3D spectroscopy with VLT/GIRAFFE. IV. Angular momentum and dynamical support of intermediate redshift galaxies

Context: One of the most outstanding problems related to numerical models of galaxy formation is the so-called "angular momentum catastrophe", i.e., the inability to theoretically explain the high angular momentum observed in local disk galaxies.
Aims: We study the evolution of the angular momentum from z∼0.6 to z=0 to better understand the mechanisms responsible for the large angular momenta of disk galaxies observed today. This study is based on a complete sample of 32, 0.4≤ z ≤0.75 galaxies observed with FLAMES/GIRAFFE at the VLT. Their kinematics had been classified as rotating disks (11 galaxies), perturbed rotators (7 galaxies), or complex kinematics (14 galaxies).
Methods: We have computed the specific angular momentum of disks (j_disk) and the dynamical support of rotating disks through the V/σ ratio. To study how angular momentum can be acquired dynamically, we compared the properties of distant and local galaxies, as a function of their kinematical class.
Results: We find that distant rotating disks have essentially the same properties (j_disk and R_d) as local disks, while distant galaxies with more complex kinematics have a significantly higher scatter in the j_disk-V_max and R_d-V_max planes. On average, distant galaxies show lower values of V/σ than local galaxies, the lowest V/σ values being reached by distant galaxies showing perturbed rotation. This can probably be attributed to heating mechanisms at work in distant disks.
Conclusions: We found observational evidence for a non-linear random-walk evolution of the angular momentum in galaxies during the past 8 Gyr. The evolution related to galaxies with complex kinematics can be attributed to mergers, but not to (smooth) gas accretion alone. If galaxies observed at intermediate redshift are related to present-day spirals, then our results match the "spiral rebuilding" scenario proposed by Hammer et al. (2005) quite closely.

Based on FLAMES/GIRAFFE Paris Observatory Guaranteed Time Observations collected at the European Southern Observatory, Paranal, Chile, ESO No. 71.A-0322(A) and 72.A-0169(A).