The effect of ISM turbulence on the gravitational instability of galactic discs

We investigate the gravitational instability of galactic discs, treatingstars and cold interstellar gas as two distinct components, and taking intoaccount the phenomenology of turbulence in the interstellar medium (ISM),i.e. the Larson-type scaling relations observed in the molecular and atomicgas. Besides deriving general properties of such systems, we analyse a largesample of galaxies from The HI Nearby Galaxy Survey (THINGS), andshow in detail how interstellar turbulence affects disc instability instar-forming spirals. We find that turbulence has a significant effect onboth the inner and the outer regions of the disc. In particular, it drivesthe inner gas disc to a regime of transition between two instability phasesand makes the outer disc more prone to star-dominated instabilities