z ∼ 2: An Epoch of Disk Assembly

Abstract

We explore the evolution of the internal gas kinematics of star-forming galaxies from the peak of cosmic star formation atz 2 to today. Measurements of galaxy rotation velocity V rot , which quantify ordered motions, and gas velocity dispersion s g , which quantify disordered motions, are adopted from the DEEP2 and SIGMA surveys. This sample covers a continuous baseline in redshift over < < z 0.1 2.5, spanning 10 Gyr. At low redshift, nearly all sufficiently massive star-forming galaxies are rotationally supported (By z=2, 50% and 70% of galaxies are rotationally supported at low ( ) stellar mass, respectively. For, 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 s g by a factor of 3 since z=2. Over the same time period, V rot increases by a factor of 1.5 in low-mass systems but does not evolve at high mass. These trends in V rot and s g 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, s g declines as before and V rot strongly increases with time for all galaxy populations, enhancing the evolution in s V g rot . These results indicate that = z 2 is a period of disk assembly, during which strong rotational support is only just beginning to emerge.

A mass threshold for galactic gas discs by spin flips

“…The observations by Simons et al (2017) also indicate in the given redshift range a redshift dependence of f disc ∝ (1 + z) 0.8 for M s = 10 9−10 M , which seems to be in apparent conflict with our general prediction of no significant redshift dependence over the larger redshift range z = 1 − 8. However, when focusing on the limited redshift range z = 0.8−2.4, where there are both simulated and observed galaxies, as in Fig.…”

“…The results from existing kinematical observations are consistent with the predicted mass dependence and threshold mass for long-lived gas discs. These include the studies based on the SAMI survey (Cortese et al 2014) and the analysis of observations by Simons et al (2017). However, the current observations hardly explore the mass range below M s ∼ 10 9 M at moderate and high redshifts, where our simulations and analysis indicate that disc disruption is expected to dominate.…”

“…The former reference spans the range M s = 10 8−10.7 M at z = 0.2 − 1.1 and the latter more comprehensive study covers M s = 10 9−11 M at z = 0.2 − 2.4. Figure 11 shows the fraction of discs (V rot /σ > 3) as a function of redshift in stellar mass bins, in the VELA simulations compared to the observational estimates by Simons et al (2017, Fig. 4b).…”

“…This is similar to what we find in the VELA simulations in the same mass and redshift range. Note that the mass range studied by Simons et al (2017) is limited to near and above the predicted transition mass.…”

A panchromatic spatially resolved analysis of nearby galaxies – I. Sub-kpc-scale main sequence in grand-design spirals

“…This set is thus well fit to study the secular evolution processes that regulate the star formation in local sources, dominated by rotationally supported systems (e.g. Law et al 2009;Förster Schreiber et al 2009;Glazebrook 2013;Wisnioski et al 2015;Simons et al 2017;Förster Schreiber et al 2018;Übler et al 2019). Some individual galaxies show peculiar variation around the Σ SFR − Σ relation presented in Fig.…”