, the longwave feedback is positive. These cloud radiation

  8. Model for a pulsed terahertz quantum cascade laser under optical feedback.

    PubMed

    Agnew, Gary; Grier, Andrew; Taimre, Thomas; Lim, Yah Leng; Bertling, Karl; Ikonić, Zoran; Valavanis, Alexander; Dean, Paul; Cooper, Jonathan; Khanna, Suraj P; Lachab, Mohammad; Linfield, Edmund H; Davies, A Giles; Harrison, Paul; Indjin, Dragan; Rakić, Aleksandar D

    2016-09-01

    Optical feedback effects in lasers may be useful or problematic, depending on the type of application. When semiconductor lasers are operated using pulsed-mode excitation, their behavior under optical feedback depends on the electronic and thermal characteristics of the laser, as well as the nature of the external cavity. Predicting the behavior of a laser under both optical feedback and pulsed operation therefore requires a detailed model that includes laser-specific thermal and electronic characteristics. In this paper we introduce such a model for an exemplar bound-to-continuum terahertz frequency quantum cascade laser (QCL), illustrating its use in a selection of pulsed operation scenarios. Our results demonstrate significant interplay between electro-optical, thermal, and feedback phenomena, and that this interplay is key to understanding QCL behavior in pulsed applications. Further, our results suggest that for many types of QCL in interferometric applications, thermal modulation via low duty cycle pulsed operation would be an alternative to commonly used adiabatic modulation. PMID:27607659

  9. The highs and lows of cloud radiative feedback: Comparing observational data and CMIP5 models

    NASA Astrophysics Data System (ADS)

    Jenney, A.; Randall, D. A.

    2014-12-01

    Clouds play a complex role in the climate system, and remain one of the more difficult aspects of the future climate to predict. Over subtropical eastern ocean basins, particularly next to California, Peru, and Southwest Africa, low marine stratocumulus clouds (MSC) help to reduce the amount of solar radiation that reaches the surface by reflecting incident sunlight. The climate feedback associated with these clouds is thought to be positive. This project looks at CMIP5 models and compares them to observational data from CERES and ERA-Interim to try and find observational evidence and model agreement for low, marine stratocumulus cloud feedback. Although current evidence suggests that the low cloud feedback is positive (IPCC, 2014), an analysis of the simulated relationship between July lower tropospheric stability (LTS) and shortwave cloud forcing in MSC regions suggests that this feedback is not due to changes in LTS. IPCC, 2013: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535 pp.

  10. A model for improving microbial biofuel production using a synthetic feedback loop

    SciTech Connect

    Dunlop, Mary; Keasling, Jay; Mukhopadhyay, Aindrila

    2011-07-14

    Cells use feedback to implement a diverse range of regulatory functions. Building synthetic feedback control systems may yield insight into the roles that feedback can play in regulation since it can be introduced independently of native regulation, and alternative control architectures can be compared. We propose a model for microbial biofuel production where a synthetic control system is used to increase cell viability and biofuel yields. Although microbes can be engineered to produce biofuels, the fuels are often toxic to cell growth, creating a negative feedback loop that limits biofuel production. These toxic effects may be mitigated by expressing efflux pumps that export biofuel from the cell. We developed a model for cell growth and biofuel production and used it to compare several genetic control strategies for their ability to improve biofuel yields. We show that controlling efflux pump expression directly with a biofuel-responsive promoter is a straight forward way of improving biofuel production. In addition, a feed forward loop controller is shown to be versatile at dealing with uncertainty in biofuel production rates.

  11. Assessment of radiative feedback in climate models using satellite observations of annual flux variation.

    PubMed

    Tsushima, Yoko; Manabe, Syukuro

    2013-05-01

    In the climate system, two types of radiative feedback are in operation. The feedback of the first kind involves the radiative damping of the vertically uniform temperature perturbation of the troposphere and Earth's surface that approximately follows the Stefan-Boltzmann law of blackbody radiation. The second kind involves the change in the vertical lapse rate of temperature, water vapor, and clouds in the troposphere and albedo of the Earth's surface. Using satellite observations of the annual variation of the outgoing flux of longwave radiation and that of reflected solar radiation at the top of the atmosphere, this study estimates the so-called "gain factor," which characterizes the strength of radiative feedback of the second kind that operates on the annually varying, global-scale perturbation of temperature at the Earth's surface. The gain factor is computed not only for all sky but also for clear sky. The gain factor of so-called "cloud radiative forcing" is then computed as the difference between the two. The gain factors thus obtained are compared with those obtained from 35 models that were used for the fourth and fifth Intergovernmental Panel on Climate Change assessment. Here, we show that the gain factors obtained from satellite observations of cloud radiative forcing are effective for identifying systematic biases of the feedback processes that control the sensitivity of simulated climate, providing useful information for validating and improving a climate model. PMID:23613585

  12. Forcing, feedbacks and climate sensitivity in CMIP5 coupled atmosphere-ocean climate models

    DOE PAGESBeta

    Andrews, Timothy; Gregory, Jonathan M.; Webb, Mark J.; Taylor, Karl E.

    2012-05-15

    We quantify forcing and feedbacks across available CMIP5 coupled atmosphere-ocean general circulation models (AOGCMs) by analysing simulations forced by an abrupt quadrupling of atmospheric carbon dioxide concentration. This is the first application of the linear forcing-feedback regression analysis of Gregory et al. (2004) to an ensemble of AOGCMs. The range of equilibrium climate sensitivity is 2.1–4.7 K. Differences in cloud feedbacks continue to be important contributors to this range. Some models show small deviations from a linear dependence of top-of-atmosphere radiative fluxes on global surface temperature change. We show that this phenomenon largely arises from shortwave cloud radiative effects overmore » the ocean and is consistent with independent estimates of forcing using fixed sea-surface temperature methods. Moreover, we suggest that future research should focus more on understanding transient climate change, including any time-scale dependence of the forcing and/or feedback, rather than on the equilibrium response to large instantaneous forcing.« less

  13. Forcing, feedbacks and climate sensitivity in CMIP5 coupled atmosphere-ocean climate models

    SciTech Connect

    Andrews, Timothy; Gregory, Jonathan M.; Webb, Mark J.; Taylor, Karl E.

    2012-05-15

    We quantify forcing and feedbacks across available CMIP5 coupled atmosphere-ocean general circulation models (AOGCMs) by analysing simulations forced by an abrupt quadrupling of atmospheric carbon dioxide concentration. This is the first application of the linear forcing-feedback regression analysis of Gregory et al. (2004) to an ensemble of AOGCMs. The range of equilibrium climate sensitivity is 2.1–4.7 K. Differences in cloud feedbacks continue to be important contributors to this range. Some models show small deviations from a linear dependence of top-of-atmosphere radiative fluxes on global surface temperature change. We show that this phenomenon largely arises from shortwave cloud radiative effects over the ocean and is consistent with independent estimates of forcing using fixed sea-surface temperature methods. Moreover, we suggest that future research should focus more on understanding transient climate change, including any time-scale dependence of the forcing and/or feedback, rather than on the equilibrium response to large instantaneous forcing.

  14. The softest Einstein AGN (active galactic nuclei)

    SciTech Connect

    Cordova, F.A.; Kartje, J.; Mason, K.O.; Mittaz, J.P.D.; Chicago Univ., IL; University Coll., London . Mullard Space Science Lab.)

    1989-01-01

    We have undertaken a coarse spectral study to find the softest sources detected with the Imaging Proportional Counter (IPC) on the Einstein Observatory. Of the nearly 7700 IPC sources, 226 have color ratios that make them candidate ultrasoft'' sources; of these, 83 have small enough errors that we can say with confidence that they have a spectral component similar to those of the white dwarfs Sirius and HZ 43, nearby stars such as {alpha} Cen and Procyon, and typical polar'' cataclysmic variables. By means of catalog searches and ground-based optical and radio observations we have thus far identified 96 of the 226 candidate soft sources; 37 of them are active galactic nuclei (AGN). In the more selective subset of 83 sources, 47 have been identified, 12 of them with AGN. The list of 47 identifications is given in Cordova et al. For one QSO in our sample, E0132.8--411, we are able to fit the pulse-height data to a power-law model and obtain a best fit for the energy spectral index of 2. 2{sub {minus}0.4}{sup +0.6}. For the remainder of the AGN in the higher confidence sample we are able to infer on the basis of their x-ray colors that they have a similar spectral component. Two-thirds of the AGN are detected below 0.5 keV only, while the remainder evidence a flatter spectral component in addition to the ultra-soft component. 14 refs., 5 figs.

  15. Active muscle response using feedback control of a finite element human arm model.

    PubMed

    Östh, Jonas; Brolin, Karin; Happee, Riender

    2012-01-01

    Mathematical human body models (HBMs) are important research tools that are used to study the human response in car crash situations. Development of automotive safety systems requires the implementation of active muscle response in HBM, as novel safety systems also interact with vehicle occupants in the pre-crash phase. In this study, active muscle response was implemented using feedback control of a nonlinear muscle model in the right upper extremity of a finite element (FE) HBM. Hill-type line muscle elements were added, and the active and passive properties were assessed. Volunteer tests with low impact loading resulting in elbow flexion motions were performed. Simulations of posture maintenance in a gravity field and the volunteer tests were successfully conducted. It was concluded that feedback control of a nonlinear musculoskeletal model can be used to obtain posture maintenance and human-like reflexive responses in an FE HBM. PMID:21294008

  16. Evaluating Effectiveness of Modeling Motion System Feedback in the Enhanced Hess Structural Model of the Human Operator

    NASA Technical Reports Server (NTRS)

    Zaychik, Kirill; Cardullo, Frank; George, Gary; Kelly, Lon C.

    2009-01-01

    In order to use the Hess Structural Model to predict the need for certain cueing systems, George and Cardullo significantly expanded it by adding motion feedback to the model and incorporating models of the motion system dynamics, motion cueing algorithm and a vestibular system. This paper proposes a methodology to evaluate effectiveness of these innovations by performing a comparison analysis of the model performance with and without the expanded motion feedback. The proposed methodology is composed of two stages. The first stage involves fine-tuning parameters of the original Hess structural model in order to match the actual control behavior recorded during the experiments at NASA Visual Motion Simulator (VMS) facility. The parameter tuning procedure utilizes a new automated parameter identification technique, which was developed at the Man-Machine Systems Lab at SUNY Binghamton. In the second stage of the proposed methodology, an expanded motion feedback is added to the structural model. The resulting performance of the model is then compared to that of the original one. As proposed by Hess, metrics to evaluate the performance of the models include comparison against the crossover models standards imposed on the crossover frequency and phase margin of the overall man-machine system. Preliminary results indicate the advantage of having the model of the motion system and motion cueing incorporated into the model of the human operator. It is also demonstrated that the crossover frequency and the phase margin of the expanded model are well within the limits imposed by the crossover model.

  17. Arctic Amplification Feedback Analysis in CMIP5 Models: Land Surfaces, Arctic Ocean and Seasonality

    NASA Astrophysics Data System (ADS)

    Laine, A.; Yoshimori, M.; Abe-Ouchi, A.

    2014-12-01

    The Arctic region is the region where surface warming associated with atmospheric green-house gas concentration increase is expected to be the greatest. This particularity is already being observed currently and is also simulated by climate models. Feedback mechanisms associated with this particularly strong warming, or Artic Amplification, are multiple. The relative role of the different feedbacks are not easy to evaluate precisely using direct model outputs. In this study, we use the "radiative kernels" method (Soden et al, 2008) to perform a multi-model intercomparison analysis. The radiative decomposition is performed at the surface instead of the top of atmosphere in order to consider surface temperature changes specifically. The kernels are derived from the MIROC3.2 model. The intercomparison includes 32 CMIP5 coupled models, whose outputs are analyzed for changes from the late 20th to the late 21st centuries following the rcp4.5 scenario. We consider results separately for land and oceanic surfaces, as the mechanisms and orders of magnitude differ substantially for these two types of surface. We also consider seasons separately as we show that seasonality in the feedback processes is determinant.

  18. Galaxy assembly, stellar feedback and metal enrichment: the view from the GAEA model

    NASA Astrophysics Data System (ADS)

    Hirschmann, Michaela; De Lucia, Gabriella; Fontanot, Fabio

    2016-09-01

    One major problem of current theoretical models of galaxy formation is given by their inability to reproduce the apparently `anti-hierarchical' evolution of galaxy assembly: massive galaxies appear to be in place since z ˜ 3, while a significant increase of the number densities of low-mass galaxies is measured with decreasing redshift. In this work, we perform a systematic analysis of the influence of different stellar feedback schemes, carried out in the framework of GAEA, a new semi-analytic model of galaxy formation. It includes a self-consistent treatment for the timings of gas, metal and energy recycling, and for the chemical yields. We show this to be crucial to use observational measurements of the metallicity as independent and powerful constraints for the adopted feedback schemes. The observed trends can be reproduced in the framework of either a strong ejective or preventive feedback model. In the former case, the gas ejection rate must decrease significantly with cosmic time (as suggested by parametrizations of the cosmological `FIRE' simulations). Irrespective of the feedback scheme used, our successful models always imply that up to 60-70 per cent of the baryons reside in an `ejected' reservoir and are unavailable for cooling at high redshift. The same schemes predict physical properties of model galaxies (e.g. gas content, colour, age, and metallicity) that are in much better agreement with observational data than our fiducial model. The overall fraction of passive galaxies is found to be primarily determined by internal physical processes, with environment playing a secondary role.

  19. Galaxy assembly, stellar feedback and metal enrichment: the view from the GAEA model

    NASA Astrophysics Data System (ADS)

    Hirschmann, Michaela; De Lucia, Gabriella; Fontanot, Fabio

    2016-06-01

    One major problem of current theoretical models of galaxy formation is given by their inability to reproduce the apparently `anti-hierarchical' evolution of galaxy assembly: massive galaxies appear to be in place since z ˜ 3, while a significant increase of the number densities of low mass galaxies is measured with decreasing redshift. In this work, we perform a systematic analysis of the influence of different stellar feedback schemes, carried out in the framework of GAEA, a new semi-analytic model of galaxy formation. It includes a self-consistent treatment for the timings of gas, metal and energy recycling, and for the chemical yields. We show this to be crucial to use observational measurements of the metallicity as independent and powerful constraints for the adopted feedback schemes. The observed trends can be reproduced in the framework of either a strong ejective or preventive feedback model. In the former case, the gas ejection rate must decrease significantly with cosmic time (as suggested by parametrizations of the cosmological "FIRE" simulations). Irrespective of the feedback scheme used, our successful models always imply that up to 60-70 per cent of the baryons reside in an `ejected' reservoir and are unavailable for cooling at high redshift. The same schemes predict physical properties of model galaxies (e.g. gas content, colour, age, and metallicity) that are in much better agreement with observational data than our fiducial model. The overall fraction of passive galaxies is found to be primarily determined by internal physical processes, with environment playing a secondary role.

  20. Visual crowding illustrates the inadequacy of local vs. global and feedforward vs. feedback distinctions in modeling visual perception

    PubMed Central

    Clarke, Aaron M.; Herzog, Michael H.; Francis, Gregory

    2014-01-01

    Experimentalists tend to classify models of visual perception as being either local or global, and involving either feedforward or feedback processing. We argue that these distinctions are not as helpful as they might appear, and we illustrate these issues by analyzing models of visual crowding as an example. Recent studies have argued that crowding cannot be explained by purely local processing, but that instead, global factors such as perceptual grouping are crucial. Theories of perceptual grouping, in turn, often invoke feedback connections as a way to account for their global properties. We examined three types of crowding models that are representative of global processing models, and two of which employ feedback processing: a model based on Fourier filtering, a feedback neural network, and a specific feedback neural architecture that explicitly models perceptual grouping. Simulations demonstrate that crucial empirical findings are not accounted for by any of the models. We conclude that empirical investigations that reject a local or feedforward architecture offer almost no constraints for model construction, as there are an uncountable number of global and feedback systems. We propose that the identification of a system as being local or global and feedforward or feedback is less important than the identification of a system's computational details. Only the latter information can provide constraints on model development and promote quantitative explanations of complex phenomena. PMID:25374554

  1. AGN Observations with STACEE

    NASA Astrophysics Data System (ADS)

    Bramel, D. A.; Boone, L. M.; Carson, J.; Chae, E.; Covault, C. E.; Fortin, P.; Gingrich, D. M.; Hanna, D. S.; Hinton, J. A.; Mukherjee, R.; Mueller, C.; Ong, R. A.; Ragan, K.; Scalzo, R. A.; Schuette, D. R.; Theoret, C. G.; Williams, D. A.; Wong, J.; Zweerink, J.

    2003-03-01

    The Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE) is a gamma-ray detector designed to study astrophysical sources at energies between 50 and 500 GeV. It uses 64 large, steerable mirrors at the National Solar Tower Test Facility near Albuquerque, NM, USA to collect Cherenkov light from extended air showers and concentrate it onto an array of photomultiplier tubes. The large light-collection area gives it a lower energy threshold than imaging-type Cherenkov detectors. STACEE is now fully operational, and we report here on the performance of the complete STACEE instrument, as well as preliminary results of recent observations of several AGN targets. This work was supported in part by the National Science Foundation (under Grant Numbers PHY-9983836, PHY-0070927, and PHY-0070953), the Natural Sciences and Engineering Research Council, Le Fond Quebecois de la Recherche sur la Nature et les Technologies (FQRNT), the Research Corporation, and the California Space Institute. CEC is a Cottrell Scholar of the Research Corporation.

  2. Feedback Regulated Star Formation in Cool Core Clusters of Galaxies

    NASA Astrophysics Data System (ADS)

    Tremblay, Grant Russell

    2011-07-01

    The classical "cooling flow" model historically associated with "cool core" clusters of galaxies fails in the absence of an external, non-gravitational heating mechanism needed to offset catastrophic radiative losses of the X-ray bright intracluster medium (ICM). Numerous proposed solutions exist, including feedback from active galactic nuclei (AGN), which may elegantly calibrate fundamental relationships such as the coupled co-evolution of black holes and the stellar component of their host galaxies. AGN feedback cannot completely offset cooling at all times, however, as the brightest cluster galaxies (BCGs) in cool core clusters harbor extensive warm (˜104 K) and cold (10 < T < 104 K) gas reservoirs whose physical properties are regulated by ongoing star formation and an unknown, non-stellar heating mechanism. We present a doctoral thesis broadly related to these issues, particularly as they pertain to cooling flows, the triggering of AGN activity, and the associated energetic feedback that may play a critical role in heating the ambient environment on tens to hundreds of kiloparsec scales. We begin with a summary of the relevant background material, and in Chapter 2 we present a multiwavelength study of effervescent AGN heating in the cool core cluster Abell 2597. Previously unpublished Chandra X-ray data show the central regions of the hot intracluster medium (ICM) to be highly anisotropic on the scale of the BCG, permeated by a network of kpc-scale X-ray cavities, the largest of which is cospatial in projection with extended 330 MHz radio emission. We present spectral maps of projected, modeled gas properties fit to the X-ray data. The X-ray temperature map reveals two discrete, "hard-edged'' structures, including a ˜15 kpc "cold filament'' and an arc of hot gas which in projection borders the inner edge of the large X-ray cavity. We interpret the latter in the context of the effervescent AGN heating model, in which cavity enthalpy is thermalized as the

  3. Analysis of Atmosphere-Ocean Surface Flux Feedbacks in Recent Satellite and Model Reanalysis Products

    NASA Technical Reports Server (NTRS)

    Roberts, J. Brent; Robertson, F. R.; Clayson, C. A.

    2010-01-01

    Recent investigations have examined observations in an attempt to determine when and how the ocean forces the atmosphere, and vice versa. These studies focus primarily on relationships between sea surface temperature anomalies and the turbulent and radiative surface heat fluxes. It has been found that both positive and negative feedbacks, which enhance or reduce sea surface temperature anomaly amplitudes, can be generated through changes in the surface boundary layer. Consequent changes in sea surface temperature act to change boundary layer characteristics through changes in static stability or turbulent fluxes. Previous studies over the global oceans have used coarse-resolution observational and model products such as ICOADS and the NCEP Reanalysis. This study focuses on documenting the atmosphere ocean feedbacks that exist in recently produced higher resolution products, namely the SeaFlux v1.0 product and the NASA Modern Era Retrospective-Analysis for Research and Applications (MERRA). It has been noted in recent studies that evidence of oceanic forcing of the atmosphere exists on smaller scales than the usually more dominant atmospheric forcing of the ocean, particularly in higher latitudes. It is expected that use of these higher resolution products will allow for a more comprehensive description of these small-scale ocean-atmosphere feedbacks. The SeaFlux intercomparisons have revealed large scatter between various surface flux climatologies. This study also investigates the uncertainty in surface flux feedbacks based on several of these recent satellite based climatologies

  4. The connection between AGN-driven dusty outflows and the surrounding environment

    NASA Astrophysics Data System (ADS)

    Ishibashi, W.; Fabian, A. C.

    2016-04-01

    Significant reservoirs of cool gas are observed in the circumgalactic medium (CGM) surrounding galaxies. The CGM is also found to contain substantial amounts of metals and dust, which require some transport mechanism. We consider AGN (active galactic nucleus) feedback-driven outflows based on radiation pressure on dust. Dusty gas is ejected when the central luminosity exceeds the effective Eddington luminosity for dust. We obtain that a higher dust-to-gas ratio leads to a lower critical luminosity, implying that the more dusty gas is more easily expelled. Dusty outflows can reach large radii with a range of velocities (depending on the outflowing shell configuration and the ambient density distribution) and may account for the observed CGM gas. In our picture, dust is required in order to drive AGN feedback, and the preferential expulsion of dusty gas in the outflows may naturally explain the presence of dust in the CGM. On the other hand, the most powerful AGN outflow events can potentially drive gas out of the local galaxy group. We further discuss the effects of radiation pressure of the central AGN on satellite galaxies. AGN radiative feedback may therefore have a significant impact on the evolution of the whole surrounding environment.

  5. Clustering, Cosmology and a New Era of Black Hole Demographics: The Conditional Luminosity Function of AGNs

    NASA Astrophysics Data System (ADS)

    Ballantyne, David R.

    2016-04-01

    Deep X-ray surveys have provided a comprehensive and largely unbiased view of AGN evolution stretching back to z˜5. However, it has been challenging to use the survey results to connect this evolution to the cosmological environment that AGNs inhabit. Exploring this connection will be crucial to understanding the triggering mechanisms of AGNs and how these processes manifest in observations at all wavelengths. In anticipation of upcoming wide-field X-ray surveys that will allow quantitative analysis of AGN environments, we present a method to observationally constrain the Conditional Luminosity Function (CLF) of AGNs at a specific z. Once measured, the CLF allows the calculation of the AGN bias, mean dark matter halo mass, AGN lifetime, halo occupation number, and AGN correlation function - all as a function of luminosity. The CLF can be constrained using a measurement of the X-ray luminosity function and the correlation length at different luminosities. The method is demonstrated at z ≈0 and 0.9, and clear luminosity dependence in the AGN bias and mean halo mass is predicted at both z. The results support the idea that there are at least two different modes of AGN triggering: one, at high luminosity, that only occurs in high mass, highly biased haloes, and one that can occur over a wide range of halo masses and leads to luminosities that are correlated with halo mass. This latter mode dominates at z<0.9. The CLFs for Type 2 and Type 1 AGNs are also constrained at z ≈0, and we find evidence that unobscured quasars are more likely to be found in higher mass halos than obscured quasars. Thus, the AGN unification model seems to fail at quasar luminosities.

