The KMOS Redshift One Spectroscopic Survey (KROSS) is an ESO guaranteed time survey of 795 typical star-forming galaxies in the redshift range z = 0.8−1.0 with the KMOS instrument on the VLT. In this paper we present resolved kinematics and star formation rates for 584 z ∼ 1 galaxies. This constitutes the largest near-infrared Integral Field Unit survey of galaxies at z ∼ 1 to date. We demonstrate the success of our selection criteria with 90% of our targets found to be Hα emitters, of which 81% are spatially resolved. The fraction of the resolved KROSS sample with dynamics dominated by ordered rotation is found to be 83 ± 5%. However, when compared with local samples these are turbulent discs with high gas to baryonic mass fractions, ∼ 35%, and the majority are consistent with being marginally unstable (Toomre Q ∼ 1). There is no strong correlation between galaxy averaged velocity dispersion and the total star formation rate, suggesting that feedback from star formation is not the origin of the elevated turbulence. We postulate that it is the ubiquity of high (likely molecular) gas fractions and the associated gravitational instabilities that drive the elevated star-formation rates in these typical z ∼ 1 galaxies, leading to the ten-fold enhanced starformation rate density. Finally, by comparing the gas masses obtained from inverting the starformation law with the dynamical and stellar masses, we infer an average dark matter to total mass fraction within 2.2 r e (9.5 kpc) of 65 ± 12%, in agreement with the results from hydrodynamic simulations of galaxy formation.

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. ABSTRACTWe 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 (v C /σ 0 > 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 ⋆ , consistent with that expected for dark matter (i.e., j DM ∝ M 2/3 DM ). 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.

We analyse the velocity dispersion properties of 472 z ∼ 0.9 star-forming galaxies observed as part of the KMOS Redshift One Spectroscopic Survey (KROSS). The majority of this sample is rotationally dominated (83 ± 5% with v C /σ 0 > 1) but also dynamically hot and highly turbulent. After correcting for beam smearing effects, the median intrinsic velocity dispersion for the final sample is σ 0 = 43.2 ± 0.8 km s −1 with a rotational velocity to dispersion ratio of v C /σ 0 = 2.6 ± 0.1. To explore the relationship between velocity dispersion, stellar mass, star formation rate and redshift we combine KROSS with data from the SAMI survey (z ∼ 0.05) and an intermediate redshift MUSE sample (z ∼ 0.5). While there is, at most, a weak trend between velocity dispersion and stellar mass, at fixed mass there is a strong increase with redshift. At all redshifts, galaxies appear to follow the same weak trend of increasing velocity dispersion with star formation rate. Our results are consistent with an evolution of galaxy dynamics driven by disks that are more gas rich, and increasingly gravitationally unstable, as a function of increasing redshift. Finally, we test two analytic models that predict turbulence is driven by either gravitational instabilities or stellar feedback. Both provide an adequate description of the data, and further observations are required to rule out either model.