We use numerical simulations to analyze the evolution and properties of superbubbles ( SBs ) , driven by multiple supernovae ( SNe ) , that propagate into the two-phase ( warm/cold ) , cloudy interstellar medium ( ISM ) .
We consider a range of mean background densities n _ { avg } = 0.1 - 10 { cm } ^ { -3 } and intervals between SNe \Delta t _ { SN } = 0.01 - 1 { Myr } , and follow each SB until the radius reaches \sim ( 1 - 2 ) H , where H is the characteristic ISM disk thickness .
Except for embedded dense clouds , each SB is hot until a time t _ { sf,m } when the shocked warm gas at the outer front cools and forms an overdense shell .
Subsequently , diffuse gas in the SB interior remains at T _ { h } \sim 10 ^ { 6 } -10 ^ { 7 } { K } with expansion velocity v _ { h } \sim 10 ^ { 2 } -10 ^ { 3 } { km } { s } ^ { -1 } ( both highest for low \Delta t _ { SN } ) .
At late times , the warm shell gas velocities are several 10 ’ s to \sim 100 { km } { s } ^ { -1 } .
While shell velocities are too low to escape from a massive galaxy , they are high enough to remove substantial mass from dwarfs .
Dense clouds are also accelerated , reaching a few to 10 ’ s of { km } { s } ^ { -1 } .
We measure the mass in hot gas per SN , \hat { M } _ { h } , and the total radial momentum of the bubble per SN , \hat { p } _ { b } .
After t _ { sf,m } , \hat { M } _ { h } \sim 10 - 100 M _ { \odot } ( highest for low n _ { avg } ) , while \hat { p } _ { b } \sim 0.7 - 3 \times 10 ^ { 5 } M _ { \odot } { km } { s } ^ { -1 } ( highest for high \Delta t _ { SN } ) .
If galactic winds in massive galaxies are loaded by the hot gas in SBs , we conclude that the mass-loss rates would generally be lower than star formation rates .
Only if the SN cadence is much higher than typical in galactic disks , as may occur for nuclear starbursts , SBs can break out while hot and expel up to 10 times the mass locked up in stars .
The momentum injection values , \hat { p } _ { b } , are consistent with requirements to control star formation rates in galaxies at observed levels .