Fathi, K.; Beckman, J. E.; Piñol-Ferrer, N.; Hernandez, O.; Martínez-Valpuesta, I.; Carignan, C.
Bibliographical reference
The Astrophysical Journal, Volume 704, Issue 2, pp. 1657-1675 (2009).
Description
We have applied the Tremaine-Weinberg method to 10 late-type barred
spiral galaxies using data cubes, in Hα emission, from the FaNTOmM
and GHAFAS Fabry-Perot spectrometers. We have combined the derived bar
(and/or spiral) pattern speeds with angular frequency plots to measure
the corotation radii for the bars in these galaxies. We base our results
on a combination of this method with a morphological analysis designed
to estimate the corotation radius to bar-length ratio using two
independent techniques on archival near-infrared images, and although we
are aware of the limitation of the application of the Tremaine-Weinberg
method using Hα observations, we find consistently excellent
agreement between bar and spiral arm parameters derived using different
methods. In general, the corotation radius, measured using the
Tremaine-Weinberg method, is closely related to the bar length, measured
independently from photometry and consistent with previous studies. Our
corotation/bar-length ratios and pattern speed values are in good
agreement with general results from numerical simulations of bars. In
systems with identified secondary bars, we measure higher Hα
velocity dispersion in the circumnuclear regions, whereas in all the
other galaxies, we detect flat velocity dispersion profiles. In the
galaxies where the bar is almost purely stellar, Hα measurements
are missing, and the Tremaine-Weinberg method yields the pattern speeds
of the spiral arms. The excellent agreement between the
Tremaine-Weinberg method results and the morphological analysis and bar
parameters in numerical simulations suggests that although the Hα
emitting gas does not obey the continuity equation, it can be used to
derive the bar pattern speed. In addition, we have analyzed the Hα
velocity dispersion maps to investigate signatures of secular evolution
of the bars in these galaxies. The increased central velocity dispersion
in the galaxies with secondary bars suggests that the formation of inner
bars or disks may be a necessary step in the formation of bulges in
late-type spiral galaxies.
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