Measuring the integrated Sachs-Wolfe effect

Abstract

Context. One of the main challenges of modern cosmology is to understand the nature of the mysterious dark energy that causes the cosmic acceleration. The integrated Sachs-Wolfe (ISW) effect is sensitive to dark energy, and if detected in a universe where modified gravity and curvature are excluded, presents an independent signature of dark energy. The ISW effect occurs on large scales where cosmic variance is high and where owing to the Galactic confusion we lack large amounts of data in the CMB as well as large-scale structure maps. Moreover, existing methods in the literature often make strong assumptions about the statistics of the underlying fields or estimators. Together these effects can severely limit signal extraction. Aims. We aim to define an optimal statistical method for detecting the ISW effect that can handle large areas of missing data and minimise the number of underlying assumptions made about the data and estimators. Methods. We first review current detections (and non-detections) of the ISW effect, comparing statistical subtleties between existing methods, and identifying several limitations. We propose a novel method to detect and measure the ISW signal. This method assumes only that the primordial CMB field is Gaussian. It is based on a sparse inpainting method to reconstruct missing data and uses a bootstrap technique to avoid assumptions about the statistics of the estimator. It is a complete method, which uses three complementary statistical methods. Results. We apply our method to Euclid-like simulations and show we can expect a ∼7σ model-independent detection of the ISW signal with WMAP7-like data, even when considering missing data. Other tests return ∼5σ detection levels for a Euclid-like survey. We find that detection levels are independent from whether the galaxy field is normally or lognormally distributed. We apply our method to the 2 Micron All Sky Survey (2MASS) and WMAP7 CMB data and find detections in the 1.0−1.2σ range, as expected from our simulations. As a by-product, we have also reconstructed the full-sky temperature ISW field from the 2MASS data.Conclusions. We present a novel technique based on sparse inpainting and bootstrapping, which accurately detects and reconstructs the ISW effect.

Removal of two large-scale cosmic microwave background anomalies after subtraction of the integrated Sachs-Wolfe effect

“…only a few a m s (not C( )s) are required to describe the data. This is easily verified directly from the data and is described in more detail in Starck et al (2013) and Dupe et al (2011).…”

“…For exact details of our selection criteria and the mask, see Rassat et al (2007) and Sect. 6.2 of Dupe et al (2011). The 2MASS overdensity map is shown with its corresponding mask on the left-hand side of Fig.…”

Planck2013 results. XIX. The integrated Sachs-Wolfe effect

“…In recent years, some effort has been invested not only to obtain the statistical cross-correlation signal between the CMB and LSS data, but also to recover a map of the ISW signal itself (Barreiro et al 2008(Barreiro et al , 2013Francis & Peacock 2010a;Dupé et al 2011). In particular, assuming the existence of a correlation between the CMB and the gravitational potential, it is possible to recover a map of the ISW fluctuations using a filtering method when one has a tracer of the gravitational potential (e.g., the galaxy catalogues described in Sect.…”

“…Based on these data, many works can be found in the literature where the authors aim at making, and subsequectly improving, the measurement of the ISW effect through correlations with tracer catalogues: 2MASS (an infrared catalogue out to low redshifts around 0.1, Afshordi et al 2004;Rassat et al 2007;Francis & Peacock 2010b;Dupé et al 2011), HEAO (an X-ray survey at low redshift, with the first positive claim of detection, Boughn & Crittenden 2004), Sloan Digital Sky Survey (SDSS, an optical survey at intermediate redshifts, Fosalba et al 2003;Scranton et al 2003;Fosalba & Gaztañaga 2004;Padmanabhan et al 2005;Cabré et al 2006;Giannantonio et al 2006;Granett et al 2009;Xia 2009;Bielby et al 2010;López-Corredoira et al 2010;Sawangwit et al 2010), the NRAO VLA Sky Survey (NVSS, a radio catalogue with high-redshift sources, Boughn & Crittenden 2005;Vielva et al 2006;Pietrobon et al 2006a;McEwen et al 2007;Raccanelli et al 2008;Hernández-Monteagudo 2010;Massardi et al 2010;Schiavon et al 2012), and combined measurements with multiple tracers (Nolta et al 2004;Ho et al 2008;Corasaniti et al 2005;Gaztañaga et al 2006;Giannantonio et al 2008Giannantonio et al , 2012. The significance of the ISW detections that can be found in the literature range between 0.9σ and 4.7σ.…”

The impact of superstructures in the Cosmic Microwave Background

“…The conventional approach is to correlate the CMB with a tracer of the matter distribution -usually galaxy surveys. Although attempted numerous times (see Dupé et al, 2011 for a review), these have yet to give a definitive and unambiguous detection of the iSW effect. This is mainly due to the shortcomings of current surveys, not deep enough and/or with too small a sky coverage.…”