TIMES I: a Systematic Observation in Multiple Molecular Lines Toward the Orion A and Ophiuchus Clouds

TL;DR

This study uses radio observations of molecular lines in Orion A and Ophiuchus clouds to analyze their structure, compare line tracers of density, and relate findings to galaxy-scale phenomena.

Contribution

It provides fully sampled molecular line maps of two star-forming regions and compares their properties to extragalactic observations, highlighting differences in dense gas tracers.

Findings

CS traces dust column density over an order of magnitude.

N2H+ best traces the highest column density regions.

HCO+-to-HCN ratio varies between clouds and galaxy types.

Abstract

We have used the Taeduk Radio Astronomy Observatory to observe the Orion A and Ophiuchus clouds in the $J=$1$-$0 lines of $^{13}$CO, C$^{18}$O, HCN, HCO$^+$, and N$_2$H$^+$ and the $J=$2$-$1 line of CS. The fully sampled maps with uniform noise levels are used to create moment maps. The variations of the line intensity and velocity dispersion with total column density, derived from dust emission maps, are presented and compared to previous work. The CS line traces dust column density over more than one order of magnitude, and the N$_2$H$^+$ line best traces the highest column density regime ($\log(N_\mathrm{H_2}$) $>$ 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.