1: Preliminaries   6:   Dynamics I 11: Star Formation  16: Cosmology
2: Morphology   7:   Ellipticals 12: Interactions 17: Structure Growth 
3: Surveys 8:   Dynamics II 13: Groups & Clusters  18: Galaxy Formation 
4: Lum. Functions  9:   Gas & Dust   14: Nuclei & BHs 19: Reionization & IGM  
5: Spirals 10: Populations    15: AGNs & Quasars 20: Dark Matter





(1) Introduction

(a) Importance of Interactions

Our view of the importance of galaxy-galaxy interactions has changed dramatically in the last 50 years.

Recognition of the importance of interactions gradually grew:

Taken together, Galaxy-Galaxy interactions are important in understanding many aspects galaxy evolution:

(b) Different Physical Regimes

To help clarify this topic, keep in mind several different regimes: [e.g. image ]


(2) Catalogs

(References below are taken from Bill Keel's web notes [o-link])

(a) Interactions

(b) Pairs

Once again mergers/interactions may be important in the history of all galaxies.


(3) Analytic Tools

We first consider four regimes which are analytically tractable as well as dynamically important.
They also develop our ability to interpret numerical simulations of more complex regimes.

    (a)   A small system moving through a larger one (dynamical friction)
    (b)   Tidally driven evaporation: the Jacobi (Roche) Limit
    (c)   "Slow" encounters, where Vinternal >> Vencounter   (adiabatic approximation)
    (d)   "Fast" encounters, where Vinternal << Vencounter   (impulse approximation; tidal shocking)

Unfortunately, major mergers do not conform to any of these regimes;
They cannot be treated analytically and require numerical simulation (see § 5)

(a) Dynamical Friction

(b) Tidally Driven Evaporation: Trunction and Disruption

(c) Adiabatic Approximation (Slow Encounter)

(d) Impulse Approximation (Fast Encounter: Tidal Shocks)


(4) Numerical Simulations: Methods


(5) Numerical Simulations: Results

Simulations have been applied in a range of circumstances

(a) Flyby and Tidal Tails

(b) Minor Mergers and Satellite Accretion

(c) Major Mergers


(6) Merger Relics

Although ongoing mergers are quite rare (they are short lived), former mergers (relics) should be common
There are a number of possible examples, though we start with a rather special one.

(a) Elliptical Galaxy Formation

(b) Counter-Rotating Disks

(c) Polar Ring Galaxies

(d) Shell Galaxies