New Insights from the Perseus Arm Molecular Survey

The Perseus Arm Molecular Survey (PAMS) has been conducted using the James Clerk Maxwell Telescope (JCMT) to study molecular clouds in the outer Perseus spiral arm of the Milky Way. This survey focuses on several molecular cloud complexes, including W5 and NGC 7538, covering an area of approximately 6 square degrees.

Key findings from the initial data analysis include:

• The survey utilized $^{13}$CO and C$^{18}$O ($J$=3$-$2) emissions, achieving an effective resolution of 17.2 arcseconds and a sensitivity of $T_{mb} = 0.7$ K in 0.3 km/s channels.
• The comparison of PAMS data with existing CO data from the CO Heterodyne Inner Milky Way Plane Survey (CHIMPS) revealed that the CO-to-H$_2$ column density $X$-factors remain consistent across different Galactocentric radii, specifically between 4 and 10 kpc.
• The study found that the emission profiles, size-linewidth, and mass-radius relationships of structures traced by $^{13}$CO are similar in both the Inner and Outer Galaxy.
• Notably, PAMS sources were observed to be more massive than their Inner Galaxy counterparts for similar size scales. This discrepancy is attributed to factors such as the Galactic gradient in gas-to-dust mass ratio and selection biases.

The data from the PAMS survey is now publicly available, which complements other CO surveys targeting various regions of the Galaxy. This accessibility may enhance further research into molecular cloud dynamics and star formation processes within our galaxy.

The findings are detailed in the paper titled "PAMS: The Perseus Arm Molecular Survey -- I. Survey description and first results" by Andrew J. Rigby and colleagues, available at arXiv:2409.01255.