Galaxy Collisions

Curtis Struck

Dept of Physics and Astronomy, Iowa State University, Ames, IA 50010 USA

E-mail: curt@iastate.edu


Table 1: Classification Variables

Timescale

Y (young)

² 108 yr.

I (intermediate)

108-108

O (old)

> 109 yr.

Hubble Type

for each galaxy

(Disk component,

gas fraction)

E

elliptical, spheroidal

D

significant disk

G

gas disk, or

irregular

Companion Mass,

Perturbation Amplitude

Small < 10%

denote by subscript

Intermediate Å 10-50%

lower case

Large > 50%

upper case

Spin-Orbit

Coupling

(for each galaxy)

+

prograde

0

orthogonal

-

retrograde

Table 2: General Types of Induced Star Formation

Type

Description

Activity Timescale

Relative Intensity

Example

Central Starbursts

Nuclear, Nuclear Rings, or Bars

Short to Intermediate

Moderate

M82

Waves in Disks

Rings, Spirals or more complicated forms

Short to Intermediate

Weak - Moderate

M51, Cartwheel

Extended Tidal Features

Tails, Bridges, etc.

Short to Intermediate

Weak

Arp 295

Mergers

Strong Central SF (plus any of the above)

Intermediate to Long

Weak to Strong

Arp 220

Table 3: Merger Rate Exponent Determinations

Source

Exponent m

Mean Survey Redshift

Zepf & Koo 1989

4.0 ± 2.5

0.25

Burkey et al. 1994

2.5 ± 0.5

0.4

Calberg, Pritchet, & Infante 1994

3.4 ± 1.0

0.4

Woods, Fahlman, & Richer 1995

Å 0

³ 0.4

Yee & Ellingson 1995

4.0 ± 1.5

0.38

Lavery et al. 1996

Å 4.5

Å 1.0

Neuschaefer et al. 1997

HST Medium Deep Survey

1.2 ± 0.4

1-2

Patton et al. 1997

2.8 ± 0.9

0.33