Galactic outflows driven by stellar feedback are crucial for explaining the inefficiency of galaxy formation .
Although strong feedback can promote the formation of galactic discs by limiting star formation at early times and removing low angular momentum gas , it is not understood how the same feedback can result in diverse objects such as elliptical galaxies or razor thin spiral galaxies .
In this work , we investigate this problem using cosmological zoom-in simulations of two galaxies forming within 10 ^ { 12 } ~ { } \mathrm { M _ { \odot } } halos with almost identical mass accretion histories .
At z > 1.5 , the two galaxies feature a surface density of star formation \Sigma _ { SFR } \simeq 10 ~ { } \mathrm { M _ { \odot } } ~ { } { yr } ^ { -1 } ~ { } { kpc } ^ { -2 } , leading to strong outflows .
After the last starburst episode , both galaxies feature a dramatic gaseous disc growth from 1 kpc to 5 kpc during 1 Gyr , a decisive epoch we dub ‘ ‘ the Grand Twirl ’ ’ .
After this episode , the evolutionary tracks diverge , with one galaxy ending up as a bulge-dominated galaxy , whereas the other ends up as a disc-dominated galaxy .
The origins of this dichotomy are the angular momentum of the accreted gas , and whether it adds constructively to the initial disc angular momentum .
The build-up of this extended disc leads to a rapid lowering of \Sigma _ { SFR } by over two orders of magnitude with \Sigma _ { SFR } \lesssim 0.1 ~ { } \mathrm { M _ { \odot } } ~ { } { yr } ^ { -1 } ~ { } { kpc } ^ % { -2 } , in remarkable agreement with what is derived from Milky Way stellar populations in the solar neighbourhood .
As a consequence , supernovae explosions are spread out and can not launch galactic outflows anymore , allowing for the persistence of a thin , gently star forming , extended disc .