Bibcode
Saha, K.; Gerhard, O.; Martinez-Valpuesta, I.
Bibliographical reference
Astronomy and Astrophysics, Volume 588, id.A42, 10 pp.
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4
2016
Journal
Citations
28
Refereed citations
24
Description
Context. Classical bulges in spiral galaxies are known to rotate, but
the origin of this observed rotational motion is not well understood. It
has been shown recently that a low-mass classical bulge (ClB) in a
barred galaxy can acquire rotation by absorbing a significant fraction
of the angular momentum emitted by the bar. Aims: Our aim here is
to investigate whether bars can also spin up more massive ClBs during
the secular evolution of the bar, and to study the kinematics and
dynamics of these ClBs. Methods: We use a set of self-consistent
N-body simulations to study the interaction of ClBs with a bar that
forms self-consistently in the disk. We use orbital spectral analysis to
investigate the angular momentum gain by the classical bulge stars. Results: We show that the ClBs gain on average 2-6% of the disk's
initial angular momentum within the bar region. Most of this angular
momentum gain occurs via low-order resonances, particularly 5:2 resonant
orbits. A density wake forms in the ClB which corotates and aligns with
the bar at the end of the evolution. The spin-up process creates a
characteristic linear rotation profile and mild tangential anisotropy in
the ClB. The induced rotation is small in the centre, but is significant
beyond ~2 bulge half mass radii, where it leads to mass-weighted
V/σ ~ 0.2, and reaches a local
Vmax/σin ~ 0.5 at around the scale of the
bar. The resulting V/σ is tightly correlated with the ratio of the
bulge size to the bar size. In all models, a box/peanut bulge forms
suggesting that composite bulges may be common. Conclusions:
Bar-bulge resonant interaction in barred galaxies can provide some
spin-up of massive ClBs, but the process appears to be less efficient
than for low-mass ClBs. Further angular momentum transfer due to nuclear
bars or gas inflow would be required to explain the observed rotation if
it is not primordial.