FORMALDEHYDE DENSITOMETRY OF GALACTIC STAR-FORMING REGIONS USING THE H{sub 2}CO 3{sub 12}-3{sub 13} AND 4{sub 13}-4{sub 14} TRANSITIONS
- National Radio Astronomy Observatory 520 Edgemont Road, Charlottesville, VA 22903 (United States)
We present Green Bank Telescope observations of the 3{sub 12}-3{sub 13} (29 GHz) and 4{sub 13}-4{sub 14} (48 GHz) transitions of the H{sub 2}CO molecule toward a sample of 23 well-studied star-forming regions. Analysis of the relative intensities of these transitions can be used to reliably measure the densities of molecular cores. Adopting kinetic temperatures from the literature, we have employed a large velocity gradient (LVG) model to derive the average hydrogen number density (n(H{sub 2})) within a 16'' beam toward each source. Densities in the range of 10{sup 5.5}-10{sup 6.5} cm{sup -3} and ortho-formaldehyde column densities per unit line width between 10{sup 13.5} and 10{sup 14.5} cm{sup -2} (km s{sup -1}){sup -1} are found for most objects, in general agreement with existing measurements. A detailed analysis of the advantages and limitations to this densitometry technique is also presented. We find that H{sub 2}CO 3{sub 12}-3{sub 13}/4{sub 13}-4{sub 14} densitometry proves to be best suited to objects with T{sub K} {approx}> 100 K, above which the H{sub 2}CO LVG models become relatively independent of kinetic temperature. This study represents the first detection of these H{sub 2}CO K-doublet transitions in all but one object in our sample. The ease with which these transitions were detected, coupled with their unique sensitivity to spatial density, makes them excellent monitors of density in molecular clouds for future experiments. We also report the detection of the 9{sub 2}-8{sub 1} A {sup -} (29 GHz) transition of CH{sub 3}OH toward six sources.
- OSTI ID:
- 21612631
- Journal Information:
- Astrophysical Journal, Vol. 742, Issue 1; Other Information: DOI: 10.1088/0004-637X/742/1/58; Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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