a) Fractions of electron captured into n shells at v = 200 km s^-1 for S¹⁶⁺ + H. The solid line is the scaling relation obtained in Gu et al. (2015), and the data points come from actual calculation by Cumbee et al. (in prep.). b) S xvi line emission, normalized to the Lyα transition for CX (black) and CIE (red) models. The CX spectra with v = 200 keV^-1 and 50 keV^-1 are shown in solid and dashed lines, respectively. The ionization temperatures are set to 3 keV in all cases, and the spectra are folded with the XMM-Newton PN response. c) All the CX lines in the 3.3–3.7 keV band, normalized to the S xvi transitions from n> 8 to the ground at 3.45–3.47 keV, and plotted as a function of ionization temperature. The solid lines are obtained by setting v = 200 keV^-1, while for S xvi transitions, we also plot, in dashed lines, the results with v = 50 keV^-1. d) A 2D color map of interaction volume V, on the plane of ionization temperature and collision velocity, to reproduce the reported ULF flux (Sect. 3.2).