Going to Higher Redshift

Questions:

How do the properties of high redshift galaxies compare to those at z=0?
How does this translate to differences (if any) in the collisional response?

What does stability depend on?

Local -- Toomre Q	Global -- Toomre X

Galaxies are (probably) more gas-rich:

Toy model for gas fraction evolution

Z_form = 3
Omega_M=0.3, Omega_L=0.7

Model	tau (Gyr)	f_b(z=0)
Sa	3	0.05
Sb	5	0.1
Sc	10	0.3

Under threshold models for star formation (e.g., Quirk 1972, Kennicutt 1989) these gas-rich galaxies may be nearer to the critical threshold for star formation:

eg, semianalytic modeling by Kauffmann 1996:

z=0	z=2.5

Gas sits at high densities and is more prone to local gravitational collapse: high-z interactions may be much more efficient at driving global, disk-wide starburst activity.

We may be seeing this in the very knotty appearance of high redshift galaxies.

HST medium deep survey image (Griffiths etal 1995)

Multiwavelength images of high-z galaxies (Bunker etal 2000)

What about inflows and nuclear starbursts? Are high-z disks any more or less stable than low-z disks?

Hints:

Out to z~1 there seems to be only mild evolution of luminous disk galaxies (eg Driver etal 1995; Vogt etal 1997; Lilly etal 1998)

N-body (Steinmetz 2000) and semi-analytic (Kauffmann 1996, Baugh etal 1996) models suggest that bulges of luminous spirals are assembled by z ~ 1-1.5 or so.

At higher redshift, there is some observational evidence for a decrease in B/D ratio

At higher redshift there is also indications that the observed galaxy population is more compact

figure from Marleau & Simard (1998);
data from Cohen etal (1996), Steidel etal (1996), Zepf etal (1997), Lowenthal etal (1997)

So where does that leave us?

z > 1-2 galaxies very unstable; highly reactive.

strong central starbursts, a la ULIRGs (SCUBA sources? Barger etal 1999, Smail etal 1999, Blain etal 2000)

But do any of these arguments apply?

0.5 < z < 1 disks more globally stable (with considerable variation), but gas-rich and locally sensitive.

Messy looking optical galaxies which look more normal in NICMOS (eg Dickinson 2000)

Mild SFR enhancements in interactions at z=0-1 (0.5 mag/2x; Le Fevre etal 2000)

z < 0.5 galaxies evolve towards more quiescent interactions.

But spectacular exceptions exist!

Unfortunately the situation is nowhere near this simple...

Stability does not really depend on B/D ratio - this is an overly simple parameterization

compare MH96 to BH96...
Little correlation between Hubble type and SFR (other than gas content effects)
More dependent on v(r) and disk surface density -- need spatially resolved (sub kpc) kinematics as a function of z...

Do galaxies build up around their bulges? (eg Steinmetz 2000) gas infall/accretion vs gas depletion...

Do minor mergers "build up" disk bulges? (vs halos? Walker etal 1996; Huang and Carlberg 1997; Johnston etal 1997; Helmi etal 1999)

What role does secular evolution play? (Norman, Pfenniger, Friedli, Sellwood, etc)

Do exponential bulges provide the same level of dynamical support as rquart bulges?
Can this process work in detail (matching ages, kinematics, structural properties of bulges?)

z > 1-2	galaxies very unstable; highly reactive.
	strong central starbursts, a la ULIRGs (SCUBA sources? Barger etal 1999, Smail etal 1999, Blain etal 2000) But do any of these arguments apply?
0.5 < z < 1	disks more globally stable (with considerable variation), but gas-rich and locally sensitive.
	Messy looking optical galaxies which look more normal in NICMOS (eg Dickinson 2000) Mild SFR enhancements in interactions at z=0-1 (0.5 mag/2x; Le Fevre etal 2000)
z < 0.5	galaxies evolve towards more quiescent interactions.
	But spectacular exceptions exist!