Research > Build up of galaxy disks

Using KMOS and MUSE we compiled a sample of ~1500 star-forming galaxies covering 10 billion years of cosmic time. We created average rotation curves for various sub-samples of the galaxies. We use these to test claims for declining rotation curves at large radii in galaxies at z~1-2 that have been interpreted as evidence for an absence of dark matter. We found the shapes of the rotation curves are sensitive to the averaging technique and only the galaxies with the highest central stellar surface densities have strong evidence for declining rotation curves. Overall, we found that the results are senDrawing comparisons with hydrodynamical simulations, we show that the average shapes of the rotation curves for our sample of massive, star-forming galaxies are consistent with those expected from lambda cold dark matter theory.

Using KMOS we created the largest ever sample of star-forming galaxies with spatially-resolved integral field unit observations at z~3.5. These galaxies exist only 1.8 billion years after the Big Bang. One of the results shows how the gas inside star-forming galaxies in the early Universe is dominated by ``random'' motions (dispersion) rather than rotation. That is, stable disks are very rare in the early Universe. This figure combines our results with early work of less distant galaxies. It shows that the motions of the gas in local star-forming galaxies are nearly all dominated by rotation, while at z~3.5, this is only the case in ~30% of star-forming galaxies.

Using KMOS Guaranteed Time Observations we have built up a sample of ~600 z~0.9 H-alpha detected galaxies with integral field unit observations. The KROSS Survey allows us to make spatially-resolved kinematic measurements to assess the dynamical state, metallicities, gas kinematics etc. of star-forming galaxies just before the global cosmic decline in star formation rate density. The left figure shows the velocity maps in the star-formation rate versus stellar mass plane. The figure below shows one of the results from the survey: that the galaxies with the lowest angular momentum (j) have the most bulge-dominated morphologies.