Numerical Simulations of Turbulent Molecular Clouds Regulated by Radiation Feedback Forces II: Radiation-Gas Interactions and Outflows

TL;DR

This study uses numerical simulations to analyze how radiation feedback from young stars interacts with turbulent molecular clouds, driving outflows and influencing cloud destruction, with implications for galactic wind mechanisms.

Contribution

It extends previous work by modeling detailed radiation-gas interactions in turbulent clouds, highlighting the effects of surface density distribution on outflow velocities and momentum transfer.

Findings

Approximately 50% of radiation is absorbed by the cloud.

Outflow velocities reach nearly 10 times the initial escape speed.

The velocity distribution of outflows is broadened by surface density variations.

Abstract

Momentum deposition by radiation pressure from young, massive stars may help to destroy molecular clouds and unbind stellar clusters by driving large-scale outflows. We extend our previous numerical radiation hydrodynamic study of turbulent, star-forming clouds to analyze the detailed interaction between non-ionizing UV radiation and the cloud material. Our simulations trace the evolution of gas and star particles through self-gravitating collapse, star formation, and cloud destruction via radiation-driven outflows. These models are idealized in that we include only radiation feedback and adopt an isothermal equation of state. Turbulence creates a structure of dense filaments and large holes through which radiation escapes, such that only ~50% of the radiation is (cumulatively) absorbed by the end of star formation. The surface density distribution of gas by mass as seen by the central cluster is roughly lognormal with sigma_ln(Sigma) = 1.3-1.7, similar to the externally-projected surface density distribution. This allows low surface density regions to be driven outwards to nearly 10 times their initial escape speed v_esc. Although the velocity distribution of outflows is broadened by the lognormal surface density distribution, the overall efficiency of momentum injection to the gas cloud is reduced because much of the radiation escapes. The mean outflow velocity is approximately twice the escape speed from the initial cloud radius. Our results are also informative for understanding galactic-scale wind driving by radiation, in particular the relationship between velocity and surface density for individual outflow structures, and the resulting velocity and mass distributions arising from turbulent sources.