Bar pattern speeds in CALIFA galaxies II. The case of weakly barred
  galaxies
  We aim at investigating the formation process of weak bars by measuring their
properties in a sample of 29 nearby SAB galaxies, spanning a wide range of
morphological types and luminosities. The sample galaxies were selected to have
an intermediate inclination, a bar at an intermediate angle between the disc
minor and major axes, and an undisturbed morphology and kinematics to allow the
direct measurement of the bar pattern speed. Combining our analysis with
previous studies, we compared the properties of weak and strong bars. We
measured the bar radius and strength from the r-band images available in SDSS
and bar pattern speed and corotation radius from the stellar kinematics
obtained by CALIFA. We derived the bar rotation rate as the ratio between the
corotation and bar radii. Thirteen out of 29 galaxies, which were
morphologically classified as SABs from a visual inspection, do not actually
host a bar component or their central elongated component is not in rigid
rotation. We successfully derived the bar pattern speed in 16 objects. Two of
them host an ultrafast bar. Using the bar strength to differentiate weak and
strong bars, we found that the SABs host shorter bars with smaller corotation
radii than their strongly barred counterparts. Weak and strong bars have
similar bar pattern speeds and rotation rates, which are all consistent with
being fast. We did not observe any difference between the bulge prominence in
SAB and SB galaxies, whereas nearly all the weak bars reside in the disc inner
parts, contrary to strong bars. We ruled out that the bar weakening is only
related to the bulge prominence and that the formation of weak bars is
triggered by the tidal interaction with a companion. Our observational results
suggest that weak bars may be evolved systems exchanging less angular momentum
with other galactic components than strong bars.
