Formaldehyde as a densitometer and thermometer in Cygnus-X, the GLOSTAR pilot region, and M8. Utilizing the ground-state transition

Measurements of the physical conditions in molecular clumps are key to our understanding of star formation. Formaldehyde (is a prevalent molecule in these regions, and it can be used as a diagnostic of the physical conditions. Here we explore a technique for determining the volume density and gas kinetic temperature in molecular clumps across various evolutionary phases and environments. The ground-state transition of pform has a critical density of n_ ̊m crit ∼ 10⁴ cm -3, allowing us to use this molecule as a densitometer at n łeq 10^ 5 ̌oldens and to lessen the discrepancy between the measurements between gas densities derived from molecular tracers and those derived from dust observations. The clumps in our study were observed with the IRAM 30-m telescope, marking the first extensive survey of the line across a large sample of sources. These observations were complemented by the J = 3-2 lines, obtained using the APEX telescope. These clumps have been surveyed in three regions, the Cygnus-X giant molecular cloud complex, the GLOSTAR pilot region covering the Galactic plane at longitudes 28 l łeq 36 and the molecular cloud associated with the regions in the Lagoon nebula (M8). We analyzed a total of 127 clumps, including 78 from Cygnus-X, 12 from the GLOSTAR pilot region, and 37 from M8. We derived the gas kinetic temperature, volume densities and in 102 clumps. We reproduced the observed line intensities in the sources with volume densities n () = 5. 4 = 16 - 219 K, and. column densities using radiative transfer modeling with pyradex+emcee H2 10⁴ - 3. 8 10⁵ ̌oldens, gas kinetic temperatures T_ ̊m gas column densities N (- 1. 6 cm = 6. 0 10^ 12 10^ 15 -2 The gas kinetic temperatures obtained from the non-local thermodynamic equilibrium (LTE) modeling with agree well with the LTE gas kinetic temperature obtained from the ratio of ̌oldens. However, we find that, at higher densities, LTE temperatures derived from this ratio are overestimated by up to 0. 5 dex. The volume densities we measured are consistent with the volume densities obtained from dust continuum measurements, thereby probing the bulk of the gas. Furthermore, we find that the volume densities and dust temperatures increase with increasing evolutionary phase. The newly available ground-state transition of pyradex+emcee and lines at densities n () łeq 10^ H2 5. 5 allows the physical conditions in various phases of star formation to be constrained more effectively.