The KMOS Redshift One Spectroscopic Survey (KROSS) : rotational velocities and angular momentum of z ≈ 0.9 galaxies.

Abstract

We present dynamical measurements for 586 Hα detected star-forming galaxies from the KMOS (K-band Multi-Object Spectrograph) Redshift One Spectroscopic Survey (KROSS). The sample represents typical star-forming galaxies at this redshift (z = 0.6–1.0), with a median star formation rate of ≈7 M⊙ yr−1 and a stellar mass range of log (M⋆[M⊙])≈9–11. We find that the rotation velocity-stellar mass relationship (the inverse of the Tully-Fisher relationship) for our rotationally-dominated sources (VC/σ0 > 1) has a consistent slope and normalisation as that observed for z = 0 disks. In contrast, the specific angular momentum (j⋆; angular momentum divided by stellar mass), is ≈0.2–0.3 dex lower on average compared to z = 0 disks. The specific angular momentum scales as j s ∝M 0.6±0.2 ⋆ js∝M⋆0.6±0.2 , consistent with that expected for dark matter (i.e., j DM ∝M 2/3 DM jDM∝MDM2/3 ). We find that z ≈ 0.9 star-forming galaxies have decreasing specific angular momentum with increasing Sérsic index. Visually, the sources with the highest specific angular momentum, for a given mass, have the most disk-dominated morphologies. This implies that an angular momentum–mass–morphology relationship, similar to that observed in local massive galaxies, is already in place by z ≈ 1.