Free-free absorption effects on Eddington luminosity

In standard treatments the Eddington luminosity is calculated by assuming that the electron-photon cross section is well described by the Thomson cross section which is gray (frequency independent). Here we discuss some consequence of the introduction of free-free opacity in the Eddington luminosity computation: in particular, due to the dependence of free-free emission on the square of the gas density, it follows that the associated absorption cross section increases linearly with the gas density, so that in high density environments Eddington luminosity is correspondingly reduced. We present a summary of an ongoing exploration of the parameter space of the problem, and we conclude that Eddington luminosity in high density environments can be lowered by a factor of ten or more, making it considerably easier for black holes to accelerate and eject ambient gas.Comment: 4 pages, to appear in "Plasmas in the Laboratory and in the Universe: new insights and new challenges", G. Bertin, D. Farina, R. Pozzoli eds., AIP Conference Proceeding

On the motion and radiation of charged particles in strong electromagnetic waves. 1 - Motion in plane and spherical waves

Motion and radiation of charged particles in strong electromagnetic waves in plane and spherical wave

Radiative Transfer and Radiative driving of Outflows in AGN and Starbursts

To facilitate the study of black hole fueling, star formation, and feedback in galaxies, we outline a method for treating the radial forces on interstellar gas due to absorption of photons by dust grains. The method gives the correct behavior in all of the relevant limits (dominated by the central point source; dominated by the distributed isotropic source; optically thin; optically thick to UV/optical; optically thick to IR) and reasonably interpolates between the limits when necessary. The method is explicitly energy conserving so that UV/optical photons that are absorbed are not lost, but are rather redistributed to the IR where they may scatter out of the galaxy. We implement the radiative transfer algorithm in a two-dimensional hydrodynamical code designed to study feedback processes in the context of early-type galaxies. We find that the dynamics and final state of simulations are measurably but only moderately affected by radiative forces on dust, even when assumptions about the dust-to-gas ratio are varied from zero to a value appropriate for the Milky Way. In simulations with high gas densities designed to mimic ULIRGs with a star formation rate of several hundred solar masses per year, dust makes a more substantial contribution to the dynamics and outcome of the simulation. We find that, despite the large opacity of dust to UV radiation, the momentum input to the flow from radiation very rarely exceeds L/c due to two factors: the low opacity of dust to the re-radiated IR and the tendency for dust to be destroyed by sputtering in hot gas environments. We also develop a simplification of our radiative transfer algorithm that respects the essential physics but is much easier to implement and requires a fraction of the computational cost.Comment: 25 pages, 17 figures, submitted to MNRA

Cosmological Shock Waves in the Large Scale Structure of the Universe: Non-gravitational Effects

Cosmological shock waves result from supersonic flow motions induced by hierarchical clustering of nonlinear structures in the universe. These shocks govern the nature of cosmic plasma through thermalization of gas and acceleration of nonthermal, cosmic-ray (CR) particles. We study the statistics and energetics of shocks formed in cosmological simulations of a concordance $\Lambda$CDM universe, with a special emphasis on the effects of non-gravitational processes such as radiative cooling, photoionization/heating, and galactic superwind feedbacks. Adopting an improved model for gas thermalization and CR acceleration efficiencies based on nonlinear diffusive shock acceleration calculations, we then estimate the gas thermal energy and the CR energy dissipated at shocks through the history of the universe. Since shocks can serve as sites for generation of vorticity, we also examine the vorticity that should have been generated mostly at curved shocks in cosmological simulations. We find that the dynamics and energetics of shocks are governed primarily by the gravity of matter, so other non-gravitational processes do not affect significantly the global energy dissipation and vorticity generation at cosmological shocks. Our results reinforce scenarios in which the intracluster medium and warm-hot intergalactic medium contain energetically significant populations of nonthermal particles and turbulent flow motions.Comment: Submitted to ApJ. Pdf with full resolution figures can be downloaded from http://canopus.cnu.ac.kr/ryu/krco.pd

The Effect of the AGN Feedback on the Interstellar Medium of Early-Type Galaxies: 2D Hydrodynamical Simulations of the Low-Rotation Case

We present 2D hydrodynamical simulations for the evolution of early-type galaxies containing central massive black holes (MBHs), starting at age 2 Gyr. The code contains accurate and physically consistent radiative and mechanical AGN wind feedback, with parsec-scale central resolution. Mass input comes from stellar evolution; energy input includes Type Ia and II supernova and stellar heating; star-formation is included. Realistic, axisymmetric dynamical models for the galaxies are built solving the Jeans' equations. The lowest mass models (Mstar = 8 10^{10}Msun) develop global outflows sustained by SNIa's heating, ending with a significantly lower amount of hot gas and new stars. In more massive models, nuclear outbursts last to the present epoch, with large and frequent fluctuations in nuclear emission and from the gas (Lx). Each burst last ~ 10^{7.5} yr, during which (for r < 2-3 kpc) cold, inflowing, and hot, outflowing gas phases coexist. The Lx-T relation for the gas matches that of local galaxies. AGN activity causes positive feedback for star formation. Roughly half of the total mass loss is recycled into new stars (DeltaMstar), just ~ 3% of it is accreted on the MBH, the remainder being ejected from the galaxy. The ratio between the mass of gas expelled to that in to new stars, the load factor, is ~0.6. Rounder galaxies shapes lead to larger final MBH masses, DeltaMstar, and Lx. Almost all the time is spent at very low nuclear luminosities, yet one quarter of the total energy is emitted at an Eddington ratio > 0.1. The duty-cycle of AGN activity approximates 4% (Abridged).Comment: 26 pages, 15 figure, submitted to ApJ. Comments welcom

Cooling flows and quasars: different aspects of the same phenomenon? I. Concepts

We present a new class of solutions for the gas flows in elliptical galaxies containing massive central black holes (BH). Modified King model galaxies are assumed. Two source terms operate: mass loss from evolving stars, and a secularly declining heating by SNIa. Relevant atomic physical processes are modeled in detail. Like the previous models investigated by Ciotti et al. (1991), these new models first evolve through three consecutive evolutionary stages: wind, outflow, and inflow. At this point the presence of the BH alters dramatically the subsequent evolution, because the energy emitted by the BH can heat the surrounding gas to above virial temperatures, causing the formation of a hot expanding central bubble. Short and strong nuclear bursts of radiation are followed by longer periods during which the X-ray galaxy emission comes from the coronal gas (Lx). The range and approximate distribution spanned by Lx are found to be in accordance with observations of X-ray early type galaxies. Moreover, although high accretion rates occur during bursting phases when the central BH has a luminosity characteristic of QSOs, the total mass accreted is very small when compared to that predicted by stationary cooling-flow solutions and computed masses are in accord with putative BH nuclear masses. In the bursting phases Lx is low and the surface brightness profile is very low compared to pre-burst or to cooling flow models. We propose that these new models, while solving some long-standing problems of the cooling flow scenario, can provide a unified description of QSO-like objects and X-ray emitting elliptical galaxies, these being the same objects observed at two different evolutionary phases.Comment: 10 pages, ApJ LaTeX, plus 5 .eps figures and TeX-macro aasms4.sty - revised version - in press on ApJ Letter