Michael Rauch's Homepage
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Michael Rauch
Astronomer
Mail:
Observatories of the
Carnegie Institution of Washington
813 Santa Barbara Street
Pasadena, CA 91101
e-mail:
mr(at)obs.carnegiescience.edu
phone: 626-304-0262
fax: 626-795-8136
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My Research Interests
I am an observational astronomer, interested in various problems in
astrophysics and cosmology. Most of my current work is done with the
10m Keck and Carnegie's two Magellan 6.5m
telescopes.
The main observational technique I have
been using is the study of the spectra of distant quasars (or
Quasi-Stellar Objects, QSOs). My colleagues and I are using these
bright ancient objects as background light sources to illuminate matter
intervening at cosmological distances between the QSO and us. The whole
setup up works very much like a gigantic slide projector of cosmic
dimensions: gas clouds in galaxies or in the intergalactic medium (IGM)
absorb light in a characteristic pattern from the beam of the
background QSO, just as slides absorb certain colors from the white
light of a projection bulb. The particular absorption pattern tells the
astronomers how far the gas cloud is away from us, how much gas there
is, and how fast it is moving internally. We can also measure its
temperature and see whether it has already been enriched with chemical
elements by stars.
The picture on the right above shows the spectrum of one such
QSO (1422+231) at redshift 3.62, when the universe was only 3
Giga-years old, about 20 % of its present age. The many ripples on top
of the smoothly varying continuum are individual absorption lines
caused by the neutral hydrogen Lyman alpha transition. There are
hundreds of individually distinguishable absorption lines, all caused
by the same transition at 1215.67 Angstrom. We are seeing this absorption
line repeated all over the place because the universe is expanding so the gas clouds are receding from us,
each cloud at a slightly different velocity, which causes a Doppler-shift
in the wavelength of the absorption line. The clouds recede the faster the further they are away from us, according to Hubble's Law.
This phenomenon is also known as the Lyman alpha forest.
since Dec, 24, 2008.