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Register a new userPhotoevaporation of Jeans-unstable molecular clumps
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We study the photoevaporation of Jeans-unstable molecular clumps by isotropic FUV (6 eV $< {rm h} u$ < 13.6 eV) radiation, through 3D radiative transfer hydrodynamical simulations implementing a non-equilibrium chemical network that includes the formation and dissociation of H$_2$. We run a set of simulations considering different clump masses ($M=10-200$ M$_odot$) and impinging fluxes ($G_0=2times 10^3-8times 10^4$ in Habing units). In the initial phase, the radiation sweeps the clump as an R-type dissociation front, reducing the H$_2$ mass by a factor 40-90%. Then, a weak ($mathcal{M}simeq 2$) shock develops and travels towards the centre of the clump, which collapses while loosing mass from its surface. All considered clumps remain gravitationally unstable even if radiation rips off most of the clump mass, showing that external FUV radiation is not able to stop clump collapse. However, the FUV intensity regulates the final H$_2$ mass available for star formation: for example, for $G_0 < 10^4$ more than 10% of the initial clump mass survives. Finally, for massive clumps ($sim 100$ M$_odot$) the H$_2$ mass increases by 25-50% during the collapse, mostly because of the rapid density growth that implies a more efficient H$_2$ self-shielding.
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We perform a suite of 3D radiation hydrodynamics simulations of photoevaporation of molecular gas clumps illuminated by external massive stars. We study the fate of solar-mass clumps and derive their lifetimes with varying the gas metallicity over a range of $10^{-3} ,Z_odot leq Z leq Z_odot $. Our simulations incorporate radiation transfer of far ultraviolet (FUV) and extreme ultraviolet (EUV) photons, and follow atomic/molecular line cooling and dust-gas collisional cooling. Nonequilibrium chemistry is coupled with the radiative transfer and hydrodynamics in a self-consistent manner. We show that radiation-driven shocks compress gas clumps to have a volume that is set by the pressure-equilibrium with the hot ambient gas. Radiative cooling enables metal-rich clumps to condense and to have small surface areas, where photoevaporative flows are launched. For our fiducial set-up with an O-type star at a distance of 0.1 parsec, the resulting photoevaporation rate is as small as $sim 10^{-5} M_{odot}/{rm yr}$ for metal-rich clumps, but is larger for metal-poor clumps that have larger surface areas. The clumps are continuously accelerated away from the radiation source by the so-called rocket effect, and can travel over $sim$1 parsec within the lifetime. We also study photoevaporation of clumps in a photo-dissociation region. Photoelectric heating is inefficient for metal-poor clumps that contain a smaller amount of grains, and thus they survive for over $10^5$ years. We conclude that the gas metallicity strongly affects the clump lifetime and thus determines the strength of feedback from massive stars in star-forming regions.
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