REVIEW
Looking for $\Lambda$ with the Rees-Sciama Effect
Astrophysics · Submitted 13 Oct 1995 · 10 references
Pith's verdict: This is the paper that turned the ISW effect into a measurable cross-correlation, and the estimator it derives is still the standard one; the one soft spot is the uncomputed SW×RS cross term used to simplify Eq. (9).
T0 · AI review
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Referee report
The paper
The paper claims
If the universe has a cosmological constant, the microwave sky should be correlated with the nearby matter distribution, and that correlation can be predicted without knowing the primordial power spectrum.
The reading
What carries the argument
The load-bearing object is the radial filter $f_l(r)$ of Eq. (6), and its large-$l$ approximation $f_l(r) �approx ġ(τ_0-r)/(2π l(l+1))$. It converts a map of local density into a predicted microwave multipole, and it does so without reference to the primordial spectrum, which is what makes the test a measurement of $Ω_Λ$ rather than a consistency check with a free amplitude. The second piece of machinery is the likelihood ratio of Eq. (8) and its signal-to-noise sum of Eq. (9), which converts the overlap between predicted and observed multipoles into a single number for how strongly a correlation would be detected.
Extended reading notes
Core claim
The central claim is that the Rees-Sciama contribution to each microwave multipole can be written as a convolution of the present-day matter density with a single radial filter, $a^{RS}_{lm} = 5.5pt plus 1.0fill$, and that for $l>2$ this filter collapses to a simple closed form proportional to the local rate of change of the potential, $f_l(r) �approx 1/(2π l(l+1)) · ġ(τ_0 - r)$. The filter contains no information about the primordial power spectrum — only the growth history, which is fixed once $Ω_Λ$ is chosen — so the predicted cross-correlation is a parameter-free prediction for each value of the cosmological constant. Summing the per-multipole signal-to-noise over an ideal full-sky survey gives $S/N ≥ 5.5$, $7.4$ and $7.9$ for $Ω_Λ = 0.6$, $0.8$ and $0.9$. The authors then show that truncating the density survey at a modest redshift costs surprisingly little, and that a weighting function modelled on the observed redshift distribution of X-ray AGN retains about $0.8$ of the ideal signal, so a ROSAT–COBE comparison is a plausible first test.
Load-bearing premise
The forecast assumes an ideal full-sky, noiseless microwave map with all multipoles measured and assumes the Rees-Sciama anisotropy is uncorrelated with the last-scattering anisotropy, even though the paper's own Figure 3 shows the signal accumulating out to $l$ of order 50 to 100 while the COBE beam it proposes to use reaches only $l$ of order 20.
Editorial extensions
If this is right
- A measured cross-correlation between a low-redshift density tracer and the large-angle microwave sky would constitute direct evidence that the gravitational potential is decaying today, which in the simplest models means a nonzero cosmological constant.
- Because the predicted filter is independent of the primordial power spectrum, the amplitude of the detected correlation is a direct handle on $Ω_Λ$ rather than a degenerate combination with the perturbation amplitude.
- Surveys need not be extremely deep: cutting the density survey off at $z_c �approx 1$ still leaves a substantial fraction of the signal, so shallow wide-field catalogues are useful for this test.
- The same logic applies beyond the cosmological constant — any model in which the potential evolves at late times, including open universes and models with cosmic defects, should produce a density–microwave correlation.
- A null result at the forecast sensitivity would bound the late-time evolution of the potential and hence constrain $Ω_Λ$ from a direction completely independent of gravitational lensing statistics.
Reading between the lines
- The forecast numbers assume every multipole is measured; a real microwave experiment with a finite beam samples only the low-$l$ part of the sum, so the quoted $S/N$ should be read as an upper bound and the realistic figure is smaller by an amount the paper does not compute.
- The claim that the Rees-Sciama and last-scattering contributions are essentially uncorrelated is what allows the cross term to be replaced by $C_l^{RS}$; if there were any correlation, for example through a late-time or reionization contribution, the forecast would shift and the test would need the full covariance.
- Cross-correlating a density tracer with the microwave sky is a cheap measurement in the sense that it needs no new instrument, only archival maps, which suggests the same statistic could be applied retrospectively to any pair of existing all-sky catalogues.
