Correlating the CMB with luminous red galaxies: The integrated Sachs-Wolfe effect

We present a 2.5 sigma detection of the Integrated Sachs-Wolfe (ISW) effect and discuss the constraints it places on cosmological parameters. We cross correlate microwave temperature maps from the Wilkinson microwave anisotropy probe (WMAP) satellite with a 4000 deg(2) luminous red galaxy (LRG) overdensity map measured by the Sloan Digital Sky Survey. These galaxies have accurate photometric redshifts (Delta z similar to 0.03) and an approximately volume limited redshift distribution from z similar to 0.2 to z similar to 0.6 well suited to detecting the ISW effect. Accurate photometric redshifts allow us to perform a reliable autocorrelation analysis of the LRGs, eliminating the uncertainty in the galaxy bias, and combined with the cross correlation signal, constrains cosmological parameters-in particular, the matter density. We use a minimum-variance power spectrum estimator that optimally weights the data according to expected theoretical templates. We find a 2.5 sigma signal in the Ka, Q, V, and W WMAP bands, after combining the information from multipoles 2 <= l < 400. This is consistent with the expected amplitude of the ISW effect but requires a lower matter density than is usually assumed: the amplitude, parametrized by the galaxy bias assuming Omega(M)=0.3, Omega(Lambda)=0.7, and sigma(8)=0.9, is b(g)=4.05 +/- 1.54 for V band, with similar results for the other bands. This should be compared to b(g)=1.82 +/- 0.02 from the autocorrelation analysis. These data provide only a weak confirmation (2.5 sigma) of dark energy but provide a significant upper limit: Omega(Lambda)=0.80(-0.06)(+0.03)(1 sigma)(-0.19)(+0.05)(2 sigma), assuming a cosmology with Omega(M)+Omega(Lambda)=1, Omega(b)=0.05, sigma(8)=0.9, and w=-1. The weak cross correlation signal rules out low matter density/high dark energy density universes and, in combination with other data, strongly constrains models with w <-1.3. We provide a simple prescription to incorporate these constraints into cosmological parameter estimation methods for (Omega(M),sigma(8),w). We find no evidence for a systematic contamination of ISW signal, either from galactic or extragalactic sources, but we do detect some large statistical fluctuations on smaller scales that could affect analyses without the template weighting.