Bar Model

The bisymmetric module extends the axisymmetric disc model with two-sided streaming terms. Use it for a galaxy with independent evidence of a bar.

Before fitting

Capivara estimates a bar-angle prior from the central white-light elongation and deprojects it relative to the kinematic disc major axis. It does not use the disc position angle as the bar angle, because that would assume alignment. Use bar_phi_deg to supply a measured in-plane angle.

Fit the bar module

library(capivara)

bar_result <- run_kinematic_analysis(
  cube_path = "/data/known_barred_galaxy.fits",
  redshift = 0.03,
  emission_line = "halpha",
  segmentation_mode = "kinematic",
  model = "bisymmetric_bar",
  knn_k = 50,
  n_segments = 25,
  model_control = list(
    disc_inc_deg = 38,
    robust_fit = TRUE
  ),
  show_plots = TRUE
)

plot(bar_result, which = "components")

The components plot is available only for the bisymmetric model. It shows the circular, tangential second-order, and radial second-order terms.

Optional bar-support prior

The model normally uses the full kinematic footprint. To add a measured bar footprint as a weak geometric prior:

model_control = list(
  bar_phi_deg = 41, # optional measured in-plane override
  use_bar_support_mask = TRUE,
  bar_support_width_deg = 25
)

Compare this result with the full-footprint model.

Start with the axisymmetric model in Kinematic Analysis. Interpret a bar only after comparing the model diagnostics with independent observations.