2025ApJ...978...83T

Supernova remnants (SNRs) can exert strong influence on molecular clouds (MCs) through interaction by shock wave and cosmic rays. In this paper, we present our mapping observation of HCO⁺ and $\mathrm{HCN}$ 1-0 lines toward 13 SNRs interacting with MCs, together with archival data of CO isotopes. Strong HCO⁺ emission is found in the fields of view of SNRs W30, G9.7-0.0, Kes 69, 3C 391, 3C 396, W51C, HC 40, and CTB109 in the local-standard-of-rest velocity intervals in which they are suggested to show evidence of SNR-MC interaction. We find an incomplete ¹²CO shell surrounding G9.7-0.0 with an expanding motion. This shell may be driven by the stellar wind of the SNR progenitor. We also find an arc of ¹²CO gas spatially coincident with the northwestern radio shell of Kes 69. As for the HCO⁺ line emission, SNRs 3C 391 and W51C exhibit significant line profile broadening indicative of shock perturbation, and CTB109 exhibits a possible blueshifted line wing brought by shock interaction. We do not find significant variation of the $I({\mathrm{HCO}}^{+})/I(\mathrm{HCN})$ line ratio between broad-line and narrow-line regions, among different SNRs, and between MCs associated with SNRs and typical Galactic MCs. Therefore, we caution on using the $I({\mathrm{HCO}}^{+})/I(\mathrm{HCN})$ line ratio as a diagnostic of SNR feedback and cosmic-ray (CR) ionization. We also estimate the N(HCO⁺)/N(CO) abundance ratio in 11 regions toward the observed SNRs, but they show little difference from the typical values in quiescent MCs, possibly because N(HCO⁺)/N(CO) is not an effective tracer of CR ionization.