Ortwin Gerhard, Inma Martinez-Valpuesta
Recent data from the VVV survey have strengthened evidence for a structural
change in the Galactic bulge inwards of |l|<=4 deg. Here we show with an N-body
barred galaxy simulation that a boxy bulge formed through the bar and buckling
instabilities effortlessly matches measured bulge longitude profiles for red
clump stars. The same simulation snapshot was earlier used to clarify the
apparent boxy bulge - long bar dichotomy, for the same orientation and scaling.
The change in the slope of the model longitude profiles in the inner few
degrees is caused by a transition from highly elongated to more nearly
axisymmetric isodensity contours in the inner boxy bulge. This transition is
confined to a few degrees from the Galactic plane, thus the change of slope is
predicted to disappear at higher Galactic latitudes. We also show that the
nuclear star count map derived from this simulation snapshot displays a
longitudinal asymmetry similar to that observed in the 2MASS data, but is less
flattened to the Galactic plane than the 2MASS map. These results support the
interpretation that the Galactic bulge originated from disk evolution, and
question the evidence advanced from star count data for the existence of a
secondary nuclear bar in the Milky Way.
View original:
http://arxiv.org/abs/1112.0179
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