Friday, August 18, 2006

C. Popovich: The star formation and assembly of high redshift galaxies

Observational constraints regarding massive galaxy formation, (i) when did the stars form; (ii) when did massive galaxies arrive at their current configuration. Comparison to theoretical predictions. Massive galaxies at high redshift are found in the red sequence of colour-magnitude diagrams (COMBO-17).

Luminosity density evolution in the red-sequence galaxies is more or less constant (mild evolution), this shows that passive evolution is not the complete explanation. Looking at SFR for galaxies of different masses show that massive galaxies start to dominate the total SF at high redshifts (>~2).

Using Spitzer 24micron observations it's found that massive galaxies at high-z (~1.5-3) are in an IR-active phase of evolution. Looking at the specific SFR C.P. finds that at z~1.5-3 massive galaxies form stars as fast or faster than the cosmic average. At z<1 the galaxies have already formed their stars and the total SF is dominated by lower mass galaxies. (Cf. talks by many others, this seems to be accepted). Understanding of the role of AGN is also important to explain these observations.

Agreement between SFRs from X-ray, IR, submm, UV by a factor of 2. This is good because Spitzer 24 micron probes restframe mid-IR at z~2 => use this data to get SFRs for these galaxies. This show an increasing cosmic SFR out to z~2. These observations might not be in line with hierarchical models (De Lucia et al. 2006).


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