Shaping the structure of a GMC with radiation and winds

Abstract

ABSTRACT We study the effect of stellar feedback (photodissociation/ionization, radiation pressure, and winds) on the evolution of a Giant Molecular Cloud (GMC), by means of a 3D radiative transfer, hydrosimulation implementing a complex chemical network featuring H2 formation and destruction. We track the formation of individual stars with mass $M\gt 1\, {\rm M}_{\odot }$ with a stochastic recipe. Each star emits radiation according to its spectrum, sampled with 10 photon bins from near-infrared to extreme ultraviolet bands; winds are implemented by energy injection in the neighbouring cells. We run a simulation of a GMC with mass $M=10^5\, {\rm M}_{\odot }$, following the evolution of different gas phases. Thanks to the simultaneous inclusion of different stellar feedback mechanisms, we identify two stages in the cloud evolution: (1) radiation and winds carve ionized, low-density bubbles around massive stars, while FUV radiation dissociates most H2 in the cloud, apart from dense, self-shielded clumps; (2) rapid star formation (SFR$\simeq 0.1\, {\rm M}_{\odot }\, {\rm yr}^{-1}$) consumes molecular gas in the dense clumps, so that UV radiation escapes and ionizes the remaining $\mathrm{H\,{\small I}}$ gas in the GMC. H2 is exhausted in 1.6 Myr, yielding a final star formation efficiency of 36 per cent. The average intensity of FUV and ionizing fields increases almost steadily with time; by the end of the simulation (t = 2.5 Myr) we find 〈G0〉 ≃ 103 (in Habing units), and a ionization parameter 〈Uion〉 ≃ 102, respectively. The ionization field has also a more patchy distribution than the FUV one within the GMC. Throughout the evolution, the escape fraction of ionizing photons from the cloud is fion, esc ≲ 0.03.