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Improving the precision of time-delay cosmography with observations of galaxies along the line of sight
Cosmology and Nongalactic Astrophysics · Submitted 14 Mar 2013
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim Although deeper multi-band observations of the field of B1608+656 are necessary to obtain a more precise estimate, we conclude that griK photometry, in addition to spectroscopy to characterize the immediate environment, is an effective way to increase the precision of time-delay cosmography.
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The abstract, sentence by sentence
In order to use strong gravitational lens time delays to measure precise and accurate cosmological parameters the effects of mass along the line of sight must be taken into account. We present a method to achieve this by constraining the probability distribution function of the effective line of sight convergence k_ext. The method is based on matching the observed overdensity in the weighted number of galaxies to that found in mock catalogs with k_ext obtained by ray-tracing through structure formation simulations. We explore weighting schemes based on projected distance, mass, luminosity, and redshift. This additional information reduces the uncertainty of k_ext from sigma_k $0.06 to ~0.04 for very overdense lines of sight like that of the system B1608+656. For more common lines of sight, sigma_k is reduced to ~<0.03, corresponding to an uncertainty of ~<3% on distance. This uncertainty has comparable effects on cosmological parameters to that arising from the mass model of the deflector and its immediate environment. Photometric redshifts based on g, r, i and K photometries are sufficient to constrain k_ext almost as well as with spectroscopic redshifts. As an illustration, we apply our method to the system B1608+656. Our most reliable k_ext estimator gives sigma_k=0.047 down from 0.065 using only galaxy counts. Although deeper multi-band observations of the field of B1608+656 are necessary to obtain a more precise estimate, we conclude that griK photometry, in addition to spectroscopy to characterize the immediate environment, is an effective way to increase the precision of time-delay cosmography.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | In order to use strong gravitational lens time delays to measure precise and accurate cosmological parameters the effects of mass along the line of sight must be taken into account. | background 1.00 | 0.06 | 0.05 | asserted 0.99 |
| s1 | We present a method to achieve this by constraining the probability distribution function of the effective line of sight convergence k_ext. | contribution 0.76 | 0.89 | 0.08 | asserted 1.00 |
| s2 | The method is based on matching the observed overdensity in the weighted number of galaxies to that found in mock catalogs with k_ext obtained by ray-tracing through structure formation simulations. | method 1.00 | 0.78 | 0.04 | asserted 1.00 |
| s3 | We explore weighting schemes based on projected distance, mass, luminosity, and redshift. | method 0.97 | 0.86 | 0.02 | asserted 0.66 |
| s4 | This additional information reduces the uncertainty of k_ext from sigma_k $0.06 to ~0.04 for very overdense lines of sight like that of the system B1608+656. | result 1.00 | 0.91 | 0.13 | asserted 0.99 |
| s5 | For more common lines of sight, sigma_k is reduced to ~<0.03, corresponding to an uncertainty of ~<3% on distance. | result 0.99 | 0.89 | 0.17 | asserted 0.99 |
| s6 | This uncertainty has comparable effects on cosmological parameters to that arising from the mass model of the deflector and its immediate environment. | interpretation 0.95 | 0.68 | 0.11 | asserted 1.00 |
| s7 | Photometric redshifts based on g, r, i and K photometries are sufficient to constrain k_ext almost as well as with spectroscopic redshifts. | result 0.94 | 0.82 | 0.09 | asserted 0.99 |
| s8 | As an illustration, we apply our method to the system B1608+656. | contribution 0.74 | 0.92 | 0.03 | asserted 0.86 |
| s9 | Our most reliable k_ext estimator gives sigma_k=0.047 down from 0.065 using only galaxy counts. | result 1.00 | 0.96 | 0.13 | asserted 1.00 |
| s10 | Although deeper multi-band observations of the field of B1608+656 are necessary to obtain a more precise estimate, we conclude that griK photometry, in addition to spectroscopy to characterize the immediate environment, is an effective way to increase the precision of time-delay cosmography. | interpretation 0.69 | 0.76 | 0.84 | asserted 0.93 |
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Original abstract
In order to use strong gravitational lens time delays to measure precise and accurate cosmological parameters the effects of mass along the line of sight must be taken into account. We present a method to achieve this by constraining the probability distribution function of the effective line of sight convergence k_ext. The method is based on matching the observed overdensity in the weighted number of galaxies to that found in mock catalogs with k_ext obtained by ray-tracing through structure formation simulations. We explore weighting schemes based on projected distance, mass, luminosity, and redshift. This additional information reduces the uncertainty of k_ext from sigma_k $0.06 to ~0.04 for very overdense lines of sight like that of the system B1608+656. For more common lines of sight, sigma_k is reduced to ~<0.03, corresponding to an uncertainty of ~<3% on distance. This uncertainty has comparable effects on cosmological parameters to that arising from the mass model of the deflector and its immediate environment. Photometric redshifts based on g, r, i and K photometries are sufficient to constrain k_ext almost as well as with spectroscopic redshifts. As an illustration, we apply our method to the system B1608+656. Our most reliable k_ext estimator gives sigma_k=0.047 down from 0.065 using only galaxy counts. Although deeper multi-band observations of the field of B1608+656 are necessary to obtain a more precise estimate, we conclude that griK photometry, in addition to spectroscopy to characterize the immediate environment, is an effective way to increase the precision of time-delay cosmography.
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7 arXiv papers cite this in 10 sentences
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The reduction of $(|)$ to just its median value, before using it to look up the appropriate $()$ from the simulated sightline ensemble, is reminiscent of the procedure followed by [ref] , and [ref] .
Reconstructing the Lensing Mass in the Universe from Photometric Catalogue Data · Discussion · 0.88
Cites it as background 1 paper
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Time delay cosmography has made the greatest advances in the last several years, with improved lens modeling [ref] , clear understanding of the cosmological leverage [ref] , high accuracy time delay estimation [ref] , and actual application to cosmological constraints on geometry and dark energy [ref] .
Doubling Strong Lensing as a Cosmological Probe · Introduction · 0.83
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