By using N -body and hydro simulations , we study the formation and evolution of bars in galaxies with significant gas content focusing on the phenomenon of the buckling instability .
The galaxies are initially composed of a spherical dark matter halo and only stellar , or stellar and gaseous , disks with parameters that are similar to the Milky Way and are evolved for 10 Gyr .
We consider different values of the gas fraction f = 0 - 0.3 and in order to isolate the effect of the gas , we kept the fraction constant during the evolution by not allowing the gas to cool and form stars .
The stellar bars that form in simulations with higher gas fractions are weaker and shorter , and they do not form at all for gas fractions that are higher than 0.3 .
The bar with a gas fraction of 0.1 forms sooner due to initial perturbations in the gas , but despite the longer evolution , it does not become stronger than the one in the collisionless case at the end of evolution .
The bars in the gas component are weaker ; they reach their maximum strength around 4 Gyr and later decline to transform into spheroidal shapes .
The distortion of the stellar bar during the buckling instability is weaker for higher gas fractions and weakens the bar less significantly , but it has a similar structure both in terms of radial profiles and in face-on projections .
For f = 0.2 , the first buckling lasts significantly longer and the bar does not undergo the secondary buckling event , while for f = 0.3 , the buckling does not occur .
Despite these differences , all bars develop boxy/peanut shapes in the stellar and gas component by the end of the evolution , although their thickness is smaller for higher gas fractions .