Mapping the three-dimensional “x-shaped structure” in models of the Galactic bulge

Journal Article · Sun Dec 20 04:00:00 EST 2015 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/815/2/L20· OSTI ID:22868729

Li, Zhao-Yu; Shen, Juntai ^[1]

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1. Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Science, 80 Nandan Road, Shanghai 200030 (China)

Numerical simulations have shown that the X-shaped structure in the Milky Way bulge can naturally arise from bar instability and buckling instability. To understand the influence of buckling amplitude on the morphology of the X-shape, we analyze three self-consistent numerical simulations of barred galaxies with different buckling amplitudes (strong, intermediate, and weak). We derive the three-dimensional density using an adaptive kernel smoothing technique. The face-on isodensity surfaces are all elliptical, while in the edge-on view, the morphology of buckled bars transitions with increasing radius from a central boxy core to a peanut bulge and then to an extended, thin bar. Based on these isodensity surfaces at different density levels, we find no clear evidence for a well-defined structure shaped like the letter X. The X-shaped structure is more peanut-like, the visual perception of which is probably enhanced by the pinched inner concave isodensity contours. The peanut bulge can reproduce qualitatively the observed bimodal distributions that were used as evidence for the discovery of the X-shape. The central boxy core is shaped like an oblong tablet, extending ∼500 pc above and below the Galactic plane (|b|∼4{sup ∘}). From the solar perspective, lines of sight passing through the central boxy core do not show bimodal distributions. This generally agrees with the observations that double peaks merge at |b| ∼ 4°–5° from the Galactic plane, indicating the presence of a possibly similar structure in the Galactic bulge.

• OSTI ID: 22868729
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 2 Vol. 815; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BUCKLING
COMPUTERIZED SIMULATION
DENSITY
GALAXY CLUSTERS
INSTABILITY
KERNELS
MILKY WAY
MORPHOLOGY
THREE-DIMENSIONAL LATTICES