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Title: Magnification-temperature correlation: The dark side of integrated Sachs-Wolfe measurements

Abstract

Integrated Sachs-Wolfe (ISW) measurements, which involve cross-correlating the microwave background anisotropies with the foreground large-scale structure (e.g. traced by galaxies/quasars), have proven to be an interesting probe of dark energy. We show that magnification bias, which is the inevitable modulation of the foreground number counts by gravitational lensing, alters both the scale dependence and amplitude of the observed ISW signal. This is true especially at high redshifts because (1) the intrinsic galaxy-temperature signal diminishes greatly back in the matter-dominated era, (2) the lensing efficiency increases with redshift and (3) the number count slope generally steepens with redshift in a magnitude limited sample. At z > or approx. 2, the magnification-temperature correlation dominates over the intrinsic galaxy-temperature correlation and causes the observed ISW signal to increase with redshift, despite dark energy subdominance--a result of the fact that magnification probes structures all the way from the observer to the sources. Ignoring magnification bias therefore can lead to (significantly) erroneous conclusions about dark energy. While the lensing modulation opens up an interesting high z window for ISW measurements, high redshift measurements are not expected to add much new information to low redshift ones if dark energy is indeed the cosmological constant. This ismore » because lensing introduces significant covariance across redshifts. The most compelling reasons for pursuing high redshift ISW measurements are to look for potential surprises such as early dark energy domination or signatures of modified gravity. We conclude with a discussion of existing measurements, the highest redshift of which is at the margin of being sensitive to the magnification effect. We also develop a formalism which might be of more general interest: to predict biases in estimating parameters when certain physical effects are ignored in interpreting observations.« less

Authors:
;  [1];  [2];  [3]
  1. Institute for Strings, Cosmology and Astro-particle Physics (ISCAP) and Department of Physics, Columbia University, New York, New York 10027 (United States)
  2. Institut de Ciencies de l'Espai, CSIC/IEEC, Campus UAB, F. de Ciencies, Torre C5 par-2, Barcelona 08193 (Spain)
  3. (Mexico)
Publication Date:
OSTI Identifier:
21011062
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. D, Particles Fields; Journal Volume: 75; Journal Issue: 4; Other Information: DOI: 10.1103/PhysRevD.75.043519; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; AMPLITUDES; ANISOTROPY; CORRELATIONS; COSMOLOGICAL CONSTANT; COSMOLOGY; GALAXIES; GRAVITATION; NONLUMINOUS MATTER; POTENTIALS; PROBES; QUASARS; RELICT RADIATION

