Time-Delay Cosmography: Spectroscopy of Galaxies in the Environment of the J1537 Lensed Quasar System

Abstract

Due to their sufficient distances and prevalence, lensed quasars have been a key site for research in gravitational lensing. In particular, researchers are interested in constraining Hubble’s constant by measuring time delays in the arrival times of multiply imaged quasars. However, a lens model will need to be created that accounts for not just the lensing galaxy, but also any perturbers nearby that could affect the light path. Even galaxy groups can have their influence when accounting for the group as a whole. Here, the J1537-3010 lensed quasar environment is investigated, and redshifts of 58 targets have been identified using Gemini-IRAF and The RANSAC Assisted Spectral CALibration (RASCAL) to reduce spectroscopic data from the Gemini Multi-Object Spectrograph (GMOS). An additional 19 redshifts were also supplied by the Multi Unit Spectroscopic Explorer (MUSE) from the immediate surroundings of the lensing galaxy. The success rate is roughly 45% across all four masks, less than the expected 60%-70%. We expect that masking out a bad amplifier contributed to the lower redshift calculation rate, as well as spurious wavelength solutions on the blue end. With these redshifts, flexion shifts ∆ 3 x were measured to determine if the observed target or identified group should be included in the lens model; only those with a log 10 ( ∆ 3 x Auger ) > -4 are considered for the lens model. An accurate lens model is fundamental for constraining the measurements of the time-delays of the quasar images and, thereby, constraining measurements for Hubble’s constant H 0 . So far, flexion shifts for all combined 77 targets were measured, as well as flexion shifts for two identified groups at z ≈ 0.394 and z ≈ 0.587