NGC 7252 - Unraveling the Atoms for Peace

 
NGC 7252: The classic merger remnant! 
(Schweizer 1978, 1982; Toomre 1977)
  • What was the interaction history like?
  • Do we require "special circumstances"?
  • Can we tie dynamical response to other properties of the system?
  • What would the future evolution look like?

 

Turn to computer simulations for assistance... 

(from Hibbard etal 1994)

 
(from Borne and Richstone 1990)
 Early simulations by Borne and Richstone (1990) used morphology and Ha kinematics of Schweizer (1982) to constrain the orbital solution.

Their result:

  • Very tightly bound, circular orbit
  • Highly retrograde disk geometries
  • Remnant had not yet settled at "current time"
The problem:
Crucial kinematic data lies within the tidal tails, and is poorly sampled in Ha. 

Compared to the fully sampled HI emission in the tidal tails (Hibbard etal 1994), the models predicted the wrong kinematic gradient for the tails.

 
 
A more astrophysical solution (Hibbard and Mihos 1995) Result:
  • A parabolic orbit
  • Largely prograde interaction
  • Timescales better:
    • Interaction age: 850 Myr
    • Merger age: 450 Myr
(from Hibbard and Mihos 1995)

 
What's in store for NGC 7252?

Freeze the potential and calculate orbits for material in the tidal debris. We see a slow, continual "drizzle" of HI back onto the remnant for many billions of years...


 
 
 
 
 
Early infall involves material with low angular momentum, and can lead to reformation of a disk in the inner regions.

Later accretion has higher angular momentum, producing extended, diffuse gaseous structures.


Perhaps looking something like Cen A  in a few billion years...

Optical: Malin etal 1983
HI: Schiminovich etal 1994

Tidal Tails and Disk Truncations

(with Stephanie Bush, Kelly Holley-Bockelmann, and John Feldmeier)

Spiral disks may be truncated (eg van der Kruit & Searle 1981, 1982); de Grijs etal 2000; Pohlen etal 2000...), at small radii...

Test tail morphology for disk truncations at Rt=2, 3, 4, 5, and 10 disk scale lengths.

Convert luminosity profile to mass profile using simple models of star formation in mergers. (Body: M/L = 2.5, Tails: M/L = 5). Caveats:
  • probably underestimating tail luminosity -- sims can live "above" observational curve.
  • constant M/L pushes "observational" curves down -- but is it realistic?
Morphology and photometry both suggest Rt= 4-5 disk scale lengths.