Citation Formats

LoVerde, Marilena, Hui, Lam, Gaztanaga, Enrique, and INAOE, Astrofisica, Tonantzintla, Puebla 7200. Magnification-temperature correlation: The dark side of integrated Sachs-Wolfe measurements. United States: N. p., 2007. Web. doi:10.1103/PHYSREVD.75.043519.
LoVerde, Marilena, Hui, Lam, Gaztanaga, Enrique, & INAOE, Astrofisica, Tonantzintla, Puebla 7200. Magnification-temperature correlation: The dark side of integrated Sachs-Wolfe measurements. United States. doi:10.1103/PHYSREVD.75.043519.
LoVerde, Marilena, Hui, Lam, Gaztanaga, Enrique, and INAOE, Astrofisica, Tonantzintla, Puebla 7200. Thu . "Magnification-temperature correlation: The dark side of integrated Sachs-Wolfe measurements". United States. doi:10.1103/PHYSREVD.75.043519.
@article{osti_21011062,
title = {Magnification-temperature correlation: The dark side of integrated Sachs-Wolfe measurements},
author = {LoVerde, Marilena and Hui, Lam and Gaztanaga, Enrique and INAOE, Astrofisica, Tonantzintla, Puebla 7200},
abstractNote = {Integrated Sachs-Wolfe (ISW) measurements, which involve cross-correlating the microwave background anisotropies with the foreground large-scale structure (e.g. traced by galaxies/quasars), have proven to be an interesting probe of dark energy. We show that magnification bias, which is the inevitable modulation of the foreground number counts by gravitational lensing, alters both the scale dependence and amplitude of the observed ISW signal. This is true especially at high redshifts because (1) the intrinsic galaxy-temperature signal diminishes greatly back in the matter-dominated era, (2) the lensing efficiency increases with redshift and (3) the number count slope generally steepens with redshift in a magnitude limited sample. At z > or approx. 2, the magnification-temperature correlation dominates over the intrinsic galaxy-temperature correlation and causes the observed ISW signal to increase with redshift, despite dark energy subdominance--a result of the fact that magnification probes structures all the way from the observer to the sources. Ignoring magnification bias therefore can lead to (significantly) erroneous conclusions about dark energy. While the lensing modulation opens up an interesting high z window for ISW measurements, high redshift measurements are not expected to add much new information to low redshift ones if dark energy is indeed the cosmological constant. This is because lensing introduces significant covariance across redshifts. The most compelling reasons for pursuing high redshift ISW measurements are to look for potential surprises such as early dark energy domination or signatures of modified gravity. We conclude with a discussion of existing measurements, the highest redshift of which is at the margin of being sensitive to the magnification effect. We also develop a formalism which might be of more general interest: to predict biases in estimating parameters when certain physical effects are ignored in interpreting observations.},
doi = {10.1103/PHYSREVD.75.043519},
journal = {Physical Review. D, Particles Fields},
number = 4,
volume = 75,
place = {United States},
year = {Thu Feb 15 00:00:00 EST 2007},
month = {Thu Feb 15 00:00:00 EST 2007}
}
  • We cross correlate the new 3 year Wilkinson Microwave Anistropy Probe (WMAP) cosmic microwave background data with the NRAO VLA Sky Survey radio galaxy data and find further evidence of late integrated Sachs-Wolfe (ISW) effect taking place at late times in cosmic history. Our detection makes use of a novel statistical method (P. Baldi, G. Kerkyacharian, D. Marinucci, and D. Picard, math.ST/0606154 and P. Baldi, G. Kerkyacharian, D. Marinucci, D. Picard, math.ST/0606599) based on a new construction of spherical wavelets, called needlets. The null hypothesis (no ISW) is excluded at more than 99.7% confidence. When we compare the measured crossmore » correlation with the theoretical predictions of standard, flat cosmological models with a generalized dark energy component parameterized by its density, {omega}{sub DE}, equation of state w and speed of sound c{sub s}{sup 2}, we find 0.3{<=}{omega}{sub DE}{<=}0.8 at 95% C.L., independently of c{sub s}{sup 2} and w. If dark energy is assumed to be a cosmological constant (w=-1), the bound on density shrinks to 0.41{<=}{omega}{sub DE}{<=}0.79. Models without dark energy are excluded at more than 4{sigma}. The bounds on w depend rather strongly on the assumed value of c{sub s}{sup 2}. We find that models with more negative equation of state (such as phantom models) are a worse fit to the data in the case c{sub s}{sup 2}=1 than in the case c{sub s}{sup 2}=0.« less
  • I discuss several issues that arise when trying to constrain the dark energy equation of state using correlations of the integrated Sachs-Wolfe effect with galaxy counts and lensing of the cosmic microwave background. These techniques are complementary to others such as galaxy shear surveys, and can use data that will already be obtained from currently planned observations. In regimes where cosmic variance and shot noise are the dominant sources of error, constraints could be made on the mean equation of state to {+-}0.33 and its first derivative to {+-}1.0. Perhaps more interesting is that the determination of dark energy parametersmore » by these types of experiments depends strongly on the presence or absence of perturbations in the dark energy fluid.« less
  • We present an analysis of the constraining power of future measurements of the integrated Sachs-Wolfe (ISW) effect on models of the equation of state of dark energy as a function of redshift, w(z). To achieve this, we employ a new parametrization of w, which utilizes the mean value of w(z) (<w>) as an explicit parameter. This helps to separate the information contained in the estimation of the distance to the last scattering surface (from the cosmic microwave background (CMB)) from the information contained in the ISW effect. We then use Fisher analysis to forecast the expected uncertainties in the measuredmore » parameters from future ISW observations for two models of dark energy with very different time evolution properties. For example, we demonstrate that the cross correlation of Planck CMB data and large synoptic survey telescope (LSST) galaxy catalogs will provide competitive constraints on w(z), compared to a supernovae acceleration probe (SNAP)-like supernovae (SNe) project, for models of dark energy with a rapidly changing equation of state (e.g. Kink models). Our work confirms that, while SNe measurements are more suitable for constraining variations in w(z) at low redshift, the ISW effect can provide important independent constraints on w(z) at high z.« less
  • Models with dark energy decaying into dark matter have been proposed in cosmology to solve the coincidence problem. We study the effect of such coupling on the cosmic microwave background temperature anisotropies. The interaction changes the rate of evolution of the metric potentials and the growth rate of matter density perturbations and modifies the integrated Sachs-Wolfe component of cosmic microwave background temperature anisotropies, enhancing the effect. Cross correlation of galaxy catalogs with cosmic microwave background maps provides a model-independent test to constrain the interaction. We particularize our analysis for a specific interacting model and show that galaxy catalogs with medianmore » redshifts z{sub m}=0.1-0.9 can rule out models with an interaction parameter strength of c{sup 2}{approx_equal}0.1 better than 99.95% confidence level. Values of c{sup 2}{<=}0.01 are compatible with the data and may account for the possible discrepancy between the fraction of dark energy derived from Wilkinson microwave anisotropy probe 3 yr data and the fraction obtained from the integrated Sachs-Wolfe effect. Measuring the fraction of dark energy by these two methods could provide evidence of an interaction.« less
  • The effect of quintessence perturbations on the integrated Sachs-Wolfe (ISW) effect is studied for a mixed dynamical scalar field dark energy (DDE) and pressureless perfect fluid dark matter. A new and general methodology is developed to track the growth of the perturbations, which uses only the equation of state (EoS) parameter w{sub DDE}(z){identical_to}p{sub DDE}/{rho}{sub DDE} of the scalar field DDE, and the initial values of the relative entropy perturbation (between the matter and DDE) and the intrinsic entropy perturbation of the scalar field DDE as inputs. We also derive a relation between the rest-frame sound speed c-circumflex{sub s,DDE}{sup 2} ofmore » an arbitrary scalar field DDE component and its EoS w{sub DDE}(z). We show that the ISW signal differs from that expected in a {lambda}CDM cosmology by as much as +20% to -80% for parametrizations of w{sub DDE} consistent with SNIa data, and about {+-}20% for parametrizations of w{sub DDE} consistent with SNIa+CMB+BAO data, at 95% confidence. Our results indicate that, at least in principle, the ISW effect can be used to phenomenologically distinguish a cosmological constant from DDE.« less