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 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 \sim 0.03 ) and an approximately volume limited redshift distribution from z \sim 0.2 to z \sim 0.6 well suited to detecting the ISW effect .
Accurate photometric redshifts allow us to perform a reliable auto-correlation analysis of the LRGs , eliminating the uncertainty in the galaxy bias , and combined with 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 \leq 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 \pm 1.54 for V band , with similar results for the other bands .
This should be compared to b _ { g } = 1.82 \pm 0.02 from the auto-correlation 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 , and \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 .