[astro-ph/0411673] Illuminating Dark Energy with Cosmic Shear

Authors:  Fergus Simpson (IoA), Sarah Bridle (UCL)
Abstract:  One of the principal goals of modern cosmology is to constrain the properties of dark energy. At present, numerous surveys are aiming to determine the equation of state, which is assumed constant due to our poor understanding of its behaviour (and since higher order parameterisations lead to unwieldy errors). However it is painfully apparent from the myriad of dark energy theories that assuming a time-independant equation of state may be quite inappropriate. This raises the question - how does our "best-fit" equation of state relate to the true function, which may vary with redshift. Saini et al (2003) have demonstrated that the value of w attained by a supernovae study is well described by a weighted integral over the true function. Adopting a similar approach, we calculate the corresponding "weight function" for a fiducial cosmic shear survey. We disentangle contributions from the angular diameter distance and the growth factor, finding that they partially cancel each other out. Consequentially, the sensitivity to w at high redshift is enhanced beyond that of supernovae studies, and even lensing of the CMB. This illustrates the complementary nature of the different techniques. Furthermore, we find that results which would naively be interpreted as inconsistent could arise from a time-dependent equation of state.
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Adam Amara
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Affiliation: ETH
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[astro-ph/0411673] Illuminating Dark Energy with Cosmic Shea

Post by Adam Amara » December 15 2004

This is a nice article that looks really interesting. It looks at the weighting function of the w parameter, which wounds like a measure of the red-shift sensitivity of different survey that measure dark energy.

Am I reading it right? From Figure 10 does it mean that if you want to constrain w between a redshift of 0.5 and 1.5 your best bet is to study cosmic shear using a Snap like survey? I'm not sure I totally understand how all the observational uncertainties come in and what role they play in determining which survey would be most sensitive in a given red-shift range.

It’s very nice to see that these two probes have very different z dependent weighting functions.

Adam

Fergus Simpson
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Affiliation: University of Barcelona

[astro-ph/0411673] Illuminating Dark Energy with Cosmic Shea

Post by Fergus Simpson » December 16 2004

Thanks Adam. Yes, so lensing does seem to be more sensitive to the higher z values of w than supernovae. This is quite encouraging since a deviation of w from -1 is likely to be more prominent at higher redshift.

For the most part, the survey parameters dont have great influence on the form of the weight function. (with the exception of the redshift distribution of observed galaxies). This is essentially because the weight function does not depend on the accuracy with which you measure w.

Cheers,
Fergus

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