Friday, 22 February 2008

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

Shapiro et al.

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.

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