Z ∼ 2: An Epoch of Disk Assembly

Raymond C. Simons, Susan A. Kassin, Benjamin J. Weiner, Sandra M. Faber, Jonathan R. Trump, Timothy M. Heckman, David C. Koo, Camilla Pacifici, Joel R. Primack, Gregory F. Snyder, Alexander De La Vega

Research output: Contribution to journalArticlepeer-review

95 Scopus citations


We explore the evolution of the internal gas kinematics of star-forming galaxies from the peak of cosmic star formation at z ∼ 2 to today. Measurements of galaxy rotation velocity Vrot, which quantify ordered motions, and gas velocity dispersion σg, which quantify disordered motions, are adopted from the DEEP2 and SIGMA surveys. This sample covers a continuous baseline in redshift over 0.1 < z < 2.5, spanning 10 Gyr. At low redshift, nearly all sufficiently massive star-forming galaxies are rotationally supported (Vrot > σg). By z = 2, 50% and 70% of galaxies are rotationally supported at low (109-1010 M⊙) and high (1010-1011M⊙) stellar mass, respectively. For Vrot > 3 σg, the percentage drops below 35% for all masses. From z = 2 to now, galaxies exhibit remarkably smooth kinematic evolution on average. All galaxies tend toward rotational support with time, and higher-mass systems reach it earlier. This is largely due to a mass-independent decline in σg by a factor of 3 since z = 2. Over the same time period, Vrot increases by a factor of 1.5 in low-mass systems but does not evolve at high mass. These trends in Vrot and σg are at a fixed stellar mass and therefore should not be interpreted as evolutionary tracks for galaxy populations. When populations are linked in time via abundance matching, σg declines as before and Vrot strongly increases with time for all galaxy populations, enhancing the evolution in Vrot σg. These results indicate that z = 2 is a period of disk assembly, during which strong rotationalsupport is only just beginning to emerge.

Original languageEnglish (US)
Article number46
JournalAstrophysical Journal
Issue number1
StatePublished - Jul 1 2017


  • Galaxies: evolution
  • Galaxies: kinematics and dynamics

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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