JWST’s PEARLS: Dust Attenuation and Gravitational Lensing in the Backlit-galaxy System VV 191

We derive the spatial and wavelength behavior of dust attenuation in the multiple-armed spiral galaxy VV 191b using backlighting by the superimposed elliptical system VV 191a in a pair with an exceptionally favorable geometry for this measurement. Imaging using the James Webb Space Telescope and Hubble Space Telescope spans the wavelength range 0.3–4.5 μ m with high angular resolution, tracing the dust in detail from 0.6–1.5 μ m. Distinct dust lanes continue well beyond the bright spiral arms, and trace a complex web, with a very sharp radial cutoff near 1.7 Petrosian radii. We present attenuation profiles and coverage statistics in each band at radii 14–21 kpc. We derive the attenuation law with wavelength; the data both within and between the dust lanes clearly favor a stronger reddening behavior ( R = A _V / E _B _− _V ≈ 2.0 between 0.6 and 0.9 μ m, approaching unity by 1.5 μ m) than found for starbursts and star-forming regions of galaxies. Power-law extinction behavior ∝ λ ^− ^β gives β = 2.1 from 0.6–0.9 μ m. R decreases at increasing wavelengths ( R ≈ 1.1 between 0.9 and 1.5 μ m), while β steepens to 2.5. Mixing regions of different column density flattens the wavelength behavior, so these results suggest a different grain population than in our vicinity. The NIRCam images reveal a lens arc and counterimage from a background galaxy at z ≈ 1, spanning 90° azimuthally at 2.″8 from the foreground elliptical-galaxy nucleus, and an additional weakly lensed galaxy. The lens model and imaging data give a mass/light ratio M / L _B = 7.6 in solar units within the Einstein radius 2.0 kpc.