paper

ATLASGAL-selected massive clumps in the inner Galaxy: VI. Kinetic temperature and spatial density measured with formaldehyde

arXiv:1711.10012 · doi:10.1051/0004-6361/201732168

Abstract

We aim to directly determine the kinetic temperature and spatial density with formaldehyde for the $\sim$ 100 brightest ATLASGAL-selected clumps at 870 $I^¼$ m representing various evolutionary stages of high-mass star formation. Ten transitions ( $J$ = 3-2 and 4-3) of ortho- and para-H $_{2}$ CO near 211, 218, 225, and 291 GHz were observed with the APEX 12 m telescope. Using non-LTE models with RADEX, we derive the gas kinetic temperature and spatial density using the measured p-H $_{2}$ CO 3 $_{21}$ -2 $_{20}$ /3 $_{03}$ -2 $_{02}$ , 4 $_{22}$ -3 $_{21}$ /4 $_{04}$ -3 $_{03}$ , and 4 $_{04}$ -3 $_{03}$ /3 $_{03}$ -2 $_{02}$ ratios. The gas kinetic temperatures derived from the p-H $_{2}$ CO 3 $_{21}$ -2 $_{20}$ /3 $_{03}$ -2 $_{02}$ and 4 $_{22}$ -3 $_{21}$ /4 $_{04}$ -3 $_{03}$ line ratios are high, ranging from 43 to $>$ 300 K with an unweighted average of 91 $\pm$ 4 K. Deduced $T_{kin}$ values from the $J$ = 3-2 and 4-3 transitions are similar. Spatial densities of the gas derived from the p-H $_{2}$ CO 4 $_{04}$ -3 $_{03}$ /3 $_{03}$ -2 $_{02}$ line ratios yield 0.6-8.3 $\times$ 10 $^{6}$ cm $^{- 3}$ with an unweighted average of 1.5 ( $\pm$ 0.1) $\times$ 10 $^{6}$ cm $^{- 3}$ . A comparison of kinetic temperatures derived from p-H $_{2}$ CO, NH $_{3}$ , and the dust emission indicates that p-H $_{2}$ CO traces a distinctly higher temperature than the NH $_{3}$ (2,2)/(1,1) transitions and the dust, tracing heated gas more directly associated with the star formation process. The H $_{2}$ CO linewidths are found to be correlated with bolometric luminosity and increase with the evolutionary stage of the clumps, which suggests that higher luminosities tend to be associated with a more turbulent molecular medium. It seems that the spatial densities measured with H $_{2}$ CO do not vary significantly with the evolutionary stage of the clumps. However, averaged gas kinetic temperatures derived from H $_{2}$ CO increase with time through the evolution of the clumps.

Accepted for publication in A&A