Dust temperature and time-dependent effects in the chemistry of photodissociation regions

G. Esplugues, S. Cazaux, P. Caselli, S. Hocuk, M. Spaans

Research output: Contribution to journalArticleScientificpeer-review

2 Citations (Scopus)

Abstract

When studying chemistry of photodissociation regions (PDRs), time dependence becomes important as visual extinction increases, since certain chemical time-scales are comparable to the cloud lifetime. Dust temperature is also a key factor, since it significantly influences gas temperature and mobility on dust grains, determining the chemistry occurring on grain surfaces. We present a study of the dust temperature impact and time effects on the chemistry of different PDRs, using an updated version of theMeijerink PDR code and combining it with the time-dependent code Nahoon. We find the largest temperature effects in the inner regions of highG0 PDRs,where high dust temperatures favour the formation of simple oxygen-bearing molecules (especially that of O2), while the formation of complex organic molecules is much more efficient at low dust temperatures. We also find that time-dependent effects strongly depend on the PDR type, since long time-scales promote the destruction of oxygen-bearing molecules in the inner parts of low G0 PDRs, while favouring their formation and that of carbon-bearing molecules in high G0 PDRs. From the chemical evolution, we also conclude that, in dense PDRs, CO2 is a late-forming ice compared to water ice, and confirm a layered ice structure on dust grains, with H2O in lower layers than CO2. Regarding steady state, the PDR edge reaches chemical equilibrium at early times (≲105 yr). This time is even shorter (<104 yr) for high G0 PDRs. By contrast, inner regions reach equilibrium much later, especially low G0 PDRs, where steady state is reached at ∼106-107 yr.

Original languageEnglish
Pages (from-to)1853-1874
Number of pages22
JournalMonthly Notices of the Royal Astronomical Society
Volume486
Issue number2
DOIs
Publication statusPublished - 1 Jun 2019

Keywords

  • astrochemistry
  • ISM: abundances
  • ISM: clouds
  • photodissociation region (PDR).

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