# Sachs-Wolfe effect and dark energy

1. Jul 27, 2006

### Chronos

An interesting paper on the ISW effect appeared on Arxiv today. It complements WMAP results affirming dark energy and might be important:

http://www.arxiv.org/abs/astro-ph/0607572
A high redshift detection of the integrated Sachs-Wolfe effect
Authors: Tommaso Giannantonio (ICG, Portsmouth), Robert G. Crittenden (ICG), Robert C. Nichol (ICG), Ryan Scranton (UPitt), Gordon T. Richards (JHU), Adam D. Myers (Illinois), Robert J. Brunner (Illinois), Alexander G. Gray (Georgia Tech), Andrew J. Connolly (UPitt), Donald P. Schneider (Penn State)
Comments: 10 pages, 11 figures
Report-no: ICG 06/33

We present evidence of a large angle correlation between the cosmic microwave background measured by WMAP and a catalog of photometrically detected quasars from the SDSS. The observed cross correlation is (0.30 +- 0.14) microK at zero lag, with a shape consistent with that expected for correlations arising from the integrated Sachs-Wolfe effect. The photometric redshifts of the quasars are centered at z ~ 1.5, making this the deepest survey in which such a correlation has been observed. Assuming this correlation is due to the ISW effect, this constitutes the earliest evidence yet for dark energy and it can be used to constrain exotic dark energy models.

2. Jul 27, 2006

### Garth

Nice paper Chronos, which appears to confirm DE in the standard model.

Note, however, that in Figure 11, page 9, the detections of the ISW effect through cross–correlation with different catalogues compiled by: i) [E. Gaztanaga, M. Manera and T. Multamaki], ii) [A. Cabre, E. Gaztanaga, M. Manera, P. Fosalba and F. Castander] and iii) the authors' [KDE–QSO measure], compared against z, are all consistent with each other (they lie on a nice curve), but fit best the non standard $\omega = -2.0$ prediction. They, bar one, are only consistent with the best fit cosmological constant model $\omega \sim -1.0$ at the limits of their error bars.

This anomaly may indicate caution is required.

(emphasis mine)

I make the observation that the conclusion that the universe is very close to spatial flatness is dependent on a GR paradigm. The angular WMAP data is actually consistent with conformal flatness as conformal transformations are angle preserving.

The possibility therefore exists that a modified GR may deliver a concordant non-spatially flat universe in which case the observed ISW effect may be caused by curvature as well as/instead of DE.

Garth

Last edited: Jul 27, 2006
3. Jul 28, 2006

### Chronos

Agreed, Garth. It is an interesting paper - among the best this year, IMO. But not conclusive. Glad you found it worthy of a comment.