VLT-VIMOS integral field spectroscopy of luminous and ultraluminous infrared galaxies - II. Evidence for shock ionization caused by tidal forces in the extra-nuclear regions of interacting and merging LIRGs

摘要: Context Luminous infrared galaxies (LIRGs) are an important class of objects in the low-z universe bridging gap between normal spirals and strongly interacting starbursting ultraluminous (ULIRGs). Since a large fraction stars Universe have been formed these objects, LIRGs also relevant high-z context. Studies two-dimensional physical properties still lacking. Aims. We aim to understand nature origin ionization mechanisms operating extra-nuclear regions as function interaction phase luminosity. Methods. This study uses optical integral field spectroscopy (IFS) data obtained with VIMOS. Our analysis is based on over 25 300 spectra 32 covering all types morphologies (isolated galaxies, pairs, advanced mergers), entire 10 11 ―10 12 L ⊙ luminosity range. Results. found strong evidence for shock ionization, clear trend dynamical status system. Specifically, we quantified variation several line ratios indicative excitation degree. While [N II]λ6584/Ha ratio does not show any significant change, [S II]λλ6717,6731/Hα [O I]λ6300/Hα higher more stages. Velocity dispersions than increase (medians 37, 46, 51 km s ―1 0-2, respectively). constrained main causing (typically distances ranging from ∼0.2―2.1 kpc ∼0.9―13.2 kpc) using diagnostic diagrams. Isolated systems mainly consistent caused by young stars. Large fractions pairs mergers shocks ν ≲ 200 . supported relation degree velocity dispersion ionized gas, which interpret but isolated galaxies. dependence (i.e. level star formation). All this indicates that tidal forces play key role ionizing regions. showed first time what appears be common log([OI]λ6300/Hα) ― log(σ) extranuclear gas (U)LIRGs 11.0 12.3 range). preliminary result needs investigated further larger sample ULIRGs.