SO emission in the HL Tau system. Left and middle: Integrated intensity maps of the SO emission. The left panel presents the map integrated from -5 to 19 km s⁻¹ zoomed in on the HL Tau disk, and the middle panel shows the emission integrated over a smaller velocity range from 5 to 13 km s⁻¹, highlighting the emission coming from primarily the streamer (white) and the molecular outflow (orange contour). The green line in the middle panel is the fit to the one-arm spiral tracing the streamer in HCO⁺ (Yen et al. 2019). Right: SO spectrum.