Mergers of Galaxies from an HI Perspective

J. E. Hibbard, NRAO

HI spectral line mapping observations are a unique probe of morphologically peculiar systems. Not only does HI imaging often reveal peculiarities that are totally unsuspected at optical wavelengths, but it opens a kinematic window into the outer dynamics of these systems that is unmatched at any other wavelength. In this review I summarize what we have learned from such studies, and what we may hope to learn from them in the future.

Published Version of Talk (.ps.gz)

Talk Vugraphs:

• Title vugraph (see above)
• ~150 major mergers or merger remnants imaged in HI (text file)
• Tidal features form from outer regions of disks, rich in HI (HI in 14 Mergers)
• What do we learn from HI mapping? (outline)
• HI reveals systems not thought to be interacting
  • HI in M81 system
  • Optically normal systems with disturbed HI
• HI gives unique mapping of kinematics
• From simulations it is clear that tidal tails are structured kinematically (E,J,vrad vs radius)
• Continuous kinematic mapping allows detailed matches to simulations
  • Match to NGC 7252 data
  • Match to NGC 4676 data
  • Match to NGC 4038/9 data
  • Match to Arp 299 data
• Bases of tails are more tightly bound, fall back and form loops & shells (NGC 7252 shell formation)
• Signature of "Fallback" observed in HI mapping observations of Shell galaxies (HI in NGC 2865)
• Striking resemblance to other perplexing HI structures (Leo Ring)
• Ends of tail are unbound and do not symmetrize (NGC 7252 late stage evolution)
• Extent of tidal features
  • Normal galaxies exhibit sharp edges to HI distribution (show NGC 3198 NHI(r) - not here)
  • Tidal HI features show same edge, implying observed features are "tip of the iceberg" (NHI vs Area for mergers)
• Substructure within tails
  • HI provides only kinematic evidence (TDGs in NGC 3921, NGC 7252)
  • Implications of substructure
• Gas not always sent into tails; often find rings or disks
  • NGC 520
  • MCG -5-7-1 vers 1, vers 2,
  • Arp 230
• Not all systems appear to be easily produced via tides (Mrk 348)
• Conclusions
• Future Plans:
  • short-term: VLA expansion will trace evolution of HI from z=0-1;
  • SKA will be 50 times more sensitive

Poster Luminosity Profiles of Merger Remnants. (.ps.gz)