The gas-to-dust ratio investigation in the massive star-forming region M17

ABSTRACT M17 is a well-known massive star-forming region, and its gas-to-dust ratio (GDR) may vary significantly compared to the other areas. The mass of gas can be traced by the ${\rm CO}$ emission observed in the Milky Way Imaging Scroll Painting project. The dust mass can be traced by analysing the interstellar extinction magnitude obtained from the United Kingdom Infrared Telescope. We computed the ratio ${W({\rm CO})/A_\mathit{ V}}$: for ${A_\mathit{ V} \le }$ 10 mag, ${{ W(^{12}{\rm CO})/ A_\mathit{ V}}= (6.27 \pm 0.19)}$${\mathrm{{K \, km\,s^{-1}}\, mag^{-1}}}$ and ${{ W(^{13}{\rm CO})/ A_\mathit{ V}} = (0.75 \pm 0.72)}$${ \mathrm{{K \, km\,s^{-1}} \, mag^{-1}}}$; whereas for ${{A_\mathit{ V}} \ge 10}$ mag, ${{ W(^{12}{\rm CO})/ A_\mathit{ V}} = (15.8 \pm 0.06) }$ ${\mathrm{{K \, km\,s^{-1}} \, mag^{-1}}}$, and ${{ W(^{13}{\rm CO})/ A_\mathit{ V}} = (3.11 \pm 0.25)}$ ${ \mathrm{{K \, km\,s^{-1}} \, mag^{-1}}}$. Then, we converted the ${W({\rm CO})/A_\mathit{ V}}$ into ${N(\rm H)/\mathit{ A}_\mathit{ V}}$. Using the WD01 model, we derived the GDR: for ${A_\mathit{ V} \le }$ 10 mag, the GDRs were ${118 \pm 9}$ for ${^{12}{\rm CO}}$ and ${83 \pm 62}$ for ${^{13}{\rm CO}}$, comparable to those of the Milky Way; however, for ${A_\mathit{ V} \ge }$ 10 mag, the GDRs increased significantly to ${296 \pm 3}$ for ${^{12}{\rm CO}}$ and ${387 \pm 40}$ for ${^{13}{\rm CO}}$, approximately three times higher than those of the Milky Way. In the discussion, we compared the results of this work with previous studies and provided a detailed discussion of the influence of massive stars and other factors on GDR.