Galactic Formaldehyde Densitometry Project

The Galactic Formaldehyde Densitometry Project is finally official and on its way. I am PI of a joint Arecibo / Green Bank Telescope project to survey formaldehyde, H2CO, in a sample of ~400 "dust clumps" in the Galactic Plane. The clumps represent condensations within larger molecular clouds that are likely to be forming stars, particularly massive stars and star clusters.

Formaldehyde is uniquely useful for measuring densities of these gas clumps. Because of a collisional selection effect, the low-lying K-doublet transitions of H2CO undergo "anti-inversion", which means their lower-energy states are overpopulated relative to the higher states, and it can therefore be seen in absorption against the cosmic microwave background. This unique property removes a key bias present in emission line studies in which variable excitation conditions can dominate the observability of a line.

For the next few posts, I will include calibration and data reduction information from the observations in this survey. The Green Bank observations are well underway, with nearly half of the sources observed (though many at poor sensitivity) and the Arecibo observations have been approved.