Zulema AbrahamThe precessing jet in the core of NGC 1275 (3C84)NGC 1275 is a giant elliptical galaxy at the center of the Perseus cluster of galaxies. It is associated to a strong radio source (3C84) and presents X-ray emission that extends well into the intergalactic medium. The X-ray maps present multiple misaligned pairs of cavities, some of them coincident with maxima in the radio emission, which had been interpreted as bubbles inflated by a precessing radio jet. Falceta-Gonalves et al. (2010, ApJ 713, L74) using 3D hydrodynamical simulations found that bubbles can be formed only under some restricted precession conditions, and proposed that the Bardeen-Peterson effect could be responsible for the torques driving this precession. In the present work we study the radio structure expected from a jet precessing according to this process and obtain the precession parameters that are compatible with both the radio image and the inflation of the X-ray bubbles. Using other properties of the radio galaxy, like bolometric luminosity and mass of the central black hole, we were also able to put limits on the accretion disk parameters and on the rotation rate of the black hole.
Rebeca AladroChemical complexity in AGNsWe will present a recent frequency line survey carried out towards the central parts of the galaxy NGC 1068 using the IRAM 30m telescope. The data allowed us to study in detail the signatures of the X-ray chemistry in the surroundings of this Seyfert 2 Active Galactic Nucleus, by comparing a complete inventory of species and their abundances with those obtained for starburst galaxies. So far, the HCO+-to-HCN ratio has been proposed as a tool to distinguish between starburst and AGN phenomena. Here, it is proposed that also some undetected species in NGC1068 can be used to characterize the AGN chemistry. In particular, CH3CCH could be very useful to differentiate between AGN and starburst activities. We will compare our observational results with theoretical models and discuss whether the molecular abundances are -or not- well reproduced by them.
Daniel AsmusMid-infrared properties of nearby low-luminosity AGN at high angular resolutionWe present high spatial resolution mid-infrared (MIR) observations of 30 nearby low-luminosity AGN (LLAGN) with VLT/VISIR and Gemini/Michelle. LLAGN are of great interest because this population is the most common among active galaxies, especially in the nearby universe. Thus, they could be studied in great detail making it possible to understand more distant AGN and investigate their evolution over cosmic timescales. Indeed, many LLAGN likely represent the final stage of an AGN's lifetime. We show that even at low luminosities and accretion rates nuclear unresolved MIR emission is present in most objects which is interpreted as thermal emission from a dusty torus at higher luminosity AGN. Furthermore, this emission is strongly correlated with the absorption corrected 2-10keV luminosity over many orders of magnitudes and independent of the accretion rate or object type! The physical implications of these results will be discussed in the context of the unification model of AGN and proposed changes in the accretion structure at low powers. Finally, the data is compared with lower spatial resolution data from Spitzer/IRS and IRAS. As expected, it exhibits much lower fluxes and different PAH emission properties in many cases. Furthermore, the LLAGN are compared to a sample of typical starburst galaxies and a few peculiar LLAGN are identified to be starburst dominated even at parsec scales.
Rainer BeckMagnetic Fields and Mass Flows around Circumnuclear StarburstsRadio continuum observations of barred galaxies revealed strong magnetic fields in the circumnuclear starbursts. Such fields are dynamically important and give rise to magnetic stress that causes inflow of gas towards the center at a rate of several solar masses per year. This may solve the long-standing question of how to feed active nuclei. Strong magnetic fields were also measured in the central outflow cone of NGC253. Faraday rotation data indicate a large-scale helical field.
Moritz BoeckWhat is lurking at the inner parsec of NGC 1052?
Markus BoettcherHigh-Energy Emission from Radio-Loud AGNThis walk will present an overview of the current state of understanding of the origin of high-energy and very-high-energy gamma-ray emission from radio-loud AGN. Both leptonic and hadronic emission scenarios will be discussed, as will be the potential role of VHE gamma-ray induced pair cascades in AGN environments.
Silke BritzenDetecting supermassive binary black holes with VLBISupermassive binary black holes on pc-scales are difficult to find although they are supposed to be formed as a consequence of galaxy mergers quite frequently. Highest angular resolution observations provided by VLBI offer a tool - probably the most promising one - to detect these systems. The most recently discovered signature of a new candidate SMBBH is being presented and discussed.
Avery BroderickImaging Black Hole Horizons with the Event Horizon TelescopeThe Event Horizon Telescope, a millimeter very long baseline array constructed from existing facilities, has already probed Sagittarius A* on sub-horizon angular scales. I will discuss what we think we now know, and what we will learn in the future, about Sgr A* as a result. This includes implications for Sgr A*'s spin and accretion flow morphology, as well as the existence and properties of black holes more generally. Finally, I will touch upon recent efforts to image M87, and the implications for jet formation theory.
Gabriele BruniThe central structure of Broad Absorption Line QSOs: observational characteristics in the cm-mm wavelengths domain.About 15% of the Quasar population shows broad absorption lines in their spectra generated from outflows with velocities up to 0.2 c. At the moment two models have been presented to explain these objects: an orientation model (Elvis 2000) and an evolutionary scenario (Becker et al. 2000). We selected a complete sample of Radio Loud Broad Absorption Line Quasars from the SDSS and the FIRST surveys, in order to study their spectral properties and orientation features at cm-mm wavelengths. High-resolution VLBI observations have been performed to study the morphology of these objects.
Rainer BuchholzNIR polarization in the central parsec of the GCRainer M. Buchholz: NIR polarization in the central parsec of the GC First time study of stellar and resolved bow-shock polarization at 8m class resolution The GC offers unique opportunities to study stellar and bow-shock polarization effects in a dusty environment. I will present NIR polarimetry of the stellar and bow-shock sources in the central parsec at NACO resolution, which also provides new insights into the nature of the known bright bow-shock sources. We used AO assisted observations obtained at the ESO VLT in the NIR, applying both high precision photometric methods specifically developed for crowded fields and a newly established polarimetric calibration for NACO to produce polarization maps of the central 3''x19'', in addition to spatially resolved polarimetry on the extended sources in this region. We find foreground polarization largely parallel to the Galactic plane, with average values of 5.5% at 15 deg (Ks-band) and 9.5% at 20 deg (H-band) in the center of the FOV and higher values resp. smaller angles towards the edges of the field. We believe this deviation may be caused by local dichroic extinction by dust grains in the Northern Arm of the Minispiral. p_H / p_Ks peaks at 1.7 \pm 0.1, corresponding to a power law index for the wavelength dependency of alpha = 2.1 \pm 0.2. These values also vary over the FOV, with higher values in the center. We were able to isolate the intrinsic polarization of the two bow-shock sources contained in our sample, IRS~21 and 1W, and both show similar intrinsic polarization degrees of 5.5% resp. 7.8% (Ks) and 6.9% (H, only 1W) at polarization angles coincident with previous MIR findings, both in total and spatially resolved. The spatial polarization pattern of both sources points to scattering on aligned elongated dust grains as the major source of intrinsic polarization (IRS-1W), resp. local dichroic extinction in the case of IRS-21. We also resolve the bow shock around IRS~21 for the first time in the Ks-band, finding the apex north of the central source and determining a standoff distance of ~400 AU. This source also shows ~50% increase in flux in the NIR over several years. Strong flux variabilities are also found for other bow-shock sources in the vicinity.
