J. E. Hibbard, W. D. Vacca & M. S. Yun

As part of several HI synthesis mapping studies of merging galaxies, we have mapped the tidal gas in three disk-disk merger systems: Arp 157 (NGC 520), Arp 220, and Arp 299 (NGC 3690). These systems differ from the majority of the mergers mapped in HI, in that their optical and gaseous tidal morphologies are very different. In particular, they exhibit large optical tidal features with little if any accompanying neutral gas and large gas-rich tidal features with little if any accompanying starlight. On a smaller scale, there are striking anti-correlations where the gaseous and optical tidal features appear to cross. We explore several possible explanations for these differences, including dust obscuration, ram pressure stripping, and ionization effects. No single explanation can account for all of the observed differences. The fact that each of these systems shows evidence for a starburst driven superwind expanding in the direction of the most dramatic tidal displacements leads us to suggest that the wind plays a role in shaping the morphology of the tidal gas.

• pdf of AJ paper (0.8 MB)
• 4 panel mosaics: R greys; HI greys+contour; Opt greys+HI contours; HI greys + Opt contours (gifs)
  • Figure 1 (NGC 520)
  • Figure 2 (Arp 299)
  • Figure 3 (Arp 220)
• Figure 4 (.gif) (Intensity profiles along "Slice")
• Figure 5 (cartoon of wind/tail geometry for Arp 299) Color gif; B/W gif; B/W eps;

• NGC 520 full FOV (.gif)
• Arp 299 full FOV (.gif)
• Arp 220 full FOV (.gif)
• Development of tail, showing the displacements that occur between the gas rich outer regions (red) and optically brighter inner regions (blue) during mergers. (.gif)
• Numerical results from Chris Mihos, showing simular results to the above figure, but in a much more aesthetically pleasing manner. (.gif)
• Some less blatant examples (.jpg) Displacements in Arp 295, stellar tails extending beyond optical tails in NGC 4676, displacement between bright stellar tails and nearby HI in NGC 520 and NGC 3921. (from appendix of Hibbard & van Gorkom 1996, and Appendix IV of my thesis. )