Photoevaporation of Jeans-unstable molecular clumps

We study the photoevaporation of Jeans-unstable molecular clumps by isotropic FUV (6 eV < hν < 13.6 eV) radiation, through 3D radiative transfer hydrodynamical simulations implementing a non-equilibrium chemical network that includes the formation and dissociation of H₂. We run a set of simulations considering different clump masses (M=10 - 200 M_{\odot }) and impinging fluxes (G₀ = 2 × 10³ to 8 × 10⁴ in Habing units). In the initial phase, the radiation sweeps the clump as an R-type dissociation front, reducing the H₂ mass by a factor 40 - 90{{ per cent}}. Then, a weak (M∼eq 2) shock develops and travels towards the centre of the clump, which collapses while losing 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 H₂ mass available for star formation: for example, for G₀ < 10⁴ more than 10 per cent of the initial clump mass survives. Finally, for massive clumps ({≳ } 100 M_{\odot }) the H₂ mass increases by 25 - 50{{ per cent}} during the collapse, mostly because of the rapid density growth that implies a more efficient H₂ self-shielding.