Leonard BurtscherThe MIDI AGN Large Programme: A statistical sample of resolved AGN tori"Interferometric observations with MIDI/VLTI in the mid-infrared made studies of the central dusty tori of Active Galactic Nuclei (AGNs) possible and proved their existence in a number of nearby galaxies. Both type 2 and type 1 galaxies showed ""tori"" whose general properties were comparable -- consistent with (but not proving) the ""unifying model"" for radio-quiet galaxies. However, the well resolved type 2 tori differ in their detailed properties and the highest resolution observations show signs for non-smooth structures, as expected both from theoretical arguments and from hydrodynamical simulations (see also talk by K. Tristram). It turned out that a more comprehensive approach was needed to overcome the differences in individual galaxies and be able to draw statistical conclusions from the study of a large number of type 1 and type 2 galaxies. This statistical basis was set up as a VLTI/MIDI Large Programme that comprises 14 AGNs for which torus properties are being determined. The observations have now been completed [at the time of the workshop] and show resolved dust emission in almost all of the sources. They represent the largest sample of resolved AGN tori so far allowing to ask a number of questions, ranging from unification to the physics of accreting galactic nuclei. In the talk, both the scope and first results from the Large Programme will be presented."
Francoise CombesDynamical processes in galaxy centersThe different processes to cause rapid gas inflow (or outflow) in galaxy centers will be reviewed. Non axisymmetries car be created or maintained by disk instabilities, or galaxy interactions. Various scenarios will be described, including gas accretion and starbursts.
Bozena CzernyThe hypothesis of the dust origin of the BLR regionWe recently showed (Czerny & Hryniewicz 2011) that the disk effective temperature at the radius coincident with the onset of the Broad Line Region is universal and equal 1000 K. We thus proposed that the strong turbulent motion needed to explain the properties of the Broad Line Region is due to the dust formation in the disk atmosphere. The efficient outflow is stoped high above the disk due to the irradiation of the gas by the central source and subsequent dust evaporation, leading to creation of a failed wind. Such a dusty failed wind covers the disk range from the inner edge of the BLR up to the dusty torus, defined as a region where dust evaporation becomes inefficient. We will discuss how IR observations can be used to verify such a picture.
Richard I. DaviesDo stellar winds play a decisive role in feeding AGN?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 for
Jason DexterTime-dependent Radiative Models of Sgr A* and M87* from Relativistic MHD Simulationsmation, and that we should be thinking of the torus as a complex dynamical entity.
Tuan DoThe structure and stellar population of the central 0.5 pc of the Milky Way nuclear star clusterI will present recent results of laser guide star adaptive optics imaging and spectroscopy from the Keck telescope of the central 0.5 pc of the Milk Way nuclear star cluster. The Galactic center black hole has a strong influence on the stellar dynamics and star formation in this region, both of which have revealed unexpected results. It has been recently shown that the spectroscopically determined sample of old stars have a radial surface density profile much flatter than expected for the formation of stellar cusps around massive black holes. Here, I present new spectroscopic results that show this flat surface density profile extends out to at least 0.5 pc from the black hole. In addition, the inclusion kinematic data has placed much stronger constraints on the slope of the true spatial density profile of the old stars. I also report on the extinction and completeness corrected luminosity function down to K ~ 15.5 mag for young stars in this region and its implication for the initial mass function of the most recent star formation event. The IMF is consistent with Salpeter along the plane of the disk of young stars, in contrast to the top-heavy IMF found in previous observations of stars predominantly perpendicular to the disk plane.
Wolfgang DuschlCosmogony of super-massive black holesWe report calculations of the evolution, under Reynolds viscosity, of the massive gaseous accretion discs thought to form in the centres of galaxies as a result of major galactic mergers at early epochs. Starting with the formation of such a disc and the postulated existence of a low mass “seed” black hole, we focus on the mass accretion rate and hence luminosity of a putative super-massive black hole in the galactic centre. The proposed scenario appears capable of accounting for many of the features of the observed quasar and AGN luminosity distribution with red-shift and seems to be a natural consequence of the formation of massive central discs following major galaxy mergers.
Andreas EckartFlare emission from Sagittarius A*test
Martin ElvisParsing the Torus: the Inner structure of AGNs"The idea of an obscuring molecular torus is revisited in light of current observations. The simple ""donut"" torus has be be replaced by set of at least 3 layers of obscuration are needed on several scales from the broad line region itself, the dust sublimation radius and the host galaxy. These 3 zones relate well to the winds and accretion that must be occuring in AGNs."
Christian FendtSimulations of MHD jet formation - relativistic jets & radiative jetsI will present recent results of MHD simulations of jet formation, discussing a variety of astrophysical setups. In the first approach the role of the disk magnetic flux profile and disk mass loss profile is investigated concerning the jet collimation degree. Our results suggest (and quantify) that in general outflows launched from a very concentrated region close to the inner disk radius tend to be uncollimated. The 2nd approach considers radiative pressure effects on jet collimation and propagation - an environment which is interesting for outflows from massive young stars and AGN). Finally, I will discuss the extension of the previous simulation setup into the relativistic regime, considering special relativistic MHD simulations of jet formation from Keplerian disks, demonstrating - for the first time - the self-collimating ability of relativistic MHD jets. We obtain Lorentz factors up to ~8 while acquiring a high degree of collimation <1 deg. These simulations can be then used to derived synchrotron radiation maps (see talk by O. Porth).