  6. Rule-Based Cell Systems Model of Aging using Feedback Loop Motifs Mediated by Stress Responses

    PubMed Central

    Kriete, Andres; Bosl, William J.; Booker, Glenn

    2010-01-01

    Investigating the complex systems dynamics of the aging process requires integration of a broad range of cellular processes describing damage and functional decline co-existing with adaptive and protective regulatory mechanisms. We evolve an integrated generic cell network to represent the connectivity of key cellular mechanisms structured into positive and negative feedback loop motifs centrally important for aging. The conceptual network is casted into a fuzzy-logic, hybrid-intelligent framework based on interaction rules assembled from a priori knowledge. Based upon a classical homeostatic representation of cellular energy metabolism, we first demonstrate how positive-feedback loops accelerate damage and decline consistent with a vicious cycle. This model is iteratively extended towards an adaptive response model by incorporating protective negative-feedback loop circuits. Time-lapse simulations of the adaptive response model uncover how transcriptional and translational changes, mediated by stress sensors NF-κB and mTOR, counteract accumulating damage and dysfunction by modulating mitochondrial respiration, metabolic fluxes, biosynthesis, and autophagy, crucial for cellular survival. The model allows consideration of lifespan optimization scenarios with respect to fitness criteria using a sensitivity analysis. Our work establishes a novel extendable and scalable computational approach capable to connect tractable molecular mechanisms with cellular network dynamics underlying the emerging aging phenotype. PMID:20585546

  7. Three years of Swift/BAT Survey of AGN: Reconciling Theory and Observations?

    SciTech Connect

    Burlon, D.; Ajello, M.; Greiner, J.; Comastri, A.; Merloni, A.; Gehrels, N.; /NASA, Goddard

    2011-02-07

    It is well accepted that unabsorbed as well as absorbed AGN are needed to explain the nature and the shape of the Cosmic X-ray background, even if the fraction of highly absorbed objects (dubbed Compton-thick sources) substantially still escapes detection. We derive and analyze the absorption distribution using a complete sample of AGN detected by Swift-BAT in the first three years of the survey. The fraction of Compton-thick AGN represents only 4.6% of the total AGN population detected by Swift-BAT. However, we show that once corrected for the bias against the detection of very absorbed sources the real intrinsic fraction of Compton-thick AGN is 20{sub -6}{sup +9}%. We proved for the first time (also in the BAT band) that the anti-correlation of the fraction of absorbed AGN and luminosity it tightly connected to the different behavior of the luminosity functions (XLFs) of absorbed and unabsorbed AGN. This points towards a difference between the two subsamples of objects with absorbed AGN being, on average, intrinsically less luminous than unobscured ones. Moreover the XLFs show that the fraction of obscured AGN might also decrease at very low luminosity. This can be successfully interpreted in the framework of a disk cloud outflow scenario as the disappearance of the obscuring region below a critical luminosity. Our results are discussed in the framework of population synthesis models and the origin of the Cosmic X-ray Background.

  8. Cloud feedbacks on greenhouse warming in the superparameterized climate model SP-CCSM4

    NASA Astrophysics Data System (ADS)

    Bretherton, Christopher S.; Blossey, Peter N.; Stan, Cristiana

    2014-12-01

    Cloud feedbacks on greenhouse warming are studied in a superparameterized version of the Community Climate System Model (SP-CCSM4) in an atmospheric component SP-CAM4 that explicitly simulates cumulus convection. A 150 year simulation in an abrupt quadrupling of CO2 is branched from a control run. It develops moderate positive global cloud feedback and an implied climate sensitivity of 2.8 K comparable to the conventionally parameterized CCSM4 and the median of other modern climate models. All of SP-CCSM4's positive shortwave cloud feedback is due to a striking decrease in low cloud over land, which is much more pronounced than in most other climate models, including CCSM4. Four other cloud responses - decreased midlevel cloud, more Arctic water and ice cloud, a slight poleward shift of midlatitude storm track cloud, and an upward shift of high clouds - are also typical of conventional global climate models. SP-CCSM4 does not simulate the large warming-induced decrease in Southern Ocean cloud found in CCSM4. Two companion uncoupled SP-CAM4 simulations, one with a uniform 4 K sea-surface temperature increase and one with quadrupled CO2 but fixed SST, suggest that SP-CCSM4's global-scale cloud changes are primarily mediated by the warming, rather than by rapid adjustments to increased CO2. SP-CAM4 show spatial patterns of cloud response qualitatively similar to the previous-generation superparameterized SP-CAM3, but with systematically more positive low cloud feedbacks over low-latitude land and ocean.

  9. Optimized feedback control system modeling of resistive wall modes for burning plasmas experiments

    NASA Astrophysics Data System (ADS)

    Katsuro-Hopkins, Oksana Nikolaevna

    A numerical study of active feedback control system performance and optimization for tokamak Resistive Wall Modes (RWM) is the subject of this thesis. The ability to accurately model and predict the performance of an active MHD control systems is critical to present and future advanced confinement scenarios and fusion reactor design studies. The computer code VALEN has been designed to calculate the performance of a MHD feedback control system in an arbitrary geometry. The simulation of realistic effects in feedback systems, such as noise, time delays and filters is of particular importance. In this work realistic measurement noise analysis was added to VALEN and used to design the RWM feedback control amplifier power level for the DIII-D experiment. Modern control theory based on a state-space formulation obtained from VALEN was applied to design an Optimal Controller and Observer based on a reduced VALEN model. A quantitative low order model of the VALEN state space was derived from the high dimensional intrinsic state space structure of the VALEN using methods of a balanced realization and matched DC gain truncation. These techniques for the design of an optimal controller and optimal observer were applied to models of the DIII-D and ITER experiments and showed an order of magnitude reduction of the required control coil current and voltage in the presence of white noise as compared to a traditional, classical PID controller. This optimal controller for the ITER burning plasma experiment was robust from the no-wall pressure limit to a pressure value well above those achieved with a classical PID controller and could approach the ideal wall limit.

  10. Model compilation for real-time planning and diagnosis with feedback

    NASA Technical Reports Server (NTRS)

    Barrett, Anthony

    2005-01-01

    This paper describes MEXEC, an implemented micro executive that compiles a device model that can have feedback into a structure for subsequent evaluation. This system computes both the most likely current device mode from n sets of sensor measurements and the n-1 step reconfiguration plan that is most likely to result in reaching a target mode - if such a plan exists. A user tunes the system by increasing n to improve system capability at the cost of real-time performance.

  11. 2D photochemical modeling of Saturn's stratosphere. Part II: Feedback between composition and temperature

    NASA Astrophysics Data System (ADS)

    Hue, V.; Greathouse, T. K.; Cavalié, T.; Dobrijevic, M.; Hersant, F.

    2016-03-01

    Saturn's axial tilt of 26.7° produces seasons in a similar way as on Earth. Both the stratospheric temperature and composition are affected by this latitudinally varying insolation along Saturn's orbital path. The atmospheric thermal structure is controlled and regulated by the amount of hydrocarbons in the stratosphere, which act as absorbers and coolants from the UV to the far-IR spectral range, and this structure has an influence on the amount of hydrocarbons. We study here the feedback between the chemical composition and the thermal structure by coupling a latitudinal and seasonal photochemical model with a radiative seasonal model. Our results show that the seasonal temperature peak in the higher stratosphere, associated with the seasonal increase of insolation, is shifted earlier than the maximum insolation peak. This shift is increased with increasing latitudes and is caused by the low amount of stratospheric coolants in the spring season. At 80° in both hemispheres, the temperature peak at 10-2 mbar is seen to occur half a season (3-4 Earth years) earlier than was previously predicted by radiative seasonal models that assumed spatially and temporally uniform distribution of coolants. This shift progressively decreases with increasing pressure, up to around the 0.5 mbar pressure level where it vanishes. On the opposite, the thermal field has a small feedback on the abundance distributions. Accounting for that feedback modifies the predicted equator-to-pole temperature gradient. The meridional gradients of temperature at the mbar pressure levels are better reproduced when this feedback is accounted for. At lower pressure levels, Saturn's stratospheric thermal structure seems to depart from pure radiative seasonal equilibrium as previously suggested by Guerlet et al. (2014). Although the agreement with the absolute value of the stratospheric temperature observed by Cassini is moderate, it is a mandatory step toward a fully coupled GCM-photochemical model.

  12. Constructing wetlands: measuring and modeling feedbacks of oxidation processes between plants and clay-rich material

    NASA Astrophysics Data System (ADS)

    Saaltink, Rémon; Dekker, Stefan C.; Griffioen, Jasper; Wassen, Martin J.

    2016-04-01

    Interest is growing in using soft sediment as a building material in eco-engineering projects. Wetland construction in the Dutch lake Markermeer is an example: here the option of dredging some of the clay-rich lake-bed sediment and using it to construct 10.000 ha of wetland will soon go under construction. Natural processes will be utilized during and after construction to accelerate ecosystem development. Knowing that plants can eco-engineer their environment via positive or negative biogeochemical plant-soil feedbacks, we conducted a six-month greenhouse experiment to identify the key biogeochemical processes in the mud when Phragmites australis is used as an eco-engineering species. We applied inverse biogeochemical modeling to link observed changes in pore water composition to biogeochemical processes. Two months after transplantation we observed reduced plant growth and shriveling as well as yellowing of foliage. The N:P ratios of plant tissue were low and were affected not by hampered uptake of N but by enhanced uptake of P. Plant analyses revealed high Fe concentrations in the leaves and roots. Sulfate concentrations rose drastically in our experiment due to pyrite oxidation; as reduction of sulfate will decouple Fe-P in reducing conditions, we argue that plant-induced iron toxicity hampered plant growth, forming a negative feedback loop, while simultaneously there was a positive feedback loop, as iron toxicity promotes P mobilization as a result of reduced conditions through root death, thereby stimulating plant growth and regeneration. Given these two feedback mechanisms, we propose that when building wetlands from these mud deposits Fe-tolerant species are used rather than species that thrive in N-limited conditions. The results presented in this study demonstrate the importance of studying the biogeochemical properties of the building material and the feedback mechanisms between plant and soil prior to finalizing the design of the eco-engineering project.

  13. Modeling of the Feedback Stabilization of the Resistive Wall Mode in Tokamak Geometry

    NASA Astrophysics Data System (ADS)

    Chance, M. S.; Okabayashi, M.; Chu, M. S.

    1999-11-01

    The VACUUM^1 code is currently being modified to simulate the feedback stabilization of the RWM in the DIII-D device^2. We formulate the problem in terms of the eigenfunctions of the surface Laplacian obtained from the matching of the fields across a thin resistive toroidally symmetric shell. The window pane feedback (C-)coils are modeled accurately in the poloidal angle θ, and approximately by a single harmonic variation in φ. VACUUM relates the perturbations on the various surfaces, i.e., the plasma, both sides of the resistive shell and the C-coil. This results in an operator made up of a set of coupled time dependent equations relating the shell response to the plasma and feedback coil. Various attributes of the system can be calculated, such as the eddy current patterns and the time responses of the eigenmodes of the surface Laplacian operator. As a first appproximation, a PEST or GATO surface eigenmode of an ideal kink is assumed, whose structure remains unchanged during the feedback process, allowing only the magnitude to change. By energizing the C-coils according to the various proposed feedback schemes we propose to correlate with the present experimental results, and also to provide helpful guidance for future runs. rule[1.ex]1.9in.005in This work supported by DoE contract No. DE-AC02-76-CHO-3073 ^1 M.S. Chance, Phys. Plasmas, 4(1997)2161 ^2 A. A. Garofalo et al., Phys. Plasmas 6(1999) 1893

  14. Investigation of land-atmosphere feedbacks through coupled hydrologic modeling (Invited)

    NASA Astrophysics Data System (ADS)

    Chow, F. K.; Rihani, J.; Maxwell, R. M.

    2010-12-01

    A three-dimensional, variably saturated groundwater model coupled to a three dimensional mesoscale atmospheric model (PF.ARPS) is used to study the two-way feedback between the subsurface, land-surface, and atmosphere for both idealized cases and a real watershed. This coupled model allows a complete representation of the hydrologic cycle and can capture feedbacks in the land-atmosphere system that occur through spatially-variable precipitation events, evapotranspiration, surface runoff, and infiltration. We ask the following key questions: How do terrain, soil moisture heterogeneity, and subsurface properties affect the planetary boundary layer? What are the effects of water table depth on land surface fluxes and boundary layer development and depth? What times of the diurnal cycle show stronger feedbacks between the subsurface and the atmosphere? These questions are first addressed with simulations over idealized terrain designed to illustrate land-atmosphere feedbacks and effects of surface and subsurface properties on atmospheric boundary layer development. Using the coupled groundwater-atmosphere model, we demonstrate correlations of soil moisture, land-surface heat fluxes, and boundary layer depth with groundwater levels over short, diurnal time scales. Spatial variations in surface moisture distribution have large impacts on the moisture and temperature structure in the atmosphere, leading to changes in boundary layer depth and convective motions, as compared to standard land-surface models. The coupled hydrologic model is then used to simulate real conditions over the Little Washita watershed in Oklahoma. Times within the diurnal cycle and locations within the watershed which show stronger feedbacks between the water table and the atmospheric boundary layer are identified. Effects of a storm system on the coupling between subsurface, land surface, and atmosphere are also discussed. The results of our coupled simulations show the importance of the

  15. Modelling Plant and Soil Nitrogen Feedbacks Affecting Forest Carbon Gain at High CO2

    NASA Astrophysics Data System (ADS)

    McMurtrie, R. E.; Norby, R. J.; Franklin, O.; Pepper, D. A.

    2007-12-01

    Short-term, direct effects of elevated atmospheric CO2 concentrations on plant carbon gain are relatively well understood. There is considerable uncertainty, however, about longer-term effects, which are influenced by various plant and ecosystem feedbacks. A key feedback in terrestrial ecosystems occurs through changes in plant carbon (C) allocation patterns. For instance, if high CO2 were to increase C allocation to roots, then plants may experience positive feedback through improved plant nutrition. A second type of feedback, associated with decomposition of soil-organic matter, may reduce soil-nutrient availability at high CO2. This paper will consider mechanistic models of both feedbacks. Effects of high CO2 on plant C allocation will be investigated using a simple model of forest net primary production (NPP) that incorporates the primary mechanisms of plant carbon and nitrogen (N) balance. The model called MATE (Model Any Terrestrial Ecosystem) includes an equation for annual C balance that depends on light- saturated photosynthetic rate and therefore on [CO2], and an equation for N balance incorporating an expression for N uptake as a function of root mass. The C-N model is applied to a Free Air CO2 Exchange (FACE) experiment at Oak Ridge National Laboratory (ORNL) in Tennessee, USA, where closed-canopy, monoculture stands of the deciduous hardwood sweetgum ( Liquidambar styraciflua) have been growing at [CO2] of 375 and 550 ppm for ten years. Features of this experiment are that the annual NPP response to elevated CO2 has averaged approximately 25% over seven years, but that annual fine-root production has almost doubled on average, with especially large increases in later years of the experiment (Norby et al. 2006). The model provides a simple graphical approach for analysing effects of elevated CO2 and N supply on leaf/root/wood C allocation and productivity. It simulates increases in NPP and fine-root production at the ORNL FACE site that are consistent

  16. SED and Emission Line Properties of Red 2MASS AGN

    NASA Astrophysics Data System (ADS)

    Kuraszkiewicz, Joanna; Wilkes, Belinda J.; Schmidt, Gary; Ghosh, Himel

    2009-09-01

    Radio and far-IR surveys, and modeling of the cosmic X-ray background suggest that a large population of obscured AGN has been missed by traditional, optical surveys. The Two Micron All-Sky Survey (2MASS) has revealed a large population (surface density comparable to that of optically selected AGN with Ks<14.5mag) of mostly nearby (median z=0.25), red, moderately obscured AGN, among which 75% are previously unidentified emission-line AGN, with 85% showing broad emission lines. We present the SED and emission line properties of 44 such red (J-Ks>2) 2MASS AGN observed with Chandra. They lie at z<0.37, span a full range of spectral types (Type 1, intermediate, Type 2),Ks-to-X-ray slopes, and polarization (<13%). Their IR-to-X-ray spectral energy distributions (SEDs) are red in the near-IR/opt/UV showing little or no blue bump. The optical colors are affected by reddening, host galaxy emission, redshift, and in few, highly polarized objects, also by scattered AGN light. The levels of obscuration obtained from optical, X-rays, and far-IR imply N_H AGN light. PCA analysis of the IR-X-ray SED and emission line properties shows that, while obscuration/inclination is important, the dominant cause of variance in the sample (eigenvector 1) is the L/L_{edd} ratio (perhaps because the red near-IR selection limits the range of inclination/obscuration values in our sample). This analysis also distinguishes two sources of obscuration: the host galaxy and circumnuclear absorption.

  17. Chaos analysis and delayed-feedback control in a discrete dynamic coupled map traffic model

    NASA Astrophysics Data System (ADS)

    Fang, Yaling; Shi, Zhongke

    2015-03-01

    The presence of chaos in traffic flow is studied using a modified discrete dynamic coupled map model which is derived from both the flow-density-speed fundamental diagram and Del Castillo's speed-density model. The modified model employs occupancy as its new variable and introduces a coupling strength with the consideration of effect of the front adjacent vehicle. And we analyze its stability of the control system and provide a procedure to design the decentralized delayed-feedback controllers for the traffic control system. These theoretical results are illustrated by numerical simulations.

  18. Cloud-radiation feedback and atmosphere-ocean coupling in a stochastic multicloud model

    NASA Astrophysics Data System (ADS)

    Frenkel, Yevgeniy; Majda, Andrew J.; Stechmann, Samuel N.

    2015-09-01

    Despite recent advances in supercomputing, current general circulation models (GCMs) have significant problems in representing the variability associated with organized tropical convection. Furthermore, due to high sensitivity of the simulations to the cloud radiation feedback, the tropical convection remains a major source of uncertainty in long-term weather and climate forecasts. In a series of recent studies, it has been shown, in paradigm two-baroclinic-mode systems and in aquaplanet GCMs, that a stochastic multicloud convective parameterization based on three cloud types (congestus, deep and stratiform) can be used to improve the variability and the dynamical structure of tropical convection, including intermittent coherent structures such as synoptic and mesoscale convective systems. Here, the stochastic multicloud model is modified with a parameterized cloud radiation feedback mechanism and atmosphere-ocean coupling. The radiative convective feedback mechanism is shown to increase the mean and variability of the Walker circulation. The corresponding intensification of the circulation is associated with propagating synoptic scale systems originating inside of the enhanced sea surface temperature area. In column simulations, the atmosphere ocean coupling introduces pronounced low frequency convective features on the time scale associated with the depth of the mixed ocean layer. However, in the presence of the gravity wave mixing of spatially extended simulations, these features are not as prominent. This highlights the deficiency of the column model approach at predicting the behavior of multiscale spatially extended systems. Overall, the study develops a systematic framework for incorporating parameterized radiative cloud feedback and ocean coupling which may be used to improve representation of intraseasonal and seasonal variability in GCMs.

  19. Modeling Feedbacks Between Individual Human Decisions and Hydrology Using Interconnected Physical and Social Models

    NASA Astrophysics Data System (ADS)

    Murphy, J.; Lammers, R. B.; Proussevitch, A. A.; Ozik, J.; Altaweel, M.; Collier, N. T.; Alessa, L.; Kliskey, A. D.

    2014-12-01

    The global hydrological cycle intersects with human decision making at multiple scales, from dams and irrigation works to the taps in individuals' homes. Residential water consumers are commonly encouraged to conserve; these messages are heard against a background of individual values and conceptions about water quality, uses, and availability. The degree to which these values impact the larger-hydrological dynamics, the way that changes in those values have impacts on the hydrological cycle through time, and the feedbacks by which water availability and quality in turn shape those values, are not well explored. To investigate this domain we employ a global-scale water balance model (WBM) coupled with a social-science-grounded agent-based model (ABM). The integration of a hydrological model with an agent-based model allows us to explore driving factors in the dynamics in coupled human-natural systems. From the perspective of the physical hydrologist, the ABM offers a richer means of incorporating the human decisions that drive the hydrological system; from the view of the social scientist, a physically-based hydrological model allows the decisions of the agents to play out against constraints faithful to the real world. We apply the interconnected models to a study of Tucson, Arizona, USA, and its role in the larger Colorado River system. Our core concept is Technology-Induced Environmental Distancing (TIED), which posits that layers of technology can insulate consumers from direct knowledge of a resource. In Tucson, multiple infrastructure and institutional layers have arguably increased the conceptual distance between individuals and their water supply, offering a test case of the TIED framework. Our coupled simulation allows us to show how the larger system transforms a resource with high temporal and spatial variability into a consumer constant, and the effects of this transformation on the regional system. We use this to explore how pricing, messaging, and

  20. Analysis of Forcing, Response, and Feedbacks in a Paleoclimate Modeling Experiment

    SciTech Connect

    Taylor, K E; Hewitt, C D; Braconnot, P; Broccoli, A J; Doutriaux, C; Mitchell, J F B

    2001-04-11

    It is often argued that paleoclimate studies are necessary to determine whether climate models and their predictions of future climate change can be trusted. An overall measure of the sensitivity of global mean surface temperature to a given radiative perturbation is provided by the global climate sensitivity parameter. In climate model experiments, this parameter appears to be moderately independent of the cause of the perturbation [see, for example, Hansen et al. (1997) and Hewitt and Mitchell (1997)], but it may differ from one model to the next by as much as a factor of three (IPCC, 1995). Moreover, there are some scientists who claim that all models are much more sensitive than the climate system itself (Lindzen, 1997). Thus it would be valuable to determine which models (if any) are consistent with the paleoclimate record and what factors are responsible for model differences in sensitivity. In an analysis of the Paleoclimate Modeling Intercomparison Project (PMIP) simulations of the Last Glacial Maximum (LGM) of 21,000 years ago, we have calculated how the ''forcing'' and feedbacks determine the climatic response. In the PMIP context, the ice sheet distribution is prescribed and the resulting increase in planetary albedo is the most important ''forcing'' factor. Also important are radiation perturbations induced by changes in atmospheric CO{sub 2} concentration. Here we describe a new, approximate method for estimating the strength of forcing and feedback factors from commonly archived model output. We also summarize preliminary results from the PMIP experiment, which show that differences in forcing and to a lesser extent differences in feedbacks can explain differences in surface temperature response.

  1. MASSIVE MOLECULAR OUTFLOWS AND NEGATIVE FEEDBACK IN ULIRGs OBSERVED BY HERSCHEL-PACS

    SciTech Connect

    Sturm, E.; Gracia-Carpio, J.; Hailey-Dunsheath, S.; Contursi, A.; Poglitsch, A.; Davies, R.; Genzel, R.; Lutz, D.; Tacconi, L.; De Jong, J. A.; Gonzalez-Alfonso, E.; Veilleux, S.; Fischer, J.; Sternberg, A.; Verma, A.; Maiolino, R.

    2011-05-20

    Mass outflows driven by stars and active galactic nuclei (AGNs) are a key element in many current models of galaxy evolution. They may produce the observed black-hole-galaxy mass relation and regulate and quench both star formation in the host galaxy and black hole accretion. However, observational evidence of such feedback processes through outflows of the bulk of the star-forming molecular gas is still scarce. Here we report the detection of massive molecular outflows, traced by the hydroxyl molecule (OH), in far-infrared spectra of ULIRGs obtained with Herschel-PACS as part of the SHINING key project. In some of these objects the (terminal) outflow velocities exceed 1000 km s{sup -1}, and their outflow rates (up to {approx}1200 M{sub sun} yr{sup -1}) are several times larger than their star formation rates. We compare the outflow signatures in different types of ULIRGs and in starburst galaxies to address the issue of the energy source (AGN or starburst) of these outflows. We report preliminary evidence that ULIRGs with a higher AGN luminosity (and higher AGN contribution to L{sub IR}) have higher terminal velocities and shorter gas depletion timescales. The outflows in the observed ULIRGs are able to expel the cold gas reservoirs from the centers of these objects within {approx}10{sup 6}-10{sup 8} years.

