Nearby AGN and the LLAMA Project

Direct evidence for external accretion in IC 5267: dust lanes and molecular gas in an oblique orbit. Adapted from Davies et al. 2014.

The Big Picture

The existence of relations between supermassive black holes and the stellar velocity dispersion, luminosity, mass, and light concentration of their host galaxies has been a major discovery of the last decade. These correlations imply that black holes and their host galaxies co-evolve, and have resulted in a widespread observational and theoretical effort to understand their physical origin. Understanding this co-evolution has become one of the most important challenges of modern astrophysics. A plausible mechanism capable of linking the innermost nuclear region to the whole galaxy is the feedback outward from an accreting black hole (an active galactic nucleus, or AGN) to the host galaxy. Equally important is the flow of gas inward from the host galaxy to the central regions where it can trigger star formation and eventually fuel a massive black hole. It is on these aspects that our work focusses.

AGN in the Local Universe

Many studies of AGN, particularly those concerned with understanding the co-evolution of black holes and their host galaxies through cosmic time, rely on observations of quasars. The reason is simply that these are the most luminous of such objects and can be studied at all redshifts. While they form an important component of the AGN population, the number density of lower luminosity AGN is orders of magnitude greater. This is particularly true in the local universe because of the effects of downsizing, which means that at low redshift black hole growth occurs primarily in Seyferts, with black hole masses < 108 Msun and moderate luminosities. This has important implications. Although most quasar activity may result from mergers of gas rich galaxies, Seyfert nuclei typically reside in disk galaxies and are likely to be fuelled via secular processes associated with disk evolution.

Gas Inflows and Outflows and Starbursts in Seyfert Galaxies

It is understood how spirals and bars in disk galaxies can drive gas in to the circumnuclear regions on kpc scales. But it is still far from clear under what conditions the gas can be transported inward to the nuclear region and what happens to it once it gets there. By analysing detailed observations that make use of instruments we have designed and built in-house, our aim is to understand:

  • how does gas flow in from kpc scales to the central tens of parsecs?
  • how prevalent are outflows in AGN? When are they molecular and how do they connect or entrain the surrounding gas?
  • what are the properties of the starbursts it triggers there?
  • what is the impact of these starbursts on the flow of gas to smaller scales?
  • how is this all related to the molecular obscuring torus that can hide the central AGN?
  • are the AGN in mergers fed by similar or fundamentally different processes?

The LLAMA Project

The AGN phenomenon is likely short-lived. Statistical evidence, e.g. from the fraction of X-ray bright, optically normal galaxies (XBONGs), as well as hydrodynamical simulations indicate that a particular AGN phase may only last for as little as 105 years. It is therefore not surprising that little differences between the host galaxy properties of active and inactive galaxies are found when assessing e.g. the host galaxy morphology which will only change on dynamical times much larger than the AGN timescale. We have therefore set up a unique study to compare the nuclear inventory of AGNs and inactive galaxy in a comprehensive way. For this we first selected the twenty most luminous local AGNs based on the sensitive ultra hard X-ray all-sky survey provided by the Swift/BAT satellite. The rationale for this selection is to only select AGNs where coherent inflow mechanisms are required due to the large luminosity or mass accretion. We further require the galaxies to be local in order to resolve the nuclear region, in particular the nuclear stellar cluster on scales of 50-100 pc. And finally we employ the ultra hard X-ray band to be largely unimpeded by obscuration which can severely affect AGN selection based on optical properties. 

The so selected AGN sample is accompanied by a sample of inactive galaxies (where no ultra hard X-ray emission has been detected) that are matched in host galaxy properties to the active sample. This sample of 39 galaxies in total is currently being observed or observations are planned with VLT/X-SHOOTER, VLT/SINFONI, APEX as well as ALMA and HST.

Team and Collaborations

The following people are part of the core LLAMA team.

Ric Davies (MPE), Thaisa Storchi-Bergmann (UFGRS, Brazil), Leonard Burtscher (Leiden Observatory), Reinhard Genzel (MPE), Erin Hicks (University of Alaska, US), Mike Koss (Eureka Scientific, US), Ming-Yi Lin (ASIAA, Taiwan), Dieter Lutz (MPE), Witold Maciejewski (Astrophysics Research Institute, Liverpool, UK), Francisco Müller-Sánchez (University of Memphis, US), Gilles Orban de Xivry (Université de Liège), David Rosario (Durham University, UK) Rogemar A. Riffel (UFSM, Brazil), Rogério Riffel (UFGRS, Brazil), Marc Schartmann (MPE), Allan Schnorr-Müller (UFGRS, Brazil), Amiel Sternberg (Tel Aviv University, Israel), Taro Shimizu (MPE), Eckhard Sturm (MPE), Linda Tacconi (MPE), Sylvain Veilleux (University of Maryland, US), Turgay Caglar (Leiden Observatory)

Publications

Please have a look at our ADS Library for an up-to-date list of our main publications. These are either publications directly resulting from in-house projects or with other major contributions from this group.

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