Juan Antonio Fernández OntiverosThe SED of Low-Luminosity AGNs at high-spatial resolution"Recent simulations suggest that the torus vanishes at low luminosities (< 10^42 erg/s; Elitzur & Schlosman 2006, Hönig & Beckert 2007), and thus the inner structure of an AGN is expected to change below this limit (Ho 2008). However, the study of low-luminosity AGNs (LLAGNs) is a complex task due to the contribution of the host galaxy, which light swamps the faint active nucleus. This is specially critical in the IR range, due to the contribution of the old stellar population and/or dust in the nuclear region. Adaptive opctics imaging in the NIR with VLT/NaCo and diffraction limited imaging in the MIR with VLT/VISIR permit us to isolate these faint nuclei for some of the nearest LLAGNs in the Southern Hemisphere. These data were extended to the optical/UV range (HST), radio (VLA) and X-rays (Chandra), in order to build a genuine spectral energy distribution (SED) for each AGN with a consistent spatial resolution (<0.5"") across the whole spectral range. From the individual SEDs, we construct an average SED for LLAGNs, sampled in all the wavebands mentioned before. Compared with previous studies using high-spatial resolution data, our average SED covers the MIR and NIR ranges. This permit us to identify intrinsic differences in the distribution of LLAGNs when compared with those of bright Seyfert and Quasars. A pure synchrotron emission model is also compared with the individual and the average SEDs. Our results are in line with the scenario in which the torus vanishes at low luminosities."
Donald FigerMassive star formation in nuclei of galaxiesThis is the review talk that I was invited to present.
Sebastian FischerA close look at Seyfert 2 nuclei with NIR integral field spectroscopyWe present AO assisted NIR integral field spectroscopy of the central hundreds of pc of ten z < 0.01 Seyfert 2 galaxies. The immediate surroundings of the nuclei are resolved at linear scales of about 50 pc. According to the classical unified scheme, the broad-line region in Seyfert-2 galaxies is hidden by a dusty torus. Since the NIR is less influenced by dust extinction, our deep observations in part reveal broad components in the H-recombination lines, supporting the unified scheme. In addition, we will discuss the excitation conditions, black hole masses, stellar content, dynamics, and the importance of extinction.
Tobias FritzThe extinction towards the galactic center and  new determination of the distance to the Galactic Center
Santiago Garcia-BurilloThe Feeding of SF and AGN Activity in Galaxies"The study of the content, distribution and kinematics of interstellar gas is a key to understand the fueling of AGN and star formation (SF) activity in galaxy disks. Current mm-interferometers provide a sharp view of the distribution and kinematics of molecular gas in the circumnuclear disks of galaxies through extensive CO line mapping. We use the high-resolution (<1"") interferometer CO maps obtained in the context of the NUclei of GAlaxies (NUGA) survey to study the mechanisms responsible to fuel AGN and Star Formation activity in the central R<1 kpc disks of a sample of 25 active galaxies at 10-100 pc scale. Information on the distribution of star formation in NUGA galaxies is also at hand through high quality HST images obtained in Halpha and/or Palpha lines. The information available on the kinematics of the gas allows us to explore the influence of 'hidden' variables (shear, streaming motions and large-scale dynamical perturbations) on the resulting SF laws. This information is a key to any quantitative assessment of the efficiency of the star formation process in galaxies in general. "
Martin HaehneltHow supermassive black holes get into galaxiesinvited review
Alexander HobbsSimulating galaxy formation: sub-grid models at the intermediate scaleUnderstanding galaxy formation and evolution through large-scale simulations requires a prolific use of sub-grid models to encapsulate the physics that is not resolved. Of particular importance to the AGN-host galaxy connection is the modelling of accretion onto the central SMBH and the subsequent outflow that is believed to have a strong link with star formation in the bulge. Here we present some new approaches to sub-grid modelling of SMBH feeding that are both timely, given the improvement in the ability of simulations to resolve smaller and smaller scales, and necessary, being physically motivated and taking account of relevant processes occurring at the intermediate (kiloparsec) scale. We discuss the impact for large-scale simulations and simulations of galaxy mergers.
Nazar IkhsanovMagnetically Controlled Spherical Accretion onto Black HolesSpherical accretion of a magnetized (beta about a unity) matter onto a supermassive black hole is considered. We show that the magnetic field in the accretion flow grows rapidly and appears to be a key parameter in the accretion process already at a large distance from the event horizon. The magnetic field of the flow tends to reduce the mass accretion rate and to disintegrate the initially homogeneous flow into dense filaments. The rate of radial motion of the filaments depends on the rate of annihilation of the magnetic field in the accretion flow. We discuss the field configuration in the vicinity of the event horizon and parameters of flashing activity of the black hole associated with the magnetic field annihilation. An application of the model to the interpretation of the accretion process onto the supermassive black hole of our Galaxy will be discussed.
Christof IserloheNIR imaging spectroscopy of the nucleus of NGC4151 with OSIRIS@Keck
Sungsoo S. KimSimulations of Nuclear Star-Forming Rings: The Case of the Milky WayWe present hydrodynamic simulations of gas clouds in the central kpc region of the Milky Way that is modeled with a three-dimensional bar potential. Our simulations consider realistic gas cooling and heating, star formation, and supernova feedback. A torus of dense gas clouds forms as a result of X1-X2 orbit transfer, and its size (~200 pc radius) coincides with the extraordinary reservoir of dense molecular clouds in the inner bulge, the Central Molecular Zone (CMZ). Our simulations show that the gas clouds accumulated in the CMZ can reach high enough densities to form stars, and the gas mass and the star formation rate in the CMZ, 2x10^7 Msun and 0.05 Msun/yr, are consistent with observations. Star formation in our simulations takes place mostly in the outermost X2 orbits, and the star formation rate per unit surface area outside the CMZ is negligible. These facts suggest that the inner Galactic bulge may harbor a mild version of the nuclear star-forming rings seen in some external disk galaxies. Furthermore, from the relatively small size of the Milky Way's nuclear cluster, which is thought to be a result of sustained star formation in the CMZ, we infer that the Galactic inner bulge probably had a shallower density profile or larger bar elongation in the past.
