SIMBAD references

We have used the Taeduk Radio Astronomy Observatory to observe the Orion A and Ophiuchus clouds in the J = 1-0 lines of ¹³CO, C¹⁸O, HCN, HCO⁺, and N₂H⁺ and the J = 2-1 line of CS. The fully sampled maps with uniform noise levels are used to create moment maps. The variations of the line intensity and velocity dispersion with total column density, derived from dust emission maps, are presented and compared to previous work. The CS line traces dust column density over more than one order of magnitude, and the N₂H⁺ line best traces the highest column density regime (log(N_H2_) > 22.8). Line luminosities, integrated over the cloud, are compared to those seen in other galaxies. The HCO⁺-to-HCN luminosity ratio in the Orion A cloud is similar to that of starburst galaxies, while that in the Ophiuchus cloud is in between those of active galactic nuclei and starburst galaxies.