Lessons from the Field

 
Dynamical modeling of isolated encounters:
 
  • Collisional perturbation
  • Self gravitating response
  • Gas inflow + activity
  • Merger


(Noguchi 1987;  Barnes 1988; Barnes & Hernquist 1991, 1996; Mihos etal 1992, 1993; Mihos & Hernquist 1994, 1996; Hernquist & Mihos 1995; Bekki 1998; Gerritsen & Icke 1999; Springel 2000)





 
 
Star formation in interacting galaxies:
  • SFR enhancements of ~ few times
  • Nuclear star formation 
  • Starburst fractions ~ few % of stellar mass
(Larson & Tinsley 1978; Hummel 1981; Condon etal 1982; Joseph etal 1982; Lonsdale etal 1984; Keel etal 1985; Kennicutt etal 1987; Bushouse 1986; Liu & Kennicutt 1995; Barton etal 2000)

 
But the action is in the infrared!
  • luminous infrared galaxies 
    • (Lfir ~ 1011 - 1012 Lsun)
  • dust enshrouded
  • close mergers
  • nuclear gas concentrations and starbursts
(Soifer etal 1984; Sanders etal 1988; Lawrence etal 1989; Kim etal 1995; Solomon etal 1997; Mihos & Bothun 1998; Rigopoulou etal 1999)
Hibbard and Yun 1997

So what determines the outcome of an interaction?
    Encounter parameters? Gas fraction? Galaxy type? Environment?


Back to the models...

Gaseous inflow and central activity are driven by gravitational torques -- i.e., the self-gravitating response of the disk (Noguchi 1987; Barnes & Hernquist 1991; Mihos & Hernquist 1996). Suppress the self-gravitational response, suppress the inflow and activity.

A variety of ways:

  • Steeply rising rotation curve (Mihos & Hernquist 1994, 1996; Gerritsen & Icke 1999; Springel 2000).
  • Reduce disk surface density (Mihos etal 1997).

  • Suppress orbital/rotational resonances (Barnes & Hernquist 1996).

Mihos & Hernquist 1996

Late-time evolution of tidal debris

Material ejected in tidal debris rains back over long timescales (Hernquist & Spergel 1992; Hibbard & Mihos 1995; Barnes 2002).

Hibbard etal 1994



(from Hibbard & Mihos 1995)

(from Mihos 2000)
 This gas can reaccrete and form extended gaseous disks on scales of several kpc (eg., Barnes 2002; Naab etal 2003).
  • HI disks, rings in ellipticals (eg van Gorkum & collaborators)
  • Disks in ellipticals (eg Bender & collaborators)
  • Rebuilding low B/D systems?