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 \emph{ Milky Way Imaging Scroll Painting (MWISP) project}. The dust mass can be traced by analyzing the interstellar extinction magnitude obtained from the \emph{ United Kingdom Infrared Telescope (UKIRT)}. We computed the ratio ${ W({ \rm CO})/A_V}$: for ${ A_V \le }$ 10 mag, ${ { W(^{ 12}{ \rm CO})/ A_V}= (6.27 \pm 0.19)}$ ${ \mathrm{ { K \cdot km/s} \cdot mag^{ -1}}}$ and ${ { W(^{ 13}{ \rm CO})/ A_V} = (0.75 \pm 0.72)}$ ${ \mathrm{ { K \cdot km/s} \cdot mag^{ -1}}}$; whereas for ${ { A_V} \ge 10}$ mag, ${ { W(^{ 12}{ \rm CO})/ A_V} = (15.8 \pm 0.06) }$ ${ \mathrm{ { K \cdot km/s} \cdot mag^{ -1}}}$ and ${ { W(^{ 13}{ \rm CO})/ A_V} = (3.11 \pm 0.25)}$ ${ \mathrm{ { K \cdot km/s} \cdot mag^{ -1}}}$. Then, we converted the ${ W({ \rm CO})/A_V}$ into ${ N(\rm H)/A_V}$. Using the WD01 model, we derived the GDR: for ${ A_V \le }$ 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 ${ A_V \ge }$ 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.
Categories: astro-ph.GA astro-ph.SR