Structure and composition of molecular clouds with CN Zeeman detections I: W3(OH)

We have carried out a multi-species study of a region which has had previous measurements of strong magnetic fields through the CN Zeeman effect in order to explore the relationship between CN and N₂H⁺, both of which have evidence that they remain in the gas phase at densities of 10⁵-10⁶cm^-3. To achieve this, we map the 1 arcmin² region around the UCHII region of W3(OH) using the Combined Array for Millimeter-wave Astronomy (CARMA). Approximately 105 hr of data were collected in multiple array configurations to produce maps with an effective resolution of ∼2″.5 at high signal-to-noise ratios (S/Ns) in CN, C¹⁸O, HCN, HCO⁺, N₂H⁺, and two continuum bands (91.2GHz and 112GHz). These data allow us to compare tracer molecules associated with both low- and high-density regions to infer gas properties. We determine that CARMA resolves out approximately 35% of the CN emission around W3(OH) when compared with spectra obtained from the IRAM 30 m telescope. The presence of strong absorption lines toward the continuum source in three of the molecular transitions infers the presence of a cold, dark, optically thick region in front of the continuum source. In addition, the presence of high-velocity emission lines near the continuum source shows the presence of hot clumpy emission behind the continuum source. These data determine that future high-resolution interferometric CN Zeeman measurements which cannot currently be performed (due to technical limitations of current telescopes) are feasible. We confirm that CN is indeed a good tracer for high-density regions; with certain objects such as W3(OH) it appears to be a more accurate tracer than N₂H⁺.