Kinemetry of SINS High-Redshift Star-Forming Galaxies: Distinguishing Rotating Disks from Major Mergers

TL;DR

This paper introduces a kinematic method using kinemetry to distinguish between rotating disks and major mergers in high-redshift galaxies, based on ionized gas dynamics, aiding understanding of galaxy formation processes.

Contribution

It develops empirical criteria using kinemetry to classify high-redshift galaxies as disks or mergers based on their gas kinematics, applicable to emission-line observations.

Findings

Over 50% of studied galaxies are consistent with rotating disks.

Remaining galaxies show signs of major mergers.

Results support rapid gas accretion as a key galaxy formation mechanism.

Abstract

We present a simple set of kinematic criteria that can distinguish between galaxies dominated by ordered rotational motion and those involved in major merger events. Our criteria are based on the dynamics of the warm ionized gas (as traced by H-alpha) within galaxies, making this analysis accessible to high-redshift systems, whose kinematics are primarily traceable through emission features. Using the method of kinemetry (developed by Krajnovic and co-workers), we quantify asymmetries in both the velocity and velocity dispersion maps of the warm gas, and the resulting criteria enable us to empirically differentiate between non-merging and merging systems at high redshift. We apply these criteria to 11 of our best-studied rest-frame UV/optical-selected z~2 galaxies for which we have near infrared integral field spectroscopic data from SINFONI on the VLT. Of these 11 systems, we find that >50% have kinematics consistent with a single rotating disk interpretation, while the remaining systems are more likely undergoing major mergers. This result, combined with the short formation timescales of these systems, provides evidence that rapid, smooth accretion of gas plays a significant role in galaxy formation at high redshift.