Thursday, August 17, 2006

F. Walter: The first galaxies and AGN

Quasars are not found at very high redshift. The record holder has been at z=6.4 for quite an amount of time and at this redshift, the universe was about 870 Myr old.

A fun fact with redshifts is that you observe different wavelengths in objects when use use a certain wavelenth for observations. Because there is a large peak of emission from dust in the mid- and far-infrared, this gets shifted into the mm-rane at high redshifts and thereby, an object that is much further away may not appear fainter than a closer one at all.

Molecular emission has been detected to redshifts over 6 as well and of course only the highest concentrations can be detected at these large distances. One can get hold of the ionisations state of the IGM via the proximity effect, which presumably is due to a large ionised sphere (formation time=10^7 yr * neutral gas fraction) and lets emission a little blueward of the lyman-limit at the quasars redshift escape.

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