The KMOS Redshift One Spectroscopic Survey (KROSS): the origin of disc turbulence in z ≈ 1 star-forming galaxies

Abstract

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.

From peculiar morphologies to Hubble-type spirals: the relation between galaxy dynamics and morphology in star-forming galaxies at z ∼ 1.5

“…Di Teodoro et al 2016) since this reduces the number of assumptions about the galaxy's dynamical state. We note, however in doing so the extracted rotation curves are effected by beam smearing but by following the procedures of Johnson et al (2018) these effects can be reduced to less than the 10 per cent level.…”

“…To put the dynamics of the galaxies in the KGES sample in the context of other high-redshift star-forming galaxy surveys, we make a comparison to the KROSS sample of ∼600 star-forming galaxies at z ∼ 0.9. Harrison et al (2017) extracts the rotation velocity of the KROSS galaxies at 2R h and applying the beam smearing corrections derived in Johnson et al (2018). The KROSS sample has a median intrinsic rotational velocity of V int = 117 ± 4 km s −1 with a 16-84th percentile range of 46 -205 km s −1 .…”

“…The KGES galaxies occupy similar σ o -SFR parameter space as galaxies with Q g = 0.25 -3.0 measure the median dispersion from the velocity dispersion map of the galaxy, examples of which are shown in Figure 4. The extracted values are then corrected for beam smearing following the methods described in Johnson et al (2018), which use model-based corrections, to derive an intrinsic velocity dispersion for each galaxy.…”

Time-average properties of z ∼ 0.6 major mergers: mergers significantly scatter high-z scaling relations

“…Epinat et al 2010;Davies et al 2011). However, here the ratio between the galaxy disc scale length and the half-width half-maximum of the typical PSF during the observations ∼1, which means that any possible systematic effect is probably ≤ 5 per cent (see appendix B of Johnson et al 2018), and can therefore be neglected.…”

“…Krumholz & Burkhart 2016). The large scatter in σ gas measurements was once again shown to hamper the comparison between the different scaling relations predicted by these models (Johnson et al 2018). Another example is provided by the scatter of the TFR that dramatically increases with z, which complicates the measurement of the evolution in zero-point and comparison with models (e.g.…”