Distribution of HCNH⁺ in Serpens South. (a) Herschel H₂ column density map of Serpens South (Könyves et al. 2015) overlaid with HCNH⁺ (2−1) integrated intensity contours. The velocity range over which the HCNH⁺ (2−1) intensity is integrated is 6.5–8.5 km s⁻¹. The contours start at 0.09 K km s⁻¹ (3σ) and increase in steps of 0.03 K km s⁻¹. The red boundary represents the region mapped by our IRAM 30 m observations. (b) Herschel dust temperature map (Könyves et al. 2015) overlaid with the HCNH⁺ (2−1) integrated intensity contours that are the same as in panel a. The SSN is further divided into two subregions, SSN1 and SSN2, which are labeled in this panel. (c) Gas kinetic temperature map derived from ammonia observations (Friesen et al. 2016) overlaid with the HCNH⁺ (2−1) integrated intensity contours, which are the same as in panel a. (d) HCNH⁺ (2−1) integrated intensity map overlaid with the CO (3−2) blueshifted and redshifted outflow lobes from the SSC (Nakamura et al. 2011). The black contours represent HCNH⁺ (2−1) integrated intensity and are the same as the contours in panel a. The beam size is shown in the lower-right corner of each panel. In all panels, the (0, 0) offset corresponds to α_J2000=18^h30^m04^s.19, δ_J2000 = −02°03′05″.5. The two purple circles represent the two 22 GHz water masers (Ortiz-León et al. 2021). The purple pluses indicate the positions of deeply embedded YSOs (Könyves et al. 2015; Sun et al. 2022), while the purple crosses mark the positions of the prestellar dense cores extracted from the Herschel dust continuum maps (Könyves et al. 2015).