The Vertical Stellar Kinematics in Face‐On Barred Galaxies: Estimating the Ages of Bars

In order to perform a detailed study of the stellar kinematics in thevertical axis of bars, we obtained high signal-to-noise spectra along the majorand minor axes of the bars in a sample of 14 face-on galaxies, and used them todetermine the line of sight stellar velocity distribution, parameterized asGauss-Hermite series. With these data, we developed a diagnostic tool thatallows one to distinguish between recently formed and evolved bars, as well asestimate their ages, assuming that bars form in vertically thin disks,recognizable by low values for the vertical velocity dispersion sigma_z.Through N-body realizations of bar unstable disk galaxies we could also checkthe time scales involved in the processes which give bars an important verticalstructure. We show that sigma_z in evolved bars is roughly around 100 Km/s,which translates to a height scale of about 1.4 Kpc, giving support toscenarios in which bulges form through disk material. Furthermore, the bars inour numerical simulations have values for sigma_z generally smaller than 50Km/s even after evolving for 2 Gyr, suggesting that a slow process isresponsible for making bars as vertically thick as we observe. We verifytheoretically that the Spitzer-Schwarzschild mechanism is quantitatively ableto explain these observations if we assume that giant molecular clouds aretwice as much concentrated along the bar as in the remaining of the disk.