Progressive Starbursts and High Velocities in the Infrared-luminous, Colliding Galaxy Arp 118

In this paper we demonstrate for the first time the connection between thespatial and temporal progression of star formation and the changing locationsof the very dense regions in the gas of a massive disk galaxy (NGC 1144) in theaftermath of its collision with a massive elliptical (NGC 1143). These twogalaxies form the combined object Arp 118, a collisional ring galaxy system.The results of 3D, time-dependent, numerical simulations of the behavior of thegas, stars, and dark matter of a disk galaxy and the stars and dark matter inan elliptical during a collision are compared with multiwavelength observationsof Arp 118. The collision that took place approximately 22 Myr ago generated astrong, non-linear density wave in the stars and gas in the disk of NGC 1144,causing the gas to became clumped on a large scale. This wave produced a seriesof superstarclusters along arcs and rings that emanate from the central pointof impact in the disk. The locations of these star forming regions match thoseof the regions of increased gas density predicted the time sequence of models.The models also predict the large velocity gradients observed across the diskof NGC 1144. These are due to the rapid radial outflow of gas coupled to largeazimuthal velocities in the expanding ring, caused by the impact of the massiveintruder.Comment: 12 pages in document, and 8 figures (figures are separate from the document's file); Submitted to Astrophysical Journal Letter