Spatially Resolved Kinematics of SLACS Lens Galaxies. I: Data and Kinematic Classification

TL;DR

This study presents high-quality spatially resolved kinematic data for 14 lensing early-type galaxies, revealing their slow rotation and providing precise measurements crucial for cosmography and galaxy evolution studies.

Contribution

First spatially resolved kinematic analysis of SLACS lens galaxies with high S/N, enabling improved cosmographic and dynamical modeling.

Findings

11 out of 14 galaxies are slow rotators.

Velocity dispersions from SDSS spectra have systematic errors (~3%).

Comparison shows measurements are consistent within a few percent.

Abstract

We obtain spatially resolved kinematics with the Keck Cosmic Web Imager (KCWI) integral-field spectrograph for a sample of 14 massive (11 < log$_{10}$ M$_*$/M$_{\odot}$ < 12) lensing early-type galaxies at z~0.15-0.35 from the Sloan Lens ACS (SLACS) Survey. We integrate kinematic maps within the effective radius and examine rotational and dispersion velocities, showing that 11/14 are slow rotators. The dataset is unprecedented for galaxy-scale strong lenses in terms of signal-to-noise ratio (S/N), sampling, and calibration. Systematics are at 1-1.4%, and positive covariance is <1% between sample galaxies and between spatial bins, with primary contibutions from stellar template library selection and fitted wavelength range. This enables cosmographic inference with lensing time delays with <2% uncertainty on H$_0$. We integrate the datacubes within various circular apertures and compare with SDSS velocity dispersions. Velocity dispersions extracted from SDSS spectra for these 14 galaxies, which have low S/N (~9/$\r{A}$) relative to the parent sample, are subject to systematic errors (and covariance) due to stellar template library selection at the level of 3(2)%, which need to be added to the random errors. Comparison between our KCWI measurements, our analysis of SDSS spectra, and previously published measurements based on SDSS spectra shows mean differences within a few percent, which are insignificant given the uncertainties of the SDSS-based measurements. Correlations between scaling relations using quantities inferred from dynamical, lensing, and stellar population models agree with previous SLACS analysis with no statistically significant change. A follow-up paper will present Jeans modeling in the context of broader studies of galaxy evolution and cosmology.