The SILCC project ( SImulating the Life-Cycle of molecular Clouds ) aims at a more self-consistent understanding of the interstellar medium ( ISM ) on small scales and its link to galaxy evolution .
We present three-dimensional ( magneto ) hydrodynamic simulations of the ISM in a vertically stratified box including self-gravity , an external potential due to the stellar component of the galactic disc , and stellar feedback in the form of an interstellar radiation field and supernovae ( SNe ) .
The cooling of the gas is based on a chemical network that follows the abundances of H ^ { + } , H , H _ { 2 } , C ^ { + } , and CO and takes shielding into account consistently .
We vary the SN feedback by comparing different SN rates , clustering and different positioning , in particular SNe in density peaks and at random positions , which has a major impact on the dynamics .
Only for random SN positions the energy is injected in sufficiently low-density environments to reduce energy losses and enhance the effective kinetic coupling of the SNe with the gas .
This leads to more realistic velocity dispersions ( \sigma _ { \mathrm { HI } } \approx 0.8 \sigma _ { 300 - 8000 \mathrm { K } } \sim 10 - 20 % \mathrm { km } \mathrm { s } ^ { -1 } , \sigma _ { \mathrm { H \alpha } } \approx 0.6 \sigma _ { 8000 - 3 \times 10 ^ { 5 } \mathrm { K } } % \sim 20 - 30 \mathrm { km } \mathrm { s } ^ { -1 } ) , and strong outflows with mass loading factors ( ratio of outflow to star formation rate ) of up to 10 even for solar neighbourhood conditions .
Clustered SNe abet the onset of outflows compared to individual SNe but do not influence the net outflow rate .
The outflows do not contain any molecular gas and are mainly composed of atomic hydrogen .
The bulk of the outflowing mass is dense ( \rho \sim 10 ^ { -25 } -10 ^ { -24 } \mathrm { g cm } ^ { -3 } ) and slow ( v \sim 20 - 40 \mathrm { km } \mathrm { s } ^ { -1 } ) but there is a high-velocity tail of up to v \sim 500 \mathrm { km } \mathrm { s } ^ { -1 } with \rho \sim 10 ^ { -28 } -10 ^ { -27 } \mathrm { g cm } ^ { -3 } .