Cross-correlatingWMAP5 with 1.5 million LRGs: a new test for the ISW effect

Abstract

We present the cross-correlation of the density map of luminous red galaxies (LRGs) and the temperature fluctuation in the cosmic microwave background (CMB) as measured by the fiveyear Wilkinson Microwave Anisotropy Probe observations. The LRG samples were extracted from imaging data of the Sloan Digital Sky Survey (SDSS) Data Release 5 based on two previous spectroscopic redshift surveys, the SDSS LRG and the 2dF-SDSS LRG and QSO (2SLAQ) surveys designed to have average redshifts of z ≈ 0.35 and z ≈ 0.55. In addition, we have added a higher redshift photometric LRG sample based on the selection of the AAOmega LRG redshift survey at z ≈ 0.7. The total LRG sample thus comprises 1.5 million galaxies, sampling a redshift range of 0.2 < z < 0.9 over ≈7600 deg 2 of the sky, probing a total cosmic volume of ≈5.5 h −3 Gpc 3 .First, we find that the new LRG sample at z ≈ 0.7 shows very little positive evidence for the Integrated Sachs-Wolfe (ISW) effect. Indeed, the cross-correlation is negative out to ≈1 • . The standard cold dark matter ( CDM) model is rejected at ≈2-3 per cent significance by the new LRG data. We then analyse the previous samples at z ≈ 0.35 and z ≈ 0.55. As found by other authors, these results appear consistent with the standard ISW model, although the statistical significance remains marginal. We also reproduce the same result for the magnitudelimited SDSS galaxy samples of Giannantonio et al. Taking the z ≈ 0.35 and z ≈ 0.55 LRG results in combination with the new z ≈ 0.7 sample, the overall result is now more consistent with a null detection than with the standard CDM model prediction.We then performed a new test on the robustness of the LRG ISW detections at z ≈ 0.35 and z ≈ 0.55. We made eight rotations through 360 • of the CMB maps with respect to the LRG samples around the galactic pole. We find that in both cases, there are stronger effects at angles other than zero. This implies that the z ≈ 0.35 and z ≈ 0.55 ISW detections may still be subject to systematic errors which combined with the known sizeable statistical errors may leave the z ≈ 0.35 and z ≈ 0.55 ISW detections looking unreliable. We have further made the rotation test on several other samples where ISW detections have been claimed and find that they also show peaks when rotated. We conclude that in the samples we have tested, the ISW effect may be absent and we argue that this result may not be in contradiction with previous results.

Measuring the integrated Sachs-Wolfe effect

“…Higher detections are reported for the NVSS survey (Pietrobon et al 2006;McEwen et al 2008;Giannantonio et al 2008), though weak and marginal detections using NVSS data are also reported (Hernández-Monteagudo 2010; Sawangwit et al 2010). High detections are often made using a wavelet analysis (Pietrobon et al 2006;McEwen et al 2008), though a similar study by McEwen et al (2007) using the same data but a different analysis method finds a weaker signal.…”

“…for SDSS Quasars; Afshordi et al 2004;Rassat et al 2007, for 2MASS), but in some cases they are controversially different (e.g., Pietrobon et al 2006 andSawangwit et al 2010 for NVSS or; Afshordi et al 2004 and;Giannantonio et al 2008 for 2MASS). We also notice that as certain surveys are revisited, there is a trend for the statistical significance to be reduced, e.g., detections from 2MASS decrease from a 2.5σ detection (Afshordi et al 2004), to 2σ (Rassat et al 2007), to 0.5σ (Giannantonio et al 2008) to "weak" (Francis & Peacock 2010b).…”

The VLT Survey Telescope ATLAS

“…Sawangwit et al 2010). This is one of the few independent tests of the accelerating expansion of the Universe and the Southern hemisphere is the only place left to improve the statistical significance of this test.…”

Revisiting the WMAP-NVSS angular cross correlation. A skeptic's view

“…All those detections were at low significance (below 4-σ), and only more recent works combining different Large Scale Structure surveys yield detections at the 4, 5-σ level, (Giannantonio et al 2008;Ho et al 2008). One must remark, however, there is a number of more recent works disputing the results on the SDSS-WMAP cross correlation, claiming that there is no statistical evidence for ISW when looking at the cross two point function between those surveys (Bielby et al 2010;López-Corredoira et al 2010;Sawangwit et al 2010). Those results are based upon the computation of the error bars of the cross two point function via different methods (Monte Carlo simulations, map rotation, bootstraping, etc.…”