TDCOSMO XXIV. First spatially resolved kinematics of the lens galaxy obtained using JWST-NIRSpec to improve time-delay cosmography

TL;DR

This paper presents the first spatially resolved stellar kinematics of a lens galaxy using JWST-NIRSpec, enhancing time-delay cosmography by improving data analysis methods and providing new insights into the Hubble constant.

Contribution

First measurement of 2D resolved stellar kinematics of a lens galaxy with JWST, introducing improved data reduction and kinematic extraction methods, and releasing software pipelines for future research.

Findings

Kinematic measurements are consistent with ground-based data within 1.1σ.

Methodological improvements enable robust deblending of galaxy and quasar spectra.

Software pipelines 'squirrel' and 'RegalJumper' are released for community use.

Abstract

Spatially resolved stellar kinematics has become a key ingredient in time-delay cosmography to break the mass-sheet degeneracy in the mass profile and in turn provide a precise constraint on the Hubble constant and other cosmological parameters. In this paper, we present the first measurements of 2D resolved stellar kinematics for the lens galaxy in the quadruply lensed quasar system RXJ1131$-$1231 using integral field spectroscopy from JWST's Near-Infrared Spectrograph (NIRSpec), marking the first such measurement conducted with JWST. In extracting robust kinematic measurements from this first-of-its-kind dataset, we have made methodological improvements both in the data reduction and kinematic extraction. In our kinematic extraction procedure, we performed joint modeling of the lens galaxy, the quasar, and its host galaxy's contributions in the spectra to deblend the lens galaxy component and robustly constrain its stellar kinematics. Our improved methodological frameworks are released as software pipelines for future use: squirrel, for extracting stellar kinematics, and RegalJumper, for JWST-NIRSpec data reduction. We incorporated additional artifact cleaning beyond the standard JWST pipeline. We compared our measured stellar kinematics from the JWST NIRSpec with previously obtained ground-based measurements from the Keck Cosmic Web Imager integral field unit and find that the two datasets are statistically consistent at a $\sim$1.1$\sigma$ confidence level. Our measured kinematics will be used in a future study to improve the precision of the Hubble constant measurement.