Detalles de publicación
PP 018117
Spiral Structure in Barred galaxies. Observational constraints to spiral arm formation mechanisms
1. Instituto de Astrofísica de Canarias, Tenerife, Spain. 2. Departamento de Astrofísica, Universidad de La Laguna, Tenerife, Spain 3. Gran Telescopio CANARIAS, La Palma, Spain 4 Astrophysics Research Centre, Liverpool John Moores University, UK 5. Reserach Center for Astronomy, Academy of Athens,Greece Greece.
A method which we have developed for determining corotation radii, has allowed us to map
in detail the radial resonant structures of barred spiral galaxies. Here we have combined this
information with new determinations of the bar strength and the pitch angle of the innermost
segment of the spiral arms to find relationships between these parameters of relevance to the
dynamical evolution of the galaxies. We show how (1) the bar mass fraction, (2) the scaled
bar angular momentum, (3) the pitch angle, and (4) the shear parameter vary along the Hubble
sequence, and we also plot along the Hubble sequence (5) the scaled bar length, (6) the ratio
of bar corotation radius to bar length, (7) the scaled bar pattern speed, and (8) the bar strength.
It is of interest to note that the parameters (2), (5), (6), (7), and (8) all show breaks in their
behaviour at type Scd. We find that bars with high shear have only small pitch angles, while
bars with large pitch angles must have low shear; we also find a generally inverse trend of
pitch angle with bar strength. An inference which at first seems counter-intuitive is that the
most massive bars rotate most slowly but have the largest angular momenta. Among a further
set of detailed results we pick out here the 2:1 ratio between the number of spiral arms and
the number of corotations ouside that of the bar. These results give a guideline to theories of
disc-bar evolution.
in detail the radial resonant structures of barred spiral galaxies. Here we have combined this
information with new determinations of the bar strength and the pitch angle of the innermost
segment of the spiral arms to find relationships between these parameters of relevance to the
dynamical evolution of the galaxies. We show how (1) the bar mass fraction, (2) the scaled
bar angular momentum, (3) the pitch angle, and (4) the shear parameter vary along the Hubble
sequence, and we also plot along the Hubble sequence (5) the scaled bar length, (6) the ratio
of bar corotation radius to bar length, (7) the scaled bar pattern speed, and (8) the bar strength.
It is of interest to note that the parameters (2), (5), (6), (7), and (8) all show breaks in their
behaviour at type Scd. We find that bars with high shear have only small pitch angles, while
bars with large pitch angles must have low shear; we also find a generally inverse trend of
pitch angle with bar strength. An inference which at first seems counter-intuitive is that the
most massive bars rotate most slowly but have the largest angular momenta. Among a further
set of detailed results we pick out here the 2:1 ratio between the number of spiral arms and
the number of corotations ouside that of the bar. These results give a guideline to theories of
disc-bar evolution.