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Date and Time of the Query: 2019-05-26 T20:15:21 PDT
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For refcode 2013ApJ...766..108M:
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2013ApJ...766..108M Formaldehyde Densitometry of Starburst Galaxies: Density-independent Global Star Formation Mangum, Jeffrey G.; Darling, Jeremy; Henkel, Christian; Menten, Karl M. Abstract. 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_2_CO). In this paper, we present an extension of our survey of the formaldehyde 1_10_-1_11_ (lambda = 6.2 cm) and 2_11_-2_12_ (lambda = 2.1 cm) K-doublet transitions of H_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_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 10^4.5^ to 10^5.5^ cm^-3^. This implies that the Schmidt-Kennicutt relation between L_IR_ and M_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_2_CO measurements to derive two separate measures of the dense gas mass which are generally smaller, in many cases by a factor of 10^2^-10^3^, than those derived using HCN. This disparity suggests that H_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 ^2^Pi_1/2_ J = 1/2 state of OH and the H111{alpha} radio recombination line taken concurrently with our H_2_CO 1_10_-1_11_ measurements. Key words: galaxies: ISM, galaxies: nuclei, galaxies: starburst, ISM: molecules, radio lines: galaxies
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