Extraordinary Colloquium: Joss Bland-Hawthorn (Director, Sydney Institute for Astronomy, U. of Sydney)
Recent observations of high-redshift galaxies (z = 1 - 9) reveal many have gas-rich discs with well-ordered rotation and elevated levels of star formation and turbulence. Some discs (z = 1 - 5) show evidence of spiral arms, and either stellar or gaseous bars. These remarkable observations have motivated us to explore a new class of dynamically self-consistent models using our updated AGAMA/Ramses N-body codes to mimic a plausible progenitor of the Milky Way. We explore gas fractions from 0 to 100%, and track the creation of stars and metals. The high gas surface densities encourage vigorous star formation, which in turn couples with the gas to drive turbulent pressure support. We explore three distinct histories: (i) there is no ongoing accretion and the gas is used up by the star formation; (ii) the star-forming gas is replenished by cooling in the hot halo gas; (iii) we revisit these models in the presence of a strong perturbing force. The turbulent gas forms a strong radial shear flow that creates a co-existing stellar and gaseous bar within a few 100 Myr. Remarkably, a gas bar is formed even when there is no stellar disc (f_gas ~ 100%). For f_gas < 70%, all bars survive to the end of the simulation (2 Gyr) but, for higher gas fractions, the bars evolve into central bulges after 1 Gyr. The gas bars are reminiscent of recent discoveries from high-redshift ALMA observations of gaseous discs.
Dec. 15, 2023, 11 a.m. – noon