  2. Modeling the optimal central carbon metabolic pathways under feedback inhibition using flux balance analysis.

    PubMed

    De, Rajat K; Tomar, Namrata

    2012-12-01

    Metabolism is a complex process for energy production for cellular activity. It consists of a cascade of reactions that form a highly branched network in which the product of one reaction is the reactant of the next reaction. Metabolic pathways efficiently produce maximal amount of biomass while maintaining a steady-state behavior. The steady-state activity of such biochemical pathways necessarily incorporates feedback inhibition of the enzymes. This observation motivates us to incorporate feedback inhibition for modeling the optimal activity of metabolic pathways using flux balance analysis (FBA). We demonstrate the effectiveness of the methodology on a synthetic pathway with and without feedback inhibition. Similarly, for the first time, the Central Carbon Metabolic (CCM) pathways of Saccharomyces cerevisiae and Homo sapiens have been modeled and compared based on the above understanding. The optimal pathway, which maximizes the amount of the target product(s), is selected from all those obtained by the proposed method. For this, we have observed the concentration of the product inhibited enzymes of CCM pathway and its influence on its corresponding metabolite/substrate. We have also studied the concentration of the enzymes which are responsible for the synthesis of target products. We further hypothesize that an optimal pathway would opt for higher flux rate reactions. In light of these observations, we can say that an optimal pathway should have lower enzyme concentration and higher flux rates. Finally, we demonstrate the superiority of the proposed method by comparing it with the extreme pathway analysis. PMID:22913632

  3. Feedback mechanisms control coexistence in a stem cell model of acute myeloid leukaemia.

    PubMed

    Crowell, Helena L; MacLean, Adam L; Stumpf, Michael P H

    2016-07-21

    Haematopoietic stem cell dynamics regulate healthy blood cell production and are disrupted during leukaemia. Competition models of cellular species help to elucidate stem cell dynamics in the bone marrow microenvironment (or niche), and to determine how these dynamics impact leukaemia progression. Here we develop two models that target acute myeloid leukaemia with particular focus on the mechanisms that control proliferation via feedback signalling. It is within regions of parameter space permissive of coexistence that the effects of competition are most subtle and the clinical outcome least certain. Steady state and linear stability analyses identify parameter regions that allow for coexistence to occur, and allow us to characterise behaviour near critical points. Where analytical expressions are no longer informative, we proceed statistically and sample parameter space over a coexistence region. We find that the rates of proliferation and differentiation of healthy progenitors exert key control over coexistence. We also show that inclusion of a regulatory feedback onto progenitor cells promotes healthy haematopoiesis at the expense of leukaemia, and that - somewhat paradoxically - within the coexistence region feedback increases the sensitivity of the system to dominance by one lineage over another. PMID:27130539

  4. Modeling the relativistic runaway electron avalanche and the feedback mechanism with GEANT4

    NASA Astrophysics Data System (ADS)

    Skeltved, Alexander Broberg; Østgaard, Nikolai; Carlson, Brant; Gjesteland, Thomas; Celestin, Sebastien

    2014-11-01

    This paper presents the first study that uses the GEometry ANd Tracking 4 (GEANT4) toolkit to do quantitative comparisons with other modeling results related to the production of terrestrial gamma ray flashes and high-energy particle emission from thunderstorms. We will study the relativistic runaway electron avalanche (RREA) and the relativistic feedback process, as well as the production of bremsstrahlung photons from runaway electrons. The Monte Carlo simulations take into account the effects of electron ionization, electron by electron (Møller), and electron by positron (Bhabha) scattering as well as the bremsstrahlung process and pair production, in the 250 eV to 100 GeV energy range. Our results indicate that the multiplication of electrons during the development of RREAs and under the influence of feedback are consistent with previous estimates. This is important to validate GEANT4 as a tool to model RREAs and feedback in homogeneous electric fields. We also determine the ratio of bremsstrahlung photons to energetic electrons Nγ/Ne. We then show that the ratio has a dependence on the electric field, which can be expressed by the avalanche time τ(E) and the bremsstrahlung coefficient α(ɛ). In addition, we present comparisons of GEANT4 simulations performed with a "standard" and a "low-energy" physics list both validated in the 1 keV to 100 GeV energy range. This comparison shows that the choice of physics list used in GEANT4 simulations has a significant effect on the results.

  5. Are Compton-thick AGNs the Missing Link between Mergers and Black Hole Growth?

    NASA Astrophysics Data System (ADS)

    Kocevski, Dale D.; Brightman, Murray; Nandra, Kirpal; Koekemoer, Anton M.; Salvato, Mara; Aird, James; Bell, Eric F.; Hsu, Li-Ting; Kartaltepe, Jeyhan S.; Koo, David C.; Lotz, Jennifer M.; McIntosh, Daniel H.; Mozena, Mark; Rosario, David; Trump, Jonathan R.

    2015-12-01

    We examine the host morphologies of heavily obscured active galactic nuclei (AGNs) at z∼ 1 to test whether obscured super-massive black hole growth at this epoch is preferentially linked to galaxy mergers. Our sample consists of 154 obscured AGNs with {N}{{H}}\\gt {10}23.5 {{cm}}-2 and z\\lt 1.5. Using visual classifications, we compare the morphologies of these AGNs to control samples of moderately obscured (1022 cm{}-2\\lt {N}{{H}}\\lt {10}23.5 {{cm}}-2) and unobscured ({N}{{H}}\\lt {10}22 {{cm}}-2) AGN. These control AGNs have similar redshifts and intrinsic X-ray luminosities to our heavily obscured AGN. We find that heavily obscured AGNs are twice as likely to be hosted by late-type galaxies relative to unobscured AGNs ({65.3}-4.6+4.1% versus {34.5}-2.7+2.9%) and three times as likely to exhibit merger or interaction signatures ({21.5}-3.3+4.2% versus {7.8}-1.3+1.9%). The increased merger fraction is significant at the 3.8σ level. If we exclude all point sources and consider only extended hosts, we find that the correlation between the merger fraction and obscuration is still evident, although at a reduced statistical significance (2.5σ ). The fact that we observe a different disk/spheroid fraction versus obscuration indicates that the viewing angle cannot be the only thing differentiating our three AGN samples, as a simple unification model would suggest. The increased fraction of disturbed morphologies with obscuration supports an evolutionary scenario, in which Compton-thick AGNs are a distinct phase of obscured super-massive black hole (SMBH) growth following a merger/interaction event. Our findings also suggest that some of the merger-triggered SMBH growth predicted by recent AGN fueling models may be hidden among the heavily obscured, Compton-thick population.

  6. Modeling Massive Cluster Formation with Stellar Feedback using Flash and AMUSE

    NASA Astrophysics Data System (ADS)

    McMillan, Stephen; Wall, Joshua; Mac Low, Mordecai-Mark

    2015-08-01

    Star cluster formation is a complex astrophysical problem combining multiple competing physical processes in a challenging computational environment, placing stringent demands on both software and hardware. Current simulations still fall short of a realistic description of the physical processes at work in star-forming regions. We are developing a hybrid simulation code to explore the formation and assembly of massive star clusters by combining the magnetohydrodynamics code Flash and the AMUSE software environment. Flash handles gas dynamics and star formation through cloud collapse, while AMUSE manages the dynamics and evolution of stars and binary systems. The gravitational interaction between the gas and the stars is treated via a symplectic gravity bridge between the codes in AMUSE. Radiative, wind, and supernova feedback are followed in FLASH based on information provided by the AMUSE system. We present some early results of this work, focusing on cluster formation and assembly, and including simplified models of feedback to study gas expulsion and cluster survival.

  7. Model-following output feedback controller for oblique-wing aircraft

    NASA Technical Reports Server (NTRS)

    Alag, Gurbux Singh

    1987-01-01

    A variable-skew oblique-wing offers a substantial aerodynamic performance advantage for aircraft missions that require both high efficiency in subsonic flight and supersonic dash or cruise. The most obvious characteristics of the oblique-wing concept is the asymmetry of the wing-skew angle that causes a significant aerodynamic and inertial cross coupling between the aircraft longitudinal and lateral-directional axes. This paper presents a technique for synthesizing a decoupling controller while providing the desired stability augmentation. The use of output feedback in control law synthesis without the requirement of state estimation is presented. An explicit model-following control system with output feedback is developed. The effectiveness of the control laws developed in achieving the desired decoupling is illustrated for a given flight condition for an oblique-wing aircraft.

  8. Impact of time-delayed feedback on spatiotemporal dynamics in the Lugiato-Lefever model

    NASA Astrophysics Data System (ADS)

    Panajotov, K.; Puzyrev, D.; Vladimirov, A. G.; Gurevich, S. V.; Tlidi, M.

    2016-04-01

    We analyze the impact of delayed optical feedback (OF) on the spatiotemporal dynamics of the Lugiato-Lefever model. First, we carry out linear stability analysis and reveal the role of the OF strength and phase on the shape of the bistable curve as well as on Turing, Andronov-Hopf, and traveling-wave instability regions. Further, we demonstrate how the OF impacts the spatial dynamics by shifting the regions with different spatial eigenvalue spectra. In addition, we reveal a clustering behavior of cavity solitons as a function of the OF strength at fixed OF phase. Depending on the feedback parameters, OF can also induce a drift bifurcation of a stationary cavity soliton, as well as an Andronov-Hopf bifurcation of a drifting soliton. We present an analytical expression for the threshold of the drift bifurcation and show that above a certain value of the OF strength the system enters a region of spatiotemporal chaos.

  9. Stability of a double inverted pendulum model during human quiet stance with continuous delay feedback control.

    PubMed

    Suzuki, Yasuyuki; Nomura, Taishin; Morasso, Pietro

    2011-01-01

    Recent debate about neural mechanisms for stabilizing human upright quiet stance focuses on whether the active and time delay neural feedback control generating muscle torque is continuous or intermittent. A single inverted pendulum controlled by the active torque actuating the ankle joint has often been used for the debate on the presumption of well-known ankle strategy hypothesis claiming that the upright quiet stance can be stabilized mostly by the ankle torque. However, detailed measurements are showing that the hip joint angle exhibits amount of fluctuations comparable with the ankle joint angle during natural postural sway. Here we analyze a double inverted pendulum model during human quiet stance to demonstrate that the conventional proportional and derivative delay feedback control, i.e., the continuous delay PD control with gains in the physiologically plausible range is far from adequate as the neural mechanism for stabilizing human upright quiet stance. PMID:22256061

  10. The Star-Forming Properties of an Ultra-Hard X-ray Selected Sample of AGN

    NASA Astrophysics Data System (ADS)

    Shimizu, Thomas Taro; Mushotzky, Richard; Melendez, Marcio; Koss, Michael

    2015-08-01

    We present results from our Herschel follow-up survey of the Swift/BAT AGN 58 month catalog. Using the PACS and SPIRE instruments, 313 AGN were imaged at 5 far-infrared (FIR) wavelengths (70, 160, 250, 350, and 500 μm) producing the largest and most complete FIR catalog of local AGN. We combine our FIR photometry with archival mid-infrared photometry to form broadband spectral energy distributions (SEDs) that for the first time reach into the sub-millimeter regime. We fit these SEDs with several models to determine the star-forming properties of the host galaxies such as star-formation rate (SFR), IR luminosity, dust temperature, and dust mass and measure their relationship with various AGN properties such as X-ray luminosity, Eddington ratio, black hole mass, and column density. We find a weak dependence of the global SFR on the AGN strength indicating either the AGN has little influence on star formation over the entire galaxy or that the variability of the AGN on short timescales washes away any correlation between star formation and the AGN. Comparing the BAT AGN to a sample of normal star-forming galaxies on the “main sequence”, we find the BAT AGN systematically have decreased levels of specific SFR (sSFR = SFR/stellar mass). This is possibly indirect evidence that the AGN has suppressed star-formation in its host galaxy. Analysis of the FIR images themselves reveals that many of the BAT AGN are compact which leads to increased levels of SFR surface density, high enough for starburst driven winds. Finally, we show the 70 μm luminosity can be heavily contaminated by AGN emission and should not be used as a SFR indicator for AGN host galaxies.

  11. First X-ray Statistical Tests for Clumpy Torii Models: Constraints from RXTE monitoring of Seyfert AGN

    NASA Astrophysics Data System (ADS)

    Markowitz, A.

    2015-09-01

    We summarize two papers providing the first X-ray-derived statistical constraints for both clumpy-torus model parameters and cloud ensemble properties. In Markowitz, Krumpe, & Nikutta (2014), we explored multi-timescale variability in line-of-sight X-ray absorbing gas as a function of optical classification. We examined 55 Seyferts monitored with the Rossi X-ray Timing Explorer, and found in 8 objects a total of 12 eclipses, with durations between hours and years. Most clouds are commensurate with the outer portions of the BLR, or the inner regions of infrared-emitting dusty tori. The detection of eclipses in type Is disfavors sharp-edged tori. We provide probabilities to observe a source undergoing an absorption event for both type Is and IIs, yielding constraints in [N_0, sigma, i] parameter space. In Nikutta et al., in prep., we infer that the small cloud angular sizes, as seen from the SMBH, imply the presence of >10^7 clouds in BLR+torus to explain observed covering factors. Cloud size is roughly proportional to distance from the SMBH, hinting at the formation processes (e.g. disk fragmentation). All observed clouds are sub-critical with respect to tidal disruption; self-gravity alone cannot contain them. External forces (e.g. magnetic fields, ambient pressure) are needed to contain them, or otherwise the clouds must be short-lived. Finally, we infer that the radial cloud density distribution behaves as 1/r^{0.7}, compatible with VLTI observations. Our results span both dusty and non-dusty clumpy media, and probe model parameter space complementary to that for short-term eclipses observed with XMM-Newton, Suzaku, and Chandra.

  12. Toward a comprehensive model for feedback by active galactic nuclei: New insights from M87 observations by LOFAR, Fermi, and H.E.S.S

    SciTech Connect

    Pfrommer, Christoph

    2013-12-10

    Feedback by active galactic nuclei (AGNs) appears to be critical in balancing radiative cooling of the low-entropy gas at the centers of galaxy clusters and in mitigating the star formation of elliptical galaxies. New observations of M87 enable us to put forward a comprehensive model for the physical heating mechanism. Low-frequency radio observations by LOFAR revealed the absence of fossil cosmic-ray (CR) electrons in the radio halo surrounding M87. This puzzle can be resolved by accounting for the CR release from the radio lobes and the subsequent mixing of CRs with the dense ambient intracluster gas, which thermalizes the electrons on a timescale similar to the radio halo age of 40 Myr. Hadronic interactions of similarly injected CR protons with the ambient gas should produce an observable gamma-ray signal in accordance with the steady emission of the low state of M87 detected by Fermi and H.E.S.S. Hence, we normalize the CR population to the gamma-ray emission, which shows the same spectral slope as the CR injection spectrum probed by LOFAR, thereby supporting a common origin. We show that CRs, which stream at the Alfvén velocity with respect to the plasma rest frame, heat the surrounding thermal plasma at a rate that balances that of radiative cooling on average at each radius. However, the resulting global thermal equilibrium is locally unstable and allows for the formation of the observed cooling multi-phase medium through thermal instability. Provided that CR heating balances cooling during the emerging 'cooling flow', the collapse of the majority of the gas is halted around 1 keV—in accordance with X-ray data. We show that both the existence of a temperature floor and the similar radial scaling of the heating and cooling rates are generic predictions of the CR heating model.

  13. Coupled Modeling of Geomorphology and Ecohydrology: Topographic feedbacks driven by solar radiation

    NASA Astrophysics Data System (ADS)

    Istanbulluoglu, E.; Flores Cervantes, J. H.; Yetemen, O.

    2012-12-01

    There is a two-way coupling between geomorphic processes and vegetation dynamics. To examine the role of vegetation on landform development, landscape evolution models (LEMs) have used relatively simple theory of erosion-vegetation interactions and vegetation dynamics based on field evidence and conjecture. Such modeling studies have described "with broad strokes" the control of vegetation on landscape relief, drainage density, and sediment yields in a range of model sensitivity studies, often without any direct field confirmation. For improved predictions of climate-landscape relations in real-world cases, and identify the need for future model development, there is strong need for field confirmations of ecohydrologic LEMs. In this talk, we first discuss some of the key findings of recent LEM studies that incorporate vegetation. Second, we introduce the role of solar radiation on ecohydrologic processes in the CHILD LEM, and confirm model predictions against observations. Using the model we examine how solar radiation control the spatio-temporal dynamics of soil moisture, vegetation biomass, and their feedback on landform development in a semi-arid climate across a latitude gradient. We identify that at the catchment scale while the initial greening usually takes places relatively uniformly in space, the growing season takes longer on north facing slopes leading to higher overall biomass on north aspects. Through eco-geomorphic feedbacks, this leads to steeper north facing slopes, and increased valley asymmetry in the modeled landscapes. These findings are important to improve the predictions of climate change impacts on the landscape system.

  14. Modeling the relativistic runaway electron avalanche and the feedback mechanism with GEANT4

    PubMed Central

    Skeltved, Alexander Broberg; Østgaard, Nikolai; Carlson, Brant; Gjesteland, Thomas; Celestin, Sebastien

    2014-01-01

    This paper presents the first study that uses the GEometry ANd Tracking 4 (GEANT4) toolkit to do quantitative comparisons with other modeling results related to the production of terrestrial gamma ray flashes and high-energy particle emission from thunderstorms. We will study the relativistic runaway electron avalanche (RREA) and the relativistic feedback process, as well as the production of bremsstrahlung photons from runaway electrons. The Monte Carlo simulations take into account the effects of electron ionization, electron by electron (Møller), and electron by positron (Bhabha) scattering as well as the bremsstrahlung process and pair production, in the 250 eV to 100 GeV energy range. Our results indicate that the multiplication of electrons during the development of RREAs and under the influence of feedback are consistent with previous estimates. This is important to validate GEANT4 as a tool to model RREAs and feedback in homogeneous electric fields. We also determine the ratio of bremsstrahlung photons to energetic electrons Nγ/Ne. We then show that the ratio has a dependence on the electric field, which can be expressed by the avalanche time τ(E) and the bremsstrahlung coefficient α(ε). In addition, we present comparisons of GEANT4 simulations performed with a “standard” and a “low-energy” physics list both validated in the 1 keV to 100 GeV energy range. This comparison shows that the choice of physics list used in GEANT4 simulations has a significant effect on the results. Key Points Testing the feedback mechanism with GEANT4 Validating the GEANT4 programming toolkit Study the ratio of bremsstrahlung photons to electrons at TGF source altitude PMID:26167437

  15. Audio Feedback -- Better Feedback?

    ERIC Educational Resources Information Center

    Voelkel, Susanne; Mello, Luciane V.

    2014-01-01

    National Student Survey (NSS) results show that many students are dissatisfied with the amount and quality of feedback they get for their work. This study reports on two case studies in which we tried to address these issues by introducing audio feedback to one undergraduate (UG) and one postgraduate (PG) class, respectively. In case study one…

  16. Anatomy of the AGN in NGC 5548. I. A global model for the broadband spectral energy distribution

    NASA Astrophysics Data System (ADS)

    Mehdipour, M.; Kaastra, J. S.; Kriss, G. A.; Cappi, M.; Petrucci, P.-O.; Steenbrugge, K. C.; Arav, N.; Behar, E.; Bianchi, S.; Boissay, R.; Branduardi-Raymont, G.; Costantini, E.; Ebrero, J.; Di Gesu, L.; Harrison, F. A.; Kaspi, S.; De Marco, B.; Matt, G.; Paltani, S.; Peterson, B. M.; Ponti, G.; Pozo Nuñez, F.; De Rosa, A.; Ursini, F.; de Vries, C. P.; Walton, D. J.; Whewell, M.

    2015-03-01

    An extensive multi-satellite campaign on NGC 5548 has revealed this archetypal Seyfert-1 galaxy to be in an exceptional state of persistent heavy absorption. Our observations taken in 2013-2014 with XMM-Newton, Swift, NuSTAR, INTEGRAL, Chandra, HST and two ground-based observatories have together enabled us to establish that this unexpected phenomenon is caused by an outflowing stream of weakly ionised gas (called the obscurer), extending from the vicinity of the accretion disk to the broad-line region. In this work we present the details of our campaign and the data obtained by all the observatories. We determine the spectral energy distribution of NGC 5548 from near-infrared to hard X-rays by establishing the contribution of various emission and absorption processes taking place along our line of sight towards the central engine. We thus uncover the intrinsic emission and produce a broadband continuum model for both obscured (average summer 2013 data) and unobscured (<2011) epochs of NGC 5548. Our results suggest that the intrinsic NIR/optical/UV continuum is a single Comptonised component with its higher energy tail creating the "softX-ray excess". This component is compatible with emission from a warm, optically-thick corona as part of the inner accretion disk. We then investigate the effects of the continuum on the ionisation balance and thermal stability of photoionised gas for unobscured and obscured epochs. Appendix A is available in electronic form at http://www.aanda.org

  17. Multidimensional modelling of X-ray spectra for AGN accretion disc outflows - III. Application to a hydrodynamical simulation

    NASA Astrophysics Data System (ADS)

    Sim, S. A.; Proga, D.; Miller, L.; Long, K. S.; Turner, T. J.

    2010-11-01

    We perform multidimensional radiative transfer simulations to compute spectra for a hydrodynamical simulation of a line-driven accretion disc wind from an active galactic nucleus. The synthetic spectra confirm expectations from parametrized models that a disc wind can imprint a wide variety of spectroscopic signatures including narrow absorption lines, broad emission lines and a Compton hump. The formation of these features is complex with contributions originating from many of the different structures present in the hydrodynamical simulation. In particular, spectral features are shaped both by gas in a successfully launched outflow and in complex flows where material is lifted out of the disc plane but ultimately falls back. We also confirm that the strong Fe Kα line can develop a weak, red-skewed line wing as a result of Compton scattering in the outflow. In addition, we demonstrate that X-ray radiation scattered and reprocessed in the flow has a pivotal part in both the spectrum formation and determining the ionization conditions in the wind. We find that scattered radiation is rather effective in ionizing gas which is shielded from direct irradiation from the central source. This effect likely makes the successful launching of a massive disc wind somewhat more challenging and should be considered in future wind simulations.

  18. Modeling of testosterone regulation by pulse-modulated feedback: An experimental data study

    NASA Astrophysics Data System (ADS)

    Mattsson, Per; Medvedev, Alexander

    2013-10-01

    The continuous part of a hybrid (pulse-modulated) model of testosterone feedback regulation is extended with infinite-dimensional and nonlinear dynamics, to better explain the testosterone concentration profiles observed in clinical data. A linear least-squares based optimization algorithm is developed for the purpose of detecting impulses of gonadotropin-realsing hormone from measured concentration of luteinizing hormone. The parameters in the model are estimated from hormone concentration measured in human males, and simulation results from the full closed-loop system are provided.

  19. A feedback control model for network flow with multiple pure time delays

    NASA Technical Reports Server (NTRS)

    Press, J.

    1972-01-01

    A control model describing a network flow hindered by multiple pure time (or transport) delays is formulated. Feedbacks connect each desired output with a single control sector situated at the origin. The dynamic formulation invokes the use of differential difference equations. This causes the characteristic equation of the model to consist of transcendental functions instead of a common algebraic polynomial. A general graphical criterion is developed to evaluate the stability of such a problem. A digital computer simulation confirms the validity of such criterion. An optimal decision making process with multiple delays is presented.

  20. The New Spectral Picture of Seyfert 1 AGNs

    NASA Astrophysics Data System (ADS)

    Miyake, K.; Noda, H.; Yamada, S.; Makishima, K.

    2014-07-01

    X-ray spectra of active galactic nuclei (AGNs) were so far considered to consist of a single power-law (PL) like primary component and a reflection component accompanied by an FeKα line. However, the assumption of ``single primary component'' has not been confirmed observationally. To overcome this limitation, we developed a method that can decompose observed AGN spectra model-independently using time-variability (Noda et al. 2011, 2013). We applied it to the bright and variable Seyfert 1 AGN, IC4329A. It was observed by Suzaku 5 times in 2007, and once in 2012. Using our method, the time-averaged spectra have been successfully decomposed into a fast-variable component and a slowly-variable one. While the former can be regarded as a PL with photon index Γ~2.1, the latter is explained as a sum of the distant reflection component and a harder PL with Γ~1.4. This harder PL component, observed in all observations of IC 4329A and in many other AGNs (Noda et al. 2011, 2013), can be interpreted neither as partially-covered Γ~2.1 PL, nor relativistic reflection that varies with the primary. Therefore, the Γ~1.4 PL is considered to be another primary component. Its recognition has a big impact on our understanding of the AGN central engine.

  1. Dusty Feedback from Massive Black Holes in Two Elliptical Galaxies

    NASA Technical Reports Server (NTRS)

    Temi, P.; Brighenti, F.; Mathews, W. G.; Amblard, A.; Riguccini, L.

    2013-01-01

    Far-infrared dust emission from elliptical galaxies informs us about galaxy mergers, feedback energy outbursts from supermassive black holes and the age of galactic stars. We report on the role of AGN feedback observationally by looking for its signatures in elliptical galaxies at recent epochs in the nearby universe. We present Herschel observations of two elliptical galaxies with strong and spatially extended FIR emission from colder grains 5-10 kpc distant from the galaxy cores. Extended excess cold dust emission is interpreted as evidence of recent feedback-generated AGN energy outbursts in these galaxies, visible only in the FIR, from buoyant gaseous outflows from the galaxy cores.

