Distinguishing `disks' from `mergers': tracing the kinematic asymmetries in local (U)LIRGs using `kinemetry'-based criteria

TL;DR

This study uses kinemetry-based analysis of local (U)LIRGs to distinguish disks from mergers, revealing how resolution loss at high redshift affects kinematic classifications and the identification of galaxy evolutionary stages.

Contribution

It introduces a kinemetry-based classification method for (U)LIRGs and evaluates the impact of angular resolution loss on high-z galaxy kinematic analysis.

Findings

Local (U)LIRGs can be classified into disks, mergers, and transition types based on kinematic asymmetry.

Resolution loss at high redshift causes galaxies to appear more kinematically regular, affecting classification accuracy.

A lower asymmetry threshold is needed for high-z galaxy classification due to resolution effects.

Abstract

The kinematic characterization of different galaxy populations is a key observational input to distinguish between different galaxy evolutionary scenarios, since it helps to determine the number ratio of rotating disks to mergers at different cosmic epochs. Local (U)LIRGs offer a unique opportunity to study at high linear resolution and S/N extreme star forming events and compare them with those observed at high-z. We obtained Very Large Telescope (VLT) VIMOS optical integral field spectroscopy (IFS) data of a sample of 38 (U)LIRGs. The `unweighted' and `weighted' {kinemetry}-based methods are used to kinematically classify our galaxies in `disk' and `merger'. We simulate our systems at z=3 to evaluate how a loss of angular resolution affects our results. From the kinemetry-based analysis we are able classify our local (U)LIRGs in three distinct kinematic groups according to their total kinematic asymmetry values (K$_{tot}$) as derived when using the weighted (unweighted) method: 1) 25 out of 50 galaxies are kinematically classified as `disk', with a K$_{tot}\leq$ 0.16 (0.14); 2) 9 out of 50 galaxies are kinematically classified as `merger', with a K$_{tot}\geq$ 0.94 (0.66); 3) 16 out of 50 galaxies lie in the `transition region', in which disks and mergers coexist, with 0.16 (0.14) $<$ K$_{tot}$ $<$ 0.94 (0.66). When we apply our criteria to the high-z simulated systems, a lower total kinematic asymmetry frontier value (K$_{tot}$ $\sim$ 0.16 ($\sim$ 0.14)) is derived with respect to that found locally. The loss of angular resolution smears out the kinematic features, thus making objects to appear more kinematically regular than actually they are.