We study gaseous outflows from disk galaxies driven by the combined effects of ram pressure on cold gas clouds and radiation pressure on dust grains .
Taking into account the gravity due to disk , bulge and dark matter halo , and assuming continuous star formation in the disk , we show that radiation or ram pressure alone is not sufficient to drive escaping winds from disk galaxies , and that both processes contribute .
We show that in the parameter space of star formation rate ( SFR ) and rotation speed of galaxies , the wind speed in galaxies with rotation speed v _ { c } \leq 200 km s ^ { -1 } and SFR \leq 100 M _ { \odot } yr ^ { -1 } , has a larger contribution from ram pressure , and that in high mass galaxies with large SFR , radiation from the disk has a greater role in driving galactic winds .
The ratio of wind speed to circular speed can be approximated as { v _ { w } \over v _ { c } } \sim 10 ^ { 0.7 } \left [ { SFR \over 50 { M } _ { \odot } { yr% } ^ { -1 } } \right ] ^ { 0.4 } \left [ { v _ { c } \over 120 km / s } \right ] ^ { -1.25 } .
We show that this conclusion is borne out by observations of galactic winds at low and high redshift and also of circumgalactic gas .
We also estimate the mass loading factors under the combined effect of ram and radiation pressure , and show that the ratio of mass loss rate to SFR scales roughly as v _ { c } ^ { -1 } \Sigma _ { g } ^ { -1 } , where \Sigma _ { g } is the gas column density in the disk .