Arp 299

 
Observations of neutral hydrogen in tidal debris sometimes reveal marked spatial offsets between the gas and stars, most notably in Arp 299 

This effect was not seen in models of galaxy interactions. 

What is happening? (Hibbard etal 2000)

  • interaction between gas tail and hot (unseen) halo gas?
  • interaction between gas tail and expanding starburst wind?
  • HI dissociation by stellar tail?
  • consequences of warped progenitor disks?

Hibbard & Yun 2000

Previous models of interacting galaxies had typically assumed exponential gas disks, and saw no offsets (e.g., Mihos & Hernquist 1996; Barnes & Hernquist 1996). Models with extended gas disks show a different behavior:
 


 (Mihos 2001)

What has happened? Compared to the stellar tails, gas in tails:

  • comes from larger initial radius,
  • is less bound, and
  • has higher specific angular momentum,
and therefore tends to lead the stellar tails. 

 
(Mihos 2001)