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Register a new userThe KMOS Redshift One Spectroscopic Survey (KROSS): the origin of disk turbulence in z~0.9 star-forming galaxies
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H. L. Johnson
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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/sigma_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 sigma_0 = 43.2 +/- 0.8 km/s with a rotational velocity to dispersion ratio of v_C/sigma_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.
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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 Halpha 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$pm$5%. However, when compared with local samples these are turbulent discs with high gas to baryonic mass fractions, ~35%, and the majority are consistent with being marginally unstable (Toomre Q~1). There is no strong correlation between galaxy averaged velocity dispersion and the total star formation rate, suggesting that feedback from star formation is not the origin of the elevated turbulence. We postulate that it is the ubiquity of high (likely molecular) gas fractions and the associated gravitational instabilities that drive the elevated star-formation rates in these typical z~1 galaxies, leading to the ten-fold enhanced star-formation rate density. Finally, by comparing the gas masses obtained from inverting the star-formation law with the dynamical and stellar masses, we infer an average dark matter to total mass fraction within 2.2$r_e$ (9.5kpc) of 65$pm$12%, in agreement with the results from hydrodynamic simulations of galaxy formation.
We investigate what drives the redshift evolution of the typical electron density ($n_e$) in star-forming galaxies, using a sample of 140 galaxies drawn primarily from KMOS$^{rm 3D}$ ($0.6lesssim{z}lesssim{2.6}$) and 471 galaxies from SAMI ($z<0.113$). We select galaxies that do not show evidence of AGN activity or outflows, to constrain the average conditions within H II regions. Measurements of the [SII]$lambda$6716/[SII]$lambda$6731 ratio in four redshift bins indicate that the local $n_e$ in the line-emitting material decreases from 187$^{+140}_{-132}$ cm$^{-3}$ at $zsim$ 2.2 to 32$^{+4}_{-9}$ cm$^{-3}$ at $zsim$ 0; consistent with previous results. We use the H$alpha$ luminosity to estimate the root-mean-square (rms) $n_e$ averaged over the volumes of star-forming disks at each redshift. The local and volume-averaged $n_e$ evolve at similar rates, hinting that the volume filling factor of the line-emitting gas may be approximately constant across $0lesssim{z}lesssim{2.6}$. The KMOS$^{rm 3D}$ and SAMI galaxies follow a roughly monotonic trend between $n_e$ and star formation rate, but the KMOS$^{rm 3D}$ galaxies have systematically higher $n_e$ than the SAMI galaxies at fixed offset from the star-forming main sequence, suggesting a link between the $n_e$ evolution and the evolving main sequence normalization. We quantitatively test potential drivers of the density evolution and find that $n_e$(rms) $simeq{n_{H_2}}$, suggesting that the elevated $n_e$ in high-$z$ H II regions could plausibly be the direct result of higher densities in the parent molecular clouds. There is also tentative evidence that $n_e$ could be influenced by the balance between stellar feedback, which drives the expansion of H II regions, and the ambient pressure, which resists their expansion.
We infer the intrinsic ionised gas kinematics for 383 star-forming galaxies across a range of integrated star-formation rates (SFR $in [10^{-3}, 10^2]$ M$_odot$ yr$^{-1}$) at $z lesssim 0.1$ using a consistent 3D forward-modelling technique. The total sample is a combination of galaxies from the SAMI Galaxy Survey and DYNAMO survey. For typical low-$z$ galaxies taken from the SAMI Galaxy Survey, we find the vertical velocity dispersion ($sigma_{v, z}$) to be positively correlated with measures of star-formation rate, stellar mass, HI gas mass, and rotational velocity. The greatest correlation is with star-formation rate surface density ($Sigma_text{SFR}$). Using the total sample, we find $sigma_{v, z}$ increases slowly as a function of integrated star-formation rate in the range SFR $in$ [$10^{-3}$, 1] M$_odot$ yr$^{-1}$ from $17pm3$ km s$^{-1}$ to $24pm5$ km s$^{-1}$ followed by a steeper increase up to $sigma_{v, z}$ $sim 80$ km s$^{-1}$ for SFR $gtrsim 1$ M$_odot$ yr$^{-1}$. This is consistent with recent theoretical models that suggest a $sigma_{v, z}$ floor driven by star-formation feedback processes with an upturn in $sigma_{v, z}$ at higher SFR driven by gravitational transport of gas through the disc.
I review here the spatially-resolved spectroscopic properties of low-redshift star-forming galaxies (and their retired counter-parts), using results from the most recent Integral Field Spectroscopy galaxy surveys. First, I briefly summarise the global spectroscopic properties of these galaxies, discussing the main ionization processes, and the global relations described between the star-formation rates, oxygen abundances, and average properties of their stellar populations (age and metallicity) with the stellar mass. Second, I present the local distribution of the ionizing processes, down to kiloparsec scales, and I show how the global scaling relations found between integrated parameters (like the star-formation main sequence, mass-metallicity relation and Schmidt-Kennicutt law) present local/resolved counter-parts, with the global ones being just integrated/avera
Using integral field spectroscopy we investigate the kinematic properties of 35 massive centrally-dense and compact star-forming galaxies (${log{overline{M}_*}}=11.1$, $log{(Sigma_mathrm{1kpc})}>9.5$, $log{(M_ast/r_e^{1.5})}>10.3$) at $zsim0.7-3.7$ within the KMOS$^mathrm{3D}$survey. We spatially resolve 23 compact star-forming galaxies (SFGs) and find that the majority are dominated by rotational motions with velocities ranging from {$95-500$ km s$^{-1}$}. The range of rotation velocities is reflected in a similar range of integrated H$alpha$ linewidths, $75-400$ km s$^{-1}$, consistent with the kinematic properties of mass-matched extended galaxies from the full KMOS$^mathrm{3D}$ sample. The fraction of compact SFGs that are classified as `rotation-dominated or `disk-like also mirrors the fractions of the full KMOS$^mathrm{3D}$ sample. We show that integrated line-of-sight gas velocity dispersions from KMOS$^mathrm{3D}$ are best approximated by a linear combination of their rotation and turbulent velocities with a lesser but still significant contribution from galactic scale winds. The H$alpha$ exponential disk sizes of compact SFGs are on average $2.5pm0.2$ kpc, $1-2times$ the continuum sizes, in agreement with previous work. The compact SFGs have a $1.4times$ higher AGN incidence than the full KMOS$^mathrm{3D}$ sample at fixed stellar mass with 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 time scale unless replenished with inflowing gas. The rotation in these compact systems suggests that their direct descendants are rotating passive galaxies.
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