Kanak Saha, Inma Martinez-Valpuesta, Ortwin Gerhard
Secular evolution is one of the key routes through which galaxies evolve
along the Hubble sequence. Not only the disk undergoes morphological and
kinematic changes, but also a preexisting classical bulge may be dynamically
changed by the secular processes driven primarily by the bar. We study the
influence of a growing bar on the dynamical evolution of a low mass classical
bulge such as might be present in galaxies like the Milky Way. Using
self-consistent high resolution {\it N}-body simulations, we study how an
initially isotropic non-rotating small classical bulge absorbs angular momentum
emitted by the bar. The basic mechanism of this angular momentum exchange is
through resonances and a considerable fraction of the angular momentum is
channeled through Lagrange point (-1:1) and ILR (2:1) orbits. In the phase of
rapid dynamical growth, also retrograde non-resonant orbits absorb significant
angular momentum. As a result of this angular momentum gain, the initially
non-rotating classical bulge transforms into a fast rotating, radially
anisotropic and triaxial object, embedded in the similarly fast rotating boxy
bulge formed from the disk. Towards the end of the evolution, the classical
bulge develops cylindrical rotation. By that time, its inner regions host a
"classical bulge-bar" whose distinct kinematics could serve as direct
observational evidence for the secular evolution in the galaxy. Some
implications of these results are discussed briefly.
View original:
http://arxiv.org/abs/1105.5797
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