We present results from the “ Ponos ” simulation suite on the early evolution of a massive , M _ { vir } ( z = 0 ) = 1.2 \times 10 ^ { 13 } M _ { \sun } galaxy .
At z \gtrsim 6 , before feedback from a central supermassive black hole becomes dominant , the main galaxy has a stellar mass \sim 2 \times 10 ^ { 9 } M _ { \sun } and a star formation rate \sim 20 M _ { \sun } yr ^ { -1 } .
The galaxy sits near the expected main sequence of star-forming galaxies at those redshifts , and resembles moderately star-forming systems observed at z > 5 .
The high specific star formation rate results in vigorous heating and stirring of the gas by supernovae feedback , and the galaxy develops a thick and turbulent disc , with gas velocity dispersion \sim 40 km s ^ { -1 } , rotation to dispersion ratio \sim 2 , and with a significant amount of gas at \sim 10 ^ { 5 } K. The Toomre parameter always exceeds the critical value for gravito-turbulence , Q \sim 1.5 - 2 , mainly due to the contribution of warm/hot gas inside the disc .
Without feedback , a nearly gravito-turbulent regime establishes with similar gas velocity dispersion and lower Q .
We propose that the “ hot and turbulent ” disc regime seen in our simulations , unlike the “ cold and turbulent ” gravito-turbulent regime of massive clumpy disc galaxies at z \sim 1 - 2 , is a fundamental characterisation of main sequence galaxies at z \gtrsim 6 , as they can sustain star formation rates comparable to those of low-mass starbursts at z = 0 .
This results in no sustained coherent gas inflows through the disc , and in fluctuating and anisotropic mass transport , possibly postponing the assembly of the bulge and causing the initial feeding of the central black hole to be highly intermittent .