Quasar-driven winds on the scale of the host galaxy are often invoked to explain why star formation appears to be suppressed in massive galaxies. However, the physical mechanism via which such large-scale outflows are accelerated is still unclear. I will demonstrate that the nature of the wind acceleration mechanism can be constrained from the ratios of emission lines that originate from the cool (T~10^4K) gas illuminated by the AGN. I will show that observed line ratios in UV-selected quasars suggest that radiation pressure dominates the acceleration in these objects at all distance scales, and that this result is apparently in conflict with the large momentum outflow rates measured in quasar winds.
C.-A. Faucher-Giguere – Physics, Observational Signatures, and Consequences of AGN-Driven Galactic Winds
My presentation will focus on the theory of galaxy-scale outflows powered by accretion disk winds in luminous AGN. I will review the basic theory of wind-blown bubbles, including the issue of momentum vs. energy conservation. I will then discuss predictions for the different ways in which galaxy-scale AGN-driven blast waves can be observed (including in narrow line region emission and absorption, molecular gas, and non-thermal emission from relativistic particles accelerated at wind shocks). Time-permitting, I will also show some results from galaxy evolution simulations aiming to understand the very uncertain effects of AGN outflows on galaxies. Specific questions that I would like to bring up for discussion include the origin of molecular gas in high-velocity outflows, the origin of momentum fluxes >> L_AGN/c inferred from outflow observations, and the effects of AGN outflows on star formation in galaxies.
S. Davis – Simulations of accretion flows with grey opacities
What role does UV opacity play in the structure and evolution of accretion disks? What can simulations tell us about how winds are launched by radiation and, in particular, how that launching feeds back on the disk structure? Given the limits of numerical simulations, how can we best design the simulations that address these issues? Do the outflows being launched at relatively small radii in accretion disk simulations connect with either the broad absorption line quasars or ultrafast outflows?
T. Kallman – Torus Evaporative Flows as the Origin of Warm Absorbers?
Warm absorbers appear to be a somewhat robust property of AGN with luminosities which are a significant fraction of the Eddington luminosity. Line widths are crudely consistent with virial motion at a distance comparable to the likely location of the obscuring torus. A torus origin for warm absorbers raises questions: 1) Can the ‘simplest’ driving mechanism, i.e. thermal evaporation, explain warm absorber observed properties? 2) Can warm absorbers help us to understand the nature of the torus itself, i.e. its dynamical support? 3) What might be the key observational and theoretical approaches to helping answer these questions?. In this talk I will briefly discuss dynamical simulations aimed at testing simple scenarios for warm absorber flows. I will show that there are promising results from such simulations, but also fundamental problems with observational comparisons. Some possible future avenues will be discussed.
D. Kazanas – AGN/XRB warm absorbers: a key to their broader phenomenology (Astro. Seminar)
An increasing number of observations have indicated the presence of blue shifted absorption features in the X-ray spectra of both AGN and accreting galactic X-ray binaries that span a large range in ionization parameter and velocity. These have been attributed and successfully modeled by accretion disk winds. Moreover, the dependence of their column density on their ionization parameter has allowed to determine the wind density profile along the observer’s LoS and hence the corresponding wind mass flux. This was found to be an increasing function of the distance from the X-ray source, with the corresponding mass flux much larger than that needed to produce, by accretion, the observed X-ray luminosity. This signifies that the disk accretion rate decreases with radius, much of is mass flux diverted into the wind. This decreasing accretion rate in the disk, then, makes it possible for its inner regions to revert to a hot, X-ray emitting ADAF state, while its cooler, BBB component to be emitted at larger radii, despite the fact that it is more luminous, in agreement with microlensing observations. It will be argued that an increase in the overall supply of matter to the black hole can under these assumptions reproduce much of the global spectral AGN/XRB phenomenology, in particular the AGN $\alpha_{OX}$ dependence on luminosity and their warm absorber properties.
J. Krolik – Outflows from TDEs
Tidal disruption events (TDEs) give a view of accretion onto supermassive black holes that is orthogonal in a number of ways with that given by AGN. Inflow is in a very different regime because the system is always in a transient state. The accretion rate onto the black hole continually changes, but can at its peak be super-Eddington. The accretion flow is in inflow equilibrium over only a limited range of radii and is incompletely circularized. Outflows are similarly contrasting. Far from the black hole, the dominant effect is the expulsion of the half of the stellar mass left unbound after the disruption, whose shocks against surrounding gas can be bright in radio-frequency synchrotron emission. Close to the black hole, collimated radiation, particularly when a jet is present, can drive a mildly-relativistic outflow most easily distinguishable by the character of its Fe Kalpha variability.
S. Kaspi – High-Velocity Outflows: A 15 years perspective
High-Velocity Outflows (HVOs) seen as absorption in X-ray spectra were first reported in 2002. Soon after the first reports other studies challenged the existence of these HVOs suggesting other interpretations to the data. After 15 years of studies we can try to assess the existence and the importance of HVOs: Are HVOs really exist or other interpretations can explain the data? Are HVOs a variable phenomenon and thus what is its real influence on the AGN environment? What are the evidences of HVOs in high-resolution spectra? What studies need to be done to shed more light on the phenomenon?
F. Tombesi – X-ray observations of UFOs and their implications for AGN feedback
Powerful winds driven by active galactic nuclei (AGN) are often invoked to play a fundamental role in the evolution of both supermassive black holes (SMBHs) and their host galaxies. Additional support for this “wind feedback mode” came from recent X-ray observation of ultrafast outflows (UFOs) in several AGNs, and the increasing evidence for their connection with galaxy-scale molecular winds, suggesting a direct link between the SMBH and the gas out of which stars form. Spectroscopic observations, especially in the UV and X-ray band, suggest that such disk winds may be common in local AGN and quasars. However, there are still several open questions that need to be discussed: what is the relation between UFOs and WAs in X-rays? And with AGN winds observed in other wavebands? What about AGN jets? Are UFOs energetic enough to drive AGN feedback? Are there evidences for AGN wind feedback in action? In this talk I will address some of these topics, and I will also show how future multi-wavelength campaigns will provide revolutionary improvements in this field.
J. Reeves – X-Ray Observations of Ultrafast Outflows
Ultra fast outflows were first discovered in 2003, from the presence of blue-shifted absorption lines from the X-ray spectra of quasars and AGN. The observational evidence for fast outflows will be reviewed, including their statistical occurrence and wider properties from observations with XMM-Newton and Suzaku. New data from large XMM-Newton and NuSTAR programs on the prototype fast outflow AGN, PDS 456 and PG 1211+143 will be shown, where the former shows a fast wide angle outflow and the latter shows highly variable absorption.
The evidence for soft X-ray absorption will also be discussed as well as the possible driving mechanisms of the winds.
Possible Open questions.
What is the statistical occurrence of the outflows. Is their still any doubt about their detection and origins?
How can we measure accurately the energetics of the winds and are they likely to be significant for feedback?
What is the evidence for the ultra fast outflows aside from at iron K?
What is the driving mechanism for the disk wind?
What is the occurrence of the winds amongst the higher luminosity (or higher redshift) QSOs. Will we need Athena to be able to address this?
K. Leighly – Understanding Broad Absorption Line Quasars
Despite decades of study, broad absorption line quasars are poorly understood. For example, we know that partial covering is important, but what is the physical nature of partial covering? Many of these questions stem from the fact that the spectra are very difficult to analyze, principally as a consequence of blending and problems constraining the continuum. I will present recent results addressing these questions.