Halfway to the Peak: Spatially Resolved Star Formation and Kinematics in a z = 0.54 Dusty Galaxy with JWST/MIRI

Abstract

We present JWST Mid-InfraRed Instrument/Medium-Resolution Spectrometer (MIRI/MRS) observations of an infrared luminous disk galaxy, FLS1, at z ∼ 0.54. With a lookback time of 5 Gyr, FLS1 is chronologically at the midpoint between the peak epoch of star formation and the present day. The MRS data provide maps of the atomic fine structure lines [Ar ii]6.99, [Ar iii]8.99, [Ne ii]12.81, and [Ne iii]15.55 μm, polycyclic aromatic hydrocarbon (PAH) features at 3.3, 6.2, and 11.3 μm, and the warm molecular gas indicators H2S(5) and H2S(3); all these emission features are spatially resolved. We find that the PAH emission is more extended along the northern side of the galaxy when compared to the well-studied star formation tracer [Ne ii]. The H2 rotational lines, which are shock indicators, are strongest and most extended on the southern side of the galaxy. [Ar ii] is the second brightest fine structure line detected in FLS1 and we show that it is a useful kinematic probe that can be detected with JWST out to z ∼ 3. Velocity maps of [Ar ii] show a rotating disk with signs of turbulence. Our results provide an example of how spatially resolved mid-infrared spectroscopy can allow us to better understand the star formation and interstellar medium conditions in a galaxy halfway back to the peak epoch of galaxy evolution.