Found 14 talks width keyword galactic nuclei

Thursday June 25, 2020
Prof. Francesco Shankar
University of Southampton


It has been claimed for decades that almost all galaxies in the local Universe host at their centre a supermassive black hole (SMBH) the mass of which appears to be tightly correlated with the stellar mass and the random motion ("velocity dispersion", sigma) of the stars in the host galaxy. In this talk I will first review the state of the art in this field. I will then highlight that significant biases affect local black hole-galaxy correlations.  I will specifically show that the majority of quiescent early-type galaxies with central black hole dynamical mass estimates have significantly higher velocity dispersions than local typical galaxies of similar stellar mass. Through aimed Monte Carlo simulations, residual analysis, and the comparison with latest AGN clustering measurements, I will then illustrate that present data sets of active and quiescent galaxies strongly favour on average lower SMBH masses than previously thought, and point to velocity dispersion as more ``fundamental'' than galaxy stellar mass, galaxy size or Sérsic index. I will then move on discussing the main implications of these findings, in particular: 1) The implied black hole radiative efficiencies and obscured fractions; 2) the consequences on feedback from active black holes and SMBH binary gravitational waves; 3) the connection to cosmological models that rely on velocity dispersion, rather than stellar mass, as main driver of black hole growth.

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Tuesday January 8, 2019
Dr. Johan Knapen


We present the discovery of a small 0.2'' (60 pc) radius kinematically decoupled core, as well as an outflow jet, in the archetypical AGN-starburst "composite" galaxy NGC 7130 from integral field data obtained with the adaptive optics-assisted MUSE-NFM instrument on the VLT. Correcting the already good natural seeing at the time of our science verification observations with the four-laser GALACSI AO system we reach an unprecedented spatial resolution of around 0.15''. We confirm the existence of star-forming knots arranged in an 0.58'' (185 pc) radius ring around the nucleus, previously observed from UV and optical  Hubble Space Telescope and CO(6-5) ALMA imaging. We determine the position of the nucleus as the location of a peak in gas velocity dispersion. A plume of material extends towards the NE from the nucleus until at least the edge of our FOV at 2'' (640 pc) radius which we interpret as an outflow jet originating in the AGN. The plume is not visible morphologically, but is clearly characterised in our data by emission lines ratios characteristic of AGN emission, enhanced gas velocity dispersion, and distinct non-circular gas velocities. Its orientation is roughly perpendicular to line of nodes of the rotating host galaxy disk. An 0.2''-radius circumnuclear area of positive and negative velocities indicates a tiny inner disk, which can only be seen after combining the integral field spectroscopic capabilities of MUSE with adaptive optics.

Wednesday June 17, 2015
Dr. Almudena Alonso
Instituto de Fisica de Cantabria (IFCA)


The fueling of black holes occurring in active galactic nuclei (AGN) is fundamental to the evolution of galaxies. AGN themselves are largely explained in the context of a unified theory, by which a geometrically and optically thick torus of gas and dust obscures the AGN central engine. The torus intercepts a substantial amount of flux from the central engine and and reradiates it in the infrared. In this talk I will present our CanariCam ESO/GTC large programme which is aimed at understanding the properties of the obscuring material around AGN, including the torus, and the role of nuclear (< 100 pc) starbursts in feeding and/or obscuring AGNs. The CanariCam nearly diffraction limited observations (median 0.3arcsecond), which were finished recently, include imaging and spectroscopy of 45 local AGN, and polarimetry for selected AGN. I will first present an overview of the spectroscopic properties of the sample. Then I will discuss results on the torus properties of different types of AGN from the modelling of the unresolved infrared emission with the CLUMPY torus models. Finally I will also show that we can use the 11.3micron PAH feature to trace star formation activity in the nuclear regions of AGN.

Tuesday May 19, 2015
Dr. Enrique Lopez Rodriguez
Universidad de Texas en San Antonio


Little is known about the mid-infrared (MIR) polarization at high-angular resolution of Active Galactic Nuclei (AGN), however, the polarimetric mode of CanariCam on the 10.4-m Gran Telescopio CANARIAS has opened a new window to reveal its core. We have found a variety of results: 1) A Highly polarized synchrotron emission in the core of Cygnus A; 2) a very complex MIR polarization structures in and around the core of NGC 1068; and 3) a very low polarized core of Mrk 231. In this talk, I will present new CanariCam polarimetric results on several AGN which provide key information on our understanding of the AGN structure and jet formation.

Tuesday March 24, 2015
Dr. Antonio Hernán-Caballero


Recent works show that the restframe colours of X-ray selected AGN host galaxies at z~1 are no different from those of inactive galaxies once stellar mass selection effects are taken into account. However, there is a clear deficit of AGN among quiescent galaxies, and the average star formation rates of AGN hosts are comparable or higher than those of inactive star-forming galaxies. These apparently contradictory findings could be a consequence of higher extinction in star-forming AGN hosts compensating for their younger stellar populations in observed colours. In this talk I will present a new method of extinction correction that breaks the degeneracy with stellar age and metallicity by comparing the restframe U-V colour with measurements of the Dn(4000) index on intermediate band photospectra from SHARDS. I'll show that the distribution of extinction corrected U-V colours and Dn(4000) for AGN hosts at z<1 is significantly different from that of comparison samples of inactive galaxies, with a clear deficit of AGN in intrinsic red galaxies and a higher prevalence among those with intermediate age stellar populations.

