The Distances of SNR W41 and overlapping HII regions

TL;DR

This study uses HI and CO spectral data to determine the distances and spatial relationships of SNR W41 and nearby HII regions, revealing their positions within the Galaxy.

Contribution

It provides new kinematic distance measurements for W41 and several HII regions using HI absorption and CO emission spectra analysis.

Findings

W41 is at a distance of 3.9 to 4.5 kpc.

G23.42-0.21 and G23.07+0.25 are at far kinematic distances (~10 kpc).

G23.07-0.37 and G23.27-0.27 are at near kinematic distances (~4 kpc).

Abstract

New HI images from the VLA Galactic Plane Survey show prominent absorption features associated with the supernovae remnant G23.3-0.3 (SNR W41). We highlight the HI absorption spectra and the $^{13}$CO emission spectra of eight small regions on the face of W41, including four HII regions, three non-thermal emission regions and one unclassified region. The maximum velocity of absorption for W41 is 78$\pm$2 km/s and the CO cloud at radial velocity 95$\pm$5 km/s is behind W41. Because an extended TeV source, a diffuse X-ray enhancement and a large molecular cloud at radial velocity 77$\pm$5 km/s are also projected at the center of W41, these yield the kinematic distance of 3.9 to 4.5 kpc for W41. For HII regions, our analyses reveal that both G23.42-0.21 and G23.07+0.25 are at the far kinematic distances ($\sim$9.9 kpc and $\sim$ 10.6 kpc respectively) of their recombination-line velocities (103$\pm$0.5 km/s and 89.6$\pm$2.1 km/s respectively), G23.07-0.37 is at the near kinematic distance (4.4$\pm$0.3 kpc) of its recombination-line velocity (82.7$\pm$2.0 km/s), and G23.27-0.27 is probably at the near kinematic distance (4.1$\pm$0.3 kpc) of its recombination-line velocity (76.1$\pm$0.6 km/s).