Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.mso.anu.edu.au/pfrancis/roleplay/html_dir/firstlight/node24.html
Дата изменения: Unknown
Дата индексирования: Tue Oct 2 15:13:27 2012
Кодировка:
Поисковые слова: ceres

Research Interests

Your main research interests lie in QSO absorption-line systems.

The wretched anglo-saxons seem fixated on seeing things: unless they have an images they can flog to the media, they are just not happy. You, however, are more enlightened about these things (it comes naturally, being French).

The trouble with trying to see galaxies in the early universe is that all you can see will generally be stars. What's wrong with that, the English-speaking fools may ask? Well, most of the universe is made up of dark matter and gas: stars are only a trace impurity, even today. And in the early universe, before most of the stars have formed, stars must be an even less significant component of the universe.

It clearly makes far more sense to study the gas in the early universe. Gas is simple: we understand how it behaves. There is far more mass in gas than stars. By looking at the dynamics, distribution and metallicities of the gas, we can learn about dark matter, nucleosynthesis and galaxy formation in ways that picture fixated astronomers will never do.

So, how do you study gas in the early universe? QSO absorption-lines, of course. You have spent a decade obtaining high resolution spectra of distant QSOs, studying the gas that lies along the sight-lines. This technique has taught the world far more about the early universe than all others combined. Highlights include:

• As stars form, they must use up gas. By watching the decline in the space density of damped Ly absorption-line systems (clouds of neutral hydrogen with column densities of , Mike Fall and collaborators were able to calculate the star formation rate of the universe as a function of time: five years before anyone else came close.
• The tiny, low column density Ly forest lines are by far the most common denizens of the high redshift universe, and probably contain more baryons than all galaxies and bigger objects combined.
• You yourselves were able to show, by comparing QSO absorption-line data with deep images and spectra of galaxies near the sight-lines, that huge halos of absorbing gas surround all galaxies out to at least redshift one.
• Max Pettini and collaborators used QSO absorption-lines to measure the average metalicity of the universe as a function of redshift, showing that it steadily increases between z=5 and today, giving a measure of the metal (and hence star) formation rate of the universe as a function of redshift.