  2. Modelling ecogeomorphic feedbacks: investigating mechanisms of land degradation in semi-arid grassland and shrubland

    NASA Astrophysics Data System (ADS)

    Turnbull, Laura; Mueller, Eva; Tietjen, Britta; Wainwright, John

    2014-05-01

    Across vast areas of the world's drylands, land degradation is exacerbated by ecohydrological processes, which alter the structure, function and connectivity of dryland hillslopes. These processes are often interlinked through feedback mechanisms in such a way that a trigger may result in a re-organization of the affected landscape. Here, we present a spatially explicit process-based ecogeomorphic model, MAHLERAN-EcoHyD to enhance our understanding of complex linkages between abiotic and biotic drivers and processes of degradation in drylands. This ecogeomorphic modelling approach is innovative in two main ways: it couples biotic and abiotic processes, and simulates intra and inter-event dynamics, thus overcoming a key limitation of previous modelling approaches in terms of their temporal scaling, by simulating key ecogeomorphic processes at process-relevant time steps. Redistribution of water, sediment and nutrients during high-intensity rainstorms is simulated at 1-sec time steps, soil moisture and transpiration dynamics at daily time steps, and vegetation dynamics (establishment, growth, mortality) at 14-day time steps, over a high-resolution 1x1 m grid. We use this innovative modelling approach to investigate soil-vegetation feedback mechanisms within a grassland-shrubland transition zone at the Sevilleta Long Term Ecological Research site in the south-western United States. Results from three modelling experiments are presented: the first modelling experiment investigates the impact of annual variations in individual high-intensity storms to assess long-term variations in runoff, soil-moisture conditions and sediment and nutrient fluxes over two decades; the second modelling experiment assesses the impact of vegetation composition on spatial changes in surface soil texture due to soil erosion by water; and the third modelling experiment investigates how long-term changes in vegetation alter feedbacks between biotic and abiotic processes using scenarios for

  3. Modeling cancelation of periodic inputs with burst-STDP and feedback.

    PubMed

    Bol, K; Marsat, G; Mejias, J F; Maler, L; Longtin, A

    2013-11-01

    Prediction and cancelation of redundant information is an important feature that many neural systems must display in order to efficiently code external signals. We develop an analytic framework for such cancelation in sensory neurons produced by a cerebellar-like structure in wave-type electric fish. Our biologically plausible mechanism is motivated by experimental evidence of cancelation of periodic input arising from the proximity of conspecifics as well as tail motion. This mechanism involves elements present in a wide range of systems: (1) stimulus-driven feedback to the neurons acting as detectors, (2) a large variety of temporal delays in the pathways transmitting such feedback, responsible for producing frequency channels, and (3) burst-induced long-term plasticity. The bursting arises from back-propagating action potentials. Bursting events drive the input frequency-dependent learning rule, which in turn affects the feedback input and thus the burst rate. We show how the mean firing rate and the rate of production of 2- and 4-spike bursts (the main learning events) can be estimated analytically for a leaky integrate-and-fire model driven by (slow) sinusoidal, back-propagating and feedback inputs as well as rectified filtered noise. The effect of bursts on the average synaptic strength is also derived. Our results shed light on why bursts rather than single spikes can drive learning in such networks "online", i.e. in the absence of a correlative discharge. Phase locked spiking in frequency specific channels together with a frequency-dependent STDP window size regulate burst probability and duration self-consistently to implement cancelation. PMID:23332545

  4. Modelling Feedback Excitation, Pacemaker Properties and Sensory Switching of Electrically Coupled Brainstem Neurons Controlling Rhythmic Activity

    PubMed Central

    Hull, Michael J.; Soffe, Stephen R.; Willshaw, David J.; Roberts, Alan

    2016-01-01

    What cellular and network properties allow reliable neuronal rhythm generation or firing that can be started and stopped by brief synaptic inputs? We investigate rhythmic activity in an electrically-coupled population of brainstem neurons driving swimming locomotion in young frog tadpoles, and how activity is switched on and off by brief sensory stimulation. We build a computational model of 30 electrically-coupled conditional pacemaker neurons on one side of the tadpole hindbrain and spinal cord. Based on experimental estimates for neuron properties, population sizes, synapse strengths and connections, we show that: long-lasting, mutual, glutamatergic excitation between the neurons allows the network to sustain rhythmic pacemaker firing at swimming frequencies following brief synaptic excitation; activity persists but rhythm breaks down without electrical coupling; NMDA voltage-dependency doubles the range of synaptic feedback strengths generating sustained rhythm. The network can be switched on and off at short latency by brief synaptic excitation and inhibition. We demonstrate that a population of generic Hodgkin-Huxley type neurons coupled by glutamatergic excitatory feedback can generate sustained asynchronous firing switched on and off synaptically. We conclude that networks of neurons with NMDAR mediated feedback excitation can generate self-sustained activity following brief synaptic excitation. The frequency of activity is limited by the kinetics of the neuron membrane channels and can be stopped by brief inhibitory input. Network activity can be rhythmic at lower frequencies if the neurons are electrically coupled. Our key finding is that excitatory synaptic feedback within a population of neurons can produce switchable, stable, sustained firing without synaptic inhibition. PMID:26824331

  5. Modelling Feedback Excitation, Pacemaker Properties and Sensory Switching of Electrically Coupled Brainstem Neurons Controlling Rhythmic Activity.

    PubMed

    Hull, Michael J; Soffe, Stephen R; Willshaw, David J; Roberts, Alan

    2016-01-01

    What cellular and network properties allow reliable neuronal rhythm generation or firing that can be started and stopped by brief synaptic inputs? We investigate rhythmic activity in an electrically-coupled population of brainstem neurons driving swimming locomotion in young frog tadpoles, and how activity is switched on and off by brief sensory stimulation. We build a computational model of 30 electrically-coupled conditional pacemaker neurons on one side of the tadpole hindbrain and spinal cord. Based on experimental estimates for neuron properties, population sizes, synapse strengths and connections, we show that: long-lasting, mutual, glutamatergic excitation between the neurons allows the network to sustain rhythmic pacemaker firing at swimming frequencies following brief synaptic excitation; activity persists but rhythm breaks down without electrical coupling; NMDA voltage-dependency doubles the range of synaptic feedback strengths generating sustained rhythm. The network can be switched on and off at short latency by brief synaptic excitation and inhibition. We demonstrate that a population of generic Hodgkin-Huxley type neurons coupled by glutamatergic excitatory feedback can generate sustained asynchronous firing switched on and off synaptically. We conclude that networks of neurons with NMDAR mediated feedback excitation can generate self-sustained activity following brief synaptic excitation. The frequency of activity is limited by the kinetics of the neuron membrane channels and can be stopped by brief inhibitory input. Network activity can be rhythmic at lower frequencies if the neurons are electrically coupled. Our key finding is that excitatory synaptic feedback within a population of neurons can produce switchable, stable, sustained firing without synaptic inhibition. PMID:26824331

  6. A neural mass model with direct and indirect excitatory feedback loops: identification of bifurcations and temporal dynamics.

    PubMed

    Garnier, Aurélie; Vidal, Alexandre; Huneau, Clément; Benali, Habib

    2015-02-01

    Neural mass modeling is a part of computational neuroscience that was developed to study the general behavior of a neuronal population. This type of mesoscopic model is able to generate output signals that are comparable to experimental data, such as electroencephalograms. Classically, neural mass models consider two interconnected populations: excitatory pyramidal cells and inhibitory interneurons. However, many authors have included an excitatory feedback on the pyramidal cell population. Two distinct approaches have been developed: a direct feedback on the main pyramidal cell population and an indirect feedback via a secondary pyramidal cell population. In this letter, we propose a new neural mass model that couples these two approaches. We perform a detailed bifurcation analysis and present a glossary of dynamical behaviors and associated time series. Our study reveals that the model is able to generate particular realistic time series that were never pointed out in either simulated or experimental data. Finally, we aim to evaluate the effect of balance between both excitatory feedbacks on the dynamical behavior of the model. For this purpose, we compute the codimension 2 bifurcation diagrams of the system to establish a map of the repartition of dynamical behaviors in a direct versus indirect feedback parameter space. A perspective of this work is, from a given temporal series, to estimate the parameter value range, especially in terms of direct versus indirect excitatory feedback. PMID:25514111

  7. Compton thick AGN in the XMM-COSMOS survey

    NASA Astrophysics Data System (ADS)

    Lanzuisi, G.; Ranalli, P.; Georgantopoulos, I.; Georgakakis, A.; Delvecchio, I.; Akylas, T.; Berta, S.; Bongiorno, A.; Brusa, M.; Cappelluti, N.; Civano, F.; Comastri, A.; Gilli, R.; Gruppioni, C.; Hasinger, G.; Iwasawa, K.; Koekemoer, A.; Lusso, E.; Marchesi, S.; Mainieri, V.; Merloni, A.; Mignoli, M.; Piconcelli, E.; Pozzi, F.; Rosario, D. J.; Salvato, M.; Silverman, J.; Trakhtenbrot, B.; Vignali, C.; Zamorani, G.

    2015-01-01

    Heavily obscured, Compton thick (CT, NH> 1024 cm-2) active galactic nuclei (AGN) may represent an important phase in AGN/galaxy co-evolution and are expected to provide a significant contribution to the cosmic X-ray background at its peak. However, unambiguously identifying CT AGN beyond the local Universe is a challenging task even in the deepest X-ray surveys, and given the expected low spatial density of these sources in the 2-10 keV band, large area surveys are needed to collect sizable samples. Through direct X-ray spectra analysis, we selected 39 heavily obscured AGN (NH>3 × 1023 cm-2) at bright X-ray fluxes (F2-10 ≳ 10-14 erg s-1 cm-2) in the 2 deg2 XMM-COSMOS survey. After selecting CT AGN based on the fit of a simple absorbed two power law model to the shallow XMM-Newton data, the presence of bona fide CT AGN was confirmed in 80% of the sources using deeper Chandra data and more complex models. The final sample comprises ten CT AGN (six of them also have a detected Fe Kα line with EW ~ 1 keV), spanning a wide range of redshifts (z ~ 0.1-2.5) and luminosity (L2-10 ~ 1043.5-1045 erg s-1) and is complemented by 29 heavily obscured AGN spanning the same redshift and luminosity range. We collected the rich multi-wavelength information available for all these sources, in order to study the distribution of super massive black hole and host properties, such as black hole mass (MBH), Eddington ratio (λEdd), stellar mass (M∗), specific star formation rate (sSFR) in comparison with a sample of unobscured AGN. We find that highly obscured sources tend to have significantly smaller MBH and higher λEdd with respect to unobscured sources, while a weaker evolution in M∗ is observed. The sSFR of highly obscured sources is consistent with the one observed in the main sequence of star forming galaxies, at all redshifts. We also present and briefly discuss optical spectra, broadband spectral energy distribution (SED) and morphology for the sample of ten CT AGN. Both

  8. THE GALACTIC SPIN OF AGN GALAXIES

    SciTech Connect

    Cervantes-Sodi, Bernardo; Hernandez, X.; Park, Changbom; Choi, Yun-Young E-mail: xavier@astroscu.unam.mx

    2011-07-01

    Using an extensive sample of galaxies selected from the Sloan Digital Sky Survey Data Release 5, we compare the angular momentum distribution of active galactic nuclei (AGNs) with non-AGN hosting late-type galaxies. To this end we characterize galactic spin through the dimensionless angular momentum parameter {lambda}, which we estimate through simple dynamical considerations. Using a volume-limited sample, we find a considerable difference when comparing the empirical distributions of {lambda} for AGNs and non-AGN galaxies, the AGNs showing typically low {lambda} values and associated dispersions, while non-AGNs present higher {lambda} values and a broader distribution. A more striking difference is found when looking at {lambda} distributions in thin M{sub r} cuts; while the spin of non-AGN galaxies presents an anticorrelation with M{sub r} , with bright (massive) galaxies having low spins, AGN host galaxies present uniform values of {lambda} at all magnitudes, a behavior probably imposed by the fact that most late-type AGN galaxies present a narrow range in color, with a typical constant {lambda} value. We also find that the fraction of AGN hosting galaxies in our sample strongly depends on galactic spin, increasing dramatically for decreasing {lambda}. For AGN host galaxies, we compute the mass of their supermassive black holes and find that this value tends to be higher for low spin galaxies, even at fixed luminosity, a result that could account, to a certain extent, for the spread on the luminosity-black-hole mass relation.

  9. The reference ear modeling method for internally feedback controlled digital hearing aid chip.

    PubMed

    Kim, Sunyoung; Lee, Seung Jin; Cho, Namjun; Song, Seong-Jun; Yoo, Hoi-Jun

    2007-01-01

    A reference ear modeling method for the real-time feedback controlled digital hearing aid chip is proposed and implemented. In order to reduce the modeling complexity and enhance the programmability, new ear modeling method using the acoustic filter theory is adopted to the digital hearing aid. To achieve the fully internal gain fitting and verification system, the responses from the damaged ear and the reference ear model are compared and the new gain parameters are processed for the multi-channel DSP. The digital hearing aid chip with reference ear model is fabricated in 0.18 microm CMOS technology, has a core area of 3.1 mm x 1.2 mm and dissipates less than 120 muA. PMID:18003331

  10. The relationships between galaxies/AGN and the circum-/intergalactic medium at z<1

    NASA Astrophysics Data System (ADS)

    Johnson, Sean; Chen, Hsiao-Wen; Mulchaey, John S.

    2016-01-01

    The growth and evolution of galaxies is governed by gas accretion from circum-/intergalactic gas reservoirs and satellites that is regulated by feedback from stars and active galactic nuclei. To constrain the relationship between these gas reservoirs and galaxy properties, I have carried out deep and highly complete surveys of several thousand galaxies in fields with high quality absorption spectra of background quasars from the Cosmic Origins Spectrograph. The survey results imply that (1) highly ionized, heavy-element enriched gas traced by OVI absorption primarily arise in low-mass, gas-rich galaxy groups rather than the warm-hot phase of the intergalactic medium and that (2) galaxies with nearby neighbors exhibit more extened OVI absorbing gas than isolated galaxies. Together, these observations suggest that galaxy and group interactions play a role in stripping bound, heavy element enriched halo gas to enrich the intergalactic medium. In addition, I carried out the first large survey of circumgalactic gas around active galactic nuclei (AGN) and quasars. The cool, heavy-element enriched gas content of AGN and quasar host halos is strongly correlated with AGN luminosity, and the gas exhibit extreme kinematics with velocity spread inconsistent with gas bound to the AGN host. These observations provide tantalizing hints at the widespread impact of AGN feedback on the extended gas reservoirs around galaxies.

  11. On the electron-positron cascade in AGN central engines

    NASA Astrophysics Data System (ADS)

    Ford, Alex; Keenan, Brett; Medvedev, Mikhail

    2016-03-01

    Processes around spinning supermassive black holes (BH) in active galactic nuclei (AGN) are believed to determine how relativistic jets are launched and how the BH energy is extracted. The key ``ingredient'' is the origin of plasma in BH magnetospheres. In order to explore the process of the electron-positron plasma production, we developed a numerical code which models a one-dimensional (along a magnetic field line) dynamics of the cascade. Our simulations show that plasma production is controlled by the spectrum of the ambient photon field, the B-field strength, the BH spin and mass. Implications of our results to the Galactic Center and AGNs are discussed.

  12. A statistical study of H i gas in nearby narrow-line AGN-hosting galaxies

    SciTech Connect

    Zhu, Yi-Nan; Wu, Hong E-mail: hwu@bao.ac.cn

    2015-01-01

    As a quenching mechanism, active galactic nucleus (AGN) feedback could suppress on going star formation in host galaxies. On the basis of a sample of galaxies selected from the Arecibo Legacy Fast ALFA (ALFALFA) H i survey, the dependence of the H i mass (M{sub H} {sub i}), stellar mass (M{sub *}), and H i-to-stellar mass ratio (M{sub H} {sub i}/M{sub *}) on various tracers of AGN activity are presented and analyzed in this paper. Almost all the AGN hostings in this sample are gas-rich galaxies, and there is not any evidence to indicate that the AGN activity could increase or decrease either M{sub H} {sub i} or M{sub H} {sub i}/M{sub *}. The position of the cold neutral gas cannot be fixed accurately based only on available H i data, due to the large beam size of ALFALFA survey. In addition, even though AGN hostings are more easily detected by an H i survey compared with absorption line galaxies, these two types of galaxies show similar star formation history. If an AGN hosting would ultimately evolve into an old red galaxy with low cold gas, then when and how the gas has been exhausted must be solved by future hypotheses and observations.

  13. AGN proximity zone fossils and the delayed recombination of metal lines

    NASA Astrophysics Data System (ADS)

    Oppenheimer, Benjamin D.; Schaye, Joop

    2013-09-01

    We model the time-dependent evolution of metal-enriched intergalactic and circumgalactic gas exposed to the fluctuating radiation field from an active galactic nucleus (AGN). We consider diffuse gas densities (nH = 10-5-10-2.5 cm-3) exposed to the extra-galactic background (EGB) and initially in thermal equilibrium (T ˜ 104-104.5 K). Once the proximate AGN field turns on, additional photo-ionization rapidly ionizes the HI and metals. The enhanced AGN radiation field turns off after a typical AGN lifetime (τAGN = 1-20 Myr) and the field returns to the EGB intensity, but the metals remain out of ionization equilibrium for time scales that can significantly exceed τAGN. We define this phase as the AGN proximity zone `fossil' phase and show that high ionization stages (e.g. OVI, NeVIII, MgX) are in general enhanced, while the abundances of low ions (e.g. CIV, OIV, MgII) are reduced. In contrast, HI re-equilibrates rapidly (≪τAGN) owing to its low neutral fraction at diffuse densities. We demonstrate that metal column densities of intervening gas observed in absorption in quasar sight lines are significantly affected by delayed recombination for a wide range of densities, metallicities, AGN strengths, AGN lifetimes and AGN duty cycles. As an example, we show that a fossil zone model can simultaneously reproduce the observed NeVIII, MgII, HI and other metal columns of the z = 0.927 PG1206+259 absorption system observed by Tripp et al. using a single, T ˜ 104 K phase model. At low redshift even moderate-strength AGN that are off for 90 per cent of the time could significantly enhance the high-ion metal columns in the circum-galactic media of galaxies observed without active AGN. Fossil proximity zones may be particularly important during the quasar era, z ˜ 2-5. Indeed, we demonstrate that at these redshifts a large fraction of the metal-enriched intergalactic medium may consist of out-of-equilibrium fossil zones. AGN proximity zone fossils allow a whole new class

  14. Reciprocal Markov Modeling of Feedback Mechanisms Between Emotion and Dietary Choice Using Experience-Sampling Data.

    PubMed

    Lu, Ji; Pan, Junhao; Zhang, Qiang; Dubé, Laurette; Ip, Edward H

    2015-01-01

    With intensively collected longitudinal data, recent advances in the experience-sampling method (ESM) benefit social science empirical research, but also pose important methodological challenges. As traditional statistical models are not generally well equipped to analyze a system of variables that contain feedback loops, this paper proposes the utility of an extended hidden Markov model to model reciprocal the relationship between momentary emotion and eating behavior. This paper revisited an ESM data set (Lu, Huet, & Dube, 2011) that observed 160 participants' food consumption and momentary emotions 6 times per day in 10 days. Focusing on the analyses on feedback loop between mood and meal-healthiness decision, the proposed reciprocal Markov model (RMM) can accommodate both hidden ("general" emotional states: positive vs. negative state) and observed states (meal: healthier, same or less healthy than usual) without presuming independence between observations and smooth trajectories of mood or behavior changes. The results of RMM analyses illustrated the reciprocal chains of meal consumption and mood as well as the effect of contextual factors that moderate the interrelationship between eating and emotion. A simulation experiment that generated data consistent with the empirical study further demonstrated that the procedure is promising in terms of recovering the parameters. PMID:26717120

  15. Reciprocal Markov modeling of feedback mechanisms between emotion and dietary choice using experience sampling data

    PubMed Central

    Lu, Ji; Pan, Junhao; Zhang, Qiang; Dubé, Laurette; Ip, Edward H.

    2015-01-01

    With intensively collected longitudinal data, recent advances in Experience Sampling Method (ESM) benefit social science empirical research, but also pose important methodological challenges. As traditional statistical models are not generally well-equipped to analyze a system of variables that contain feedback loops, this paper proposes the utility of an extended hidden Markov model to model reciprocal relationship between momentary emotion and eating behavior. This paper revisited an ESM data set (Lu, Huet & Dube, 2011) that observed 160 participants’ food consumption and momentary emotions six times per day in 10 days. Focusing on the analyses on feedback loop between mood and meal healthiness decision, the proposed Reciprocal Markov Model (RMM) can accommodate both hidden (“general” emotional states: positive vs. negative state) and observed states (meal: healthier, same or less healthy than usual) without presuming independence between observations and smooth trajectories of mood or behavior changes. The results of RMM analyses illustrated the reciprocal chains of meal consumption and mood as well as the effect of contextual factors that moderate the interrelationship between eating and emotion. A simulation experiment that generated data consistent to the empirical study further demonstrated that the procedure is promising in terms of recovering the parameters. PMID:26717120

  16. The Cusp/Core problem: supernovae feedback versus the baryonic clumps and dynamical friction model

    NASA Astrophysics Data System (ADS)

    Del Popolo, A.; Pace, F.

    2016-05-01

    In the present paper, we compare the predictions of two well known mechanisms considered able to solve the cusp/core problem (a. supernova feedback; b. baryonic clumps-DM interaction) by comparing their theoretical predictions to recent observations of the inner slopes of galaxies with masses ranging from dSphs to normal spirals. We compare the α-V_{rot} and the α-M_{ast} relationships, predicted by the two models with high resolution data coming from Adams et al. (Astrophys. J. 789, 63, 2014), Simon et al. (Astrophys. J. 621, 757, 2005), LITTLE THINGS (Oh et al. in Astron. J. 149, 180, 2015), THINGS dwarves (Oh et al. in Astron. J. 141, 193, 2011a; Oh et al. in Astron. J. 142, 224, 2011b), THINGS spirals (Oh et al. in Astron. J. 149, 180, 2015), Sculptor, Fornax and the Milky Way. The comparison of the theoretical predictions with the complete set of data shows that the two models perform similarly, while when we restrict the analysis to a smaller subsample of higher quality, we show that the method presented in this paper (baryonic clumps-DM interaction) performs better than the one based on supernova feedback. We also show that, contrarily to the first model prediction, dSphs of small mass could have cored profiles. This means that observations of cored inner profiles in dSphs having a stellar mass <106 M_{⊙} not necessarily imply problems for the ΛCDM model.

  17. Modeling and control of non-square MIMO system using relay feedback.

    PubMed

    Kalpana, D; Thyagarajan, T; Gokulraj, N

    2015-11-01

    This paper proposes a systematic approach for the modeling and control of non-square MIMO systems in time domain using relay feedback. Conventionally, modeling, selection of the control configuration and controller design of non-square MIMO systems are performed using input/output information of direct loop, while the output of undesired responses that bears valuable information on interaction among the loops are not considered. However, in this paper, the undesired response obtained from relay feedback test is also taken into consideration to extract the information about the interaction between the loops. The studies are performed on an Air Path Scheme of Turbocharged Diesel Engine (APSTDE) model, which is a typical non-square MIMO system, with input and output variables being 3 and 2 respectively. From the relay test response, the generalized analytical expressions are derived and these analytical expressions are used to estimate unknown system parameters and also to evaluate interaction measures. The interaction is analyzed by using Block Relative Gain (BRG) method. The model thus identified is later used to design appropriate controller to carry out closed loop studies. Closed loop simulation studies were performed for both servo and regulatory operations. Integral of Squared Error (ISE) performance criterion is employed to quantitatively evaluate performance of the proposed scheme. The usefulness of the proposed method is demonstrated on a lab-scale Two-Tank Cylindrical Interacting System (TTCIS), which is configured as a non-square system. PMID:26453020

  18. Tracing outflows in the AGN forbidden region with SINFONI

    NASA Astrophysics Data System (ADS)

    Kakkad, D.; Mainieri, V.; Padovani, P.; Cresci, G.; Husemann, B.; Carniani, S.; Brusa, M.; Lamastra, A.; Lanzuisi, G.; Piconcelli, E.; Schramm, M.

    2016-08-01

    Context. Active galactic nucleus (AGN) driven outflows are invoked in numerical simulations to reproduce several observed properties of local galaxies. The z > 1 epoch is of particular interest as it was during this time that the volume averaged star formation and the accretion rate of black holes were at their maximum. Radiatively driven outflows are therefore believed to be common during this epoch. Aims: We aim to trace and characterize outflows in AGN hosts with high mass accretion rates at z > 1 using integral field spectroscopy. We obtain spatially resolved kinematics of the [O iii] λ5007 line in two targets which reveal the morphology and spatial extension of the outflows. Methods: We present SINFONI observations in the J band and the H + K band of five AGNs at 1.2 < z < 2.2. To maximize the chance of observing radiatively driven outflows, our sample was pre-selected based on peculiar values of the Eddington ratio and the hydrogen column density of the surrounding interstellar medium. We observe high velocity (~600-1900 km s-1) and kiloparsec scale extended ionized outflows in at least three of our targets, using [O iii] λ5007 line kinematics tracing the AGN narrow line region. We estimate the total mass of the outflow, the mass outflow rate, and the kinetic power of the outflows based on theoretical models and report on the uncertainties associated with them. Results: We find mass outflow rates of ~1-10 M⊙/yr for the sample presented in this paper. Based on the high star formation rates of the host galaxies, the observed outflow kinetic power, and the expected power due to the AGN, we infer that both star formation and AGN radiation could be the dominant source for the outflows. The outflow models suffer from large uncertainties, hence we call for further detailed observations for an accurate determination of the outflow properties to confirm the exact source of these outflows.

