Gas Excitation in ULIRGS: Maps of Diagnostic Emission-Line Ratios in
  Space and Velocity
  Emission-line spectra extracted at multiple locations across 39 ultraluminous
infrared galaxies have been compiled into a spectrophotometric atlas. Line
profiles of H alpha, [N II], [S II], [O I], H beta, and [O III] are resolved
and fit jointly with common velocity components. Diagnostic ratios of these
line fluxes are presented in a series of plots, showing how the Doppler shift,
line width, gas excitation, and surface brightness change with velocity at
fixed position and also with distance from the nucleus. One general
characteristic of these spectra is the presence of shocked gas extending many
kiloparsecs from the nucleus. In some systems, the shocked gas appears as part
of a galactic gas disk based on its rotation curve. These gas disks appear
primarily during the early stages of the merger. The general characteristics of
the integrated spectra are also presented.
