The KMOS3D Survey: Rotating Compact Star-forming Galaxies and the Decomposition of Integrated Line Widths

Abstract

Using integral field spectroscopy, we investigate the kinematic properties of 35 massive centrally dense and compact star-forming galaxies (SFGs; logM[Ṁ] = 11.1, log (σ 1kpc[Ṁ kpc-2]) > 9.5 log (M∗/re1.5 (Ṁ kpc1.5])> 10.3) at z ∼ 0.7-3.7within the KMOS3D survey. We spatially resolve 23 compact SFGs and find that the majority are dominated by rotational motions with velocities ranging from 95 to 500 km s-1. The range of rotation velocities is reflected in a similar range of integrated 1DUMMYα line widths, 75400 km s-1, consistent with the kinematic properties of mass-matched extended galaxies from the full KMOS3D sample. The fraction of compact SFGs that are classified as rotation-dominated" or "disklike" also mirrors the fractions of the full KMOS3D sample. We show that integrated lineof-sight gas velocity dispersions from KMOS3Dare best approximated by a linear combination of their rotation and turbulent velocities with a lesser but still significant contribution from galactic-scale winds. The 1DUMMYα exponential disk sizes of compact SFGs are, on average, 2.5 ± 0.2 kpc, 1-2 × the continuum sizes, in agreement with previous work. The compact SFGs have a 1.4 × higher active galactic nucleus (AGN) incidence than the full KMOS3D sample at fixed stellar mass with an average AGN fraction of 76%. Given their high and centrally concentrated stellar masses, as well as stellar-to-dynamical mass ratios close to unity, the compact SFGs are likely to have low molecular gas fractions and to quench on a short timescale unless replenished with inflowing gas. The rotation in these compact systems suggests that their direct descendants are rotating passive galaxies.