  19. Sensory feedback, error correction, and remapping in a multiple oscillator model of place-cell activity.

    PubMed

    Monaco, Joseph D; Knierim, James J; Zhang, Kechen

    2011-01-01

    Mammals navigate by integrating self-motion signals ("path integration") and occasionally fixing on familiar environmental landmarks. The rat hippocampus is a model system of spatial representation in which place cells are thought to integrate both sensory and spatial information from entorhinal cortex. The localized firing fields of hippocampal place cells and entorhinal grid-cells demonstrate a phase relationship with the local theta (6-10 Hz) rhythm that may be a temporal signature of path integration. However, encoding self-motion in the phase of theta oscillations requires high temporal precision and is susceptible to idiothetic noise, neuronal variability, and a changing environment. We present a model based on oscillatory interference theory, previously studied in the context of grid cells, in which transient temporal synchronization among a pool of path-integrating theta oscillators produces hippocampal-like place fields. We hypothesize that a spatiotemporally extended sensory interaction with external cues modulates feedback to the theta oscillators. We implement a form of this cue-driven feedback and show that it can retrieve fixed points in the phase code of position. A single cue can smoothly reset oscillator phases to correct for both systematic errors and continuous noise in path integration. Further, simulations in which local and global cues are rotated against each other reveal a phase-code mechanism in which conflicting cue arrangements can reproduce experimentally observed distributions of "partial remapping" responses. This abstract model demonstrates that phase-code feedback can provide stability to the temporal coding of position during navigation and may contribute to the context-dependence of hippocampal spatial representations. While the anatomical substrates of these processes have not been fully characterized, our findings suggest several signatures that can be evaluated in future experiments. PMID:21994494

  20. Optical variability of the Kepler AGN

    NASA Astrophysics Data System (ADS)

    Edelson, Rick

    2014-01-01

    Kepler has opened a new era for the study of AGN optical variability, producing light curves with ~0.1% errors (for a ~15th magnitude source), 30 min sampling, >90% duty cycle and durations of years. Thanks to an intensive identification campaign, the number of Seyfert 1s/quasars monitored by Kepler rose from just one (Zw 229-15) in the first year to 37 by the time of May 2013 reaction wheel failure. We measured the optical power spectral density (PSD) functions of these Kepler AGN finding that that on timescales of ~6 hr to 1 month, the PSDs are typically well-fitted with a slop of ~-3, steeper than seen in the X-rays. In a few sources there is also evidence for a flattening at the longest timescales. We also find a broad correlation between rms variability and flux level. These results broadly support the model in which the optical fluctuations are due to vicious instabilities in the accretion disk. I will also present the light curve for W2R1926+42, the only rapidly variable BL Lac object known to be monitored by Kepler. With data covering over a year and sampling rates of 1-30 min, this may be the information-richest AGN light curve ever gathered at any wavelength. The PSD appears to bend from a slope of -2.6 to -1.2 on a ~7 hr timescale, but fits are formally unacceptable. These data indicate that the phenomenon of blazar "microvariability" (sporadic variations on timescales shorter than the ~12 hour window available from the ground) actually results from a combination of rapid, powerful variability interspersed with longer, relatively quiescent periods.

  1. Feedback loops and temporal misalignment in component-based hydrologic modeling

    NASA Astrophysics Data System (ADS)

    Elag, Mostafa M.; Goodall, Jonathan L.; Castronova, Anthony M.

    2011-12-01

    In component-based modeling, a complex system is represented as a series of loosely integrated components with defined interfaces and data exchanges that allow the components to be coupled together through shared boundary conditions. Although the component-based paradigm is commonly used in software engineering, it has only recently been applied for modeling hydrologic and earth systems. As a result, research is needed to test and verify the applicability of the approach for modeling hydrologic systems. The objective of this work was therefore to investigate two aspects of using component-based software architecture for hydrologic modeling: (1) simulation of feedback loops between components that share a boundary condition and (2) data transfers between temporally misaligned model components. We investigated these topics using a simple case study where diffusion of mass is modeled across a water-sediment interface. We simulated the multimedia system using two model components, one for the water and one for the sediment, coupled using the Open Modeling Interface (OpenMI) standard. The results were compared with a more conventional numerical approach for solving the system where the domain is represented by a single multidimensional array. Results showed that the component-based approach was able to produce the same results obtained with the more conventional numerical approach. When the two components were temporally misaligned, we explored the use of different interpolation schemes to minimize mass balance error within the coupled system. The outcome of this work provides evidence that component-based modeling can be used to simulate complicated feedback loops between systems and guidance as to how different interpolation schemes minimize mass balance error introduced when components are temporally misaligned.

  2. A stage structure pest management model with impulsive state feedback control

    NASA Astrophysics Data System (ADS)

    Pang, Guoping; Chen, Lansun; Xu, Weijian; Fu, Gang

    2015-06-01

    A stage structure pest management model with impulsive state feedback control is investigated. We get the sufficient condition for the existence of the order-1 periodic solution by differential equation geometry theory and successor function. Further, we obtain a new judgement method for the stability of the order-1 periodic solution of the semi-continuous systems by referencing the stability analysis for limit cycles of continuous systems, which is different from the previous method of analog of Poincarè criterion. Finally, we analyze numerically the theoretical results obtained.

  3. VIDEO MODELING BY EXPERTS WITH VIDEO FEEDBACK TO ENHANCE GYMNASTICS SKILLS

    PubMed Central

    Boyer, Eva; Miltenberger, Raymond G; Batsche, Catherine; Fogel, Victoria

    2009-01-01

    The effects of combining video modeling by experts with video feedback were analyzed with 4 female competitive gymnasts (7 to 10 years old) in a multiple baseline design across behaviors. During the intervention, after the gymnast performed a specific gymnastics skill, she viewed a video segment showing an expert gymnast performing the same skill and then viewed a video replay of her own performance of the skill. The results showed that all gymnasts demonstrated improved performance across three gymnastics skills following exposure to the intervention. PMID:20514194

  4. Feedbacks between climate, CO2 and N2O quantified by a fully coupled Earth system model

    NASA Astrophysics Data System (ADS)

    Kracher, D.; Reick, C. H.

    2013-12-01

    Climate change is evoked by an anthropogenic increase of green house gases (GHG) in the atmosphere, induced by direct emissions from industrial processes or indirectly due to human impacts on ecosystems. Those indirect GHG emissions are strongly influenced by climatic conditions implying several feedback loops in the climate - carbon (C) - nitrogen (N) system. In our study we aim at quantifying the climate - nitrous oxide (N2O) feedback strength in comparison to other feedback mechanisms by applying an Earth system model with explicit representation of interactive N2O in the atmosphere-land-ocean system. Beside the feedbacks emerging due to the temperature sensitivity of biogenic CO2 and N2O emissions, another feedback addressed arises from additional inter-linkages between climate and C and N cycles. Future increased atmospheric CO2 leads to enhanced primary productivity ('CO2 fertilization') causing changes in N availability in the different land and ocean ecosystems. As N2O emissions are driven by availability of N, increased atmospheric CO2 concentrations will impact the climate system also via modifications in N2O emissions. Those changes in N2O emissions will feed back to the climate and will hence also modify the natural biogenic release of CO2 into the atmosphere. This and other associated feedbacks are quantified by applying MPI-ESM, the Earth system model of the Max Planck Institute for Meteorology in Hamburg. MPI-ESM is an atmosphere and ocean global circulation model with model components for land and ocean biogeochemistry. For both CO2 and N2O, land-atmosphere and ocean-atmosphere exchange as well as atmospheric transport are simulated explicitly. Hence, different feedback components in the climate-C-N system can be quantified by cutting artificially single feedback pathways in the model.

  5. Short- and Long-Term Feedbacks on Vegetation Water Use: Unifying Evidence from Observations and Modeling

    NASA Astrophysics Data System (ADS)

    Mackay, D. S.

    2001-05-01

    Recent efforts to measure and model the interacting influences of climate, soil, and vegetation on soil water and nutrient dynamics have identified numerous important feedbacks that produce nonlinear responses. In particular, plant physiological factors that control rates of transpiration respond to soil water deficits and vapor pressure deficits (VPD) in the short-term, and to climate, nutrient cycling and disturbance in the long-term. The starting point of this presentation is the observation that in many systems, in particular forest ecosystems, conservative water use emerges as a result of short-term closure of stomata in response to high evaporative demand, and long-term vegetative canopy development under nutrient limiting conditions. Evidence for important short-term controls is presented from sap flux measurements of stand transpiration, remote sensing, and modeling of transpiration through a combination of physically-based modeling and Monte Carlo analysis. A common result is a strong association between stomatal conductance (gs) and the negative evaporative gain (∂ gs/∂ VPD) associated with the sensitivity of stomatal closure to rates of water loss. The importance of this association from the standpoint of modeling transpiration depends on the degree of canopy-atmosphere coupling. This suggests possible simplifications to future canopy component models for use in watershed and larger-scale hydrologic models for short-term processes. However, further results are presented from theoretical modeling, which suggest that feedbacks between hydrology and vegetation in current long-term (inter-annual to century) models may be too simple, as they do not capture the spatially variable nature of slow nutrient cycling in response to soil water dynamics and site history. Memory effects in the soil nutrient pools can leave lasting effects on more rapid processes associated with soil, vegetation, atmosphere coupling.

  6. Four perspectives on climate feedbacks

    NASA Astrophysics Data System (ADS)

    Feldl, N.; Roe, G. H.

    2013-08-01

    The spatial pattern of climate feedbacks depends on how the feedbacks are defined. We employ an idealized aquaplanet simulation with radiative kernels diagnosed for the precise model setup and characterize the meridional structure of feedbacks under four different definitions: local feedbacks, global feedbacks, nondimensional feedback factors, and relative humidity feedbacks. First, the spatial pattern of the reference response (i.e., the Planck feedback) is found to vary with definition, largely as a consequence of polar-amplified warming, which affects other high-latitude feedbacks as well. Second, locally defined feedbacks allow for decomposition of the surface temperature response as a function of feedbacks, forcing, and heat transport. Third, different insights into the dynamical and thermodynamical underpinnings of the subtropical moisture response are gained by comparing different versions of humidity feedbacks. Thus, alternative approaches to the conventional, global definition of feedbacks offer several advantages for understanding patterns of warming and, ultimately, regional climate predictability.

  7. Climate sensitivity of a one-dimensional radiative-convective model with cloud feedback

    NASA Technical Reports Server (NTRS)

    Wang, W.-C.; Rossow, W. B.; Yao, M.-S.; Wolfson, M.

    1981-01-01

    The potential complexity of the feedback between global mean cloud amount and global mean surface temperature when variations of the vertical cloud distribution are included is illustrated. This is done by studying the behavior of a one-dimensional radiative-convective model with two types of cloud variation: (1) variable cloud cover with constant optical thickness and (2) variable optical thickness with constant cloud cover. The variable parameter is calculated on the assumption that a correlation exists between cloud amount and precipitation or the vertical flux convergence of latent heat. Since the vertical latent heat flux is taken to be a fraction of the total heat flux, modeled by convective adjustment, the sensitivity of the results to two different critical lapse rates is examined. These are a constant 6.5 K/km lapse rate and a temperature-dependent, moist adiabatic lapse rate. The effects of the vertical structure of climate perturbations on the nature of the cloud feedback are also examined. The model results reveal that changes in the vertical cloud distribution and mean cloud optical thickness can be as important to climate variations as are changes in the total cloud cover.

  8. Investigation of biogeophysical feedback on the African climate using a two-dimensional model

    NASA Technical Reports Server (NTRS)

    Xue, Yongkang; Liou, Kuo-Nan; Kasahara, Akira

    1990-01-01

    A numerical scheme is specifically designed to develop a time-dependent climate model to ensure the conservation of mass, momentum, energy, and water vapor, in order to study the biogeophysical feedback for the climate of Africa. A vegetation layer is incorporated in the present two-dimensional climate model. Using the coupled climate-vegetation model, two tests were performed involving the removal and expansion of the Sahara Desert. Results show that variations in the surface conditions produce a significant feedback to the climate system. It is noted that the simulation responses to the temperature and zonal wind in the case of an expanded desert agree with the climatological data for African dry years. Perturbed simulations have also been performed by changing the albedo only, without allowing the variation in the vegetation layer. It is shown that the variation in latent heat release is significant and is related to changes in the vegetation cover. As a result, precipitation and cloud cover are reduced.

  9. A mathematical modelling framework for elucidating the role of feedback control in translation termination.

    PubMed

    de Silva, Eric; Krishnan, J; Betney, Russell; Stansfield, Ian

    2010-06-01

    Translation is the final stage of gene expression where messenger RNA is used as a template for protein polymerization from appropriate amino acids. Release of the completed protein requires a release factor protein acting at the termination/stop codon to liberate it. In this paper we focus on a complex feedback control mechanism involved in the translation and synthesis of release factor proteins, which has been observed in different systems. These release factor proteins are involved in the termination stage of their own translation. Further, mutations in the release factor gene can result in a premature stop codon. In this case translation can result either in early termination and the production of a truncated protein or readthrough of the premature stop codon and production of the complete release factor protein. Thus during translation of the release factor mRNA containing a premature stop codon, the full length protein negatively regulates its production by its action on a premature stop codon, while positively regulating its production by its action on the regular stop codon. This paper develops a mathematical modelling framework to investigate this complex feedback control system involved in translation. A series of models is established to carefully investigate the role of individual mechanisms and how they work together. The steady state and dynamic behaviour of the resulting models are examined both analytically and numerically. PMID:20176033

  10. An enhanced fraction of starbursting galaxies among high Eddington ratio AGNs

    NASA Astrophysics Data System (ADS)

    Bernhard, E.; Mullaney, J. R.; Daddi, E.; Ciesla, L.; Schreiber, C.

    2016-04-01

    We investigate the star-forming properties of 1620 X-ray selected AGN host galaxies as a function of their specific X-ray luminosity (i.e., X-ray luminosity per unit host stellar mass) - a proxy of the Eddington ratio. Our motivation is to determine whether there is any evidence of a suppression of star-formation at high Eddington ratios, which may hint toward "AGN feedback" effects. Star-formation rates (SFRs) are derived from fits to Herschel-measured far-infrared spectral energy distributions, taking into account any contamination from the AGN. Herschel-undetected AGNs are included via stacking analyses to provide average SFRs in bins of redshift and specific X-ray luminosity (spanning 0.01 ≲ L_X/M_{ast } ≲ 100 L_{⊙} M_{⊙}^{-1}). After normalising for the effects of mass and redshift arising from the evolving galaxy main sequence, we find that the SFRs of high specific luminosity AGNs are slightly enhanced compared to their lower specific luminosity counterparts. This suggests that the SFR distribution of AGN hosts changes with specific X-ray luminosity, a result reinforced by our finding of a significantly higher fraction of starbursting hosts among high specific luminosity AGNs compared to that of the general star-forming galaxy population (i.e., 8-10 per cent vs. 3 per cent). Contrary to our original motivation, our findings suggest that high specific luminosity AGNs are more likely to reside in galaxies with enhanced levels of star-formation.

  11. An enhanced fraction of starbursting galaxies among high Eddington ratio AGNs

    NASA Astrophysics Data System (ADS)

    Bernhard, E.; Mullaney, J. R.; Daddi, E.; Ciesla, L.; Schreiber, C.

    2016-07-01

    We investigate the star-forming properties of 1620 X-ray selected active galactic nuclei (AGN) host galaxies as a function of their specific X-ray luminosity (i.e. X-ray luminosity per unit host stellar mass) - a proxy of the Eddington ratio. Our motivation is to determine whether there is any evidence of a suppression of star formation at high Eddington ratios, which may hint towards `AGN feedback' effects. Star formation rates (SFRs) are derived from fits to Herschel-measured far-infrared spectral energy distributions, taking into account any contamination from the AGN. Herschel-undetected AGNs are included via stacking analyses to provide average SFRs in bins of redshift and specific X-ray luminosity (spanning 0.01 ≲ L_X/M_{ast } ≲ 100 L_{{⊙}} M_{{⊙}}^{-1}). After normalizing for the effects of mass and redshift arising from the evolving galaxy main sequence, we find that the SFRs of high specific luminosity AGNs are slightly enhanced compared to their lower specific luminosity counterparts. This suggests that the SFR distribution of AGN hosts changes with specific X-ray luminosity, a result reinforced by our finding of a significantly higher fraction of starbursting hosts among high specific luminosity AGNs compared to that of the general star-forming galaxy population (i.e. 8-10 per cent versus 3 per cent). Contrary to our original motivation, our findings suggest that high specific luminosity AGNs are more likely to reside in galaxies with enhanced levels of star formation.

  12. Inefficient Driving of Bulk Turbulence By Active Galactic Nuclei in a Hydrodynamic Model of the Intracluster Medium

    NASA Astrophysics Data System (ADS)

    Reynolds, Christopher S.; Balbus, Steven A.; Schekochihin, Alexander A.

    2015-12-01

    Central jetted active galactic nuclei (AGNs) appear to heat the core regions of the intracluster medium (ICM) in cooling-core galaxy clusters and groups, thereby preventing a cooling catastrophe. However, the physical mechanism(s) by which the directed flow of kinetic energy is thermalized throughout the ICM core remains unclear. We examine one widely discussed mechanism whereby the AGN induces subsonic turbulence in the ambient medium, the dissipation of which provides the ICM heat source. Through controlled inviscid three-dimensional hydrodynamic simulations, we verify that explosive AGN-like events can launch gravity waves (g-modes) into the ambient ICM, which in turn decays to volume-filling turbulence. In our model, however, this process is found to be inefficient, with less than 1% of the energy injected by the AGN activity actually ending up in the turbulence of the ambient ICM. This efficiency is an order of magnitude or more too small to explain the observations of AGN-feedback in galaxy clusters and groups with short central cooling times. Atmospheres in which the g-modes are strongly trapped/confined have an even lower efficiency since, in these models, the excitation of turbulence relies on the g-modes’ ability to escape from the center of the cluster into the bulk ICM. Our results suggest that, if AGN-induced turbulence is indeed the mechanism by which the AGN heats the ICM core, its driving may rely on physics beyond that captured in our ideal hydrodynamic model.

  13. Climate Model Tests Of Anthropogenic Influence On Greenhouse-Induced Climate Change: The Role Of Plant Physiology Feedbacks

    NASA Astrophysics Data System (ADS)

    Philippon, G.; Vavrus, S.; Kutzbach, J. E.; Ruddiman, W. F.

    2008-12-01

    We use the NCAR's Community Climate System Model (CCSM3) forced by greenhouse gas concentrations that are lower than nominal pre-industrial (~1750 AD) levels and instead based on natural levels that were reached in similar stages of previous interglaciations. The aim is to test the plant physiology feedback from the vegetation model with the coupled atmosphere-slab ocean configuration at a moderate resolution (T42). According to previous modeling work allowing interactive vegetation but no physiology feedback, the response of this model to lowered greenhouse gases is a global cooling of about 3 K and an expansion of arctic snow area, resulting from an arctic desert expansion and a decrease mainly of boreal trees and also tundra. We focus on the comparison of two experiments with both the vegetation feedbacks (interactive vegetation) but one with no plant physiology feedback (NOANTHRO_VEG) and the other with plant physiology feedback (PHYSIO). The physiology feedback produces an even cooler northern hemisphere high latitude climate, about -0.5 K on average. But the land winter temperature difference can reach 2 K near the northern pole. Furthermore, the physiology feedback amplifies the decrease of boreal tree cover in high latitudes and the tundra area in many places except on the southern limit (South-west and south-east Russia and south-east Canada), where the tundra is increasing. Viewed from the perspective of explaining the unusual late-Holocene increases of CO2 that occurred prior to the Industrial Revolution, these simulated changes in the vegetation support the hypothesis that early agriculture played a role in initiating anomalous warming that thwarted incipient glaciation beginning several thousand years ago. In this work, we will show the impact of the vegetation feedback and the physiology effect on the climate.

  14. Feedbacks of the plant physiology in a coupled climate model under a "hypothical" cooler climate during the Holocene

    NASA Astrophysics Data System (ADS)

    Philippon, G.; Vavrus, S.; Kutzbach, J. E.; Ruddiman, W. F.

    2009-04-01

    We use the NCAR's Community Climate System Model (CCSM3) forced by greenhouse gas concentrations that are lower than nominal pre-industrial (~1750 AD) levels and instead based on natural levels that were reached in similar stages of previous interglaciations. The aim is to test the plant physiology feedback from the vegetation model with the coupled atmosphere-slab ocean configuration at a moderate resolution (T42). According to previous modeling work allowing interactive vegetation but no physiology feedback, the response of this model to lowered greenhouse gases is a global cooling of about 3 K and an expansion of arctic snow area, resulting from an arctic desert expansion and a decrease mainly of boreal trees and also tundra. We focus on the comparison of two experiments with both the vegetation feedbacks (interactive vegetation) but one with no plant physiology feedback (NOANTHRO_VEG) and the other with plant physiology feedback (NOANTHRO_VEG_PHYSIO). The physiology feedback produces an even cooler northern hemisphere high latitude climate, about -0.5 K on average. But the land winter temperature difference can reach 2 K near the northern pole. Furthermore, the physiology feedback amplifies the decrease of boreal tree cover in high latitudes and the tundra area in many places except on the southern limit (South-west and south-east Russia and south-east Canada), where the tundra is increasing. In some tropical forest regions, the physiology effect interacts with the recycling and affects the evaporation, the evapo-transpitation locally. Viewed from the perspective of explaining the unusual late-Holocene increases of CO2 that occurred prior to the Industrial Revolution, these simulated changes in the vegetation support the hypothesis that early agriculture played a role in initiating anomalous warming that thwarted incipient glaciation beginning several thousand years ago. In this work, we will show the impact of the vegetation feedback and the physiology effect

  15. Coupled map car-following model and its delayed-feedback control

    NASA Astrophysics Data System (ADS)

    Konishi, Keiji; Kokame, Hideki; Hirata, Kentaro

    1999-10-01

    This paper proposes a coupled map car-following traffic model, which describes a dynamical behavior of a group of road vehicles running in a single lane without overtaking. This model consists of a lead vehicle and following vehicles, which have a piecewise linear optimal velocity function. When the lead-vehicle speed is varied, we can observe a traffic jam in the group of the vehicles. We derive a condition under which the traffic jam never occurs in our model. Furthermore, in order to suppress the traffic jam, for each vehicle we use a dynamic version of decentralized delayed-feedback control proposed in [Konishi, Hirai, and Kokame, Phys. Rev. E 58, 3055 (1998)], and provide a systematic procedure for designing the controller.

  16. Modeling laser-induced periodic surface structures: Finite-difference time-domain feedback simulations

    SciTech Connect

    Skolski, J. Z. P. Vincenc Obona, J.; Römer, G. R. B. E.; Huis in 't Veld, A. J.

    2014-03-14

    A model predicting the formation of laser-induced periodic surface structures (LIPSSs) is presented. That is, the finite-difference time domain method is used to study the interaction of electromagnetic fields with rough surfaces. In this approach, the rough surface is modified by “ablation after each laser pulse,” according to the absorbed energy profile, in order to account for inter-pulse feedback mechanisms. LIPSSs with a periodicity significantly smaller than the laser wavelength are found to “grow” either parallel or orthogonal to the laser polarization. The change in orientation and periodicity follow from the model. LIPSSs with a periodicity larger than the wavelength of the laser radiation and complex superimposed LIPSS patterns are also predicted by the model.

  17. Nonlinear feedback in a six-dimensional Lorenz Model: impact of an additional heating term

    NASA Astrophysics Data System (ADS)

    Shen, B.-W.

    2015-03-01

    In this study, a six-dimensional Lorenz model (6DLM) is derived, based on a recent study using a five-dimensional (5-D) Lorenz model (LM), in order to examine the impact of an additional mode and its accompanying heating term on solution stability. The new mode added to improve the representation of the steamfunction is referred to as a secondary streamfunction mode, while the two additional modes, that appear in both the 6DLM and 5DLM but not in the original LM, are referred to as secondary temperature modes. Two energy conservation relationships of the 6DLM are first derived in the dissipationless limit. The impact of three additional modes on solution stability is examined by comparing numerical solutions and ensemble Lyapunov exponents of the 6DLM and 5DLM as well as the original LM. For the onset of chaos, the critical value of the normalized Rayleigh number (rc) is determined to be 41.1. The critical value is larger than that in the 3DLM (rc ~ 24.74), but slightly smaller than the one in the 5DLM (rc ~ 42.9). A stability analysis and numerical experiments obtained using generalized LMs, with or without simplifications, suggest the following: (1) negative nonlinear feedback in association with the secondary temperature modes, as first identified using the 5DLM, plays a dominant role in providing feedback for improving the solution's stability of the 6DLM, (2) the additional heating term in association with the secondary streamfunction mode may destabilize the solution, and (3) overall feedback due to the secondary streamfunction mode is much smaller than the feedback due to the secondary temperature modes; therefore, the critical Rayleigh number of the 6DLM is comparable to that of the 5DLM. The 5DLM and 6DLM collectively suggest different roles for small-scale processes (i.e., stabilization vs. destabilization), consistent with the following statement by Lorenz (1972): If the flap of a butterfly's wings can be instrumental in generating a tornado, it can

  18. Nonlinear feedback in a six-dimensional Lorenz model: impact of an additional heating term

    NASA Astrophysics Data System (ADS)

    Shen, B.-W.