Makoto KishimotoProbing the inner dusty accretion in AGN tori with near-IR and mid-IR interferometers"We are now probing the inner region of the putative dusty tori in AGNs with the Keck interferometer (KI) and VLTI. We are focused on Type 1 AGNs here, where we can directly scrutinize the innermost region without much of inclination effects. We now have successfully observed 15 targets - 9 by the KI and 9 by VLTI/MIDI, with 3 objects by both (Kishimoto et al. 2011, A&A, 527, 121; Kishimoto et al. 2011b, in prep), including two QSOs at redshift up to 0.16. One of our primary goals is to see if the inner radial distribution of the accreting material is closely related to the mode of the central engine. Based on the near-IR results so far, this might indeed be the case: there is tentative evidence that jet-launching objects possess a very steep and compact distribution of inner accreting material. Together with our mid-IR VLTI/MIDI data probing slightly outer material, an emerging, new, quantitative picture is that, there is a relatively generic flat distribution of density in the outer ~1pc region, while there is more concentration of the material toward ~0.1pc region, with the latter radial steepness being dependent on each object. These structures will be discussed with the radio connection described above. "
Alfred KrabbeSOFIA: First Science Observations
Michael KramerStudying the Galactic Centre using Pulsars: I. Finding pulsars and GC astrophysics"For a number of reasons, we expect to find a large number of pulsars to exist in the Galactic centre region. In addition to the ""normal"" neutron star remnants of massive stars, the high stellar density also allows for evolution scenarios of binary systems which could otherwise only happen in Globular Clusters. The potential millisecond pulsars resulting from such processes are difficult to find, due to the severe interstellar scattering which has prevented even a detection of any pulsar in the central kiloparsec so far. Hence, the way forward are searches at higher frequencies (>10 GHz) with sensitive telescopes. The result is a population of pulsars which will not only allow us to probe the space time of SGR A* with remarkable precision but also allows us to obtain information about the central interstellar medium (e.g. turbulence, magnetic field, electron density) and to infer the star formation history of the inner part of our Galaxy. This talk will review current and future attempts to find pulsars in the Galactic Centre and will summarize their astrophysical applications. A second talk by Wex will detail the amazing potential to probe the properties of the central black hole with those pulsars."
Melanie KripsMultiple-Line Study of NGC1068: Hot Molecular Gas Caused by Jet-Gas Interaction in the Central 100pc?A multiple molecular line and line transitions study will be presented for the circumnuclear disk (CND) of the proto-typical Seyfert galaxy NGC1068. A detailed analysis of the kinematics and excitation conditions of the molecular gas, as traced by 12CO, 13CO, HCN and HCO+, suggests that part of the molecular gas in the CND is shocked, expanding and heated to high kinetic temperatures most likely as a consequence of an interaction between the radio jet and the CND. We further find support for an X-ray altered chemistry of the molecular gas in the CND through an HCN abundance which is significantly increased compared to star-forming, starbursting or quiescent gas regions.
Sabine KönigThe Arp 220 merger on kpc scales
Ari LaorLineless QuasarsThe optical-UV continuum of quasars is broadly consistent with the emission from a geometrically thin optically thick accretion disk (AD). The AD produces the ionizing continuum which powers the broad and narrow line emission. The maximum AD effective temperature is given by Teff=f_max*(Mdot/M^2)^1/4, where M is the black hole mass, Mdot the accretion rate, and f_max is set by the black hole spin a_*. Here we point out that for a low enough value of Mdot/M^2, depending on a_*, the AD may become too cold to produce ionizing photons. Such an object will appear as a lineless quasar, a luminous source with a quasar continuum, and no line emission. This occurs for a local blackbody AD at a luminosity L_opt=10^46 erg/s for M>3.6*10^9Msun if a_*=0, and for M>1.4*10^10Msun if a_*=0.998. Using the AD based Mdot, derived from M and L_opt, and the reverberation based M, derived from L_opt and the Hbeta FWHM, v, gives Teff~L_opt^(-0.13)v^(-1.45). Thus, Teff is mostly set by v. Quasars can become lineless for v> 8,000km/s for a_*=0, and for v> 16,000km/s for a_*=0.998. This may drive the observed sharp drop in line emitting quasars at v>10,000km/s, independent of luminosity. Weak low ionization lines may still be present if the X-ray continuum is luminous enough, and such objects may form a population of weak emission line quasars (WLQ). If correct, such WLQ should show a steeply falling SED at lambda<1000A. Such an SED was observed by Hryniewicz et al. in the WLQ SDSS J094533.99+100950.1, and is well modeled by a relatively cold AD SED.
Christian LeipskiThe warm dust emission of tori in high-redshift quasars"The detection of powerful near infrared emission in high redshift (z>5) quasars demonstrates that very hot dust is present close to the AGN also in the very early universe. While the comparison with local AGN spectral energy distributions (SEDs) showed a reasonable match, the existing data only go out to rest frame wavelengths smaller than ~4 microns, i.e. only sampling the very hottest dust. Currently, our Herschel key project ""The Dusty Young Universe"" extents the photometric coverage into the restframe MIR for over 80 high redshift (z>5) quasars. The combined Herschel and Spitzer data will provide infrared SEDs between ~3 and ~30 microns (rest frame), thus sampling the important warm dust component where the luminosity of the torus peaks. Because the AGN outshines all other contributors to its SED for our high luminosity (L~10^47 erg/s) sources, the rest frame MIR emission effectively isolates the torus emission. The wavelength range covered by these data also matches the wavelengths currently observed interferometrically in the nearby universe (lambda ~ 10-20mu, see talk by L. Burtscher), where a scaling of the torus size with the square root of the luminosity of the AGN could recently be measured. Assuming torus models verfied by such high-resolution observations at low-redshift, we estimate dust radii for our high-redshift and high luminosity sources. By extending the size-luminosity relation by almost two orders of magnitude in luminosity, these models predict extremely large torus radii of up to 300pc at ~12mu. If the use of the local models is appropriate, this implies that the central kiloparsec in these sources is heavily influenced by the torus. The last assumption is of course crucial and needs to be tested. Our future plans therefore involve the building of dedicated torus models for very high-luminosity AGN which will be tailored to our observed photometry."
