NRAO/Socorro Colloquium Series

Ron Allen

Space Telescope Science Institute


Anomalous H2CO Absorption as a Tracer for Dense Molecular Clouds in the Galaxy


Absorption of the CMB radiation by anomalously-excited ortho-formaldehyde in the ISM was discovered more than 35 years ago by Palmer and his colleagues. Several surveys were quickly undertaken to establish the Galactic extent of the absorption features, but they were generally unsuccessful in identifying any detectable CMB absorption. However, there are convincing reasons to expect that such absorption could offer another useful diagnostic on physical conditions in the cold ISM, and would offer an interesting complement to CO studies. I will describe two new "pilot" experiments we have conducted to tease out the absorption through long integrations with a modest radio telescope:

- a blind search in the general direction of the Galactic Anticenter, and;

- a detailed mapping of the large Galactic dust cloud Lynds 1204.

Both these studies have been successful, thanks to several generous allocations of telescope time with the 25-m Radio Telescope at Onsala. I will summarize the results and discuss our first attempts to understand the relationship of the anomalous H2CO absorption to the CO(1-0) emission from the same regions.






12 January 2007
11:00 a.m. MT

Array Operations Center Auditorium

All NRAO employees are invited to attend via video, available in Charlottesville Room 230, Green Bank Room 137 and Tucson 525.

Local Host: Miller Goss