    2015-12-01

    In this study, a six-dimensional Lorenz model (6DLM) is derived, based on a recent study using a five-dimensional (5-D) Lorenz model (LM), in order to examine the impact of an additional mode and its accompanying heating term on solution stability. The new mode added to improve the representation of the streamfunction is referred to as a secondary streamfunction mode, while the two additional modes, which appear in both the 6DLM and 5DLM but not in the original LM, are referred to as secondary temperature modes. Two energy conservation relationships of the 6DLM are first derived in the dissipationless limit. The impact of three additional modes on solution stability is examined by comparing numerical solutions and ensemble Lyapunov exponents of the 6DLM and 5DLM as well as the original LM. For the onset of chaos, the critical value of the normalized Rayleigh number (rc) is determined to be 41.1. The critical value is larger than that in the 3DLM (rc ~ 24.74), but slightly smaller than the one in the 5DLM (rc ~ 42.9). A stability analysis and numerical experiments obtained using generalized LMs, with or without simplifications, suggest the following: (1) negative nonlinear feedback in association with the secondary temperature modes, as first identified using the 5DLM, plays a dominant role in providing feedback for improving the solution's stability of the 6DLM, (2) the additional heating term in association with the secondary streamfunction mode may destabilize the solution, and (3) overall feedback due to the secondary streamfunction mode is much smaller than the feedback due to the secondary temperature modes; therefore, the critical Rayleigh number of the 6DLM is comparable to that of the 5DLM. The 5DLM and 6DLM collectively suggest different roles for small-scale processes (i.e., stabilization vs. destabilization), consistent with the following statement by Lorenz (1972): "If the flap of a butterfly's wings can be instrumental in generating a tornado, it can

  19. A model simulation of leaf physiological feedbacks on evapotranspiration and climate

    NASA Astrophysics Data System (ADS)

    Pu, B.; Dickinson, R.

    2011-12-01

    Observational studies have shown that elevated carbon dioxide concentration ([CO2]) have a "down-regulation" effect on vegetation that reduces leaf photosynthesis from the initial CO2-enhanced level and decreases the leaf conductance further beyond that of the CO2-induced reduction in some species (Ainsworth 2007). Bounoua et al. (2010) took into account the leaf area index (LAI) responses to vegetation down-regulation effects in a climate simulation (SiB2-GCM) and found an overall cooling effect. However, their model has a relatively low resolution (7.2 by 9 degrees) and equilibrium climate sensitivity (ECS; 1.94 degree Celsius). Here we investigate the leaf physiological effects in the Community Earth System Model (CESM) with a higher resolution (1.9 by 2.5 degrees) and ECS (3.07 degree C). When the maximum rate of RuBP carboxylation (Vcmax) is down-regulated in a doubled [CO2] climate, gross primary production (GPP) decreases about 15% and canopy transpiration decreases 13%. Evapotranspiration also decreases, and global mean surface temperature increases 0.19 degree C in addition to the CO2 induced warming. The warming effect is partially offset when LAI is increased. The overall physiological feedbacks enhance CO2-induced warming by 0.17 degree globally and 0.22 degree over land and increases precipitation about 0.04 mm day-1 over land (~24% of CO2-induced precipitation increase). In addition to the warming effect of Vcmax down-regulation, variations in surface albedo associated with increased LAI and cloud and long wave feedbacks further modulate local surface energy budget. The overall effects enhance CO2-induced warming by 8% over the Amazon, 14% over the Eastern U.S., and 11% over Siberia. Comparison with the results of SiB2-GCM simulations shows that at mid to high latitudes the overall negative (or positive) feedbacks associated with evapotranspiration reduction are weaker (or stronger) in the SiB2-GCM than those in the CESM and thus lead to an overall

  20. Bifurcation analysis of a delay reaction-diffusion malware propagation model with feedback control

    NASA Astrophysics Data System (ADS)

    Zhu, Linhe; Zhao, Hongyong; Wang, Xiaoming

    2015-05-01

    With the rapid development of network information technology, information networks security has become a very critical issue in our work and daily life. This paper attempts to develop a delay reaction-diffusion model with a state feedback controller to describe the process of malware propagation in mobile wireless sensor networks (MWSNs). By analyzing the stability and Hopf bifurcation, we show that the state feedback method can successfully be used to control unstable steady states or periodic oscillations. Moreover, formulas for determining the properties of the bifurcating periodic oscillations are derived by applying the normal form method and center manifold theorem. Finally, we conduct extensive simulations on large-scale MWSNs to evaluate the proposed model. Numerical evidences show that the linear term of the controller is enough to delay the onset of the Hopf bifurcation and the properties of the bifurcation can be regulated to achieve some desirable behaviors by choosing the appropriate higher terms of the controller. Furthermore, we obtain that the spatial-temporal dynamic characteristics of malware propagation are closely related to the rate constant for nodes leaving the infective class for recovered class and the mobile behavior of nodes.

  1. Quantifying the Negative Feedback of Vegetation to Greenhouse Warming: A Modeling Approach

    NASA Technical Reports Server (NTRS)

    Bounous, L.; Hall, F. G.; Sellers, P. J.; Kumar, A.; Collatz, G. J.; Tucker, C. J.; Imhoff, M. L.

    2010-01-01

    Several climate models indicate that in a 2 x CO2 environment, temperature and precipitation would increase and runoff would increase faster than precipitation. These models, however, did not allow the vegetation to increase its leaf density as a response to the physiological effects of increased CO2 and consequent changes in climate. Other assessments included these interactions but did not account for the vegetation down-regulation to reduce plant's photosynthetic activity and as such resulted in a weak vegetation negative response. When we combine these interactions in climate simulations with 2 x CO2, the associated increase in precipitation contributes primarily to increase evapotranspiration rather than surface runoff, consistent with observations, and results in an additional cooling effect not fully accounted for in previous simulations with elevated CO2. By accelerating the water cycle, this feedback slows but does not alleviate the projected warming, reducing the land surface warming by 0.6 C. Compared to previous studies, these results imply that long term negative feedback from CO2-induced increases in vegetation density could reduce temperature following a stabilization of CO2 concentration.

  2. Predicting Shortwave Cloud Feedback in Models and Observations Based on the Seasonal Cycle of Liquid Water Path

    NASA Astrophysics Data System (ADS)

    Ceppi, P.; McCoy, D.; Hartmann, D. L.

    2014-12-01

    Shortwave cloud (SWcld) feedbacks in the midlatitudes are primarily caused by changes in cloud optical depth, in turn related to liquid water path (LWP). However, large uncertainties in the LWP response to climate change cause inter-model spread in SW feedbacks. Here we present a novel method to compare extratropical shortwave cloud feedbacks in models and observations based on the sensitivity of liquid water path to temperature and humidity in a reference climate.We first regress monthly-mean LWP onto 850 hPa temperature and relative humidity at each point across the seasonal cycle in the historical climate of CMIP5 models and in observations, and multiply the regression coefficients by the RCP8.5 temperature and humidity response to yield a "predicted LWP response." This compares very well with the actual response (0.70 < r < 0.95) across the extratropics (35°-70° N and S) in the annual and zonal mean. We then determine the relationship between historical monthly-mean LWP and SW cloud-radiative effect (CRE) for each model, latitude, and month, excluding land gridpoints. For observations, the LWP data are combined with CERES retrievals for 2000-2008. These LWP-SWCRE relationships then allow us to predict the SW response for a given LWP change.The predicted SWcld feedback is generally well-correlated with the actual SWcld feedback in the Southern Hemisphere (0.45 < r < 0.75), while the prediction has less skill in the Northern Hemisphere. In the Southern Hemisphere, the SW feedback prediction has a mean negative bias of about 1 W m-2, likely due to changes in cloud microphysics not accounted for by our model. Importantly, however, the SWcld feedback predicted from observations agrees very well in magnitude and meridional structure with the multi-model mean predicted SWcld feedback. Both models and observations tend to predict a meridional dipole in SWcld feedback with a transition from negative values in the midlatitudes to positive values in the subtropics

  3. Response of an interactive two-dimensional model to ozone changes - An estimate of the radiative dynamical feedback effect

    NASA Technical Reports Server (NTRS)

    Schneider, Hans R.; Ko, Malcolm K. W.

    1990-01-01

    The response of the interactive two-dimensional stratospheric model described by Schneider et al. (1989) to an increased chemical removal of ozone and the sensitivity of the calculated assessments to the choice of eddy diffusion coefficients are investigated using a simplified ozone chemistry model. It was found that the radiative dynamical feedback in the model leads to ozone losses at high altitudes to be about one third smaller than predicted by a model with fixed temperature and circulation. The radiative feedback has a smaller effect on ozone (losses decrease by about one sixth) in the lower stratosphere. Predicted ozone losses increase with decreasing dissipation and eddy diffusion in the lower stratosphere.

  4. The Contribution of Compton-Thick AGN/ULIRGs to the X-Ray Background

    NASA Astrophysics Data System (ADS)

    Nardini, Emanuele

    Accretion onto the supermassive black holes located at the centre of Active Galactic Nuclei(AGN) is one of the most efficient power sources in the Universe, and provides a significant contribution to the energy radiated over cosmic times. The spectral shape of the X-ray background and its progressive resolution strongly suggests that most AGN are heavily obscured by large amounts of dust and gas. Their primary radiation field is reprocessed and re-emitted at longer wavelengths, driving a huge IR luminosity. Ultraluminous Infrared Galaxies (ULIRGs) are the local counterparts of the high-redshift (z < 1 3) IR systems that harbour the bulk of obscured nuclear activity in the early Universe. We have been recently awarded Suzaku observations of two ULIRGs, IRAS 00182 7112 and IRAS 12127 1412, for a total exposure time of 150 ks. Both the sources are known to host an elusive AGN whose intrinsic luminosity is estimated to fall in the quasar range. Although classified as Low-Ionization Nuclear Emission-line Regions in the optical, these ULIRGs sport the typical features of buried AGN in the mid-IR. IRAS 12127 1412 was observed for the first time in the X-rays by our group. Its Chandra spectrum clearly shows the signatures of AGN reflection at 2 10 keV. Similar properties were previously found in IRAS 00182 7112. Our Suzaku observations will allow to pinpont the AGN emission above 10 keV, and will provide fundamental information on the physical and geometrical structure of Compton-thick AGN embedded in a nuclear starburst. These sources are believed to experience the very initial phase of the AGN feedback on the surrounding environment, eventually leading to the formation of powerful optically- bright quasars. Besides this, we stress another remarkable opportunity related to the study of these two ULIRGs. Due to their really unique mid-IR and hard X-ray spectral properties, IRAS 00182 7112 and IRAS 12127 1412 can be considered as representative templates for a significant

  5. Bridging the Gap between Expert-Novice Differences: The Model-Based Feedback Approach

    ERIC Educational Resources Information Center

    Ifenthaler, Dirk

    2011-01-01

    The study adds to the body of knowledge about different types of feedback. Feedback is considered a fundamental component for supporting and regulating learning processes. Especially in computer-based and self-regulated learning environments, the nature of feedback is of critical importance. Hence, this study investigates different types of…

  6. The Listening Circle: Using the SBI Model to Enhance Peer Feedback

    ERIC Educational Resources Information Center

    Bommelje, Rick

    2012-01-01

    The Listening Circle is a learning activity that is designed to provide students with the opportunity to connect listening knowledge with observed behaviors and to strengthen student peer feedback. Not knowing how to give feedback can result in messages that are confusing, tactless, and counter-productive. Many feedback messages leave the receiver…

  7. Modeling the feedback between aerosol and boundary layer processes: a case study in Beijing, China.

    PubMed

    Miao, Yucong; Liu, Shuhua; Zheng, Yijia; Wang, Shu

    2016-02-01

    Rapid development has led to frequent haze in Beijing. With mountains and sea surrounding Beijing, the pollution is found to be influenced by the mountain-plain breeze and sea-land breeze in complex ways. Meanwhile, the presence of aerosols may affect the surface energy balance and impact these boundary layer (BL) processes. The effects of BL processes on aerosol pollution and the feedback between aerosol and BL processes are not yet clearly understood. Thus, the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) is used to investigate the possible effects and feedbacks during a haze episode on 23 September 2011. Influenced by the onshore prevailing wind, sea-breeze, and upslope breeze, about 45% of surface particulate matter (PM)2.5 in Beijing are found to be contributed by its neighbor cities through regional transport. In the afternoon, the development of upslope breeze suppresses the growth of BL in Beijing by imposing a relatively low thermal stable layer above the BL, which exacerbates the pollution. Two kinds of feedback during the daytime are revealed as follows: (1) as the aerosols absorb and scatter the solar radiation, the surface net radiation and sensible heat flux are decreased, while BL temperature is increased, resulting in a more stable and shallower BL, which leads to a higher surface PM2.5 concentration in the morning and (2) in the afternoon, as the presence of aerosols increases the BL temperature over plains, the upslope breeze is weakened, and the boundary layer height (BLH) over Beijing is heightened, resulting in the decrease of the surface PM2.5 concentration there. PMID:26490909

  8. Understanding subtropical cloud feedbacks in anthropogenic climate change simulations of CMIP5 models

    NASA Astrophysics Data System (ADS)

    Myers, T. A.; Norris, J. R.

    2014-12-01

    Subtropical marine boundary layer clouds over the eastern subtropics are poorly simulated by climate models and contribute substantially to inter-model differences in climate sensitivity. The aim of the present study is to better understand inter-model differences in projected cloud changes and to constrain the cloud feedback to warming. To do this, we compute independent relationships of cloud properties (cloud fraction, cloud-top height, and cloud radiative effect) to interannual variations in sea surface temperature, estimated inversion strength, horizontal surface temperature advection, free-tropospheric humidity, and subsidence using observations and as simulated by models participating in the Coupled Model Intercomparison Project phase 5. Each relationship is considered to be independent because it represents the association between some cloud property and a meteorological parameter when the other parameters are held constant. We approximate modelled cloud trends in climate change simulations as the sum of the simulated cloud/meteorology relationships multiplied by the respective meteorological trends. We compare these estimated cloud trends to the sum of the observed cloud/meteorology relationships multiplied by the simulated meteorological trends. This method allows us to better understand the sources of inter-model differences in projected cloud changes, including whether cloud/meteorology relationships or meteorological trends dominate the spread of cloud changes. We approximate the true cloud trend due to climate change as the sum of the observed cloud/meteorology relationships multiplied by the multi-model mean meteorological trends. The results may provide an observational and model constraint on climate sensitivity.

  9. Importance of positive feedbacks and overconfidence in a self-fulfilling Ising model of financial markets

    NASA Astrophysics Data System (ADS)

    Sornette, Didier; Zhou, Wei-Xing

    2006-10-01

    Following a long tradition of physicists who have noticed that the Ising model provides a general background to build realistic models of social interactions, we study a model of financial price dynamics resulting from the collective aggregate decisions of agents. This model incorporates imitation, the impact of external news and private information. It has the structure of a dynamical Ising model in which agents have two opinions (buy or sell) with coupling coefficients, which evolve in time with a memory of how past news have explained realized market returns. We study two versions of the model, which differ on how the agents interpret the predictive power of news. We show that the stylized facts of financial markets are reproduced only when agents are overconfident and mis-attribute the success of news to predict return to herding effects, thereby providing positive feedbacks leading to the model functioning close to the critical point. Our model exhibits a rich multifractal structure characterized by a continuous spectrum of exponents of the power law relaxation of endogenous bursts of volatility, in good agreement with previous analytical predictions obtained with the multifractal random walk model and with empirical facts.

  10. Extremely efficient Zevatron in rotating AGN magnetospheres

    NASA Astrophysics Data System (ADS)

    Osmanov, Z.; Mahajan, S.; Machabeli, G.; Chkheidze, N.

    2014-12-01

    A novel model of particle acceleration in the magnetospheres of rotating active galactic nuclei (AGN) is constructed. The particle energies may be boosted up to 1021 eV in a two-step mechanism: in the first stage, the Langmuir waves are centrifugally excited and amplified by means of a parametric process that efficiently pumps rotational energy to excite electrostatic fields. In the second stage, the electrostatic energy is transferred to particle kinetic energy via Landau damping made possible by rapid `Langmuir collapse'. The time-scale for parametric pumping of Langmuir waves turns out to be small compared to the kinematic time-scale, indicating high efficiency of the first process. The second process of `Langmuir collapse' - the creation of caverns or low-density regions - also happens rapidly for the characteristic parameters of the AGN magnetosphere. The Langmuir collapse creates appropriate conditions for transferring electric energy to boost up already high particle energies to much higher values. It is further shown that various energy loss mechanism are relatively weak, and do not impose any significant constraints on maximum achievable energies.

  11. Radio Loud AGNs are Mergers

    NASA Astrophysics Data System (ADS)

    Chiaberge, Marco; Gilli, Roberto; Lotz, Jennifer M.; Norman, Colin

    2015-06-01

    We measure the merger fraction of Type 2 radio-loud and radio-quiet active galactic nuclei (AGNs) at z\\gt 1 using new samples. The objects have Hubble Space Telescope (HST) images taken with Wide Field Camera 3 (WFC3) in the IR channel. These samples are compared to the 3CR sample of radio galaxies at z\\gt 1 and to a sample of non-active galaxies. We also consider lower redshift radio galaxies with HST observations and previous generation instruments (NICMOS and WFPC2). The full sample spans an unprecedented range in both redshift and AGN luminosity. We perform statistical tests to determine whether the different samples are differently associated with mergers. We find that all (92%-14%+8%) radio-loud galaxies at z\\gt 1 are associated with recent or ongoing merger events. Among the radio-loud population there is no evidence for any dependence of the merger fraction on either redshift or AGN power. For the matched radio-quiet samples, only 38%-15+16 are merging systems. The merger fraction for the sample of non-active galaxies at z\\gt 1 is indistinguishable from radio-quiet objects. This is strong evidence that mergers are the triggering mechanism for the radio-loud AGN phenomenon and the launching of relativistic jets from supermassive black holes (SMBHs). We speculate that major black hole (BH)–BH mergers play a major role in spinning up the central SMBHs in these objects.

  12. Accretion and Feedback Processes in Supermassive Black Holes

    NASA Astrophysics Data System (ADS)

    Zubovas, Kastytis

    2012-10-01

    Supermassive black holes (SMBHs) have been gradually recognised as important elements of galaxy and cosmic structure evolution. Their connection with the large-scale environment is maintained via feedback processes - communication of a fraction of the accretion luminosity to the host galaxy. Feedback is conjectured to expel gas from galaxies, quench star formation and establish the observed correlations between SMBH mass and host galaxy properties. Efficient feedback requires rapid gas accretion and is therefore usually investigated within the context of quasar activity phases in SMBH evolution. In this Thesis, I investigate several implications of an SMBH wind feedback model, advancing our understanding of feedback processes and the immediate environment of SMBHs. I consider analytically the large-scale outflows and their observable properties. I find that rapidly accreting SMBHs may sweep galaxies clear of gas, turning them into red-and-dead spheroids. I apply the same feedback model to our Galaxy. Its SMBH, Sgr A*, is currently exceptionally quiescent, although it must have been more active in the past in order to have grown to its present size. I investigate, both analytically and numerically, a short burst of activity which may have occurred ∼ 6 million years ago, producing an outflow which formed two large γ-ray emitting bubbles perpendicular to the Galactic plane. The results show that dynamical footprints of outflows may persist for a long time and provide evidence of past AGN activity in quiescent galaxies. I also present a model for the short-timescale flares observed daily in Sgr A*, based on tidal disruption and evaporation of asteroids in the vicinity of the SMBH. The model explains some observed flare properties, and thus improves our understanding of the processes occurring close to the SMBH. It also provides predictions for observable effects as the quiescent luminosity of Sgr A* varies on long timescales.

  13. Star-formation and stellar feedback recipes in galaxy evolution models

    NASA Astrophysics Data System (ADS)

    Hensler, Gerhard; Recchi, Simone; Ploeckinger, Sylvia; Kuehtreiber, Matthias; Steyrleithner, Patrick; Liu, Lei

    2015-08-01

    Modeling galaxy formation and evolution is critically depending on star formation (SF). Since cosmological and galaxy-scale simulations cannot resolve the spatial and density scales on which SF acts, a large variety of methods are developed and applied over the last decades. Nonetheless, we are still in the test phase how the choice of parameters affects the models and how they agree with observations.As a simple ansatz, recipes are based on power-law SF dependences on gas density as justified by gas cooling and collapse timescales. In order to prevent SF spread throughout the gas, temperature and density thresholds are also used, although gas dynamical effects, like e.g. gas infall, seem to trigger SF significantly.The formed stars influence their environment immediately by energetic and materialistic feedback. It has been experienced in numerical models that supernova typeII explosions act with a too long time delay to regulate the SF, but that winds and ionizing radiation by massive stars must be included. The implementation of feedback processes, their efficiencies and timescales, is still in an experimental state, because they depend also on the physical state of the surrounding interstellar medium (ISM).Combining a SF-gas density relation with stellar heating vs. gas cooling and taking the temperature dependence into account, we have derived an analytical expression of self-regulated SF which is free of arbitrary parameters. We have performed numerical models to study this recipe and different widely used SF criteria in both, particle and grid codes. Moreover, we compare the SF behavior between single-gas phase and multi-phase treatments of the ISM.Since dwarf galaxies (DGs) are most sensitive to environmental influences and contain only low SF rates, we explore two main affects on their models: 1. For external effects we compare SF rates of isolated and ram-pressure suffering DGs. Moreover, we find a SF enhancement in tidal-tail DGs by the compressive tidal

  14. New insights into AGN coronae

    NASA Astrophysics Data System (ADS)

    Lohfink, Anne; Fabian, Andrew C.; Malzac, Julien; Belmont, Renaud; Buisson, Douglas

    2016-04-01

    Active galactic nuclei (AGN) are some of the most energetic sources of radiation in the Universe. The conversion of gravitational energy into radiation is thought to take place in an accretion disk/corona system just outside the black hole. In this system thermal, UV/optical photons from the accretion disk are upscattered in a corona of hot electrons situated above the accretion disk producing X-rays. The nature of this Comptonizing corona remains a key open question in AGN physics. The NuSTAR satellite provides the opportunity to study the Comptonization spectrum produced by the corona in great detail. In our talk we will show some key results from these new studies of the Comptonization spectrum. We explore how, together with our growing knowledge of coronal sizes, we are able to draw first conclusions about the physics taking place in the corona. We find evidence for coronae to be hot and radiatively compact, putting them close to the boundary of the region in the compactness-temperature diagram which is forbidden due to runaway pair production. This suggests that pair production and annihilation are essential ingredients in the coronae of AGN and that they control the coronal temperature and shape of the observed spectra.

  15. Microfluidic droplet trapping, splitting and merging with feedback controls and state space modelling.

    PubMed

    Wong, David; Ren, Carolyn L

    2016-08-16

    We combine image processing and feedback controls to regulate droplet movements. A general modelling approach is provided to describe droplet motion in a pressure-driven microfluidic channel network. A state space model is derived from electric circuit analogy and validated with experimental data. We then design simple decentralized controllers to stabilize droplet movement. The controllers can trap droplets at requested locations by fine tuning inlet pressures constantly. Finally, we demonstrate the ability to split and merge the same droplet repeatedly in a simple T-junction. No embedded electrodes are required, and this technique can be implemented solely with a camera, a personal computer, and commercially available E/P transducers. PMID:27435753

  16. FinCC and the National Documentation Model in EHR--user feedback and development suggestions.

    PubMed

    Kinnunen, Ulla-Mari; Junttila, Kristiina; Liljamo, Pia; Sonninen, Anna Liisa; Härkönen, Mikko; Ensio, Anneli

    2014-01-01

    The structure of the Finnish nursing documentation model is based on the decision-making process and a standardized nursing terminology: Finnish Care Classification (FinCC). Nearly 20,000 nurses use the FinCC although not all healthcare organizations utilize it. Development projects for the common national nursing documentation framework have been carried out, for example, in 2010-2011 the aim of a project by the Ministry of Social Affairs and Health and the National Institute of Health and Welfare was to suggest recommendations for the Finnish nursing documentation model. The final report of the project was sent to different organizations all over the country for further feedback statements. The aim of this paper is to summarize the message of the statements (n=37) from primary and specialized care, universities including universities of applied science, professional nursing associations, trade unions and national authorities. Development suggestions for the FinCC and electronic health records will be introduced. PMID:24943544

  17. Positive water vapour feedback in climate models confirmed by satellite data

    NASA Technical Reports Server (NTRS)

    Rind, D.; Lerner, J.; Chiou, E.-W.; Chu, W.; Larsen, J.; Mccormick, M. P.; Mcmaster, L.