Jonathan Leon-TavaresThe interplay between the jet, BLR and gamma-ray emission at several parsecs away from the central engine of superluminal AGN.Using a sample of 45 northern extragalactic radio sources, Leon-Tavares et al. (2011) have presented evidence that the most intense gamma-ray flares are produced several parsecs away from the central engine via inverse Compton scattering of local seed photons by electrons in the jet. In the current AGN paradigm, the sources of seed photons to produce gamma-rays at distances well beyond the canonical BLR (< 1 pc) could be provided by either a dusty torus or by the jet itself (SSC mechanisms). Nevertheless, firm detection of IR emission associated to a hot dusty torus has been so far limited to a couple of bright gamma-ray sources, and, as is well known, SSC models in general fail to produce the observed amounts of gamma-ray emission. Recently, however, Leon-Tavares et al. (2010) and Arshakian et al. (2010) have shown that superluminal sources may power an outflow related component of the broad-line emission which can be located parsecs downstream of the canonical BLR. In effect, the relativistic flow drags a part of the BLR with it. We will discuss an alternative scenario, where the strong gamma-ray events are produced in disturbances (i.e shocks) propagating downstream the jet by upscattering external photons provided by the outflowing BLR. Arshakian et al., 2010, MNRAS, 401, 1231 Leon-Tavares et al. 2010, ApJ, 715, 355 Leon-Tavares et al. 2011, A&A submitted, arxiv:1102.1290
Noriyuki MatsunagaClassical Cepheids and episodic star formation in the Galactic Nuclear Bulge"We report the discovery of classical Cepheids in the Galactic Nuclear Bulge, the central ~200 pc region of our Galaxy. Classical Cepheids are important distance indicators as well as tracers to investigate galaxy structure and evolution. However, the known classical Cepheids in our Galaxy had been limited to a region of about 4 kpc radius around the Sun, due mainly to the strong interstellar extinction. We conducted a monitoring survey for the 0.33° by 0.5° area around the Galactic Centre in the JHKs bands between 2001 and 2008. All three of the classical Cepheids we discovered have pulsation periods near 20 days and an age of close to 25 Myr. In contrast, the absence of shorter-period Cepheids shows that the star formation rate was much lower between 30 and 70 Myr ago. Combined with evidence for a decrease in the star formation rate during the recent 0.1 Myr (Yusef-Zadeh et al. 2009, ApJ, 702, 178), this illustrates that star formation in this region occurred on a time scale of a few tens of Myr, consistent with the time scale suggested for gas inflow into the central region (Stark et al. 2004, ApJ, 614, L41; Hopkins & Quataert, 2010, MNRAS, 407, 1529). Such detailed star formation histories have never been obtained for central parts of this or other galaxies. Our discovery suggests a correlation between the gas inflow and star formation around the Galactic Centre, and opens a new path to study the process driving the evolution of pseudobulges."
Satoki Matsushita10 pc scale circumnuclear molecular gas imaging in nearby AGNsWe present the images and kinematics of circumnuclear molecular gas from 100 pc scale down to 10 pc scale in nearby AGNs using SMA and PdBI. We have observed several nearby galaxies that host AGNs, such as radio galaxy Centaurus A, Seyfert 2 galaxy M51, Seyfert 1 galaxy NGC 1097, and Seyfert 2 / starburst composit galaxy NGC 4945, in CO lines to see the molecular gas distribution, kinematics, and physical conditions at 10 - 100 pc scale. In 100 pc scale, most of the circumnuclear molecular gas shows regular rotating feature, and the physical conditions often shows dense and warm nature, suggesting the existence of active sources to make the gas dense and warm. In 10 pc scale, on the other hand, the molecular gas kinematics shows various characteristics, some shows very disturbed kinematics such as a jet-entrained feature, but some still shows regular rotation feature that the AGN unified model predicts. Our results will be a good precursor for the circumnuclear molecular gas studies in the coming ALMA era.
David MeierResolving Gas Chemistry at Arcsecond Scales in Nearby Spiral NucleiThe central few hundred parsecs of spiral nuclei represent unique environments to study the evolution of star formation and the interstellar medium (ISM), replete with feedback from active galactic nuclei and massive young clusters as well as dynamical shocks from nuclear bars/spirals. Pronounced modifications to the gas chemistry on giant molecular cloud scales betray the exist of such disturbing influences. Arcsecond resolution molecular line imaging provide insights into the detailed physical state of the the ISM in the presence of these dynamical influences. We discuss 30 pc resolution imaging of selected astrochemical species including HNCO, HC3N, N2H+ and C2H, across the nucleus of the nearby star forming spirals, IC 342, Maffei II and NGC 6946, obtained with the (E)VLA, OVRO/CARMA, and the PdB interferometers. Attention is focused on three new results. First, a multi-transition survey of HC3N in IC 342 and NGC 6946 to trace the physical conditions of the densest molecular component. The combination of morphology and line ratio data is used to reveal changing star formation efficiencies on 10 Myr timescales associated with aging starbursts. Second, the HCO+(1-0)/N2H+(1-0) line ratio is shown to be a new, powerful tracer of photo-dissociation region (PDR) gas in NGC 6946 and especially Maffei II. Finally, comparisons of the morphology and kinematics of four different shock tracers, SiO, HNCO, CH3OH and H2CO across each nuclear bar show it is possible to constrain the nature of the dynamical shock from the gas chemistry directly. These results will be compared with observations of the Galactic Center and put in the context of the future cm/mm wave interferometers, ALMA and the EVLA.
Mark MorrisGas Dynamics near Sgr A*Within a few arcseconds of SgrA*, there is a confluence of multiple streams of ionized gas, leading to a network of shocks, and to the likelihood of occasional enhanced accretion events. With the OSIRIS integral field spectrometer behind laser guide star adaptive optics at the Keck Observatory, we have produced an unprecedentedly detailed image of the gas motions near Sgr A*. The velocity trends will be presented and interpreted in terms of the implications for the accretion history of this region. collaborators: Tuan Do (UCI), Andrea Ghez (UCLA), Randall Campbell (WMKO)
Jihane MoultakaIces in the Galactic Center?Will come later
Stefanie MuehleMolecular gas in high-energy environmentsStar formation processes and their feedback play a crucial role in galaxy evolution, locally as well as at high redshifts. The question whether or not the initial mass function (IMF) is universal, i.e. the same in all kinds of environments, is still subject to intense debate. A number of recent observations have been interpreted as evidence for a top-heavy IMF, spanning a variety of objects, from the Galactic centre to circumnuclear starburst regions. Hydrodynamical simulations can reproduce such a top-heavy IMF if the raw material of star formation, the dense molecular gas, is assumed to have a kinetic temperature of ~100K. Such a molecular gas phase is not observed in the dense cores in the Galactic plane, but may be present in high-energy environments near AGN or in the cores of starburst galaxies. Unfortunately, the kinetic temperature of the molecular gas in many external galaxies is not well constrained, because many of the most common extragalactic tracer molecules suffer from a degeneracy between the kinetic temperature and the gas density in a non-LTE line ratio analysis. We demonstrate the diagnostic power of a selected set of para-formaldehyde lines as tracers of the kinetic temperature as well as the gas density in external galaxies using our non-LTE radiative transfer model. With this new observational tool, we have engaged in characterizing the properties of the dense molecular gas phase in a number of nearby starburst galaxies and near AGN. Our first results suggest the existence of a dense molecular gas phase in these high-energy environments that is significantly warmer than the dust and much warmer than dense molecular gas found in the Milky Way disk.
