2019/06/06 by Hannah D. N. Übler, Reinhard Genzel, Emily Wisnioski +27 · 1 citation
Physics and Astronomy · #astro-ph.GA
paper · pdf · doi:10.3847/1538-4357/ab27cc
~30 pages, 16 figures, 9 tables; accepted for publication in ApJ
arxiv created 2019/06/06 · arxiv updated 2019/07/31
We present the 0.6<z<2.6 evolution of the ionized gas velocity dispersion in 175 star-forming disk galaxies based on data from the full KMOS\rm 3D integral field spectroscopic survey. In a forward-modelling Bayesian framework including instrumental effects and beam-smearing, we fit simultaneously the observed galaxy velocity and velocity dispersion along the kinematic major axis to derive the intrinsic velocity dispersion σ0. We find a reduction of the average intrinsic velocity dispersion of disk galaxies as a function of cosmic time, from σ0∼45 km s-1 at z∼2.3 to σ0∼30 km s-1 at z∼0.9. There is substantial intrinsic scatter (σ_σ0, \rm int≈10 km s-1) around the best-fit σ0-z-relation beyond what can be accounted for from the typical measurement uncertainties (δσ0≈12 km s-1), independent of other identifiable galaxy parameters. This potentially suggests a dynamic mechanism such as minor mergers or variation in accretion being responsible for the scatter. Putting our data into the broader literature context, we find that ionized and atomic+molecular velocity dispersions evolve similarly with redshift, with the ionized gas dispersion being ∼10-15 km s-1 higher on average. We investigate the physical driver of the on average elevated velocity dispersions at higher redshift, and find that our galaxies are at most marginally Toomre-stable, suggesting that their turbulent velocities are powered by gravitational instabilities, while stellar feedback as a driver alone is insufficient. This picture is supported through comparison with a state-of-the-art analytical model of galaxy evolution.