    1991-01-01

    It has recently been suggested that GCMs used to evaluate climate change overestimate the greenhouse effect due to increased concentrations of trace gases in the atmosphere. Here, new satellite-generated water vapor data are used to compare summer and winter moisture values in regions of the middle and upper troposphere that have previously been difficult to observe with confidence. It is found that, as the hemispheres warm, increased convection leads to increased water vapor above 500 mbar in approximate quantitative agreement with results from current climate models. The same conclusion is reached by comparing the tropical western and eastern Pacific regions. Thus, water vapor feedback is not overestimated in models and should amplify the climate response to increased trace-gas concentrations.

  18. Phytotoxicity of salt and plant salt uptake: Modeling ecohydrological feedback mechanisms

    NASA Astrophysics Data System (ADS)

    Bauer-Gottwein, Peter; Rasmussen, Nikolaj F.; Feificova, Dagmar; Trapp, Stefan

    2008-04-01

    A new model of phytotoxicity of salt and plant salt uptake is presented and is coupled to an existing three-dimensional groundwater simulation model. The implementation of phytotoxicity and salt uptake relationships is based on experimental findings from willow trees grown in hydroponic solution. The data confirm an s-shaped phytotoxicity relationship as found in previous studies. Uptake data were explained assuming steady state salt concentration in plant roots, passive salt transport into the roots, and active enzymatic removal of salt from plant roots. On the one hand, transpiration strongly depends on groundwater salinity (phytotoxicity); on the other hand, transpiration significantly changes the groundwater salinity (uptake). This feedback loop generates interesting dynamic phenomena in hydrological systems that are dominated by transpiration and are influenced by significant salinity gradients. Generic simulations are performed for the Okavango island system and are shown to reproduce essential phenomena observed in nature.

  19. Interpreting the IR SED of z~0.3-2.8 IR-Luminous Galaxies and AGN Using Hydrodynamic Simulations

    NASA Astrophysics Data System (ADS)

    Roebuck, Eric John; Sajina, Anna; Hayward, Christopher C.; Pope, Alexandra; Kirkpatrick, Allison; Hernquist, Lars E.; Yan, Lin

    2016-01-01

    We use three-dimensional hydrodynamical galaxy merger simulations to further investigate the nature of a sample of 342 24 μm-selected (ultra) luminous infrared galaxies at z~0.3-2.8. All of our sources have low-resolution Spitzer/IRS spectra -- the largest such sample outside the local universe. These spectra allow us to determine that our sample consists of a mixture of star forming galaxies (SFGs), AGN, and composites. We address the question of how well do empirical IR AGN fraction estimates trace the intrinsic AGN fraction (i.e. the AGN-to-total power in the galaxy prior to dust re-processing), including how they relate to galaxy properties such as merger stage, dust/gas content, and star formation rates. We do this by fitting the observed SEDs of our sample with theoretical SEDs based on GADGET hydrodynamic merger simulations additionally processed through the SUNRISE radiative transfer code. We additionally investigate systematic uncertainties associated with these quantities using the goodness of fits to our model library. The key findings are: 1) our simulation-based fits are in broad agreement with the empirical model-based fits, 2) much of the AGN fraction of LIR is missed if the AGN's contribution to heating the host galaxy dust is not accounted for, and 3) the IR AGN fraction traces the intrinsic AGN fraction up to the coalescence stage, however may underestimate the intrinsic AGN fraction post coalescence.

  20. Fast Ionized X-ray Absorbers in AGNs

    NASA Astrophysics Data System (ADS)

    Fukumura, K.; Tombesi, F.; Kazanas, D.; Shrader, C.; Behar, E.; Contopoulos, I.

    2015-07-01

    We present a study of X-ray ionization of MHD accretion-disk wind models in an effort to explain the highly-ionized ultra-fast outflows (UFOs) identified as X-ray absorbers recently detected in various sub-classes of Seyfert AGNs. Our primary focus is to show that magnetically-driven outflows are physically plausible candidates to account for the AGN X-ray spectroscopic observations. We calculate its X-ray ionization and the ensuing X-ray absorption line spectra in comparison with an XXM-Newton/EPIC spectrum of the narrow-line Seyfert AGN, PG 1211+143. We find, through identifying the detected features with Fe Kα transitions, that the absorber has a characteristic ionization parameter of log(xi[erg cm/s]) = 5-6 and a hydrogen-equivalent column density on the order of 1e23 cm-2, outflowing at a sub-relativistic velocity of v/c = 0.1-0.2. The best-fit model favors its radial location at R = 200 Rs (Rs is the Schwarzschild radius), with a disk inner truncation radius at Rt = 30Rs. The overall K-shell feature in data is suggested to be dominated by Fe XXV with very little contribution from Fe XXVI and weakly-ionized iron, which is in a good agreement with a series of earlier analysis of the UFOs in various AGNs including PG 1211+143.

  1. Feedback stabilization of an oscillating vertical cylinder by POD Reduced-Order Model

    NASA Astrophysics Data System (ADS)

    Tissot, Gilles; Cordier, Laurent; Noack, Bernd R.

    2015-01-01

    The objective is to demonstrate the use of reduced-order models (ROM) based on proper orthogonal decomposition (POD) to stabilize the flow over a vertically oscillating circular cylinder in the laminar regime (Reynolds number equal to 60). The 2D Navier-Stokes equations are first solved with a finite element method, in which the moving cylinder is introduced via an ALE method. Since in fluid-structure interaction, the POD algorithm cannot be applied directly, we implemented the fictitious domain method of Glowinski et al. [1] where the solid domain is treated as a fluid undergoing an additional constraint. The POD-ROM is classically obtained by projecting the Navier-Stokes equations onto the first POD modes. At this level, the cylinder displacement is enforced in the POD-ROM through the introduction of Lagrange multipliers. For determining the optimal vertical velocity of the cylinder, a linear quadratic regulator framework is employed. After linearization of the POD-ROM around the steady flow state, the optimal linear feedback gain is obtained as solution of a generalized algebraic Riccati equation. Finally, when the optimal feedback control is applied, it is shown that the flow converges rapidly to the steady state. In addition, a vanishing control is obtained proving the efficiency of the control approach.

  2. Measuring and modelling water related soil-vegetation feedbacks in a fallow plot

    NASA Astrophysics Data System (ADS)

    Ursino, N.; Cassiani, G.; Deiana, R.; Vignoli, G.; Boaga, J.

    2013-08-01

    Land fallowing is one possible response to shortage of water for irrigation. Leaving the soil unseeded implies a change of the soil functioning that has an impact on the water cycle. The development of a soil crust in the open spaces between the patterns of grass weed affects the soil properties and the field scale water balance. The objectives of this study are to test the potential of integrated non invasive geophysical methods and ground-image analysis and to quantify the effect of the soil vegetation interaction on the water balance of a fallow land at the local and plot scale. We measured repeatedly in space and time local soil saturation and vegetation cover over two small plots located in southern Sardinia, Italy, during a controlled irrigation experiment. One plot was left unseeded and the other was cultivated. The comparative analysis of ERT maps of soil moisture evidenced a considerably different hydrologic response to irrigation of the two plots. Local measurements of soil saturation and vegetation cover were repeated in space to evidence a positive feedback between weed growth and infiltration at the fallow plot. A simple bucket model captured the different soil moisture dynamics at the two plots during the infiltration experiment and was used to estimate the impact of the soil vegetation feedback on the yearly water balance at the fallow site.

  3. Feedback Regulation in a Cancer Stem Cell Model can Cause an Allee Effect.

    PubMed

    Konstorum, Anna; Hillen, Thomas; Lowengrub, John

    2016-04-01

    The exact mechanisms of spontaneous tumor remission or complete response to treatment are phenomena in oncology that are not completely understood. We use a concept from ecology, the Allee effect, to help explain tumor extinction in a model of tumor growth that incorporates feedback regulation of stem cell dynamics, which occurs in many tumor types where certain signaling molecules, such as Wnts, are upregulated. Due to feedback and the Allee effect, a tumor may become extinct spontaneously or after therapy even when the entire tumor has not been eradicated by the end of therapy. We quantify the Allee effect using an 'Allee index' that approximates the area of the basin of attraction for tumor extinction. We show that effectiveness of combination therapy in cancer treatment may occur due to the increased probability that the system will be in the Allee region after combination treatment versus monotherapy. We identify therapies that can attenuate stem cell self-renewal, alter the Allee region and increase its size. We also show that decreased response of tumor cells to growth inhibitors can reduce the size of the Allee region and increase stem cell densities, which may help to explain why this phenomenon is a hallmark of cancer. PMID:27113934

  4. Measuring and modeling water-related soil-vegetation feedbacks in a fallow plot

    NASA Astrophysics Data System (ADS)

    Ursino, N.; Cassiani, G.; Deiana, R.; Vignoli, G.; Boaga, J.

    2014-03-01

    Land fallowing is one possible response to shortage of water for irrigation. Leaving the soil unseeded implies a change of the soil functioning that has an impact on the water cycle. The development of a soil crust in the open spaces between the patterns of grass weed affects the soil properties and the field-scale water balance. The objectives of this study are to test the potential of integrated non-invasive geophysical methods and ground-image analysis and to quantify the effect of the soil-vegetation interaction on the water balance of fallow land at the local- and plot scale. We measured repeatedly in space and time local soil saturation and vegetation cover over two small plots located in southern Sardinia, Italy, during a controlled irrigation experiment. One plot was left unseeded and the other was cultivated. The comparative analysis of ERT maps of soil moisture evidenced a considerably different hydrologic response to irrigation of the two plots. Local measurements of soil saturation and vegetation cover were repeated in space to evidence a positive feedback between weed growth and infiltration at the fallow plot. A simple bucket model captured the different soil moisture dynamics at the two plots during the infiltration experiment and was used to estimate the impact of the soil vegetation feedback on the yearly water balance at the fallow site.

  5. Feedback Regulation in a Cancer Stem Cell Model can Cause an Allee Effect

    PubMed Central

    Konstorum, Anna; Hillen, Thomas; Lowengrub, John

    2016-01-01

    The exact mechanisms of spontaneous tumor remission or complete response to treatment are phenomena in oncology that are not completely understood. We use a concept from ecology, the Allee effect, to help explain tumor extinction in a model of tumor growth that incorporates feedback regulation of stem cell dynamics, which occurs in many tumor types where certain signaling molecules, such as Wnts, are upregulated. Due to feedback and the Allee effect, a tumor may become extinct spontaneously or after therapy even when the entire tumor has not been eradicated by the end of therapy. We quantify the Allee effect using an ‘Allee index’ that approximates the area of the basin of attraction for tumor extinction. We show that effectiveness of combination therapy in cancer treatment may occur due to the increased probability that the system will be in the Allee region after combination treatment versus monotherapy. We identify therapies that can attenuate stem cell self-renewal, alter the Allee region and increase its size. We also show that decreased response of tumor cells to growth inhibitors can reduce the size of the Allee region and increase stem cell densities, which may help to explain why this phenomenon is a hallmark of cancer. PMID:27113934

  6. Modeling Prairie Wetland Weather and Climate Feedbacks in the Northern Great Plains

    NASA Astrophysics Data System (ADS)

    Capehart, W. J.; Taylor, J. A.

    2005-05-01

    Storm-scale simulations of the Northern Great Plains have shown that the prairie wetland systems in the region influence warm-season convective systems even under synoptic-scale forcings. These complex surface water systems, in turn, swell in surface area during wet cycles and contract (and in some cases completely disappear into the cropland/pastureland land cover matrix) during dry cycles. Since the early-to-mid 1990s, these wetland systems have expanded to their historical maximum. The resulting expansions have had an impact on surface hydrology, and agricultural practices (including new crop rotation regimes in the affected areas) and may impact regional climate feedbacks. To examine the potential for these feedbacks, we shall present results of regional climate simulations of the recent decadal period featuring comparisons of precipitation and evaporation patterns with the ambient land cover regimes currently used in mesoscale and regional climate models (which do not include any reference to the larger wetland system in the region), and approximations of the pre-expansion and current wetland states using modified land cover and soil moisture patterns as a proxy. These latter simulations represent a first step in developing a companion wetland parameterization which could facilitate not only coupled hydroclimatological studies of the region, but ecological and biogeochemical studies as well.

  7. Measuring and Modelling water related soil - vegetation feedbacks in a fallow plot

    NASA Astrophysics Data System (ADS)

    Ursino, Nadia; Cassiani, Giorgio; Deiana, Rita; Vignoli, Giulio; Boaga, Jacopo

    2013-04-01

    Land fallowing is one possible response to shortage of water for irrigation. Leaving the soil unseeded implies a change of the soil functioning that has an impact on the water cycle. The development of a soil crust in the open spaces between the patterns of grass weed affects the soil properties and the field scale water balance. The objective of this study was to test the potential of integrated non invasive geophysics and ground-image analysis and to quantify the effect of the soil vegetation interaction on the water balance of a fallow land at the local and plot scale. We measured repeatedly in space and time local soil saturation and vegetation cover over two small plots located in southern Sardinia, Italy, during an infiltration experiment. One plot was left unseeded and the other was cultivated. The comparative analysis of the experimental data evidenced a positive feedback between weed growth and infiltration at the fallow plot. A simple bucket model captured the different soil moisture dynamics at the two plots during the infiltration experiment and was used to estimate the impact of the soil vegetation feedback on the yearly water balance at the site.

  8. Inferring Instantaneous, Multivariate and Nonlinear Sensitivities for the Analysis of Feedback Processes in a Dynamical System: Lorenz Model Case Study

    NASA Technical Reports Server (NTRS)

    Aires, Filipe; Rossow, William B.; Hansen, James E. (Technical Monitor)

    2001-01-01

    A new approach is presented for the analysis of feedback processes in a nonlinear dynamical system by observing its variations. The new methodology consists of statistical estimates of the sensitivities between all pairs of variables in the system based on a neural network modeling of the dynamical system. The model can then be used to estimate the instantaneous, multivariate and nonlinear sensitivities, which are shown to be essential for the analysis of the feedbacks processes involved in the dynamical system. The method is described and tested on synthetic data from the low-order Lorenz circulation model where the correct sensitivities can be evaluated analytically.

  9. Coupled atmospheric, land surface, and subsurface modeling: Exploring water and energy feedbacks in three-dimensions

    NASA Astrophysics Data System (ADS)

    Davison, Jason H.; Hwang, Hyoun-Tae; Sudicky, Edward A.; Lin, John C.

    2015-12-01

    Human activities amplified by climate change pose a significant threat to the sustainability of water resources. Coupled climate-hydrologic simulations commonly predict these threats by combining shallow 1-D land surface models (LSMs) with traditional 2-D and 3-D hydrology models. However, these coupled models limit the moisture and energy-feedback dynamics to the shallow near-surface. This paper presents a novel analysis by applying an integrated variably-saturated subsurface/surface hydrology and heat transport model, HydroGeoSphere (HGS), as a land surface model (LSM). Furthermore, this article demonstrates the coupling of HGS to a simple 0-D atmospheric boundary layer (ABL) model. We then applied our coupled HGS-ABL model to three separate test cases and reproduced the strong correlation between the atmospheric energy balance to the depth of the groundwater table. From our simulations, we found that conventional LSMs may overestimate surface temperatures for extended drought periods because they underestimate the heat storage in the groundwater zone. Our final test case of the atmospheric response to drought conditions illustrated that deeper roots buffered the atmosphere better than shallow roots by maintaining higher latent heat fluxes, lower sensible heat fluxes, and lower surface and atmospheric temperatures.

  10. AGN-stimulated cooling of hot gas in elliptical galaxies

    NASA Astrophysics Data System (ADS)

    Valentini, Milena; Brighenti, Fabrizio

    2015-04-01

    We study the impact of relatively weak active galactic nucleus (AGN) feedback on the interstellar medium (ISM) of intermediate and massive elliptical galaxies. We find that the AGN activity, while globally heating the ISM, naturally stimulates some degree of hot gas cooling on scales of several kpc. This process generates the persistent presence of a cold ISM phase, with mass ranging between 104 and ≳ 5 × 107 M⊙, where the latter value is appropriate for group centred, massive galaxies. Widespread cooling occurs where the ratio of cooling to free-fall time before the activation of the AGN feedback satisfies tcool/tff ≲ 70, that is we find a less restrictive threshold than commonly quoted in the literature. This process helps explaining the body of observations of cold gas (both ionized and neutral/molecular) in Ellipticals and, perhaps, the residual star formation detected in many early-type galaxies. The amount and distribution of the off-centre cold gas vary irregularly with time. The cold ISM velocity field is irregular, initially sharing the (outflowing) turbulent hot gas motion. Typical velocity dispersions of the cold gas lie in the range 100-200 km s-1. Freshly generated cold gas often forms a cold outflow and can appear kinematically misaligned with respect to the stars. We also follow the dust evolution in the hot and cold gas. We find that the internally generated cold ISM has a very low dust content, with representative values of the dust-to-gas ratio of 10-4-10-5. Therefore, this cold gas can escape detection in the traditional dust-absorption maps.

  11. The Average 0.5-200 keV Spectrum of AGNs at 0

    NASA Astrophysics Data System (ADS)

    Ballantyne, David R.

    2013-04-01

    The X-ray spectra of AGNs span nearly three decades in energy and are comprised of many separate components: a power-law with a high energy cutoff, reflection from the accretion disk as well as distant material, and, in many cases, a soft excess. Aside from a small number of bright sources observed with BeppoSAX, the full energy range of AGN spectra has only been studied in piecemeal by a fleet of X-ray observatories that can only focus on a small part of the entire spectrum. Therefore, while catalogues of the spectral properties of hundreds of AGNs have been published in different energy bands, these results are isolated from one another and a clear picture of the broadband spectral properties of typical AGNs remains elusive. In this work, we make use of the 0 X-ray luminosity functions of AGNs in the 0.5-2 keV, 2-10 keV, 3-20 keV, 15-55 keV and 14-195 keV bands to construct the spectral model of an average AGN that can simultaneously account for all 5 luminosity functions. Enhanced iron abundances, disk reflection, and the presence or absence of the X-ray Baldwin Effect are considered, along with the traditional parameters of photon index and cutoff energy. Applications to X-ray background modelling and AGN physics are discussed.

  12. Constraining AGN triggering mechanisms through the clustering analysis of active black holes

    NASA Astrophysics Data System (ADS)

    Gatti, M.; Shankar, F.; Bouillot, V.; Menci, N.; Lamastra, A.; Hirschmann, M.; Fiore, F.

    2016-02-01

    The triggering mechanisms for active galactic nuclei (AGN) are still debated. Some of the most popular ones include galaxy interactions (IT) and disc instabilities (DIs). Using an advanced semi-analytic model (SAM) of galaxy formation, coupled to accurate halo occupation distribution modelling, we investigate the imprint left by each separate triggering process on the clustering strength of AGN at small and large scales. Our main results are as follows: (i) DIs, irrespective of their exact implementation in the SAM, tend to fall short in triggering AGN activity in galaxies at the centre of haloes with Mh > 1013.5 h-1 M⊙. On the contrary, the IT scenario predicts abundance of active central galaxies that generally agrees well with observations at every halo mass. (ii) The relative number of satellite AGN in DIs at intermediate-to-low luminosities is always significantly higher than in IT models, especially in groups and clusters. The low AGN satellite fraction predicted for the IT scenario might suggest that different feeding modes could simultaneously contribute to the triggering of satellite AGN. (iii) Both scenarios are quite degenerate in matching large-scale clustering measurements, suggesting that the sole average bias might not be an effective observational constraint. (iv) Our analysis suggests the presence of both a mild luminosity and a more consistent redshift dependence in the AGN clustering, with AGN inhabiting progressively less massive dark matter haloes as the redshift increases. We also discuss the impact of different observational selection cuts in measuring AGN clustering, including possible discrepancies between optical and X-ray surveys.

  13. Examining vegetation feedbacks on global warming in the Community Earth System Model

    NASA Astrophysics Data System (ADS)

    Pu, Bing; Dickinson, Robert E.

    2012-10-01

    Leaves close their stomates in response to increases of CO2. Such a rapid physiological response is included in the land component of comprehensive climate models. However, observational studies have shown that they can further close their stomates as a consequence of "down-regulation," further reducing canopy conductance. However, they may also increase the area of their leaves, hence increasing their canopy conductance. Changes of canopy conductance change surface ET, a reduction leading to surface warming. A simulation considering these mechanisms of modifying canopy conductance is carried out for the assumption of a doubled atmospheric CO2concentration, using the Community Earth System model. It finds that down-regulation as formulated in previous studies could have as large a warming impact on land temperatures as the standard leaf physiological response. Increases in LAI, if they were to occur, appear to have but a small cooling effect. The reduction of latent cooling in the model is amplified by a reduction of low-level cloud cover, hence enhanced net absorption of solar radiation. Reduction of low level cloudiness appears to be necessary to maintain global radiation balance as reported in a previous study. Over mid to high latitudes, decreases in surface albedo associated with reduced snow cover also contribute to amplifying the warming. The physiological feedbacks of leaf stomates in the simulation increase warming by 0.6 ± 0.2°C over land and 0.3 ± 0.1°C globally, not inconsistent with previous studies. Enhanced interhemispheric temperature differences weaken the southward shift of the ITCZ associated with CO2radiative warming. Regions with relatively high LAI tend to have greater vegetation feedback; but increases in large-scale precipitation may weaken this local warming effect.

  14. Adaptive Control Model Reveals Systematic Feedback and Key Molecules in Metabolic Pathway Regulation

    PubMed Central

    Moffitt, Richard A.; Merrill, Alfred H.; Wang, May D.

    2011-01-01

    Abstract Robust behavior in metabolic pathways resembles stabilized performance in systems under autonomous control. This suggests we can apply control theory to study existing regulation in these cellular networks. Here, we use model-reference adaptive control (MRAC) to investigate the dynamics of de novo sphingolipid synthesis regulation in a combined theoretical and experimental case study. The effects of serine palmitoyltransferase over-expression on this pathway are studied in vitro using human embryonic kidney cells. We report two key results from comparing numerical simulations with observed data. First, MRAC simulations of pathway dynamics are comparable to simulations from a standard model using mass action kinetics. The root-sum-square (RSS) between data and simulations in both cases differ by less than 5%. Second, MRAC simulations suggest systematic pathway regulation in terms of adaptive feedback from individual molecules. In response to increased metabolite levels available for de novo sphingolipid synthesis, feedback from molecules along the main artery of the pathway is regulated more frequently and with greater amplitude than from other molecules along the branches. These biological insights are consistent with current knowledge while being new that they may guide future research in sphingolipid biology. In summary, we report a novel approach to study regulation in cellular networks by applying control theory in the context of robust metabolic pathways. We do this to uncover potential insight into the dynamics of regulation and the reverse engineering of cellular networks for systems biology. This new modeling approach and the implementation routines designed for this case study may be extended to other systems. Supplementary Material is available at www.liebertonline.com/cmb. PMID:21314456

  15. Probing AGN Unification with galaxy neighbours: pitfalls and prospects

    NASA Astrophysics Data System (ADS)

    Villarroel, B.

    2015-09-01

    Statistical tests of AGN unification harbour many caveats. One way of constraining the validity of the AGN unification is through studies of close neighbours to Type-1 and Type-2 AGN. Examining thousands of AGN- galaxy pairs from the Sloan Digital Sky Survey Data Release 7 and the Galaxy Zoo project, we found that Type-2 AGN appear to reside in more star-forming environments than Type-1 AGN.

  16. Estimating Climate System Feedbacks and Sensitivities using Linear Inverse Modeling versus the Fluctuation-Dissipation Theorem

    NASA Astrophysics Data System (ADS)

    Sardeshmukh, P. D.; Penland, M. C.

