Results of the Gaussian fit to the H₂CO line emission toward Per-emb-50. Left: central velocity V_LSR and velocity dispersion σ_v of the H₂CO streamer are shown in the top and bottom panels, respectively. These are obtained from the Gaussian model for H₂CO emission of each spectra with S/N > 4. The red star represents the central position of Per-emb-50. Black labeled crosses mark the positions where we extract spectra, shown to the right. Dashed black contours correspond to the continuum emission at a brightness level of 7 mJy beam⁻¹ (see Fig. A.1). Dashed white lines represent the primary beam FWHM, centered at the location of Per-emb-50. The beam is drawn in the lower left corners of each image. Right: H₂CO spectra at selected positions along the streamer, together with the Gaussian that best fits each spectrum. Blue lines indicate the H₂CO spectra and the dashed black lines represent the best fit Gaussian function. The uncertainty in T_MB is 0.3 K. The dotted gray line represents the protostar’s V_lsr = 7.5 km s⁻¹.