TESTING STAR FORMATION THEORIES - VLA OBSERVATIONS OF H2CO IN THE BOK GLOBULE B335

The H2CO 6 cm line was observed with the VLA toward B335. The line is seen in absorption against the cosmic background radiation in a ring-shaped region centered on the infrared source. The data were analyzed with both LVG and microturbulent radiative transfer models. The two models agree qualitatively but differ quantitatively. The microturbulent model, which is physically more appropriate for this source, yields a best-fit power-law density profile of the form n ∝ r-α, with α = 1.5-2.0, a temperature of 13-15 K, and a H2CO abundance of 2 × 10-9. Comparison of our observations with theoretical models for low-mass star formation in the subcritical and superumbral regime (Shu, Adams, and Lizano) shows good agreement. Our density estimates are considerably lower than previous density estimates from dust emission. By considering the effects of temperature and density gradients, we are able to produce a better agreement between the estimates from dust and H2CO. If most of the dust emission does not arise in a very compact core (∼2″), then the far-infrared dust opacities of Mathis, Mezger, and Panagia are favored over those of Draine and Lee.