We report on the first phase of our study of cloud irradiation. We study irradiation by means of numerical, two-dimensional time-dependent radiation-hydrodynamic simulations of a cloud irradiated by a strong radiation. We adopt a very simple treatmen
t of the opacity, neglect photoionization and gravity, and instead focus on assessing the role of the type and magnitude of the opacity on the cloud evolution. Our main result is that even relatively dense clouds that are radiatively heated (i.e., with significant absorption opacity) do not move as a whole instead they undergo a very rapid and major evolution in its shape, size and physical properties. In particular, the cloud and its remnants become optical thin within less than one sound crossing time and before they can travel over a significant distance (a distance of a few radii of the initial cloud). We also found that a cloud can be accelerated as a whole under quite extreme conditions, e.g., the opacity must be dominated by scattering. However, the acceleration due to the radiation force is relatively small and unless the cloud is optically thin the cloud quickly changes its size and shape. We discuss implications for the modelling and interpetation broad line regions of active galactic nuclei.
We review the main results from axisymmetric, time-dependent hydrodynamical simulations of radiation driven disk winds in AGN. We illustrate the capability of such simulations to provide useful insights into the three domains of observational astrono
my: spectroscopy, time-variability, and imaging. Specifically, the synthetic line profiles predicted by the simulations resemble the broad absorption lines observed in quasars. The intrinsically time dependent nature of radiation driven disk winds that have been predicted by the simulations can be supported by a growing number of the observed dramatic variability in the UV absorption lines. And finally, the intensity maps predicted by the simulations give physical and geometrical justification to the phenomenologically deduced fact that a proper interpretation of the observed line absorption requires the wind covering factor to be considered as being partial, inhomogeneous, and velocity dependent.
We present the results of hydrodynamical simulations of the disk photosphere irradiated by strong X-rays produced in the inner most part of the disk. As expected, the irradiation heats the photosphere and drives a thermal wind. To apply our results t
o the well-studied X-ray transient source GRO J1655-40, we adopted the observed mass of its black hole, and the observed properties of its X-ray radiation. To compare the results with the observations, we also computed transmitted X-ray spectra based on the wind solution. Our main finding is: the density of the fast moving part of the wind is more than one order of magnitude lower than that inferred from the observations. Consequently, the model fails to predict spectra with line absorption as strong and as blueshifted as those observed. However, despite the thermal wind being weak and Compton thin, the ratio between the mass-loss rate and the mass accretion rate is about seven. This high ratio is insensitive to the accretion luminosity, in the limit of lower luminosities. Most of the mass is lost from the disk between 0.07 and 0.2 of the Compton radius. We discovered that beyond this range the wind solution is self-similar. In particular, soon after it leaves the disk, the wind flows at a constant angle with respect to the disk. Overall, the thermal winds generated in our comprehensive simulations do not match the wind spectra observed in GRO J1655-40. This supports the conclusion of Miller et al. and Kallman et al. that the wind in GRO J1655-40, and possibly other X-ray transients, may be driven by magnetic processes. This in turn implies that the disk wind carries even more material than our simulations predict and as such has a very significant impact on the accretion disk structure and dynamics.
We summarize the results from numerical simulations of mass outflows from AGN. We focus on simulations of outflows driven by radiation from large-scale inflows. We discuss the properties of these outflows in the context of the so-called AGN feedback
problem. Our main conclusion is that this type of outflows are efficient in removing matter but inefficient in removing energy.
We present a brief summary of the main results from our multi-dimensional, time-dependent simulations of gas dynamics in AGN. We focus on two types of outflows powered by radiation emitted from the AGN: disk winds and winds driven from large-scale in
flows. We show spectra predicted by the simulations and discuss their relevance to observations of broad- and narrow-line regions of the AGN. We finish with a few remarks on whether these outflows can have a significant impact on their environment and host galaxy.
We study the axisymmetric, time-dependent hydrodynamics of rotating flows that are under the influence of supermassive black hole gravity and radiation from an accretion disk surrounding the black hole. This work is an extension of the earlier work p
resented by Proga, where nonrotating flows were studied. Here, we consider effects of rotation, a position-dependent radiation temperature, density at large radii, and uniform X-ray background radiation. As in the non-rotating case, the rotating flow settles into a configuration with two components (1) an equatorial inflow and (2) a bipolar inflow/outflow with the outflow leaving the system along the pole. However, with rotation the flow does not always reach a steady state. In addition, rotation reduces the outflow collimation and the outward flux of mass and kinetic energy. Moreover rotation increases the outward flux of the thermal energy and can lead to fragmentation and time-variability of the outflow. We also show that a position-dependent radiation temperature can significantly change the flow solution. In particular, the inflow in the equatorial region can be replaced by a thermally driven outflow. Generally, as it have been discussed and shown in the past, we find that self-consistently determined preheating/cooling from the quasar radiation can significantly reduce the rate at which the central BH is fed with matter. However, our results emphasize also a little appreciated feature. Namely, quasar radiation drives a non-spherical, multi-temperature and very dynamic flow. These effects become dominant for luminosities in excess of 0.01 of the Eddington luminosity.
