Panel a: HNC (1–0) spectrum averaged over 3 × 3 pixels centered at an offset of (−40′′, 40′′) in Fig. 2 to increase the signal-to-noise level. Panel b: similar to panel a, but for an offset of (100′′, −120′′). Panel c: similar to panel a, but for CS (2–1). Panel d: similar to panel b, but for CS (2–1). All these lines are modeled with the Hill5 model (De Vries & Myers 2005; see Sect. 4.3). These offsets are given with respect to α_J2000 = 18^h28^m49.^s642, δ_J2000 = 00°50′01.′′08. The fitted parameters and their uncertainties are given in the upper right of each panel.