Hot Disks And Delayed Bar Formation
  We present observational evidence for the inhibition of bar formation in
dispersion-dominated (dynamically hot) galaxies by studying the relationship
between galactic structure and host galaxy kinematics in a sample of 257
galaxies between 0.1 $<$ z $\leq$ 0.84 from the All-Wavelength Extended Groth
Strip International Survey (AEGIS) and the Deep Extragalactic Evolutionary
Probe 2 (DEEP2) survey. We find that bars are preferentially found in galaxies
that are massive and dynamically cold (rotation-dominated) and on the stellar
Tully-Fisher relationship, as is the case for barred spirals in the local
Universe. The data provide at least one explanation for the steep ($\times$3)
decline in the overall bar fraction from z=0 to z=0.84 in L$^*$ and brighter
disks seen in previous studies. The decline in the bar fraction at high
redshift is almost exclusively in the lower mass (10 $<$ log M$_{*}$(\Msun)$<$
11), later-type and bluer galaxies. A proposed explanation for this
"downsizing" of the bar formation / stellar structure formation is that the
lower mass galaxies may not form bars because they could be dynamically hotter
than more massive systems from the increased turbulence of accreting gas,
elevated star formation, and/or increased interaction/merger rate at higher
redshifts. The evidence presented here provides observational support for this
hypothesis. However, the data also show that not every disk galaxy that is
massive and cold has a stellar bar, suggesting that mass and dynamic coldness
of a disk are necessary but not sufficient conditions for bar formation -- a
secondary process, perhaps the interaction history between the dark matter halo
and the baryonic matter, may play an important role in bar formation.
