High-Redshift Galaxy Kinematics: Constraints on Models of Disk Formation

Abstract

Integral field spectroscopy of galaxies at redshift z~2 has revealed a population of early-forming, rotationally supported disks. These high-redshift systems provide a potentially important clue to the formation processes that build disk galaxies in the universe. A particularly well-studied example is the z=2.38 galaxy BzK 15504, which was shown by Genzel and coworkers to be a rotationally supported disk despite the fact that its high star formation rate and short gas consumption timescale require a very rapid acquisition of mass. Previous kinematical analyses have suggested that z~2 disk galaxies like BzK 15504 did not form through mergers because their line-of-sight velocity fields display low levels of asymmetry. We perform the same kinematical analysis on a set of simulated disk galaxies formed in gas-rich mergers of the type that may be common at high redshift, and show that the remnant disks display low velocity field asymmetry and satisfy the criteria that have been used to classify high-redshift galaxies as disks observationally. Further, we compare one of our remnants to the bulk properties of BzK 15504 and show that it has a star formation rate, gas surface density, and a circular velocity-to-velocity dispersion ratio that matches BzK 15504 remarkably well. We suggest that observations of high-redshift disk galaxies like BzK 15504 are consistent with the hypothesis that gas-rich mergers play an important role in disk formation at high redshift.