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: http://www.mso.anu.edu.au/pfrancis/roleplay/html_dir/firstlight/node6.html
Дата изменения: Unknown Дата индексирования: Tue Oct 2 14:53:15 2012 Кодировка: Поисковые слова: m 13 |
Your main research interests concern redshift surveys.
Why are people so fixated with redshifts above 3? Over half the history of the universe has occurred since redshift one. If we observe out to redshift 1.5, that is around 70% of the whole history of the universe! And we don't need fancy new-fangled techniques to work at these redshifts: tried and tested techniques will work just fine, and the galaxies we find and study are close enough that we can really learn something about them.
You are world authorities at redshift surveys. You start off by getting deep images of some part of the sky. Then, using the multi-fibre or multi-slit instruments you have pioneered, you obtain spectra of them all. This sounds simple, but the scientific pay-off has been huge, especially when combined with Hubble Space Telescope imaging of the galaxies, to determine their colours and morphologies.
Little evolution in the numbers of elliptical galaxies is seen out to redshift one. The major evolution is in a vast population of small blue galaxies, the so-called `faint blue galaxies', which were abundant at redshift one, but which have mostly disappeared by now. They have probably faded into obscurity, as their initial burst of star formation dies away.
The nett effect of all of this is that the star formation rate per unit co-moving volume was much higher at redshift one than it is today, which actually agrees well with theoretical calculations.
Galaxy clusters have also changed: at redshifts around one, clusters seem to contain more spiral galaxies, fewer S0s and the same number of giant elliptical galaxies as we see today. This is presumably because the spirals are merging to form S0s. One puzzle: the velocity dispersions, weak gravitational lensing measurements and X-ray fluxes of these high redshift clusters imply that they are just as massive as clusters today, which is in strong contradiction to most current theoretical models. If this holds up with better data, it implies that something may be wrong with theories of structure formation in the universe.
You are now working on enlarging your samples, and actually measuring velocity dispersions for galaxies at redshifts around 1, to derive their masses. This will really help nail down the evolution of different types of galaxy.