H0LiCOW – II. Spectroscopic survey and galaxy-group identification of the strong gravitational lens system HE 0435−1223

Abstract

Galaxies located in the environment or on the line of sight towards gravitational lenses can significantly affect lensing observables, and can lead to systematic errors on the measurement of H 0 from the time-delay technique. We present the results of a systematic spectroscopic identification of the galaxies in the field of view of the lensed quasar HE 0435−1223 using the W. M. Keck, Gemini and ESO-Very Large telescopes. Our new catalog triples the number of known galaxy redshifts in the direct vicinity of the lens, expanding to 102 the number of measured redshifts for galaxies separated by less than 3 from the lens. We complement our catalog with literature data to gather redshifts up to 15 from the lens, and search for galaxy groups or clusters projected towards HE 0435−1223. We confirm that the lens is a member of a small group that includes at least 12 galaxies, and find 8 other group candidates near the line of sight of the lens. The flexion shift, namely the shift of lensed images produced by high order perturbation of the lens potential, is calculated for each galaxy/group and used to identify which objects produce the largest perturbation of the lens potential. This analysis demonstrates that i) at most three of the five brightest galaxies projected within 12 of the lens need to be explicitly used in the lens models, and ii) the groups can be treated in the lens model as an external tidal field (shear) contribution.

A Spectroscopic Survey of the Fields of 28 Strong Gravitational Lenses: Implications for H0

“…These values are still larger than the other estimates of convergence, so Sluse et al (2017) suggest that the group centroid may actually lie even farther from the lens sightline, or that the lens is actually at the center of its group halo. Additional observations of this field might further constrain the group properties and reconcile these differences.…”

“…Sluse et al (2017) conclude, using flexion shifts, that the groups they identify in this field can be approximated with external shear rather than being modeled explicitly. Rusu et al (2017) constrain ext k to be near zero ( 0.004…”

“…Previous work has indicated that many galaxy-scale lenses are located in groups or clusters and/or in fields with projected LOS structures (e.g., Kundic et al 1997;Fassnacht & Lubin 2002;Momcheva et al 2006;Auger et al 2008;Sluse et al 2017). However, only small footprints on the sky around a few galaxy-scale lens systems have been observed with deep follow-up spectroscopy.…”

COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses

“…Courbin et al 2005) and H0LiCOW programmes (H 0 Lenses in COSMOGRAIL's Wellspring; Suyu et al 2017), focussing on five well-selected bright lensed quasars. Recent results can be found in Bonvin et al (2017), Wong et al (2017), Rusu et al (2017), Sluse et al (2016) who infer H 0 = 71.9 +2.4 −3.0 km s −1 Mpc −1 from three of the H0LiCOW lenses in a flat ΛCDM Universe.…”

Analysis of the Angular Dependence of Time Delay in Gravitational Lensing

“…The most important modern techniques arise from the study of the perturbations of the Cosmic Microwave Background (CMB) [7], the Supernovae 1A (SN 1A) [6] and the effect of Gravitational Lensing (GL) [8][9][10][11][12][13]. Nevertheless, the different measurements are not compatible one with each other, and still a slight tension about the correct value of H 0 does remain [14].…”