Bar Diagnostics in Edge‐on Spiral Galaxies. I. The Periodic Orbits Approach

We develop diagnostics to detect the presence and orientation of a bar in anedge-on disk, using its kinematical signature in the position-velocity diagram(PVD) of a spiral galaxy observed edge-on. Using a well-studied barred spiralgalaxy mass model, we briefly review the orbital properties of two-dimensionalnon-axisymmetric disks and identify the main families of periodic orbits. Weuse those families as building blocks to model real galaxies and calculate thePVDs obtained for various realistic combinations of periodic orbit families andfor a number of viewing angles with respect to the bar. We show that the globalstructure of the PVD is a reliable bar diagnostic in edge-on disks.Specifically, the presence of a gap between the signatures of the families ofperiodic orbits in the PVD follows directly from the non-homogeneousdistribution of the orbits in a barred galaxy. Similarly, material in the twoso-called forbidden quadrants of the PVD results from the elongated shape ofthe orbits. We show how the shape of the signatures of the dominant x1 and x2families of periodic orbits in the PVD can be used efficiently to determine theviewing angle with respect to the bar and, to a lesser extent, to constrain themass distribution of an observed galaxy. We also address the limitations of themodels when interpreting observational data.Comment: 22 pages, 9 figures (AASTeX, aaspp4.sty). Accepted for publication in The Astrophysical Journa