BIMA¹³CO Observations of W3

The W3 molecular cloud core has been observed with the BIMA and NRAO 12 m telescopes in the ¹³CO (J = 1-0) and C¹⁸O (J = 1-0) lines. Two BIMA fields were imaged, centered on the infrared sources IRS 5 and IRS 4 (80'' west of IRS 5). In order to observe large-scale structure, a full-synthesis cube was made with a resolution of 95 × 80. Additionally, a high-resolution cube was made with only the IRS 5 pointing of BIMA to investigate the distribution of gas near IRS 5 at high angular resolution.

The total H₂ masses of the molecular cores associated with IRS 4 and IRS 5 are 1700 and 1100 M_☉, respectively. Six clumps are identified. Derived H₂ masses of the clumps are between 120 and 480 M_☉, and under simple geometrical assumptions, n(H₂) is between 1.8 and 4.5 × 10⁵ cm^-3. The virial masses of the clumps are within 30% of the derived H₂ masses. For the clumps located at IRS 5 and 20'' south of IRS 4, the ¹³CO opacities derived were 0.3 and 0.7, respectively. At the positions of IRS 4 and IRS 5, individual clumps are observed; the IRS 4 clump in particular has a n(H₂) a factor of 2 larger than the other clumps.

At the position of IRS 5, the high-resolution data show a velocity structure suggestive of two clumps, one north and another south of IRS 5. Integrating the emission from these clumps gives an H₂ mass of 110 M_☉. Using the derived H₂ column density toward IRS 5 and a previous H I Zeeman result, we can derive the ratio | B |/N_H (which is proportional to the magnetic flux-to-mass ratio Φ_B/M). The determined ratio is near the magnetically critical value, which is consistent with the standard theory of high-mass star formation.