CHIMPS2: 13CO J = 3→2 emission in the central molecular zone.

We present the initial data for the |$(J = 3 \rightarrow 2)$| transition of |$^{13}\text{CO}$| obtained from the central molecular zone (CMZ) of the Milky Way as part of the CO Heterodyne Inner Milky Way Plane Survey 2 (CHIMPS2). Covering |$359^{\circ } \le l \le 1^{\circ }$| and |$|b| \le 0.5^{\circ }$| with an angular resolution of 19 arcsec, velocity resolution of 1 km s |$^{-1}$|⁠ , and rms |$\Delta {T_{\rm A}^{*}} = 0.59\, \mathrm{K}$| at these resolutions, our observations unveil the complex structure of the CMZ molecular gas in improved detail. Complemented by the |$\rm {^{12}CO}$| CHIMPS2 data, we estimate a median optical depth of |$\tau _{13} = 0.087$|⁠. The preliminary analysis yields a median |$^{13}\text{CO}$| column-density range equal to |$N(^{13}{\rm CO}) = 2{\!-\!}5 \times 10^{18}\, \mathrm{cm}^{-2}$|⁠ , median H |$_{2}$| column density equal to |$N(\mathrm{H_{2}}) = 4 \times 10^{22}\, \mathrm{cm}^{-2}$| to |$1 \times 10^{23}\, \mathrm{cm}^{-2}$|⁠. We derive |$N({\rm H_{2}})$| -based total mass estimates of |$M({\rm H}_{2}) = 2{\!-\!}6 \times 10^{7}\, \mathrm{M}_{\odot }$|⁠ , in agreement with previous studies. We analyse the relationship between the integrated intensity of |$^{13}\text{CO}$| and the surface density of compact sources identified by Herschel Hi-GAL, and find that younger Hi-GAL sources detected at 500  |$\rm{\mu m}$| but not at 70  |$\rm{\mu m}$| follow the dense gas of the CMZ more closely than those that are bright at 70  |$\rm{\mu m}$|⁠. The latter, actively star-forming sources appear to be more associated with material in the foreground spiral arms. [ABSTRACT FROM AUTHOR]