Cornelia MüllerZooming into Centaurus A - Subparsec scale imaging with TANAMIThe radio galaxy Centaurus A is the closest active galactic nucleus (AGN) at a distance of about 3.8Mpc. Due to its proximity, Cen A is a key target for studying extragalactic jets at the highest possible spatial resolution. Multi-epoch Very Long Baseline Interferometry (VLBI) observations of Cen A conducted in the framework of the TANAMI program (Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry) offer an exceptional opportunity to study this AGN on a linear scale as small as 15 milliparsec. TANAMI is a monitoring program observing a sample of jets south of -30° declination with the Australian Long Baseline Array (LBA) and associated telescopes in South Africa, Chile and Antarctica bimonthly at 8GHz and 22GHz. I will give a short overview of the TANAMI program and will focus on the first results of the ongoing analysis of Cen A. With the first epoch TANAMI dual-frequency images at an angular resolution of about (0.7x0.4)mas we can construct the best resolved spectral index map of the sub-parsec scale jet-counterjet system of Cen~A (Müller et al. 2011). We can identify multiple possible sites as the origin of gamma-ray emission recently detected by the Fermi Large Area Telescope. Investigating the gamma-ray/radio connection in Cen~A is crucial for our understanding of the formation and broadband emission mechanism of extragalactic jets.
Bradley PetersonSupermassive Black Holes and Their Relationships with Their Host GalaxiesThe masses of the supermassive black holes at the centers of galaxies have been measured by direct methods (stellar dynamics, gas dynamics, and reverberation mapping) for nearly 100 galaxies. These define empirical relationships between the black hole mass and host-galaxy properties such as the bulge stellar velocity dispersion and the bulge luminosity. As the database improves in both quality and quantity, some of these relationships appear to become more complicated: host galaxy properties have some differences based on black hole mass and, in the case of galaxies with active nuclei, the specific type of active nucleus (e.g., narrow-line Seyfert 1 galaxies appear to be in different hosts than other active galaxies). I will discuss the state of black hole mass measurement by both direct and indirect methods and the current state of the correlations between black hole masses and activity and host galaxies properties.
Jesus-Martin Pintado
Oliver PorthSignatures of synchrotron radiation from the relativistic jet base"We show the results of large scale axisymmetric simulations of two-component jet acceleration in special relativistic magnetohydrodynamics. Within one parsec from the accretion disk, the component dominated by Poynting flux accelerates to relativistic velocities Γ ∼ 8 but is still far from equipartition. In the near-stationary end-state, we solve the polarized Synchrotron radiation transport incorporating self-absorption and (internal) Faraday rotation. With mock-observations of the parsec scale jet base in radio and sub-mm wavelength we obtain observational signatures of the model. These comprise radio maps, spectra, polarization structure (revealing spin direction), frequency dependent depolarization, core shift and Faraday rotation measure. We also specify the detectability of such features depending on the available resolution, predicting the discovery of rotation measure gradients with the advance of space-VLBI and global mm-VLBI featuring resolutions of 100 Schwarzschild radii. The presented work represents a near complete toolbox to test the present diagnostics used in radio observations of AGN cores. "
Jörg-Uwe PottHigh-resolution infrared observations of active galactic nucleiInterferometric resolution at IR wavelengths offers for the first time the possibility to zoom into the nuclei of galaxies beyond the circumnuclear stellar structures and spatially resolve gas and dust in the innermost regions (0.05-5pc), dominated by the central black hole. Ultimate goal is to reveal new aspects of AGN feeding, and interaction with its host galaxy. After first successes of resolving AGN with infrared interferometry (VLTI, Keck-IF), the second generation of high-resolution interferometric imagers behind 8m class telescopes is currently being built. First, I will present recent VLTI and Keck-I results on NGC 4151 as pathfinder. In the second part, the many MPIA activities will be summarized, which focus on providing extended capabilities for VLTI-MIDI and -MATISSE, LBT-LINC-NIRVANA and Keck-ASTRA to study a larger sample of AGN in greater detail.
Almudena PrietoThe central parsecs of active galactic nuclei across the electromagnetic spectrum"Currently available subarcsec resolution information in the near to mid IR for the nearest, most well known, AGN have allowed us to construct parsecs-scale spectral energy distribution of the core of these galaxies from the UV to the radio-cm range. These genuine AGN-core SEDs are characterised by two major features: a narrow IR bump with the maximum in the 2 -10 μm range, and an increasing X-ray spectrum with frequency in the 1 to  200 keV range. These dominant features are common to type 1 and 2 AGNs alike. It is found however that the shape of these SEDs and inferred bolometric luminosity are largely departing from those derived from large aperture data. In particular, AGN luminosities can be overestimated by up to two orders of magnitude if relying on IR satellite data. Over the nine orders of frequency covered by these SEDs, the derived energy balance results in >~ 70% of the total energy output in these objects being released in the IR bump, the remaining power being mostly produced above 20 keV."
Cristina Ramos AlmeidaTesting the Unification Model for AGN in the Infrared: are the obscuring tori of Type 1 and 2 Seyferts different?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.
Nadeen SabhaThe Galactic Center in Mid-InfraredTBD
Tuomas SavolainenParsec-scale jet properties and gamma-ray emission in the MOJAVE sample of blazarsThe MOJAVE program (Monitoring of Jets in AGN with VLBA Experiments) is one of the most extensive VLBA monitoring programs aimed at studying the long-term evolution of the parsec-scale radio jets in blazars. The current monitoring list has about 300 sources, including both a complete radio flux density limited sub-sample, as well as a gamma-ray selected sub-sample based on the First Fermi-LAT catalog. Since MOJAVE sources are selected by their relativistically beamed jet emission, they form an excellent sample for investigating statistical correlations between the gamma-ray emission and the parsec-scale jet properties like compactness, apparent jet speed, Doppler factor, core polarization, and jet opening angle. We summarize the recent results from these studies, as well as discuss radio and gamma-ray flux-flux correlation, and the dependence of the gamma-ray-to-radio flux ratio on the jet properties.
