Time-average properties of z ∼ 0.6 major mergers: mergers significantly scatter high-z scaling relations

Abstract

Interpreting the scaling relations measured by recent large kinematic surveys of z 1 galaxies has remained hampered by large observational scatter. We show that the observed ISM and morpho-dynamical properties along the average z ∼ 0.6 major merger describe a very selfconsistent picture in which star formation is enhanced during first passage and fusion as a result of gravitational perturbations due to the interaction, while the gas velocity dispersion is simultaneously enhanced through shocks that convert kinematic energy associated with bulk orbital motions into turbulence at small scales. Angular momentum and rotation support in the disc are partly lost during the most perturbing phases, resulting in a morphologically compact phase. The fractions of present-day E/S0 versus later type galaxies can be predicted within only a few per cent, confirming that roughly half of local discs were reformed in the past 8-9 Gyr after gas-rich major mergers. Major mergers are shown to strongly scatter scaling relations involving kinematic quantities (e.g. the Tully-Fisher or Fall relations). Selecting high-z discs relying only on V/σ turns out to be less efficient than selecting discs from multiple criteria based on their morpho-kinematic properties, which can reduce the scatter of high-z scaling relations down to the values measured in local galaxy samples.

From peculiar morphologies to Hubble-type spirals: the relation between galaxy dynamics and morphology in star-forming galaxies at z ∼ 1.5

“…Merger events and interactions also enhance gas velocity dispersion and reduce a galaxy's angular momentum, introducing significant scatter into dynamical scaling relations (e.g. Puech et al 2019) In order to quantify how the angular momentum of high-redshift star-forming galaxies affects the emergence of the Hubble-type disc galaxies, and the role feedback plays in defining a galaxy's morphology, we require two key quantities. First, we need to derive the internal dynamics and second, we need to measure rest-frame optical morphology of the galaxies at this epoch both, parametrically and non-parametrically, which requires high resolution multiwavelength imaging of the galaxies.…”