Friday, September 26, 2008

Old and older

O'Neil et al (2008) have found what appear to be the Earth's oldest unmodified rocks. Using samarium/neodynium isotopic analysis they found rocks in the Nuvvuagittuq greenstone (on the eastern edge of Hudson Bay) that are 4.28 +/- 0.05 billion years old. These beats the previous record holder from the Acasta gneiss (also Canadian) of 4.03 billion years old.

Read the commentary in Science, Nature or on the BBC.

Guo and White (submitted) report on nature and fate of different populations of high redshift galaxies using theoretical models. They find that the redshift z~3 Lyman Break Galaxies (LBGs), the redshift z~2 optically selected star forming galaxies (BXs) and the z~2 Distant Red Galaxies (DRGs) are predominantly disk-like galaxies at those epochs (~11.5 billion years ago and 10.3 billion years ago, or ~2.2 and ~3.3 billion years after the Big Bang), but the LBGs and DRGs will predominantly end up as present day elliptical galaxies - consistent with prior expectations based on clustering.

More interesting from my perspective they find that (a) about half of the z~3 LBGs would be observed as z~2 BXs, and (b) the current z~0 descendent's of these galaxies grow in stellar mass by roughly and order of magnitude by a mixture of star formation and galaxy merging.

References:
O'Neil, J., Carlson, R. W., Francis, D. & Stevenson, R. K. Science 321, 1828–1831 (2008).
Guo, Q & White S.D.M, MNRAS, submitted (arXiv:0809.4259v2).

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