Tuesday December 9, 2014
Dr. Rodriguez Ardila
Laboratorio Nacional de Astrofísica (Itajubá, Brasil)


FeII comprises up to one third of the line emission in AGNs. For that reason it is an important coolant that needs to be taken into accountto fully understand the energetics of the broad line region (BLR). In thistalk I will discuss new approaches to study the excitation mechanisms ofthe FeII based on a semi-empirical template we derived in thenear-infrared region (NIR). We correlate the strength of the NIR andoptical iron lines to assess the relative contribution of the differentmechanisms that produces that emission. We found that in all casesLy_alpha fluorescence plays an important role, being a process that needsto be considered in any approach aimed at understanding this complexemission. We also compare the width of the individual FeII lines with thatof other lines emitted in BLR. Our results confirm previous assumptionsand results from variabilty studies that the gas responsible for the FeIIemission is the outer portion of the BLR.

Tuesday July 8, 2014
Dr. Omaira Gonzalez Martin


The active galactic nuclei is conformed by a number of classes. Optically they are defined using diagnostics based on optical emission lines. At X-rays they are classified by the power of the AGN continuum and the shape of the X-ray spectra. Therefore, optical and X-ray classes are independent classifications. However, optical and X-ray classes show many discrepancies not fully understood yet. Some AGN at X-rays do not show any AGN signature at optical wavelengths (called optical elusive). Classical obscured AGN are ’sometimes’ not obscured at X-rays.

We have studied the ‘synapses’ between them using artificial neural networks (Gonzalez-Martin+14). To do so, we used flux-calibrated X-ray spectra of a sample of 90 emission line nuclei (ELN) observed with XMM-Newton. It includes starbursts (SB), transition objects (T2), LINERs (L1.8 and L2), and Seyferts (S1, S1.8, and S2).

The ELN can be classified into six classes, based on the shape of their X-ray spectra. These classes are associated with most of the optical classes. The key parameters to explain them at X-rays are three. The first parameter is an AGN-like component, which is present in all of them (even non-AGN at optical wavelengths!). The second one is obscuration, which almost certainly drives the Type-1/Type-2 dichotomy, but may also explain why L1.8 are more similar to S1s while L2/T2 are more similar to S1.8s. The third component is star-forming activity happening at the host galaxy and contributing at X-rays. The AGN strength, relative to the host-galaxy component, determines the average X-ray spectrum for these classes as follows: S1 -> S1.8 -> L1.8/S2 -> L2/T2/ -> SB.

Thursday June 26, 2014
Prof. Clive Tadhunter
University of Sheffield


There is increasing speculation that quasars are intimately linked to the evolution of their host galaxies. Not only are they triggered as galaxies build up mass through gas accretion, but they also have the potential to drive massive outflows that can directly affect galaxy evolution by heating the gas and expelling it from galaxy bulges. However, there remain considerable uncertainties about how, when and where quasars are triggered as galaxies evolve, and the true energetic significance for the quasar-induced outflows and their acceleration mechanism have yet to be established. In this talk I will present new Gemini, VLT, Spitzer and Herschel results on samples of luminous AGN in the local Universe which provide key information on the triggering mechanisms for quasars and physics of their outflows.

Tuesday February 28, 2012
Dr. Almudena Alonso Herrero
Instituto de Astrofísica de Cantabria, Spain


Luminous Infrared Galaxies (LIR=10^11-10^12Lsun) have star formation rates in the range of ~20-200Msun/yr. In the local Universe ~50% LIRGs show AGN or AGN/SB composite nuclear activity from optical spectroscopy. We decompose Spitzer/IRS 5-35micron spectra of a complete sample of 50 local (d<75Mpc) LIRGs using SB and AGN clumpy torus model templates. We derive a mid-IR AGN detection rate in our sample of local LIRGs of 50%. We also compare the continuum mid-IR AGN detection with other indicators in the mid-IR, optical and X-rays. We estimate for the first time the AGN bolometric contribution to the IR luminosity of the galaxies in local LIRGs. We find that one-third of local LIRGs have LAGN(bol)/LIR>0.05, with only ~10% having a significant contribution LAGN(bol)/LIR>0.25. This is in line with results of Nardini et al. (2010) that only at LIR>3x10^12Lsun the AGN starts dominating bolometrically the IR luminosity in the majority of the systems.

Tuesday April 26, 2011
Dr. Cristina Ramos Almeida
University of Sheffield, UK


I will present new mid-infrared imaging data for a sample of ~20 nearby Seyfert galaxies obtained with T-ReCS and MICHELLE on the Gemini Telescopes at subarcsecond resolution. Our aim is to compare the properties of Type-1 and Type-2 Seyfert tori using clumpy torus models and a Bayesian approach to fit the infrared nuclear spectral energy distributions (SEDs). These dusty tori have physical sizes smaller than 10 pc radius, as derived from our fits. Unification schemes of AGN account for a variety of observational differences in terms of viewing geometry. However, we find evidence that strong unification may not hold, and that the immediate dusty surroundings of Type-1 and Type-2 Seyfert nuclei are intrinsically different. The Type-2 tori studied here are broader, have more clumps, and these clumps have lower optical depths than those of Type-1 tori. The larger the covering factor of the torus, the smaller the probability of having direct view of the AGN, and vice-versa. In our sample, Seyfert 2 tori have larger covering factors and smaller escape probabilities than those of Seyfert 1. Thus, on the basis of the results presented here, the classification of a Seyfert galaxy as a Type-1 or Type-2 depends more on the intrinsic properties of the torus rather than on its mere inclination, in contradiction with the simplest unification model.

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Upcoming talks

  • TBD
    Dr. Mahmoudreza Oshagh
    Tuesday November 10, 2020 - 12:30  (Online)
  • Galacto-archeology (TBC)
    Dr. Andrea Miglio
    Tuesday November 17, 2020 - 12:30  (Aula)

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