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  • 1
    Electronic Resource
    Electronic Resource
    The central dusty torus in the active nucleus of NGC 1068 (2004)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 429 (2004), S. 47-49 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Active galactic nuclei (AGNs) display many energetic phenomena—broad emission lines, X-rays, relativistic jets, radio lobes—originating from matter falling onto a supermassive black hole. It is widely accepted that orientation effects play a major role in explaining the ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature02531
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    Paper (German National Licenses)
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  • 2
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    Kinetic AGN feedback effects on cluster cool cores simulated using SPH (2016)
    Oxford University Press
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    Publication Date: 2016-07-07
    Description: 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 10 14 h –1 M ), which is initially evolved to form a dense cool core, having central T ≤ 10 6  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 10 7 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.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    The early phases of galaxy clusters formation in IR: coupling hydrodynamical simulations with GRASIL-3D (2015)
    Oxford University Press
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    Publication Date: 2015-04-26
    Description: We compute and study the infrared and sub-mm properties of high-redshift ( z   1) simulated clusters and protoclusters. The results of a large set of hydrodynamical zoom-in simulations including active galactic nuclei (AGN) feedback, have been treated with the recently developed radiative transfer code grasil-3d , which accounts for the effect of dust reprocessing in an arbitrary geometry. Here, we have slightly generalized the code to adapt it to the present purpose. Then we have post-processed boxes of physical size 2 Mpc encompassing each of the 24 most massive clusters identified at z  = 0, at several redshifts between 0.5 and 3, producing IR and sub-mm mock images of these regions and spectral energy distributions (SEDs) of the radiation coming out from them. While this field is in its infancy from the observational point of view, rapid development is expected in the near future thanks to observations performed in the far-IR and sub-mm bands. Notably, we find that in this spectral regime our prediction are little affected by the assumption required by this post-processing, and the emission is mostly powered by star formation (SF) rather than accretion on to super massive black hole (SMBH). The comparison with the little observational information currently available, highlights that the simulated cluster regions never attain the impressive star formation rates suggested by these observations. This problem becomes more intriguing taking into account that the brightest cluster galaxies (BCGs) in the same simulations turn out to be too massive. It seems that the interplay between the feedback schemes and the star formation model should be revised, possibly incorporating a positive feedback mode.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    Black hole accretion preferentially occurs in gas-rich galaxies (2014)
    Oxford University Press
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    Publication Date: 2014-05-06
    Description: We have investigated the gas content of a sample of several hundred AGN host galaxies at z  〈 1 and compared it with a sample of inactive galaxies, matched in bins of stellar mass and redshift. Gas masses have been inferred from the dust masses, obtained by stacked Herschel far-IR and sub-mm data in the GOODS and COSMOS fields, under reasonable assumptions and metallicity scaling relations for the dust-to-gas ratio. We find that AGNs are on average hosted in galaxies much more gas rich than inactive galaxies. In the vast majority of stellar mass bins, the average gas content of AGN hosts is higher than that in inactive galaxies. The difference is up to a factor of 10 higher in low-stellar-mass galaxies, with a significance of 6.5. In almost half of the AGN sample, the gas content is three times higher than that in the control sample of inactive galaxies. Our result strongly suggests that the probability of having an AGN activated is simply driven by the amount of gas in the host galaxy; this can be explained in simple terms of statistical probability of having a gas cloud falling into the gravitational potential of the black hole. The increased probability of an AGN being hosted by a star-forming galaxy, identified by previous works, may be a consequence of the relationship between gas content and AGN activity, found in this paper, combined with the Schmidt–Kennicutt law for star formation.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Characterizing diffused stellar light in simulated galaxy clusters (2013)
    Oxford University Press
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    Publication Date: 2013-12-06
