Bar-Driven Evolution and 2D Spectroscopy of Bulges

Abstract

A multi-faceted approach is described to constrain the importance of bar-driven evolution in disk galaxies, with a special emphasis on bulge formation. N-body simulations of bars are compared to the stellar kinematics and near-infrared morphology of 30 edge-on spirals, most with a boxy bulge. The N-body simulations allow to construct stellar kinematic bar diagnostics for edge-on systems and to quantify the expected vertical structure of bars. Long-slit spectra of the sample galaxies show characteristic double-hump rotation curves, dispersion profiles with secondary peaks and/or flat maxima, and correlated h ₃ and V profiles, indicating that most of them indeed harbor edge-on bars. The stellar kinematics also suggests the presence of cold, quasi-axisymmetric central stellar disks. The ionized-gas distribution and kinematics further suggests that those disks formed through bar-driven gaseous inflow and subsequent star formation, which are absent in our simulations. Minimally affected by dust and dominated by Population II stars, K-band imaging of the same galaxies spectacularly highlights radial variations of the bars’ scaleheights, as expected from vertical disk instabilities. The light profiles also vary radially in shape but never approach a classic deVaucouleurs law. Filtering of the images further isolates the specific orbit families at the origin of the boxy structure, which can be directly related to periodic orbit calculations in generic 3D barred potentials. Bars are thus shown to contribute substantially to the formation of both large-scale triaxial bulges and embedded central disks. Relevant results from the SAURON survey of the stellar/ionized-gas kinematics and stellar populations of spheroids are also briefly described. Specific examples supporting the above view are used to illustrate the potential of coupling stellar kinematics and linestrengths (age and metallicity), here specifically to unravel the dynamical evolution and related chemical enrichment history of bars and bulges.