Image of Alice in Wonderland at the Mad Hatter's tea party You are cordially invited to afternoon tea and biscuits wine and chocolate

Astronomy Tea Talks at Caltech

Mondays, Robinson 106
Tea:  4.00pm
Talk: 4.15pm

Organised by:

2007 - 2008 season:
15 October 2007 David Rapetti (KIPAC/Stanford)

"Probing cosmology with X-ray galaxy clusters"


Most of the energy density of the Universe appears to be in the form of dark matter and dark energy, and yet these two components
are the most intriguing mysteries in current cosmology. Using two complementary X-ray galaxy cluster studies we present new
constraints on the mean matter density of the Universe, dark energy density, normalization of the density fluctuation power
spectrum, and dark energy equation of state. First, using Chandra measurements of the X-ray gas mass fraction in 42 hot, X-ray
luminous, dynamically relaxed galaxy clusters spanning the redshift range 0.05 constant, H_0, and the mean baryon density, w_bh^2, we obtain tight constraint on the mean matter density and a detection of the
effects of dark energy on the distances to the clusters comparable in significance to recent type Ia supernovae (SNIa) studies.
Second, using the X-ray luminosity function of the Massive Cluster Survey (MACS) in combination with the local BCS and REFLEX
galaxy cluster samples, the mass function predictions of Jenkins et al. (2001), a mass-luminosity relation calibrated using the
data of Reiprich and Bohringer (2002), and standard priors on H_0 and w_bh^2, we obtain the first precise determination of the
dark energy equation of state from measurements of the growth of cosmic structure in galaxy clusters. Combining our results with
independent constraints from cosmic microwave background and SNIa studies removes the need for priors on H_0 and w_bh^2 and leads
to tighter constraints. Both of our results represent strong, independent evidences for cosmic acceleration.
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