    Description: In this paper, we carry out a detailed analysis of the performance of two different methods to identify the diffuse stellar light in cosmological hydrodynamical simulations of galaxy clusters. One method is based on a dynamical analysis of the stellar component, which separates the brightest central galaxy (BCG) from the stellar component not gravitationally bound to any galaxy, what we call ’diffuse stellar component’ (DSC). The second method is closer to techniques commonly employed in observational studies. We generate mock images from simulations, and assume a standard surface brightness limit (SBL) to disentangle the BCG from the intra-cluster light (ICL). Both the dynamical method and the method based on the SBL criterion are applied to the same set of hydrodynamical simulations for a large sample of about 80 galaxy clusters. We analyse two sets of radiative simulations: a first set includes the effect of cooling, star formation, chemical enrichment and galactic outflows triggered by supernova feedback (CSF set); a second one also includes the effect of thermal feedback from active galactic nuclei triggered by gas accretion on to supermassive black holes (AGN set). We find significant differences between the ICL and DSC fractions computed with the two corresponding methods, which amounts to about a factor of 2 for the AGN simulations, and a factor of 4 for the CSF set. We also find that the inclusion of AGN feedback boosts the DSC and ICL fractions by a factor of 1.5–2, respectively, while leaving the BCG+ICL and BCG+DSC mass fraction almost unchanged. The sum of the BCG and DSC mass stellar mass fraction is found to decrease from ~80 per cent in galaxy groups to ~60 per cent in rich clusters, thus in excess of that found from observational analysis. We identify the average SBLs that yield the ICL fraction from the SBL method close to the DSC fraction from the dynamical method. These SBLs turn out to be brighter in the CSF than in the AGN simulations. This is consistent with the finding that AGN feedback makes BCGs to be less massive and with shallower density profiles than in the CSF simulations. The BCG stellar components, as identified by both methods, are slightly older and more metal-rich than the stars in the diffuse component. Relaxed clusters have somewhat higher stellar mass fractions in the diffuse component. The metallicity and age of both the BCG and diffuse components in relaxed clusters are also richer in metals and older.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    GRASIL-3D: an implementation of dust effects in the SEDs of simulated galaxies (2014)
    Oxford University Press
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    Publication Date: 2014-03-25
    Description: We introduce a new model for the spectral energy distribution of galaxies, grasil-3d , which includes a careful modelling of the dust component of the interstellar medium. grasil-3d is an entirely new model based on the formalism of an existing and widely applied spectrophotometric model, grasil , but specifically designed to be interfaced with galaxies with any arbitrarily given geometry, such as galaxies calculated by theoretical hydrodynamical galaxy formation codes. grasil-3d is designed to separately treat radiative transfer in molecular clouds and in the diffuse cirrus component. The code has a general applicability to the outputs of simulated galaxies, either from Lagrangian or Eulerian hydrodynamic codes. As an application, the new model has been interfaced to the p-deva and gasoline smoothed particle hydrodynamic codes, and has been used to calculate the spectral energy distribution for a variety of simulated galaxies from UV to sub-millimetre wavelengths, whose comparison with observational data gives encouraging results. In addition, grasil-3d allows 2D images of such galaxies to be obtained, at several angles and in different bands.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    The main sequence and the fundamental metallicity relation in MaGICC Galaxies: evolution and scatter (2014)
    Oxford University Press
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    Publication Date: 2014-06-19
    Description: Using cosmological galaxy simulations from the MaGICC project, we study the evolution of the stellar masses, star formation rates and gas-phase abundances of star-forming galaxies. We derive the stellar masses and star formation rates using observational relations based on spectral energy distributions by applying the new radiative transfer code grasil-3d to our simulated galaxies. The simulations match well the evolution of the stellar mass–halo mass relation, have a star-forming main sequence that maintains a constant slope out to redshift z  ~ 2, and populate projections of the stellar mass – star formation – metallicity plane, similar to observed star-forming disc galaxies. We discuss small differences between these projections in observational data and in simulations, and the possible causes for the discrepancies. The light-weighted stellar masses are in good agreement with the simulation values, the differences between the two varying between 0.06 and 0.20 dex. We also find good agreement between the star formation rate tracer and the true (time-averaged) simulation star formation rates. Regardless, if we use mass- or light-weighted quantities, our simulations indicate that bursty star formation cycles can account for the scatter in the star-forming main sequence.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Brightest cluster galaxies in cosmological simulations: achievements and limitations of active galactic nuclei feedback models (2013)
