Modeling Star Formation: Implications for Remnants

From Mihos & Hernquist (1996) 
Thumbnail physics:
Inflows and starbursts can be altered by disk stability:
  • Presence/absence of a central bulge (Mihos & Hernquist 1994, 1996)
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  • Reduced disk surface density (eg, LSBs; Mihos, McGaugh, & de Blok 1997; Mihos 1999)
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  • Suppressing orbital resonances (Barnes & Hernquist 1996)

Comparing different models:

  • Inflow mechanism and starburst timescales fairly robust, but absolute SFRs less so. Depends on the compressibility of the gas (cf. MH96, GI99, S00).
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  • Qualitative morphology (ie, disk vs nuclear) good, but details remain unresolved.
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  • Distribution of starburst population very sensitive to detailed physics, and computational implementation. One robust result: starburst cores.

Implications for Remnants: Qualitative Inferences

Finally, be careful about progenitor evolution !

If present-day ellipticals formed from mergers at higher redshifts, the progenitors may have systematically different structural and gas properties compared to z=0 spirals

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).

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

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

Could this deplete the galaxies of fuel needed to drive ULIRG-type nuclear starbursts?



Bunker etal 2000 high z galaxies


How will these differences translate back into structural properties of remnants?
Are low-z merger remnants the same as high-z remnants?