Document Type

Article

Publication Date

2-3-2020

Publication Title

Monthly Notices of the Royal Astronomical Society

Publisher

Oxford University Press

Volume

493

Issue

1

First page number:

437

Last page number:

445

Abstract

We study how different opacity–temperature scalings affect the dynamical evolution of irradiated gas clouds using time-dependent radiation-hydrodynamics simulations. When clouds are optically thick, the bright side heats up and expands, accelerating the cloud via the rocket effect. Clouds that become more optically thick as they heat accelerate ∼35 per cent faster than clouds that become optically thin. An enhancement of ∼85 per cent in the acceleration can be achieved by having a broken power-law opacity profile, which allows the evaporating gas driving the cloud to become optically thin and not attenuate the driving radiation flux. We find that up to ∼2 per cent of incident radiation is re-emitted by accelerating clouds, which we estimate as the contribution of a single accelerating cloud to an emission or absorption line. Re-emission is suppressed by ‘bumps’ in the opacity–temperature relation since these decrease the opacity of the hot, evaporating gas, primarily responsible for the reradiation. If clouds are optically thin, they heat nearly uniformly, expand and form shocks. This triggers the Richtmyer–Meshkov instability, leading to cloud disruption and dissipation on thermal time-scales. Our work shows that, for some parameters, the rocket effect due to radiation-ablated matter leaving the back of the cloud is important for cloud acceleration. We suggest that this rocket effect can be at work in active galactic nuclei outflows.

Keywords

Hydrodynamics; Radiation: dynamics; Stars: massive; Stars: winds; Outflows; Quasars: general; X-rays: galaxies

Disciplines

Stars, Interstellar Medium and the Galaxy

File Format

pdf

File Size

1.885 KB

Language

English

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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