The KMOS Deep Survey (KDS) - I. Dynamical measurements of typical star-forming galaxies at z ≃ 3.5

M. Cirasuolo, C. M. Harrison, R. J. McLure, J. S. Dunlop, A. M. Swinbank, D. Sobral, J. Matthee, R. M. Sharples

Research output: Contribution to journalArticlepeer-review


We present dynamical measurements from the KMOS (K-band multi-object spectrograph) Deep Survey (KDS), which comprises 77 typical star-forming galaxies at z ≃ 3.5 in the mass range 9.0 <log (M⋆/M⊙) <10.5. These measurements constrain the internal dynamics, the intrinsic velocity dispersions (σint) and rotation velocities (VC) of galaxies in the high-redshift Universe. The mean velocity dispersion of the galaxies in our sample is σ _int = 70.8^{+3.3}_{-3.1} km s^{-1}, revealing that the increasing average σint with increasing redshift, reported for z ≲ 2, continues out to z ≃ 3.5. Only 36 ± 8 per cent of our galaxies are rotation-dominated (VC/σint > 1), with the sample average VC/σint value much smaller than at lower redshift. After carefully selecting comparable star-forming samples at multiple epochs, we find that the rotation-dominated fraction evolves with redshift with a z-0.2 dependence. The rotation-dominated KDS galaxies show no clear offset from the local rotation velocity-stellar mass (i.e. VC-M⋆) relation, although a smaller fraction of the galaxies are on the relation due to the increase in the dispersion-dominated fraction. These observations are consistent with a simple equilibrium model picture, in which random motions are boosted in high-redshift galaxies by a combination of the increasing gas fractions, accretion efficiency, specific star formation rate and stellar feedback and which may provide significant pressure support against gravity on the galactic disc scale.
Original languageEnglish
Pages (from-to)1280-1320
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Publication statusPublished - 3 Jun 2017


  • galaxies: evolution
  • galaxies: high-redshift
  • galaxies: kinematics and dynamics


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