摘要：Context.The gas kinetic temperature (TK) determines the physical and chemical evolution of the interstellar medium (ISM). However, obtaining reliableTKestimates usually requires expensive observations including the combination of multi-line analysis and dedicated radiative transfer calculations.Aims.This work explores the use of HCN and HNC observations, and particularly theI(HCN)-to-I(HNC) intensity ratio (I(HCN)/I(HNC)) of theirJ= 1–0 lines, as direct probe of the gas kinetic temperature in the molecular ISM.Methods.We obtained a new set of large-scale observations of the HCN and HNC (1–0) lines throughout the Integral Shape Filament (ISF) in Orion. In combination with ancillary gas and dust temperature measurements, we find a systematic temperature dependence of the observedI(HCN)-to-I(HNC) intensity ratio throughout our maps. Additional comparisons with chemical models demonstrate that these observedI(HCN)/I(HNC) variations are driven by the effective destruction and isomerization mechanisms of HNC under low-energy barriers.Results.The observed variations ofI(HCN)/I(HNC) withTKcan be described with a two-part linear function. This empirical calibration is then used to create a temperature map of the entire ISF. Comparisons with similar dust temperature measurements in this cloud, as well as in other regions and galactic surveys, validate this simple technique for obtaining direct estimates of the gas kinetic temperature in a wide range of physical conditions and scales with an optimal working range between 15 K ≲TK≤ 40 K.Conclusions.Both observations and models demonstrate the strong sensitivity of theI(HCN)/I(HNC) ratio to the gas kinetic temperature. Since these lines are easily obtained in observations of local and extragalactic sources, our results highlight the potential use of this observable as new chemical thermometer for the ISM.
关键词：Key wordsenISM: cloudsISM: moleculesISM: structurestars: formationsubmillimeter: ISM
