Cosmology from Gravitational Lens Time Delays and Planck Data
Abstract
Under the assumption of a flat ΛCDM cosmology, recent data from the Planck satellite point toward a Hubble constant that is in tension with that measured by gravitational lens time delays and by the local distance ladder. Prosaically, this difference could arise from unknown systematic uncertainties in some of the measurements. More interestingly—if systematics were ruled out—resolving the tension would require a departure from the flat ΛCDM cosmology, introducing, for example, a modest amount of spatial curvature, or a nontrivial dark energy equation of state. To begin to address these issues, we present an analysis of the gravitational lens RXJ11311231 that is improved in one particular regard: we examine the issue of systematic error introduced by an assumed lens model density profile. We use more flexible gravitational lens models with baryonic and dark matter components, and find that the exquisite Hubble Space Telescope image with thousands of intensity pixels in the Einstein ring and the stellar velocity dispersion of the lens contain sufficient information to constrain these more flexible models. The total uncertainty on the timedelay distance is 6.6% for a single system. We proceed to combine our improved timedelay distance measurement with the WMAP9 and Planck posteriors. In an open ΛCDM model, the data for RXJ11311231 in combination with Planck favor a flat universe with Ω _k=0.00^{+0.01}_{0.02} (68% credible interval (CI)). In a flat wCDM model, the combination of RXJ11311231 and Planck yields w=1.52^{+0.19}_{0.20} (68% CI).
 Publication:

The Astrophysical Journal
 Pub Date:
 June 2014
 DOI:
 10.1088/20418205/788/2/L35
 arXiv:
 arXiv:1306.4732
 Bibcode:
 2014ApJ...788L..35S
 Keywords:

 distance scale;
 galaxies: individual: RXJ11311231;
 gravitational lensing: strong;
 methods: data analysis;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 6 pages, 5 figures, accepted for publication in ApJL