N2H+ & CCS abundances in HII star forming regions

Among our 88 UC H IIs, 87 and 33 sources were detected in the N_2_H^+^J=1-0 and CCS J_N_=8_7_-7_6_ lines, respectively. For the CCS 7_7_-6_6_ transition, we detected emission in 10 out of 82 targeted sources, all of which also exhibited emission in the CCS J_N_=8_7_-7_6_ line.

Physical parameters are derived for our detections, including the optical depth and excitation temperature of N_2_H^+^, the rotational temperature of CCS and the column density. Combining our results and previous observation results in different stages of high-mass star-forming regions (HMSFRs), we found that the column density ratio N(N_2_H^+^)/N(CCS) increases from high-mass starless cores through high-mass protostellar cores to UC H IIs.