    Oxford University Press
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    Publication Date: 2013-11-14
    Description: We analyse the basic properties of brightest cluster galaxies (BCGs) produced by state of the art cosmological zoom-in hydrodynamical simulations. These simulations have been run with different subgrid physics included. Here we focus on the results obtained with and without the inclusion of the prescriptions for supermassive black hole growth and of the ensuing active galactic nuclei (AGN) feedback. The latter process goes in the right direction of decreasing significantly the overall formation of stars. However, BCGs end up still containing too much stellar mass, a problem that increases with halo mass, and having an unsatisfactory structure. This is in the sense that their effective radii are too large, and that their density profiles feature a flattening on scales much larger than observed. We also find that our model of thermal AGN feedback has very little effect on the stellar velocity dispersions, which turn out to be very large. Taken together, these problems, which to some extent can be recognized also in other numerical studies typically dealing with smaller halo masses, indicate that on one hand present day subresolution models of AGN feedback are not effective enough in diminishing the global formation of stars in the most massive galaxies, but on the other hand they are relatively too effective in their centres. It is likely that a form of feedback generating large-scale gas outflows from BCGs precursors, and a more widespread effect over the galaxy volume, can alleviate these difficulties.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    On the role of AGN feedback on the thermal and chemodynamical properties of the hot intracluster medium (2014)
    Oxford University Press
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    Publication Date: 2014-01-16
    Description: We present an analysis of the properties of the intracluster medium (ICM) in an extended set of cosmological hydrodynamical simulations of galaxy clusters and groups performed with the treepm + sph gadget-3 code. Besides a set of non-radiative simulations, we carried out two sets of simulations including radiative cooling, star formation, metal enrichment and feedback from supernovae (SNe), one of which also accounts for the effect of feedback from active galactic nuclei (AGN) resulting from gas accretion on to supermassive black holes. These simulations are analysed with the aim of studying the relative role played by SN and AGN feedback on the general properties of the diffuse hot baryons in galaxy clusters and groups: scaling relations, temperature, entropy and pressure radial profiles, and ICM chemical enrichment. We find that simulations including AGN feedback produce scaling relations between X-ray observable quantities that are in good agreement with observations at all mass scales. Observed pressure profiles are also shown to be quite well reproduced in our radiative simulations, especially when AGN feedback is included. However, our simulations are not able to account for the observed diversity between cool-core and non-cool-core clusters, as revealed by X-ray observations: unlike for observations, we find that temperature and entropy profiles of relaxed and unrelaxed clusters are quite similar and resemble more the observed behaviour of non-cool-core clusters. As for the pattern of metal enrichment, we find that an enhanced level of iron abundance is produced by AGN feedback with respect to the case of purely SN feedback. As a result, while simulations including AGN produce values of iron abundance in groups in agreement with observations, they over-enrich the ICM in massive clusters. The efficiency of AGN feedback in displacing enriched gas from haloes into the intergalactic medium at high redshift also creates a widespread enrichment in the outskirts of clusters and produces profiles of iron abundance whose slope is in better agreement with observations. By analysing the pattern of the relative abundances of silicon and iron and the fraction of metals in the stellar phase, our results clearly show that different sources of energy feedback leave different imprints in the enrichment pattern of the hot ICM and stars. Our results confirm that including AGN feedback goes in the right direction of reconciling simulation predictions and observations for several observational ICM properties. Still a number of important discrepancies highlight that the model still needs to be improved to produce the correct interplay between cooling and feedback in central cluster regions.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    Kinematics of molecular gas in the nucleus of NGC 1068, from H$ oldmathmathsf{_{2}}$ line emission observed with VLT (2001)
    EDP Sciences
    Details
    Publication Date: 2001-04-01
    Print ISSN: 0004-6361
    Electronic ISSN: 1432-0746
    Topics: Physics
    Published by EDP Sciences
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