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

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.