Formaldehyde densitometry of starburst galaxies: density-independent global star formation.
MANGUM J.G., DARLING J., HENKEL C. and MENTEN K.M.
Abstract (from CDS):
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 (H2CO). In this paper, we present an extension of our survey of the formaldehyde 110-111(λ = 6.2 cm) and 211-212(λ = 2.1 cm) K-doublet transitions of H2 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 NH3 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 104.5 to 105.5/cm3. This implies that the Schmidt-Kennicutt relation between LIR and Mdense(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 H2 CO measurements to derive two separate measures of the dense gas mass which are generally smaller, in many cases by a factor of 102-103, than those derived using HCN. This disparity suggests that H2 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 λ = 6.3 cm 2Π1/2 J = 1/2 state of OH and the H111α radio recombination line taken concurrently with our H2 CO 110-111measurements.
galaxies: ISM - galaxies: nuclei - galaxies: starburst - ISM: molecules - radio lines: galaxies