...applied to clusters

So what's different in the cluster environment?

faster collisions inside the cluster (although not on the outskirts),

cluster effects:

global tides: strip away loosely bound outer parts of galaxies, add energy to bound groups.
the hot ICM: strip out low density ISM in galaxies.

and, at higher redshift, more differences:

z=2 galaxies ¹ z=0 galaxies,
differing cluster dynamics.

Faster collisions:

Whereas slow encounters drive activity in all spirals (albeit at a range of levels)...

...fast collisions affect mainly those low luminosity galaxies with slowly rising rotation curves (just restating Moore etal).

Early type spirals should experience weakly enhanced, disk-wide star formation.

Low luminosity, late type spirals respond more strongly: starbursts, inflow, activity (again, Moore etal, Lake etal).

If harassment is the whole story, it's hard to drive central starburst/AGN activity in luminous cluster spirals at moderate redshift (and how does this play into "upsizing" of poststarburst galaxies at higher z?).

Global tides and the hot ICM:

Cartoon model: merging in a tidal field, but will apply to any tidal interaction.

Tidal debris stripped away, hard to detect (the ICL!)

Unbinding of slow enounters

Late infall of stripped material is limited.

Gaseous tails will be very low density and patchy. Now factor in RPS.

"Priming the pump" for tidally stripping galaxies.

r_s	0.3 Mpc
r₂₀₀	2 Mpc
M₂₀₀	10¹⁵ M_sun
r_peri	0.5 Mpc
r_apo	2.0 Mpc

Differences at higher redshifts

The Evolution in B:D ratio

When did bulges form? When did disks? N-body (Steinmetz) and semi-analytic models (e.g., Kauffman and Baugh) suggest that bulges of luminous spirals are largely in place by z ~ 1 - 1.5. Observationally, there is some evidence for evolution in B:D ratio (e.g., Marleau and Simard 1998) past z=1, but Koo says luminous bulges already well-established.

More globally unstable at high z? Easier to drive nuclear accretion/starbursts/AGN?

Local vs global instabilities:

High redshift galaxies are also probably more gas-rich and perhaps more prone to local instabilities (e.g., Kauffmann 1996):

z=0

z=2.5

Encounters at higher redshift may very easily drive extremely luminous disk-wide starbursts, perhaps explaining the very knotty appearance of many high-z interactions.

Bunker etal 2000 high z galaxies

Going to higher redshifts yet:

clusters not yet virialized, in subclumps -- slow encounters more likely.
progenitor extrapolation even dicier!