Shaping the structure of a GMC with radiation and winds

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 H-2 formation and destruction. We track the formation of individual stars with mass M > 1 M-circle dot 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) M-circle dot, 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 H-2 in the cloud, apart from dense, self-shielded clumps; (2) rapid star formation (SFR similar or equal to 0.1 M-circle dot yr(-1)) consumes molecular gas in the dense clumps, so that UV radiation escapes and ionizes the remaining HI gas in the GMC. H-2 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 < G(0)> similar or equal to 10(3) (in Habing units), and a ionization parameter < U-ion > similar or equal to 10(2), 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 f(ion, esc) less than or similar to 0.03.