A radial decrease in kinetic temperature measured with formaldehyde in 30 Doradus
arxiv(2024)
摘要
Feedback from star formation is a critical component of the evolution of
galaxies and their interstellar medium. At parsec scales internal to molecular
clouds, however, the observed signatures of that feedback on the physical
properties of CO-emitting gas have often been weak or inconclusive. We present
sub-parsec observations of H2CO in the 30 Doradus region, which contains the
massive star cluster R136 that is clearly exerting feedback on its neighboring
gas. H2CO provides a direct measure of gas kinetic temperature, and we find a
trend of decreasing temperature with projected distance from R136 that may be
indicative of gas heating by the stars. While it has been suggested that
mechanical heating affects H2CO-measured temperature, we do not observe any
correlation between TK and line width. The lack of an enhancement in mechanical
feedback close to R136 is consistent with the absence of a radial trend in
gravitational boundedness seen the ALMA CO observations. Estimates of cosmic
ray flux in the region are quite uncertain but can plausibly explain the
observed temperatures, if R136 itself is the dominant local source of energetic
protons. The observations presented here are also consistent with the
H2CO-emitting gas near R136 being dominated by direct radiation from R136 and
photoelectric heating in the photodissociation regions.
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