Julia ScharwaechterCircum-nuclear molecular hydrogen emission in nearby Seyfert galaxiesMolecular hydrogen emission is a prominent feature in the near-infrared spectra of many AGN. The H_2 lines provide insights into excitation mechanisms and can be used as kinematic tracers. I will discuss examples of molecular hydrogen emission in the circum-nuclear regions of nearby AGN based on high-angular-resolution observations with NIFS and CRIRES.
Rainer SchoedelNew constraints on the infrared emission of Sagittarius A*The massive black hole at the center of the Milky Way, Sagittarius A* (SgrA*) is, in relative terms, the weakest accreting black hole accessible to observations. It is therefore of fundamental importance for theoretical models of radiatively inefficient accretion. Unfortunately, our knowledge of the mean SED of Sgr A* is very limited due to numerous observational difficulties. Current models rely almost exclusively on cm to mm mean flux measurements and only on upper limits at infrared to X-ray wavelengths. Here, we present a new analysis of existing imaging data of the Galactic center (GC) at 2.2 to 8.6 microns. Among other, we present the currently most sensitive GC images at 3.8, 4.8, and 8.6 microns. No counterpart of Sgr A* is detected at 8.6 microns. At this wavelength, Sgr A* is located right on top of a dust ridge, which considerably complicates the search for a potential point-source. Based on the available data, it is argued that Sgr A* cannot be detected in the MIR, not even during flares, with currently available instruments. In the M, L, and K-bands Sgr A* is detected at all times. We measure the time-averaged mean fluxes of Sgr A* at these wavelengths and show that these new values provide significant constraints on the parameters of theoretical models.
Semir SmajicUnveiling NGC 7172I will present the results of near-infrared (NIR) H+K ESO-SINFONI integral field spectroscopy (IFS) of the Seyfert 2 galaxy NGC 7172. The aim is to investigate the central 800pc, concentrating on excitation conditions, morphology and stellar content. The NIR is less influenced by dust extinction than optical light and it is sensitive to mass-dominating stellar populations. I will present emission and absorption line measurements in the central 800pc of NGC 7172. The detection of [SiVI] and broad Pa alpha and Br gamma components are clear signs of an accreting super-massive black hole (SMBH) which hides behind the prominent dustlane. Hot temperatures of about 1400K show evidence of a dusty torus in the nuclear region. Narrow components of Pa alpha and Br gamma allow for an extinction measurement. The molecular hydrogen lines, hydrogen recombination lines and [FeII] point out that the excitation of these lines is caused by an AGN. The central region of the galaxy disk is predominantly inhabited by gas, dust and an old K type giant stellar population. The gaseous, molecular and stellar velocity maps show a related structure and similar velocities. We find evidence for nuclear activity located behind the prominent dustlane crossing the central region of the galaxy. The nucleus of NGC 7172 is a Seyfert 1 nucleus either surrounded or hidden by a molecular dust torus. Our observation aids the unified model scheme in its basic proposition. However, an evolutionary scenario cannot be ruled out by our observation.
Jonathan SternThe continuum and emission line properties of low luminosity type-1 AGN"We explore the spectral energy distributions (SED) and emission line properties of low luminosity type-1 AGN, as a function of the broad H-alpha luminosity (L_bHa), optical slope, and broad Ha width (FWHM). The analysis is performed on a new sample of type-1 AGN, selected from the SDSS galaxy and quasar catalogs according to the presence of broad Ha emission. We measure the luminosity and profile of the broad Ha feature, along with the narrow line luminosities, by carefully decomposing the broad profile from adjacent narrow lines. The result of this process is 3,824 objects with 7e39 < L_bHa < 1e44 erg/s and 1,000 < FWHM < 25,000 km/s, supplemented by UV, NIR and X-ray data from the GALEX, 2MASS and ROSAT surveys. We present the mean SED of AGN in L_bHa-bins. These mean SED are consistent with the mean SED of luminous quasars scaled by L_bHa, plus the mean SED of inactive SDSS galaxies with the same redshift distribution. To explore the range of SED at a given L_bHa, we further divide each luminosity bin to sub-bins based either on optical slope or on FWHM. These sub-bins demonstrate the possible effect of Eddington ratio, black hole mass and reddening on the distribution of SED forms and spectral features. The results imply that the optically thick accretion disk mechanism persists at low AGN luminosities. Also, we find significant trends in: 1. the narrow line to broad line luminosity ratio, with luminosity; 2. the narrow line ratios (position in the BPT diagrams), with AGN attributes. These results connect the properties of the gas in the central kiloparsec with the properties of the AGN."
Ladislav SubrDynamical evolution of the young stellar disc in the Galactic CentreI will present results of a recent numerical and semi-analytical study of the evolution of the young stellar disc in the GC under the influence of a massive molecular torus (CND). I will show that this massive perturber very likely has a considerable impact on the evolution of the stellar orbits. In particular, it forces a differential precession that leads to warping (or even destruction) of the initial disc-like structure. I will discuss under which circumstances the inner part of the disc may survive the tidal forces of the CND due to the gravitational coupling of the stellar orbits.
Alexander TchekhovskoyGeneral Relativistic Modeling of Magnetized Jets from Black HolesRecent advances in magnetohydrodynamic modeling of jets offer unprecedented insights into the inner workings of accreting black holes that power the jets in active galactic nuclei (AGN). I will present the results of recent studies that determine spin-dependence of jet power and discuss the implications for AGN radio loud/quiet dichotomy and recent observations of high jet power in a number of AGN.
Konrad TristramThe complexity of parsec-scaled dusty tori in AGNA torus of molecular gas and dust is one of the key components of unified schemes of AGN. It provides the material for accretion onto the supermassive black hole and is held responsible for the orientation-dependent obscuration of the central engine. The AGN heated dust distributions turned out to be very compact with sizes on scales of about a parsec (i.e. less than a few tens of mas). Thus only infrared interferometry currently provides the necessary angular resolution for their direct study. Interferometric observations of several nearby AGN have now shown that both the hot inner rim as well as the warm body of the torus scale with the square root of the luminosity. We find the warm dust in the body of the torus to be located at about 30 times larger radii than the inner hot rim. The large scatter about the size-luminosity relation hints at significant differences between the tori in the individual galaxies, questioning the current picture of the same dusty doughnut in all AGN. For two galaxies, extensive new interferometric data sets were obtained: In the Circinus galaxy, the closest Seyfert 2 galaxy, the nucleus is interferometrically well resolved. This allows for a precise determination of the properties of the individual dust components and the profile of the radial dust distribution. The radio loud quasar 3C273, on the other hand, seems to be resolved only slightly, pointing at an either very compact dust distribution or at a significant contribution of synchrotron radiation from the jet to its mid-infrared emission.
