H₀ from ten well-measured time delay lenses

¹ Indian Institute of Astrophysics, II Block, Koramangala, 560 034 Bangalore, India
e-mail: rathna@iiap.res.in
² Physical Research Laboratory, Navrangpura, 380 009 Ahmedabad, India

Received: 10 April 2014
Accepted: 27 May 2015

Abstract

In this work, we present a homogeneous curve-shifting analysis using the difference-smoothing technique of the publicly available light curves of 24 gravitationally lensed quasars, for which time delays have been reported in the literature. The uncertainty of each measured time delay was estimated using realistic simulated light curves. The recipe for generating such simulated light curves with known time delays in a plausible range around the measured time delay is introduced here. We identified 14 gravitationally lensed quasars that have light curves of sufficiently good quality to enable the measurement of at least one time delay between the images, adjacent to each other in terms of arrival-time order, to a precision of better than 20% (including systematic errors). We modeled the mass distribution of ten of those systems that have known lens redshifts, accurate astrometric data, and sufficiently simple mass distribution, using the publicly available PixeLens code to infer a value of H₀ of 68.1 ± 5.9 km s^-1 Mpc^-1 (1σ uncertainty, 8.7% precision) for a spatially flat universe having Ω_m = 0.3 and Ω_Λ = 0.7. We note here that the lens modeling approach followed in this work is a relatively simple one and does not account for subtle systematics such as those resulting from line-of-sight effects and hence our H₀ estimate should be considered as indicative.