    2011-12-01

    Improving climate predictions from subseasonal to centennial scales, including responses to projected increases of greenhouse gases (GHGs) and other radiative forcings, is the outstanding challenge in climate science today. Despite decades of model development, however, comprehensive coupled atmosphere-ocean models remain deficient in many respects in this regard, and also disagree substantially among themselves. They differ in their representations of ENSO and longer-term oceanic variability, and also generate substantially different global and regional climate responses to radiative forcing. A key global metric, global climate sensitivity (defined as the globally averaged equilibrium surface temperature response to a doubling of carbon dioxide), differs by more than a factor of three among the models, which is highly inconvenient for climate policy. To discriminate between the models and also possibly to improve them, independent estimations of climate sensitivities and feedbacks from knowledge of observed past system behavior would be highly desirable. There are two apparently distinct approaches currently available to accomplish this: the Fluctuation-Dissipation Theorem (FDT) and Linear Inverse Modeling (LIM). Both use knowledge of the time-lag covariance matrices C(tau) of the system. The former estimates the system response matrix R for small external forcing using C(tau) integrated from zero to infinite lag, whereas the latter estimates it using C(tau) for a single lag, tau-0. If C(tau) decays exponentially with lag, the two approaches are formally identical. The authors and others have demonstrated in numerous publications that C(tau) does indeed decay approximately exponentially with lag in the climate system, and have used this property to construct forecast models that remain highly competitive with state-of-the-art comprehensive subseasonal and seasonal forecast models. A practical difficulty with using the FDT to estimate R is that it requires accurate

  17. Disc outflows and high-luminosity true type 2 AGN

    NASA Astrophysics Data System (ADS)

    Elitzur, Moshe; Netzer, Hagai

    2016-06-01

    The absence of intrinsic broad-line emission has been reported in a number of active galactic nuclei (AGN), including some with high Eddington ratios. Such `true type 2 AGN' are inherent to the disc-wind scenario for the broad-line region: broad-line emission requires a minimal column density, implying a minimal outflow rate and thus a minimal accretion rate. Here we perform a detailed analysis of the consequences of mass conservation in the process of accretion through a central disc. The resulting constraints on luminosity are consistent with all the cases where claimed detections of true type 2 AGN pass stringent criteria, and predict that intrinsic broad-line emission can disappear at luminosities as high as ˜4 × 1046 erg s-1 and any Eddington ratio, though more detections can be expected at Eddington ratios below ˜1 per cent. Our results are applicable to every disc outflow model, whatever its details and whether clumpy or smooth, irrespective of the wind structure and its underlying dynamics. While other factors, such as changes in spectral energy distribution or covering factor, can affect the intensities of broad emission lines, within this scenario they can only produce true type 2 AGN of higher luminosity then those prescribed by mass conservation.

  18. Time Series Analysis of the UV Flickering in AGN

    NASA Technical Reports Server (NTRS)

    Robinson, Edward L.; Welsh, William F.

    2001-01-01

    Many active galactic nuclei (AGN) exhibit large-amplitude luminosity fluctuations on short timescales. The fluctuations lead to a profound conclusion: The size of the emitting region is remarkably small. This observational fact is one of the pillars supporting the AGN paradigm: Prodigious amounts of gravitational potential energy are liberated in an accretion disk around a supermassive black hole. The goals of the research were to extract from the IUE Archive the very best observational characterizations of AGN flickering, and to use these to test and develop models for AGN variability. We hoped to answer these specific questions: 1) What does the intrinsic flickering continuum spectrum look like? 2) What do the intrinsic flickering emission-line profiles look like? 3) What is the power spectrum of the flickering? 4) What is the wavelength dependence of the power spectrum? 5) Is the flickering spectrum timescale dependent? and 6) What do the high-order cross correlation functions look like? A short summary of the papers produced by this research is presented.

  19. Fast ionized X-ray absorbers in AGNs

    NASA Astrophysics Data System (ADS)

    Fukumura, K.; Tombesi, F.; Kazanas, D.; Shrader, C.; Behar, E.; Contopoulos, I.

    2016-05-01

    We investigate the physics of the X-ray ionized absorbers often identified as warm absorbers (WAs) and ultra-fast outflows (UFOs) in Seyfert AGNs from spectroscopic studies in the context of magnetically-driven accretion-disk wind scenario. Launched and accelerated by the action of a global magnetic field anchored to an underlying accretion disk around a black hole, outflowing plasma is irradiated and ionized by an AGN radiation field characterized by its spectral energy density (SED). By numerically solving the Grad-Shafranov equation in the magnetohydrodynamic (MHD) framework, the physical property of the magnetized disk-wind is determined by a wind parameter set, which is then incorporated into radiative transfer calculations with xstar photoionization code under heating-cooling equilibrium state to compute the absorber's properties such as column density N_H, line-of-sight (LoS) velocity v, ionization parameter ξ, among others. Assuming that the wind density scales as n ∝ r-1, we calculate theoretical absorption measure distribution (AMD) for various ions seen in AGNs as well as line spectra especially for the Fe Kα absorption feature by focusing on a bright quasar PG 1211+143 as a case study and show the model's plausibility. In this note we demonstrate that the proposed MHD-driven disk-wind scenario is not only consistent with the observed X-ray data, but also help better constrain the underlying nature of the AGN environment in a close proximity to a central engine.

  20. Is There an Obscured AGN in the Normal Galaxy IRASF01063-8034

    NASA Technical Reports Server (NTRS)

    Greenhill, Lincoln J.

    2005-01-01

    The XMM target for this program is ostensibly a "normal" galaxy, but the presence of water maser emission indicated that it may be an obscured AGN. Our primary goal is to test this hypothesis; detection hard X-ray emission and a reflection-dominated spectrum would indicate an AGN is present. Demonstration that the local universe contains obscured AGN is important to constraining models of the hard cosmic X-ray background, as is identification of efficient methods to locate them (e.g., ground-based detection of maser emission at microwave frequencies).

  1. Feedback control for car following model based on two-lane traffic flow

    NASA Astrophysics Data System (ADS)

    Ge, Hong-xia; Meng, Xiang-pei; Zhu, Hui-bing; Li, Zhi-Peng

    2014-08-01

    In the paper, two-lane traffic flow considering lane changing behaviors has been discussed based on the control theory, and the friction interference which is from the neighbor lane has been taken into account. By using the control method, the stability condition is derived. The feedback signals, which include vehicular information from both lanes, acting on the two-lane traffic system have been introduced into the Full Velocity Difference car-following model. In the end, simulations are conducted to examine the validity and reasonability of the control method. It is proven that lane changing behaviors can aggravate the traffic perturbation. The traffic flow congestion could be suppressed by using the control method and the simulation results are in good agreement with the theoretical analysis.

  2. Modeling of Millimeter-Wave Modulation Characteristics of Semiconductor Lasers under Strong Optical Feedback

    PubMed Central

    Bakry, Ahmed

    2014-01-01

    This paper presents modeling and simulation on the characteristics of semiconductor laser modulated within a strong optical feedback (OFB-)induced photon-photon resonance over a passband of millimeter (mm) frequencies. Continuous wave (CW) operation of the laser under strong OFB is required to achieve the photon-photon resonance in the mm-wave band. The simulated time-domain characteristics of modulation include the waveforms of the intensity and frequency chirp as well as the associated distortions of the modulated mm-wave signal. The frequency domain characteristics include the intensity modulation (IM) and frequency modulation (FM) responses in addition to the associated relative intensity noise (RIN). The signal characteristics under modulations with both single and two mm-frequencies are considered. The harmonic distortion and the third order intermodulation distortion (IMD3) are examined and the spurious free dynamic range (SFDR) is calculated. PMID:25383381

  3. Feedback control scheme of traffic jams based on the coupled map car-following model

    NASA Astrophysics Data System (ADS)

    Zhou, Tong; Sun, Di-Hua; Zhao, Min; Li, Hua-Min

    2013-09-01

    Based on the pioneering work of Konishi et al. [Phys. Rev. E (1999) 60 4000], a new feedback control scheme is presented to suppress traffic jams based on the coupled map car-following model under the open boundary condition. The effect of the safe headway on the traffic system is considered. According to the control theory, the condition under which traffic jams can be suppressed is analyzed. The results are compared with the previous results concerning congestion control. The simulations show that the suppression performance of our scheme on traffic jams is better than those of the previous schemes, although all the schemes can suppress traffic jams. The simulation results are consistent with theoretical analyses.

  4. Haptic feedback control in medical robots through fractional viscoelastic tissue model.

    PubMed

    Kobayashi, Yo; Moreira, Pedro; Liu, Chao; Poignet, Philippe; Zemiti, Nabil; Fujie, Masakatsu G

    2011-01-01

    In this paper, we discuss the design of an adaptive control system for robot-assisted surgery with haptic feedback. Through a haptic device, the surgeon teleoperates the medical instrument in free space, fixed on a remote robot or in contact. In free space, the surgeon feels the motion of the robot. In the present paper, we evaluated the performance of the controller on viscoelastic tissue, modeled by a fractional derivative equation. In addition, we propose a novel controller using an integer formalization process that is suitable for these tissue properties. The simulation results suggested that performance, in terms of force control and telepresence, became poorer when the conventional controller, which was designed for elastic target object, was applied to the viscoelastic tissues. In contrast, the results suggested that our proposed controller maintained its performance on the viscoelastic tissues. PMID:22255877

  5. Dissipative two-mode Tavis-Cummings model with time-delayed feedback control

    NASA Astrophysics Data System (ADS)

    Kopylov, Wassilij; Radonjić, Milan; Brandes, Tobias; Balaž, Antun; Pelster, Axel

    2015-12-01

    We investigate the dynamics of a two-mode laser system by extending the two-mode Tavis-Cummings model with dissipative channels and incoherent pumping and by applying the mean-field approximation in the thermodynamic limit. To this end we analytically calculate up to four possible nonequilibrium steady states (fixed points) and determine the corresponding complex phase diagram. Various possible phases are distinguished by the actual number of fixed points and their stability. In addition, we apply three time-delayed Pyragas feedback control schemes. Depending on the time delay and the strength of the control term, this can lead to the stabilization of unstable fixed points or to the selection of a particular cavity mode that is macroscopically occupied.

  6. Modelling and analysis of gene regulatory network using feedback control theory

    NASA Astrophysics Data System (ADS)

    El-Samad, H.; Khammash, M.

    2010-01-01

    Molecular pathways are a part of a remarkable hierarchy of regulatory networks that operate at all levels of organisation. These regulatory networks are responsible for much of the biological complexity within the cell. The dynamic character of these pathways and the prevalence of feedback regulation strategies in their operation make them amenable to systematic mathematical analysis using the same tools that have been used with success in analysing and designing engineering control systems. In this article, we aim at establishing this strong connection through various examples where the behaviour exhibited by gene networks is explained in terms of their underlying control strategies. We complement our analysis by a survey of mathematical techniques commonly used to model gene regulatory networks and analyse their dynamic behaviour.

  7. Simulated star formation rate functions at z ˜ 4-7, and the role of feedback in high-z galaxies

    NASA Astrophysics Data System (ADS)

    Tescari, E.; Katsianis, A.; Wyithe, J. S. B.; Dolag, K.; Tornatore, L.; Barai, P.; Viel, M.; Borgani, S.

    2014-03-01

    We study the role of feedback from supernovae (SN) and black holes in the evolution of the star formation rate function (SFRF) of z ˜ 4-7 galaxies. We use a new set of cosmological hydrodynamic simulations, ANGUS (AustraliaN GADGET-3 early Universe Simulations), run with a modified and improved version of the parallel TreePM-smoothed particle hydrodynamics code GADGET-3 called P-GADGET3(XXL), that includes a self-consistent implementation of stellar evolution and metal enrichment. In our simulations both SN-driven galactic winds and active galactic nuclei (AGN) act simultaneously in a complex interplay. The SFRF is insensitive to feedback prescription at z > 5, meaning that it cannot be used to discriminate between feedback models during reionization. However, the SFRF is sensitive to the details of feedback prescription at lower redshift. By exploring different SN-driven wind velocities and regimes for the AGN feedback, we find that the key factor for reproducing the observed SFRFs is a combination of `strong' SN winds and early AGN feedback in low-mass galaxies. Conversely, we show that the choice of initial mass function and inclusion of metal cooling have less impact on the evolution of the SFRF. When variable winds are considered, we find that a non-aggressive wind scaling is needed to reproduce the SFRFs at z ≳ 4. Otherwise, the amount of objects with low SFRs is greatly suppressed and at the same time winds are not effective enough in the most massive systems.

  8. Modeling 3D soil and sediment distributions for assessing catchment structure and hydrological feedbacks

    NASA Astrophysics Data System (ADS)

    Maurer, Thomas; Brück, Yasemine; Hinz, Christoph; Gerke, Horst H.

    2015-04-01

    . The established initial sediment distributions provide a basis for the consecutive modelling of feedbacks between surface and subsurface water flow and changes in soil properties, e.g. by using a landscape evolution model. The results should allow conclusions about the effect of different initial structural setups on the further dynamic landscape development at catchment scale.

  9. Mechano-logical model of C. elegans germ line suggests feedback on the cell cycle

    PubMed Central

    Atwell, Kathryn; Qin, Zhao; Gavaghan, David; Kugler, Hillel; Hubbard, E. Jane Albert; Osborne, James M.

    2015-01-01

    The Caenorhabditis elegans germ line is an outstanding model system in which to study the control of cell division and differentiation. Although many of the molecules that regulate germ cell proliferation and fate decisions have been identified, how these signals interact with cellular dynamics and physical forces within the gonad remains poorly understood. We therefore developed a dynamic, 3D in silico model of the C. elegans germ line, incorporating both the mechanical interactions between cells and the decision-making processes within cells. Our model successfully reproduces key features of the germ line during development and adulthood, including a reasonable ovulation rate, correct sperm count, and appropriate organization of the germ line into stably maintained zones. The model highlights a previously overlooked way in which germ cell pressure may influence gonadogenesis, and also predicts that adult germ cells might be subject to mechanical feedback on the cell cycle akin to contact inhibition. We provide experimental data consistent with the latter hypothesis. Finally, we present cell trajectories and ancestry recorded over the course of a simulation. The novel approaches and software described here link mechanics and cellular decision-making, and are applicable to modeling other developmental and stem cell systems. PMID:26428008

  10. Ocean biogeochemical response to phytoplankton-light feedback in a global model

    NASA Astrophysics Data System (ADS)

    Manizza, Manfredi; Le QuéRé, Corinne; Watson, Andrew J.; Buitenhuis, Erik T.

    2008-10-01

    Oceanic phytoplankton, absorbing solar radiation, can influence the bio-optical properties of seawater and hence upper ocean physics. We include this process in a global ocean general circulation model (OGCM) coupled to a dynamic green ocean model (DGOM) based on multiple plankton functional types (PFT). We not only study the impact of this process on ocean physics but we also explore the biogeochemical response due to this biophysical feedback. The phytoplankton-light feedback (PLF) impacts the dynamics of the upper tropical and subtropical oceans. The change in circulation enhances both the vertical supply in the tropics and the lateral supply of nutrients from the tropics to the subtropics boosting the subtropical productivity by up to 60 gC m-2 a-1. Physical changes, due to the PLF, impact on light and nutrient availability causing shifts in the ocean ecosystems. In the extratropics, increased stratification favors calcifiers (by up to ˜8%) at the expense of mixed phytoplankton. In the Southern Ocean, silicifiers increase their biomass (by up to ˜10%) because of the combined alleviation of iron and light limitation. The PLF has a small effect globally on air-sea fluxes of carbon dioxide (CO2, 72 TmolC a-1 outgassing) and oxygen (O2, 46 TmolO2 a-1 ingassing) because changes in biogeochemical processes (primary production, biogenic calcification, and export production) highly vary regionally and can also oppose each other. From our study it emerges that the main impact of the PLF is an amplification of the seasonal cycle of physical and biogeochemical properties of the high-latitude oceans mostly driven by the amplification of the SST seasonal cycle.

  11. A Sub-Arcsecond Mid-Infrared Survey of X-Ray-Selected AGN

    NASA Astrophysics Data System (ADS)

    Levenson, N. A.; Alonso-Herrero, A.; Packham, Chris; Los Piratas AGN Science Team

    2015-08-01

    Detailed studies of local active galactic nuclei (AGN) following X-ray selection yields significant measurements of the physical properties of the AGN and their host galaxies. In turn, the complete analysis of the nearby cases at high spatial resolution---to distinguish multiple physical components---and high signal-to-noise ratio informs broader surveys of more distant examples where such observations are not possible. We apply these methods in the Los Piratas survey, which emphasizes new observations at mid-infrared wavelengths obtained using CanariCam on the 10.4m Gran Telescopio Canarias. We measure intrinsic bolometric luminosity of the roughly 100 AGN in the sample using X-rays, ensuring a span of luminosity over a range of activity level (from low-ionization nuclei through Seyfert galaxies and quasars), optical type, and radio loudness. The mid-infrared observations at resolution of ~0.3arcsec correspond to typical spatial scales of 60 pc for the low-luminosity AGN and Seyferts and 400 pc for other types. We isolate the AGN emission that is reprocessed by dust in the central regions, which we model in a clumpy distribution. We distinguish this emission from the stellar contributions on larger scales. Across types, the AGN-heated dust emission is overall well-correlated with the X-ray flux, but stellar contributions can be significant on larger scales, especially at moderate AGN luminosity.

  12. Do Radio Jets Contribute to Driving Ionized Gas Outflows in Moderate Luminosity Type 2 AGN?

    NASA Astrophysics Data System (ADS)

    Fowler, Julia; Sajina, Anna; Lacy, Mark

    2016-01-01

    This poster examines the role of AGN-driven feedback in low to intermediate power radio galaxies. We begin with [OIII] measurements of ionized gas outflows in 29 moderate AGN-luminosity z~0.3-0.7 dust-obscured Type 2 AGN. We aim to examine the relative role of the AGN itself, of star-formation and of nascent radio jets in driving these outflows. The strength of the AGN and star formation are based on the [OIII] luminosities, and the far-IR luminosities respectively. For the radio jets, we present multi-frequency radio (X, S, and L-bands) JVLA imaging of our sample, which allows us both to constrain the overall radio power, but also look for signatures of young radio sources, including Giga-hertz Peaked Spectrum (GPS) sources, as well as small-scale jets. While radio jet-driven outflows are well known for powerful radio-loud galaxies, this study allows us to constrain the degree to which this mechanism is significant at more modest radio luminosities of L5GHz~10^22-25 W/Hz.

  13. Galaxy Zoo: Evidence for rapid, recent quenching within a population of AGN host galaxies

    NASA Astrophysics Data System (ADS)

    Smethurst, R. J.; Lintott, C. J.; Simmons, B. D.; Schawinski, K.; Bamford, S. P.; Cardamone, C. N.; Kruk, S. J.; Masters, K. L.; Urry, C. M.; Willett, K. W.; Wong, O. I.

    2016-09-01

    We present a population study of the star formation history of 1244 Type 2 AGN host galaxies, compared to 6107 inactive galaxies. A Bayesian method is used to determine individual galaxy star formation histories, which are then collated to visualise the distribution for quenching and quenched galaxies within each population. We find evidence for some of the Type 2 AGN host galaxies having undergone a rapid drop in their star formation rate within the last 2 Gyr. AGN feedback is therefore important at least for this population of galaxies. This result is not seen for the quenching and quenched inactive galaxies whose star formation histories are dominated by the effects of downsizing at earlier epochs, a secondary effect for the AGN host galaxies. We show that histories of rapid quenching cannot account fully for the quenching of all the star formation in a galaxy's lifetime across the population of quenched AGN host galaxies, and that histories of slower quenching, attributed to secular (non-violent) evolution, are also key in their evolution. This is in agreement with recent results showing both merger-driven and non-merger processes are contributing to the co-evolution of galaxies and supermassive black holes. The availability of gas in the reservoirs of a galaxy, and its ability to be replenished, appear to be the key drivers behind this co-evolution.

  14. SWIFT BAT Survey of AGN

    NASA Technical Reports Server (NTRS)

    Tueller, J.; Mushotzky, R. F.; Barthelmy, S.; Cannizzo, J. K.; Gehrels, N.; Markwardt, C. B.; Skinner, G. K.; Winter, L. M.

    2008-01-01

    We present the results1 of the analysis of the first 9 months of data of the Swift BAT survey of AGN in the 14-195 keV band. Using archival X-ray data or follow-up Swift XRT observations, we have identified 129 (103 AGN) of 130 objects detected at [b] > 15deg and with significance > 4.8-delta. One source remains unidentified. These same X-ray data have allowed measurement of the X-ray properties of the objects. We fit a power law to the logN - log S distribution, and find the slope to be 1.42+/-0.14. Characterizing the differential luminosity function data as a broken power law, we find a break luminosity logL*(ergs/s)= 43.85+/-0.26. We obtain a mean photon index 1.98 in the 14-195 keV band, with an rms spread of 0.27. Integration of our luminosity function gives a local volume density of AGN above 10(exp 41) erg/s of 2.4x10(exp -3) Mpc(sup -3), which is about 10% of the total luminous local galaxy density above M* = -19.75. We have obtained X-ray spectra from the literature and from Swift XRT follow-up observations. These show that the distribution of log nH is essentially flat from nH = 10(exp 20)/sq cm to 10(exp 24)/sq cm, with 50% of the objects having column densities of less than 10(exp 22)/sq cm. BAT Seyfert galaxies have a median redshift of 0.03, a maximum log luminosity of 45.1, and approximately half have log nH > 22.

  15. Reduced-order Model Based Feedback Control of Cavity Flows -- Changes in the Flow Characteristics

    NASA Astrophysics Data System (ADS)

    Samimy, Mo; Little, Jesse; Debiasi, Marco; Caraballo, Edgar; Serrani, Andrea; Yuan, Xin

    2006-11-01

    We have developed and experimentally implemented reduced-order model based feedback control of subsonic cavity flows. Reduced-order models were developed via Proper Orthogonal Decomposition (POD) using particle imaging velocimetry (PIV) in conjunction with the Galerkin projection of the governing Navier-Stokes equations onto the resulting spatial eigenfunctions. The stochastic estimation technique using simultaneous PIV and surface pressure measurements was used to establish correlation between the flow field and surface pressure. For the implementation of the controller, dynamic surface pressure measurements were used for the estimation of the POD modal coefficients. The reduced-order model was linearized around the equilibrium point and a linear-quadratic optimal controller was designed and implemented in the experiments. The actuator was a compression driver type and its output was channeled through a one millimeter slit spanning the entire width of the cavity leading edge. Models based on one or more flow conditions for a Mach 0.3 cavity flow were developed and used, which suppressed the cavity resonant modes. We will compare and contrast the flow characteristics for the open- and closed-loop controlled flows.

  16. A modeling investigation of the Arctic sea ice-atmosphere feedback

    NASA Astrophysics Data System (ADS)

    Liptak, Jessica; Strong, Courtenay

    2016-01-01

    We examine the effects of a general sea ice-atmosphere feedback (SAF) over the Barents Sea by turning it on and off in a coupled climate model. The SAF is "turned off" by forcing the atmosphere with surface turbulent and longwave heat fluxes and surface temperatures that reflect climatological sea ice cover over the Barents Sea, while allowing the sea ice and sea surface temperature (SST) to freely evolve. Suppressing the SAF reduces the variability of near-surface air temperature (T), sea ice concentration (I) , and SST averaged over the Barents Sea by up to 35 %, confirming the existence of a positive thermodynamically-driven SAF found in prior uncoupled modeling studies. Decreased interannual variability accounts for most of the total reduction in I, T, and SST variability, and the largest reductions in variability occur during the winter sea ice growth and spring melt seasons. In contrast to the results from the coupled model experiment, the total variances of I, T, and SST do not significantly change in response to suppressing the SAF in a simple vector autoregressive model, indicating that the SAF is nonlinear.

  17. A model-based approach to predict muscle synergies using optimization: application to feedback control

    PubMed Central

    Sharif Razavian, Reza; Mehrabi, Naser; McPhee, John

    2015-01-01

    This paper presents a new model-based method to define muscle synergies. Unlike the conventional factorization approach, which extracts synergies from electromyographic data, the proposed method employs a biomechanical model and formally defines the synergies as the solution of an optimal control problem. As a result, the number of required synergies is directly related to the dimensions of the operational space. The estimated synergies are posture-dependent, which correlate well with the results of standard factorization methods. Two examples are used to showcase this method: a two-dimensional forearm model, and a three-dimensional driver arm model. It has been shown here that the synergies need to be task-specific (i.e., they are defined for the specific operational spaces: the elbow angle and the steering wheel angle in the two systems). This functional definition of synergies results in a low-dimensional control space, in which every force in the operational space is accurately created by a unique combination of synergies. As such, there is no need for extra criteria (e.g., minimizing effort) in the process of motion control. This approach is motivated by the need for fast and bio-plausible feedback control of musculoskeletal systems, and can have important implications in engineering, motor control, and biomechanics. PMID:26500530

  18. Mechano-electric feedback in one-dimensional model of myocardium.

    PubMed

    Vikulova, Nathalie A; Katsnelson, Leonid B; Kursanov, Alexander G; Solovyova, Olga; Markhasin, V