IMPROVING THE PRECISION OF TIME-DELAY COSMOGRAPHY WITH OBSERVATIONS OF GALAXIES ALONG THE LINE OF SIGHT
- Department of Physics, University of California, Santa Barbara, CA 93106-9530 (United States)
- Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, 452 Lomita Mall, Stanford, CA 94035 (United States)
- Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
- Department of Physics, University of Oxford, Keble Road, Oxford, OX1 3RH (United Kingdom)
- Department of Physics, University of California, One Shields Avenue, Davis, CA 95616 (United States)
- Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800 9700 AV Groningen (Netherlands)
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 {kappa}{sub ext}. The method is based on matching the observed overdensity in the weighted number of galaxies to that found in mock catalogs with {kappa}{sub 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 {kappa}{sub ext} from {sigma}{sub {kappa}} {approx} 0.06 to {approx}0.04 for very overdense LOSs like that of the system B1608+656. For more common LOSs, {sigma}{sub {kappa}} is reduced to {approx}<0.03, corresponding to an uncertainty of {approx}< 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 {kappa}{sub ext} almost as well as with spectroscopic redshifts. As an illustration, we apply our method to the system B1608+656. Our most reliable {kappa}{sub ext} estimator gives {sigma}{sub {kappa}} = 0.047 down from 0.065 using only galaxy counts. Although deeper multiband 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.
- OSTI ID:
- 22126829
- Journal Information:
- Astrophysical Journal, Vol. 768, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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