Potential Protostars in Cloud Cores: H 2CO Observations of Serpens

The Serpens cloud contains a large number of heavily embedded protostellar cores. We present results of a formaldehyde survey of the strongest submillimeter continuum sources here in an attempt to determine the gas properties in these objects. The formaldehyde transitions we have measured trace exceptionally dense gas to which most other commonly observed molecular species, or dust, are not sensitive. In the four sources observed in at least three H2CO transitions, we find higher gas kinetic temperatures than have been derived previously, ranging from 40 to 190 K. The gas densities in this region are also large, in the range of nH2 ∼ 106-106.5 cm-3. Some of the objects exhibit strong self-reversal features that may indicate infall, and two of them possess exceptionally broad line wings, which may be associated with molecular flows. Several of these sources may represent extremely young protostars that have not yet accreted the bulk of their mass from their surrounding circumstellar envelopes.