H0LiCOW – IX. Cosmographic analysis of the doubly imaged quasar SDSS 1206+4332 and a new measurement of the Hubble constant

Abstract

We present a blind time-delay strong lensing (TDSL) cosmographic analysis of\nthe doubly imaged quasar SDSS 1206+4332. We combine the relative time delay\nbetween the quasar images, Hubble Space Telescope imaging, the Keck stellar\nvelocity dispersion of the lensing galaxy, and wide-field photometric and\nspectroscopic data of the field to constrain two angular diameter distance\nrelations. The combined analysis is performed by forward modelling the\nindividual data sets through a Bayesian hierarchical framework, and it is kept\nblind until the very end to prevent experimenter bias. After unblinding, the\ninferred distances imply a Hubble constant $H_0 = 68.8^{+5.4}_{-5.1}$\nkms$^{-1}$Mpc$^{-1}$, assuming a flat Lambda cold dark matter cosmology with\nuniform prior on $\\Omega_{\\rm m}$ in [0.05, 0.5]. The precision of our\ncosmographic measurement with the doubly imaged quasar SDSS 1206+4332 is\ncomparable with those of quadruply imaged quasars and opens the path to perform\non selected doubles the same analysis as anticipated for quads. Our analysis is\nbased on a completely independent lensing code than our previous three H0LiCOW\nsystems and the new measurement is fully consistent with those. We provide the\nanalysis scripts paired with the publicly available software to facilitate\nindependent analysis. The consistency between blind measurements with\nindependent codes provides an important sanity check on lens modelling\nsystematics. By combining the likelihoods of the four systems under the same\nprior, we obtain $H_0 = 72.5^{+2.1}_{-2.3}$kms$^{-1}$Mpc$^{-1}$. This\nmeasurement is independent of the distance ladder and other cosmological\nprobes.\n