- Because the filter is proportional to $ġ$, a detection would also measure the shape of the growth history, so the test could in principle distinguish a cosmological constant from modified gravity scenarios that produce a similar late-time decay.
Original abstract
In models with a cosmological constant, a significant component of the large scale cosmic microwave background (CMB) anisotropy is produced at rather low redshifts, z < 1. In these models, the gravitational potential perturbations begin to evolve at late times. Photons passing through these time varying potentials aquire frequency shifts, an effect first noted by Rees and Sciama. Since the gravitational potential is associated with matter at observable redshifts, the local matter density (or some tracer thereof) is correlated with the CMB anisotropy on the sky. We outline the optimal method of measuring this correlation, and discuss the prospects for using an X-ray/COBE comparison to detect a cosmological constant.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
In models with a cosmological constant, a significant component of the large scale cosmic microwave background (CMB) anisotropy is produced at rather low redshifts, z < 1. In these models, the gravitational potential perturbations begin to evolve at late times. Photons passing through these time varying potentials aquire frequency shifts, an effect first noted by Rees and Sciama. Since the gravitational potential is associated with matter at observable redshifts, the local matter density (or some tracer thereof) is correlated with the CMB anisotropy on the sky. We outline the optimal method of measuring this correlation, and discuss the prospects for using an X-ray/COBE comparison to detect a cosmological constant.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | In models with a cosmological constant, a significant component of the large scale cosmic microwave background (CMB) anisotropy is produced at rather low redshifts, z < 1. | background 0.99 | 0.10 | 0.12 | asserted 1.00 |
| s1 | In these models, the gravitational potential perturbations begin to evolve at late times. | background 1.00 | 0.06 | 0.04 | asserted 1.00 |
| s2 | Photons passing through these time varying potentials aquire frequency shifts, an effect first noted by Rees and Sciama. | background 1.00 | 0.04 | 0.05 | asserted 1.00 |
| s3 | Since the gravitational potential is associated with matter at observable redshifts, the local matter density (or some tracer thereof) is correlated with the CMB anisotropy on the sky. | background 0.65 | 0.10 | 0.23 | asserted 0.99 |
| s4 | We outline the optimal method of measuring this correlation, and discuss the prospects for using an X-ray/COBE comparison to detect a cosmological constant. | contribution 0.80 | 0.67 | 0.26 | asserted 0.37 |
What was examined, and what was not
- arXiv listing abstract v1
- full text
- figures and tables
- references and citing sentences
- relations to other papers
- P abstract
- S sections
- T body sentences
- C citations
- R cross-paper relations
Figures
Figures reproduced from arXiv:astro-ph/9510072 by the authors.
References
How the literature uses it
51 arXiv papers cite this in 62 sentences
Papers citing it · 40 sentences without a confident label
Uses its method or tool 1 paper
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In the Limber approximation [ref] , the spherical harmonic power spectrum between CMB temperature anisotropies and a tracer $i$ of the LSS becomes: [ref] [equation] where $T_CMB$ denotes the mean temperature of the CMB today, $i ∈{δ_g, γ}$ and $W^i(χ(z))$ represents the window functions defined in Equations [ref] and [ref].
Integrated approach to cosmology: Combining CMB, large-scale structure and weak lensing · Theoretical predictions · 0.94
Cites it as background 18 papers
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The residual $𝒪(f_NL^2)$ variance is a result of the late-time, large-scale integrated Sachs-Wolfe (ISW) effect, in which CMB anisotropies are generated by gravitational potential decay along the line-of-sight [ref] .
An improved estimator for non-Gaussianity in cosmic microwave background observations · Introduction · 0.83
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A CMB photon traveling through time-varying gravitational potentials $Φ$ and $Ψ$ in the metricmetric will suffer a change in energy, resulting in a change in the observed CMB temperature: the so-called Integrated Sachs-Wolfe (ISW) effect ( [ref] , see [ref] for a review).
Galaxy-CMB Cross-Correlation as a Probe of Alternative Models of Gravity · Integrated Sachs-Wolfe Effect · 1.00
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The seminal work by [ref] proposed to use a galaxy catalogue as LSS tracer, and the first positive detection following this approach was done by [ref] using data and radio and $X$-ray tracers.
Planck 2015 results. XXI. The integrated Sachs-Wolfe effect · CMB correlation with tracers of the gravitational potential · 0.97
Discussion
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