FORMALDEHYDE DENSITOMETRY OF STARBURST GALAXIES: DENSITY-INDEPENDENT GLOBAL STAR FORMATION
- National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States)
- Center for Astrophysics and Space Astronomy, Department of Astrophysical and Planetary Sciences, Box 389, University of Colorado, Boulder, CO 80309-0389 (United States)
Accurate techniques that allow for the derivation of the spatial density in star formation regions are rare. A technique that has found application for the derivation of spatial densities in Galactic star formation regions utilizes the density-sensitive properties of the K-doublet transitions of formaldehyde (H{sub 2}CO). In this paper, we present an extension of our survey of the formaldehyde 1{sub 10}-1{sub 11} ({lambda} = 6.2 cm) and 2{sub 11}-2{sub 12} ({lambda} = 2.1 cm) K-doublet transitions of H{sub 2}CO in a sample of 56 starburst systems. We have extended the number of galaxies in which both transitions have been detected from 5 to 13. We have improved our spatial density measurements by incorporating kinetic temperatures based upon NH{sub 3} measurements of 11 of the galaxies with a total of 14 velocity components in our sample. Our spatial density measurements lie in a relatively narrow range from 10{sup 4.5} to 10{sup 5.5} cm{sup -3}. This implies that the Schmidt-Kennicutt relation between L{sub IR} and M{sub dense} (1) is an indication of the dense gas mass reservoir available to form stars and (2) is not directly dependent upon a higher average density driving the star formation process in the most luminous starburst galaxies. We have also used our H{sub 2}CO measurements to derive two separate measures of the dense gas mass which are generally smaller, in many cases by a factor of 10{sup 2}-10{sup 3}, than those derived using HCN. This disparity suggests that H{sub 2}CO traces a denser, more compact component of the giant molecular clouds in our starburst galaxy sample. We also report measurements of the rotationally excited {lambda} = 6.3 cm {sup 2}{Pi}{sub 1/2} J = 1/2 state of OH and the H111{alpha} radio recombination line taken concurrently with our H{sub 2}CO 1{sub 10}-1{sub 11} measurements.
- OSTI ID:
- 22167501
- Journal Information:
- Astrophysical Journal, Vol. 766, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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