Analysis of the Interaction Effects in the Southern Galaxy Pair Tol 1238−364 and ESO 381‐G009

In the context of the connection among galaxy-galaxy interaction, starburstsand nuclear activity, we present and discuss a quantitative morphologicalanalysis based on BVR images and a detailed spectroscopic investigation of twointeracting galaxies, the Seyfert 2 Tol1238-364 (IC 3639) and its companionESO381-G009, forming a triple system with ESO381-G006. Broad-band opticalphotometry is complemented by Halpha imaging, which provides information aboutthe distribution of star forming regions across the galaxies. Long-slitspectroscopic data obtained at different position angles of the slit areemployed to determine the physical conditions of circumnuclear and extranuclearregions. A mixture of thermal and non-thermal ionizing radiation is found inthe surroundings of the nucleus of Tol1238-364 and the energy budget supportsthe presence of a circumnuclear starburst.Several regions in both the galaxiesshow anomalous line ratios: additional ionization by shock-heating and lowionization of some extranuclear HII regions are suggested as possibleexplanations. An analysis of the emission-line profiles reveals the presence ofa broad Halpha component in the nuclear region of Tol1238-364. Independentestimates of the star formation rates (SFR) were obtained throughflux-calibrated Halpha-images and FIR emission in the four IRAS bands. OverallSFR densities have been compared with the SFR densities derived from Halphaemission in the individual regions of the galaxies sampled by long-slitspectra. In both galaxies an enhancement of the star formation activity withrespect to isolated galaxies is revealed. The prevalence of starburst ornuclear activity has been examined through FIR color indices. The interactionscenario is discussed on the basis of the observed galaxy properties.