Ayse Ulubay-SiddikiOn the Possibility of a Warped Disk Origin of the Inclined Stellar Disks at the Galactic CenterThe Galactic Center (GC) hosts a population of young stars some of which seem to form a system of mutually inclined warped disks. While the presence of young stars in the close vicinity of the massive black hole is already problematic, their orbital configuration makes the situation even more bizarre. We present a possible warped disk origin scenario for these stars, which assumes an initially flat accretion disk becoming warped due to Pringle instability, or Bardeen-Petterson effect. By working out the critical radii and the time scales involved, we demonstrate the plausibility of star formation taking place after disk warping. We construct time evolution models of warped disks for parameters relevant to the GC environment considering the disk’s self-gravity, and the torques exerted by the surrounding old star cluster. Our simulations suggest that: i) when the disk-to-black hole mass ratio M_d/M_bh ~ 0.001, the disk precesses with its integrity maintained in both the purely self-gravitating model, and in the model where the star cluster torques are taken into account. ii) When M_d/M_bh~ 0.01, the disk breaks into pieces which precess as independent disks in the case of the purely self-gravitating disk, and becomes disrupted due to differential precession in the presence of the star cluster. iii) For high enough masses of order M_d/M_bh 0.1, the evolution of the disk is mainly governed by self-gravity, and despite being broken, the disks evolve without being disrupted. A comparison of our models with the observations show that low mass, self-gravity-only models agree better with the observations.
Petri VaisanenCentral regions of LIRGs: super star clusters, SNe, and ringsI will report on initial results of an on-going survey using NIR adaptive optics imaging of several dozen LIRGs. The targets are at various stages of merging, interaction, or isolation, and lie at distances between 40 to 150 Mpc. We have detected highly obscured core-collapse SNe in the central kpc, and determined characteristics of hundreds of super star clusters in and around the core region. In particular, we have derived the first extra-galactic NIR luminosity functions of SSCs. Finally, I will report on a study of a nuclear PAH ring outside of a star-forming ring in a strong merger LIRG.
Monica Valencia-S.Looking at the nucleus of IRAS 01072+4954 with Integral-Field Spectroscopy: A powerful engine hidden by starbursts.IRAS 01072+4954 is a Starbust/Seyfert composite galaxy, an enigmatic object that combines strong star formation with an active galactic nucleus (AGN). Its X-ray emission is typical of Seyfert 1 galaxies (Lx~10^42 erg/s with very little extinction) and it is unclear why Seyfert features (like broad lines) are not present at visible/infrared wavelengths. We performed high-resolution near-infrared integral-field spectroscopic observations of this galaxy in order to dissect its central region. We find very little cold dust obscuration (Av ~ 3.0) and evidences of a non-thermal source and/or hot dust in the central ~300pc. From stellar kinematics and photometric scaling-correlation we estimate the mass of the SMBH to be ~10^6 solar masses, which places it at the lower end of the BH mass range for AGNs with an Eddington ratio indicative of relatively high accretion efficiency. On the other hand, compact clumps of star forming regions are detected in a ring-like structure of ~170pc radius around the center of the galaxy. The presence of starburst regions is also indicated in the soft X-ray band. The relation between the radio and the infrared emission of IRAS 01072+4954 follows the expected correlation for starburst galaxies, although the star formation rate (SFR =0.3-5.0 solar masses per year) is very low.
Sylvain VeilleuxThe Latest Results from QUESTThe main results from QUEST (Quasar-ULIRG Evolution Study) will be described with an emphasis on the recent scientific breakthroughs on the issue of quasar feedback.
Q.Daniel WangX-raying the circum-nuclear regions of nearby galaxies at high spatial and spectral resolutions"I will review recent X-ray studies of the circum-nuclear regions of nearby ""normal"" galaxies, including M31, M51, M82, and M83. These regions, though showing no or very weak current AGN activities, are all associated with enhanced diffuse X-ray line emission. Surprisingly, X-ray grating observations show spectroscopic properties of the emission (e.g., large forbidden to resonance line ratios of He-like ion Kalpha triples) that are inconsistent with a pure collisionally excited plasma origin. Spatially resolved spectroscopy and comparison with various imaging data are being carried out. The results can have important implications for understanding physical processes in the circum-nuclear regions, including the charge exchange of hot plasma with cold gas and/or the photo-ionization by recent AGN activities. "
Norbert WexStudying the Galactic Centre using Pulsars: II. Probing the spacetime of Sgr A*The discovery of a pulsar in a close orbit around Sgr A* would open tremendous possibilities for a detailed investigation of the spacetime of the super-massive black hole in the center of our Galaxy. A pulsar in a few months orbit around Sgr A* would allow the determination of the mass, the spin (magnitude and orientation), and the quadrupole moment of the black hole with high precision, consequently providing a novel test of the cosmic censorship conjecture and the no-hair theorem for Kerr black holes.
Gunther WitzelTime series of near-infrared flux densities of Sagittarius A*"The NIR counterpart to SgrA* is extremely variable with short periods of increased emission. These ""flares"" occur four to six times a day and last typically for about 100 minutes. The origin of the variablity is subject to a vivid discussion within the community. While synchrotron and synchrotron self-compton processes are suited to explain the general time behavior and wavelength dependency, the contribution of relativistic effects like lensing or boosting and - as a tracer of these - quasi-periodic time behavior are still under debate. In my talk I want to present a concise analysis of the VLT data that could be obtained during the last 8 years."
Farhad Yusef-ZadehThe Origin of Circumnuclear and Megamaser Disks in the Nuclei of GalaxiesI will discuss the origin of one or two disks of massive stars found within 0.5 pc of Sgr A* and then apply it to megamaser disks in the nuclei of Seyfert galaxies. The disk formation is interpreted in terms of the partial accretion of extended Galactic center clouds that temporarily pass through the central region of the Galaxies. I will also present signatures of young massive star forming regions in the 2-5pc molecular ring orbiting Sgr A*.
Mohammad ZamaninasabThe quasar 3C454.3: Results of 1995-2011 VLBI and single dish monitoringTBD
Jens ZutherMERLIN observations of Broad Absorption Line QSOs with Narrow Line Seyfert 1 characteristics: Signatures of youth?