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Retrieving physical conditions from interstellar H2 emission lines: a non linear fitting technique

Silvia Casu and Cesare Cecchi-Pestellini

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The importance of the formation pumping on the rovibrational level distribution of H2 is revisited. A detailed comparison of different formation mechanisms on dust surfaces and in the gas-phase is carried out, and it is found that dust surface formation dominates the formation pumping. It is shown that formation pumping in a cold gas can mimic the excitation conditions found in hotter regions. The presence of a significant fraction of molecular hydrogen in very high rotational levels observed towards OMC-1 Peak 1 is explained by means of pumping by newly formed H2 molecules and does not require high temperature gas.


PACS

98.58.Bz Atomic, molecular, chemical, and grain processes

98.58.Ca Interstellar dust grains; diffuse emission; infrared cirrus

95.30.Ft Molecular and chemical processes and interactions

Subjects

Atomic and molecular physics

Astrophysics and astroparticles

Dates

Issue 1 (2005)



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