BAR DIAGNOSTICS IN EDGE-ON SPIRAL GALAXIES. III. N-BODY SIMULATIONS OF DISKS

摘要

Present in over 45% of local spirals, boxy and peanut-shaped bulges are generally interpreted as edge-on bars and may represent a key phase in bar evolution. Aiming to test such claims, the kinematic properties of self-consistent three-dimensional N-body simulations of bar-unstable disks are studied. Using Gauss-Hermite polynomials to describe the major-axis stellar kinematics, a number of characteristic bar signatures are identified in edge-on disks: (1) a major-axis light profile with a quasi-exponential central peak and a plateau at moderate radii (Freeman type II profile); (2) a "double-hump" rotation curve; (3) a sometimes flat central velocity dispersion peak with a plateau at moderate radii and occasional local central minimum and secondary peak; and (4) an h_3-V correlation over the projected bar length. All of these kinematic features are spatially correlated and can easily be understood from the orbital structure of barred disks. They thus provide a reliable and easy-to-use tool to identify edge-on bars. Interestingly, they are all produced without dissipation and are increasingly realized to be common in spirals, lending support to bar-driven evolution scenarios for bulge formation. So called "figure-of-eight" position-velocity diagrams are never observed, as expected for realistic orbital configurations. Although not uniquely related to triaxiality, line-of-sight velocity distributions with a high-velocity tail (i.e., an h_3-V correlation) appear as particularly promising tracers of bars. The stellar kinematic features identified grow in strength as the bar evolves and vary only slightly for small inclination variations. Many can be used to trace the bar length. Comparisons with observations are encouraging and support the view that boxy and peanut-shaped bulges are simply thick bars viewed edge-on.