Linking Dense Gas from the Milky Way to External Galaxies

Ian W. Stephens; James M. Jackson; J. Scott Whitaker; Yanett Contreras; Andrés E. Guzmán; Patricio Sanhueza; Jonathan B. Foster; Jill M. Rathborne

doi:10.3847/0004-637X/824/1/29

paper

Linking Dense Gas from the Milky Way to External Galaxies

arXiv:1603.09341 · doi:10.3847/0004-637X/824/1/29

Abstract

In a survey of 65 galaxies, Gao & Solomon (2004) found a tight linear relation between the infrared luminosity ( $L_{IR}$ , a proxy for the star formation rate) and the HCN(1-0) luminosity ( $L_{HCN}$ ). Wu et al. (2005, 2010) found that this relation extends from these galaxies to the much less luminous Galactic molecular high-mass star-forming clumps ( $\sim$ 1 pc scales), and posited that there exists a characteristic ratio $L_{IR}$ / $L_{HCN}$ for high-mass star-forming clumps. The Gao-Solomon relation for galaxies could then be explained as a summation of large numbers of high-mass star-forming clumps, resulting in the same $L_{IR}$ / $L_{HCN}$ ratio for galaxies. We test this explanation and other possible origins of the Gao-Solomon relation using high-density tracers (including HCN(1-0), N $_{2}$ H $^{+}$ (1-0), HCO $^{+}$ (1-0), HNC(1-0), HC $_{3}$ N(10-9), and C $_{2}$ H(1-0)) for $\sim$ 300 Galactic clumps from the Millimetre Astronomy Legacy Team 90 GHz (MALT90) survey. The MALT90 data show that the Gao-Solomon relation in galaxies cannot be satisfactorily explained by the blending of large numbers of high-mass clumps in the telescope beam. Not only do the clumps have a large scatter in the $L_{IR}$ / $L_{HCN}$ ratio, but also far too many high-mass clumps are required to account for the Galactic IR and HCN luminosities. We suggest that the scatter in the $L_{IR}$ / $L_{HCN}$ ratio converges to the scatter of the Gao-Solomon relation at some size-scale $≳$ 1 kpc. We suggest that the Gao-Solomon relation could instead result from of a universal large-scale star formation efficiency, initial mass function, core mass function, and clump mass function.

arXiv commentAccepted for Publication in ApJ; minor updates, primarily based on redline

Linking Dense Gas from the Milky Way to External Galaxies

Abstract

References in corpus (53)

Cited by in corpus (39)