A high redshift detection of the integrated Sachs-Wolfe effect

TL;DR

This study detects a weak, high-redshift CMB-quasar cross-correlation consistent with the integrated Sachs-Wolfe effect, using the NBC–KDE SDSS quasar catalog (mean redshift $z \approx 1.5$) and WMAP data. By first characterizing the quasar auto-correlation and stellar contamination (quasar bias $b \approx 2.3$ and stellar fraction $k \approx 0.05$), the authors extract a cross-correlation amplitude $A \approx 0.30 \pm 0.14$ $\mu$K, with a significance of about $2.1$–$2.5\sigma$ and little frequency dependence. Interpreting the result within $\Lambda$CDM, they place constraints on $\Omega_m$ and the dark-energy equation of state $w$, finding consistency with a cosmological constant and highlighting the potential to constrain dark-energy evolution at high redshift ($z \sim 1.5$). The work demonstrates the value of high-redshift tracers for ISW studies and points to future refinements via larger sky coverage and multi-survey combinations to sharpen dark-energy tests.

Abstract

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.

Figures (11)

• Figure 1: Redshift distribution of the quasars. A spline fit of this is used for the theoretical calculations.
• Figure 2: Foregrounds masks for extinction, seeing, point sources and sky brightness in the $r$ band. The 20% of pixels with the worst contamination are shown in light green. The most relevant of these effects is the extinction of the sources.
• Figure 3: Auto--correlation function of the quasars measured for all the sample, for a single foreground mask and for all masks joint. A similar result is obtained for $g$ band masks.
• Figure 4: The auto--correlation function of the quasar catalog with the reddening mask. The square (black) points are the observations $\hat{c}^{tt}$, the dashed line is the expectation $c^{tt}$, and the solid and pointed lines are its component (theoretical quasars and stellar contamination). We plot also the last points (red triangles) of the ACF measured by Myers:2005jk for comparison.
• Figure 5: Cross--correlation function of the quasars and the CMB measured for various foreground masks. Similar results are obtained for $g$ band masks.