A radial decrease in kinetic temperature measured with formaldehyde in 30 Doradus

TL;DR

This study uses sub-parsec observations of formaldehyde in 30 Doradus to reveal a radial decrease in gas temperature influenced by star cluster R136, highlighting the roles of radiation and cosmic rays in interstellar heating.

Contribution

It provides the first detailed measurement of kinetic temperature variation at sub-parsec scales in 30 Doradus using H2CO, linking temperature trends to stellar feedback mechanisms.

Findings

Temperature decreases with distance from R136.

No correlation between temperature and line width, suggesting minimal mechanical heating.

Cosmic rays or radiation likely dominate the heating processes.

Abstract

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.