2006PASJ...58..979D

We have identified a weak thermal line, U42.767, which has been detected only in the directions toward Sgr A and Sgr B2, as the HOCO⁺ 2₀₂-1₀₁ transition. Because of the proximity of this line to the SiO maser line at 42.821GHz (J = 1-0 v = 2), it was observable simultaneously in ∼43GHz SiO maser searches at Nobeyama. From the past data of SiO maser surveys of infrared objects in the Galactic center, we created a map of emission distribution of HOCO⁺ in the Sgr A molecular cloud as well as maps of the ²⁹SiO J = 1 - 0 v = 0 thermal emission and H53 α emission. The emission distribution of HOCO⁺ was quite similar to that of ²⁹SiO emission. This suggests that an enhancement of the HOCO⁺ abundance in the galactic center is induced by shock activities, which release CO₂ molecules frozen on grains into gases.